Keywords: Low-Field MRI, RF Arrays & Systems

Motivation: RF Coil design for low frequencies.

Goal(s): Demonstrate the impact of  losses in different matching network topologies

Approach: we compared three- and four-element matching networks on 12 cm diameter coils at 10, 23.55, and 63.6 MHz. and evaluated coil loss and SNR. 

Results: At 10 and 23.55MHz, the coils with three-element (single stage) matching networks exhibited approximately 50% lower unloaded Q compared to coils with four-element matching networks, whereas unloaded Q values were within 3% for three- and four-element matched coils at 63.6MHz. SNR at 23.55MHz (0.55T) was approximately 30% higher for the four-element matched coil over the three-element matched coil.

Impact: Resistive losses in four-element matching networks can be significantly lower than those of three-element networks at low frequencies or for lightly loaded coils, resulting in higher quality factor and SNR.

Keywords: High-Field MRI, New Devices

Motivation: Eddy currents induced in the RF shield cause vibrations which generate acoustic noise.   

Goal(s): To develop an RF shield that minimizes eddy currents and preserve the B₁⁺ efficiency.

Approach: It was established that eddy-currents induced in the RF shield of the transmit coil are the primary source of acoustic noise in our 7T scanner. Therefore, the conventional slotted double layered RF shield was replaced by a segmented phosphor bronze mesh (PBM) to minimize eddy-currents and acoustic noise.

Results: Measurements performed at both ear locations of an anthropometric phantom demonstrate that the segmented PBM-based RF shield reduces the acoustic noise by up to 10dB.

Impact: Acoustic noise reduction could be achieved by using segmented PBM without compromising the transmit B1 field compared to the conventional double-layered slotted shield. Further improvements might be achieved with different mesh configurations besides the one implemented in this work.

Keywords: High-Field MRI, High-Field MRI, artifacts, MSK

Motivation: Advanced metal-artifact reduction sequences (MARS) are currently only available in parallel transmission (pTx) research mode at 7T, while clinically approved RF coils are single-channel transmit (sTx) coils.

Goal(s): Our goal was to build an adapter to connect a sTx knee coil to a pTx system, and to evaluate MARS techniques in phantom and in vivo scans.

Approach: An evaluation of artifact reduction using advanced MARS techniques was performed in a phantom study. Knees of three volunteers with metallic suture plates were imaged.

Results: Optimized bandwidth and view-angle-tilting (VAT) effectively reduced metal artifacts while keeping acquisition time and SAR load acceptable.

Impact: A hardware adaption for connecting a sTx coil to a pTx system was evaluated for safe in vivo usage. The application of MARS was demonstrated for the first time at 7T in volunteers with metallic suture plates after ACL reconstruction.

Keywords: High-Field MRI, Motion Correction

Motivation: Long scan durations and ultra-high field both facilitate the acquisition of high-resolution quantitative brain MRI, but they increase motion sensitivity.

Goal(s): We aimed to limit the occurrence of deliberate motion by testing a device (‘MinMo’) designed to increase head stability at 7T.

Approach: Using two k-space phase encoding orders with different motion sensitivity profiles we obtained data with and without the MinMo device.

Results: This showed that the MinMo increased image quality visually and as measured quantitatively via reduced gradient entropy in scans of ~10 and ~20 minute duration.     

Impact: Reducing head motion would have a significant impact on image quality in high-resolution long duration research scans and clinical imaging.  A preliminary investigation of a prototype device aiming to stabilize the head showed efficacy in most subjects, warranting further investigation.

Keywords: High-Field MRI, High-Field MRI, human 14T RF front-end

Motivation: The ultra-high field magnetic resonance imaging system can obtain ultra-high sensitivity and signal-to-noise ratio magnetic resonance imaging information,  has become an important tool for basic research in brain science .

Goal(s): However, with the increase of field strength and operating frequency, the RF signal processing module, faces problems such as clutter interference,  mirror frequency interference, which seriously affects the performance of the RF system and the final image quality. 

Approach: We have solved these problems using methods such as secondary mixing.

Results: After key parameter testing and verification, it meets the application requirements of the human 14T ultra-high field magnetic resonance imaging system.
 

Impact: Our work has provided conditions for the construction of multi-channel RF modules in ultra-high fields, improving the quality of RF signal processing. Provided a hardware foundation for improving the quality of MRI images in ultra-high fields.

Keywords: System Imperfections, System Imperfections: Measurement & Correction

Motivation: NMR field probe methods for field monitoring are limited by probe signal loss due to relaxation, dephasing, or both.

Goal(s): To develop a method for characterizing sequences with higher resolution or readout length than allowed by current field monitoring approaches.

Approach: Long-duration 2D spiral readout gradients were characterized by acquiring and stitching multiple segment-specific dynamic field measurements per segmentation of the readout gradient determined by a signal loss model.

Results: For both long-duration and ultrahigh-resolution readouts, our method resulted in plausible 0^th-2^nd order dynamic field measurements throughout the entire spiral readout, correcting erroneous k-space traversal observed with a traditional approach.

Impact: The proposed stitching method provides an effective means to characterize challenging imaging gradients using commercially available hardware and without assuming a linear gradient system, thereby having utility for dynamic field measurements in ultrahigh-resolution MRI using a standard field monitoring system.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: Low-field MRI has garnered significant attention in recent years due to its unique advantages in safety, cost-effectiveness and accessibility. However, lower field strength comes with an inherently lower SNR as its primary limitation.

Goal(s): In this work, we introduce a novel volume RF coil design using coupled stack-up resonators to mitigate this challenge.

Approach: To demonstrate the proposed design, we take 0.5T as an example field strength and designed a prototype coupled stack-up volume coil operating in the 20MHz range. 

Results: Compared to the birdcage coil, the proposed design significantly improves RF field efficiency and homogeneity, ultimately enhancing the performance of low-field MRI.

Impact: The proposed stack-up volume coil outperforms the standard birdcage coil in B1 efficiency and field homogeneity at low fields, ultimately improving the performance of low-field MRI and advancing its applications.

Keywords: Non-Array RF Coils, Antennas & Waveguides, High-Field MRI

Motivation: In this work, we investigated the performance of a coaxial dipole antenna compared with a single wire for dental MRI at 3 T.

Goal(s): A fully flexible coaxial dipole antenna was designed and optimized with an aim to improve the signal-to-noise ratio, image quality, and sensitivity while maintaining safety performances.

Approach: Based on electromagnetic simulations and MRI results it is demonstrated that in single conductor has a current distribution, which is strongly inhomogeneous leading to inhomogeneous B1⁺ field distribution. 

Results: In contrast, coaxial cable with multiple gaps offers homogenous current distribution yielded to optimum B1⁺ field distribution.  

Impact: The development of a fully flexible coaxial intraoral antenna with lightweight, capable of overcoming impedance and homogeneity challenges, has the potential to revolutionize dental MRI. Enhanced patient comfort and adaptability improve image quality, advancing dental MRI's utility in medical imaging.

Keywords: Hybrid & Novel Systems Technology, High-Field MRI, RF Systems, Parallel transmit

Motivation: Ultra-high field imaging has several advantages like high SNR but require expensive RF shimming hardware to mitigate image shading artifacts caused by transmit RF field inhomogeneity.

Goal(s): We developed a low-cost, highly customizable hardware solution to extend conventional RF shimming capabilities.

Approach: We used array compressed parallel transmission system with an optimal network and fixed optimal weights designed to sit inside the bore with the coil array

Results: The optimal network achieved about two-fold improvement in RF homogeneity compared to conventional circularly polarized network.

Impact: This is the first time a design framework is described to optimize a full acpTx system for a desired imaging application. This hardware-centric approach has no additional pre-scan preparation or time considerations, lending itself to future clinical use.

Keywords: High-Field MRI, High-Field MRI, Radiofrequency coil, Neurovascular imaging

Motivation: Current methods for neuroimaging at 7T require separate coils for brain and c-spine imaging or rely on a 16-channel transmission setup for combined imaging.

Goal(s): To develop a neurovascular (NV) coil with eight transmit channels (industry standard) with extended longitudinal coverage from the brain to the neck region. 

Approach: Based on coupled electromagnetic and circuit optimization, a modified coil configuration with six-upper and two-lower transceiver elements was constructed and integrated with a 56-channel receive array.

Results: Measurements in vivo suggest that the proposed NV coil delivers diagnostic-quality images of the brain and spinal cord in a single acquisition.  

Impact: The 7T neurovascular coil, designed for concurrent brain and c-spine imaging, will extend the high-resolution capability of 7T-MRI to the routine diagnosis of diseases affecting soft tissues and vessels in the head and neck regions in clinical practice.

Keywords: Parallel Transmit & Multiband, Parallel Transmit & Multiband, 7 Tesla, Spinal Cord, Universal Shim

Motivation: Addressing the issue of lengthy parallel transmit (pTx) adjustment times caused by the absence of a dedicated spinal cord (SC) coil setting, which limits SC imaging at ultra-high field.

Goal(s): Enhance imaging efficiency by universal shim modes that can be applied without the need for additional adjustment time for different SC regions and coils.

Approach: We have built a library of channel-wise B₁⁺ maps and optimized universal RF shims to optimize transmit homogeneity and efficiency.

Results: The proposed universal shims significantly improve B₁⁺ efficiency, achieving a 50% enhancement compared to the default shim mode, while eliminating the need for subject-specific pTx adjustments.

Impact: The development of universal shims not only enhances SC imaging efficiency at ultra-high field but also streamlines the process by eliminating lengthy subject-specific pTx adjustments, expecting SC imaging to become more usable for non-pTx experts.

Keywords: RF Arrays & Systems, Pediatric, RF Coil, High Field MRI, 7T

Motivation: To develop a safe, size-adaptive RF head coil with an integrated commercial field monitoring system for pediatric imaging at 7T MRI.

Goal(s): Performance of the size-adaptive RF head coil was quantitatively evaluated and compared to that of a commercial receive adult head coil (Nova Medical).

Approach: The coil performance was evaluated at the largest and smallest dimensions of the receive former, with and without integrated field probes.

Results: Simulations of transmit coil demonstrated that the coil is safe for pediatric imaging of subjects below 30 kg at 7T. The SNR performance of the coil was comparable to the commercial coil. 

Impact: The eight channel dipole transmit and 32 channel size-adaptive receive array with integrated 16 NMR commercial field monitoring probes for imaging pediatric (4-9 years old) brain at 7T enables safe and high-quality imaging of subjects below 30 kg at 7T.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: RF challenges increase with field strength, and novel RF coil solutions are essential to capture the potential benefits at 11.7T

Goal(s): To develop an efficient 8-channel transmit array in combination with a 31-channel receive array for whole brain MRI at 11.7T

Approach: Combined electromagnetic and RF pulse design simulations were performed. A folded-end RF shield was developed to minimise signal loss due to wave propagation. The receive array was optimally integrated to preserve the spatial distribution of the B₁⁺ field.

Results: Whole-brain coverage was achieved with 8-channel transmit array and excellent agreement between simulation and measurements was observed.

Impact: Identifying the coil losses and engineering solutions to mitigate them provides substantial gains in transmit performance, especially at 11.7T where the losses due to radiation is high. This approach can be extended to transmit array designs at other field strengths.  

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Ultra-low MRI systems provide a reduced SNR.

Goal(s): Our goal is to improve the SNR by incorporating SQUID-based RF detection into the ULF MRI system.

Approach: We build a custom-made SQUID MRI system and acquire the first 2D image of a phantom as proof of concept.

Results: we successfully acquired a 2D image of a phantom in 4 hours with a resolution of 15×12.5 mm²

Impact: Striving for MRI accessibility, we develop a portable ultra-low field scanner using highly sensitive SQUID detection. Our first 2D image marks the initial stride toward achieving clinically competitive image quality.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Accurate RF excitation in MRI requires a linear response from the radio-frequency power amplifier (RFPA). However, the conventional RF power amplifier (RFPA) used in MRI is typically located in the equipment room, which introduces complexity and significant signal losses. Additionally, it poses challenges to direct control of RF signals at the RF coil side.

Goal(s): Design high power and high linearity RFPA which can operate in a strong magnetic field environment.

Approach: The design incorporates non-magnetic high-power circuits and a negative feedback control module.

Results: The amplifier exhibits high power and linearity characteristics during the bench testing.

Impact: The proposed design method for non-magnetic RFPA can enhance the efficiency and linearity of RF excitation in MRI, multiple non-magnetic RFPAs will be fabricated to facilitate parallel transmission in 5T MRI.

Keywords: Data Acquisition, Software Tools, Radiofrequency, MaRCoS, open-source

Motivation: MaRCoS is an open-source tool integrating hardware, firmware, and software for low-field MRI system control. But releases lacked user-friendly features, requiring technicians to handle automatable operations manually.

Goal(s): To simplify clinical workflows, we developed a device for RF coil impedance tuning and matching in systems controlled by MaRCoS.

Approach: Our approach involved designing a TM device using switchable capacitors and testing it in a real clinical environment on a portable 72 mT system.

Results: The auto-TM system, tested on 20 volunteers (40 protocols), significantly accelerated and improved workflow compared to manual methods, marking a substantial advancement in MRI system efficiency and usability.

Impact: The introduction of our automatic tuning and matching device eases low-field MRI systems controlled by MaRCoS. By simplifying clinical workflows and improving efficiency, this innovation enhances the user experience, simplifing the workflow under clinical environments.

Keywords: New Devices, Hybrid & Novel Systems Technology

Motivation: Detection of vital signs in MRI is hampered by the harsh environment of the MR-scanner and requires setup time.

Goal(s): Use integrated (i.e. no setup time) sensors that are fully MR-compatible and provide reliable cardiac and respiratory signals. 

Approach: Fiber Bragg Grating (FBG) based sensors (optical sensors) are integrated into the headrest of an MR-coil and the MR-bed for detection of heart beat and respiratory cycle. 

Results: MR-system integrated FBG sensors pick up cardiac and respiratory signals. The challenge lies in the realtime filtering of these signals to be able to use them for triggering of the scanner. 

Impact: Patient setup time can be reduced for exams requiring cardiac and/or respiratory signals by using MR-system integrated FBG sensors.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Conventional MRI breast screening is performed in the prone position with rigid RF coils. These coils are uncomfortable and imaging area limited by patient size and positioning.  

Goal(s): Our goals were to improve patient comfort, accommodate varying breast sizes, and provide faster screening through an adaptable breast coil utilizing stretchable elements.

Approach: A 20-channel breast coil was created with stretchable elements to accommodate varying bust sizes. Bench and phantom scans comparisons were made against an industry-standard flexible coil.

Results: Compared to industry-standard, highly-flexible coils, this coil demonstrated better adaptability to larger breasts, with improved sensitivity along the breast contour, and better acceleration.

Impact: Compared to the use of a traditional flexible coil of similar channel count for supine breast imaging, this coil can adapt to a wider range of breast sizes with easier setup, enhanced patient comfort, and performs better at greater acceleration.

Keywords: New Devices, New Devices

Motivation: The balun or cable trap circuits associated with the RF coil are favored to be miniaturized, light-weighting, and even flexible.

Goal(s):  We proposed a reproducible and miniaturized Bazooka balun using printed coaxial capacitors.

Approach: EM simulations were performed to guide the practical fabrication. The miniaturized Bazooka balun is made of the double-layer printed circuit board, allowing mass manufacturing ability in practice.

Results: The extremely thin layer in the printed capacitor (25 micrometers) provides a large capacitance of tens of pF per centimeter and allows the total length to be much shorter.

Impact: This reproducible and miniaturized balun is ideal for flexible and wearable RF coil designs, enhancing patient comfort and MRI image quality in diagnosis.

Keywords: New Devices, Relaxometry

Motivation: Bioreactor cell density measurements currently require removing samples from the culture. This limits how many samples can be taken in a day and precludes real-time culture monitoring.

Goal(s): We sought to take nondestructive cell density measurements every ten minutes without removing cells from the bioreactor.

Approach: We built a system that takes T₂ relaxometry measurements through the bioreactor’s silicone tubing every ten minutes and compared these to measurements taken by a commercial cytometry system.

Results: The T₂ relaxation data closely tracks the true cell density. Changes made to the culture are detected much more quickly by the relaxometer. 

Impact: Magnetic resonance relaxometry can be used to track bioreactor culture growth in real time, and makes it possible to identify and correct problems with the culture before the culture fails.

Keywords: New Devices, New Devices, Metamaterials

Motivation: High permittivity metamaterials have shown benefits in UHF MRI. However, precise dielectric constant measurement method for metamaterials is in absence, which may lead to bias in field manipulation.

Goal(s): Developing a precise measurement method to better mimicking dielectric materials’ role in field manipulation, where samples are placed at the reactive near-field region.

Approach: A microstrip line resonator was used to measure resonances of metamaterials. The resonance of dielectric materials with particular properties were chosen as the reference. Their difference in resonance frequency is required to be minimized.

Results: Metamaterials designed using our approach exhibited superior accuracy in mimicking the target dielectric pad.

Impact: The proposed method leads to better mimicking dielectric materials’ role in field manipulation at reactive near region. Metamaterials designed with this method exhibit enhanced B₁ field and lower SAR, signifying a significant advancement in UHF MRI and promising precise diagnoses.

Keywords: Phantoms, Thermometry

Motivation: To demonstrate the utility of inexpensive easy-to-use commercial MRI-readable thermometers for monitoring phantom temperatures during imaging and enable temperature corrections in an MSK relaxometry phantom developed for inter-site relaxation time (T1, T2, T1ρ) comparisons.
 

Goal(s): Provide convenient thermometry for temperature corrections for phantom based intersite comparisons of relaxation time and diffusion measurements.

Approach: Commercial incubator thermometers with a temperature range of 15°C to 50°C were characterized for phantom thermometry.

Results: Commercial incubator thermometers demonstrated to be MRI readable with an accuracy of ±0.2°C using standard imaging protocols, as long as the thermometer axis is perpendicular to the readout direction.

Impact: Easy to use MRI-readable thermometry is available to enable temperature corrections to minimize confounding factors in inter-site comparisons.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Wireless clock synchronization must be implemented to achieve a wireless MRI receive coil architecture.

Goal(s): Our goal was to implement atomic clock timing via global navigation satellites signals (GNSS) to the receive coil in the scanner for high precision clock correction and synchronization. 

Approach: We performed benchtop measurements to measure the precision of clock correction achievable with GNSS and precision time protocol (PTP), as well as modified an iRFW coil to receive these GNSS signal from within the scanner bore.

Results: Bench-top clock  measurements showed nanosecond precision time-synchronization using PTP-GNSS, and the iRFW-GNSS successfully acquired atomic clock time signals within the scanner bore. 

Impact: The iRFW-GNSS coil design can perform the wireless transfer MRI data and clock-syntonization regardless of scanner platform allowing for wide spread adoption of wireless MRI for new and existing scanners.   

Keywords: Hybrid & Novel Systems Technology, Hybrid & Novel Systems Technology

Motivation: The threshold to efficient use of field cameras is high and they could benefit from being less dependent on the scanner system they're being used in.

Goal(s): The aim of this work is to develop an independent field monitoring system that can synchronize itself with and make targeted measurements of MR sequences.

Approach: We employ a commercial NMR field probe system and trigger it externally using a host PC for data processing and an FPGA as a timing system.

Results: We are able to independently synchronize the monitoring system, make targeted measurements of a sequence and decompose a set of gradient waveforms.

Impact: This work is a step towards enabling scanner independent monitoring of MR sequences with NMR field probes. This could be useful in cases where the integration of a field camera is not an option. 

Keywords: Parallel Transmit & Multiband, RF Arrays & Systems, FPGA, RFPA

Motivation: Careful attention to safety is required for human research with novel parallel transmission (PTx) MRI technologies, particularly when they may cause harmful interactions with implanted devices.

Goal(s): Our goal was to add an additional layer of safety during experiments with a custom PTx research platform.

Approach: A system supervisor was created to monitor and react to a variety of amplifier faults and power conditions.

Results: Initial tests showed that it could safely disable the PTx system with acceptably short and stable response times.

Impact: A system supervisor was developed and tested for parallel transmission MRI research. The presence of such a supervisor may accelerate acceptance of PTx research systems by safety-conscious researchers and reviewers.

Keywords: New Devices, Brain, Optical position tracking

Motivation: Optical position tracking (OPT) systems have been used successfully in motion correction, however, the comparison of new and pre-existing OPT systems remains challenging due to lengthy calibration procedures.

Goal(s): Our goal was to create a testing platform capable of operating two systems concurrently for validating new OPT methods.

Approach: Two dual camera systems were set up in the magnet room with a custom calibration stage. A phantom was used to transform coordinates from the camera to the magnet coordinate frame.

Results: Camera calibration is limited to 30-minutes and outputs expected values. The pre-existing OPT system is accurate.

Impact: With this testing platform, two optical position tracking (OPT) systems can be compared simultaneously on participants in the MR environment, rather than individually on the benchtop. This allows validation of OPT methods that are highly dependent on the testing environment.

Keywords: New Devices, Hyperpolarized MR (Gas)

Motivation: In the Spin Exchange Optical Pump (SEOP) technique, the spare space between pump cell and gas manifold, called dead space, might impact polarization through dilution and dark rubidium depolarization.

Goal(s): This study aims to improve the design of the stop-flow polarizer to minimize dead gas and thus increase the polarization efficiency.

Approach: A magnetic-compatible actuator was designed for automatic control of cell stem valves opening/closing in our homemade polarizer, with good adaptability of main pumping field, Class I laser regulation and mechanical deviation. 

Results: Results show that under the same temperature, the polarization levels with actuator were always better than the control group.

Impact: The application of actuator in stop-flow polarizer shows the feasibility of improving polarization through minimizing dead space. It can be quite useful when acquiring small amount of HP gas but with higher requirement on polarization.

Keywords: RF Arrays & Systems, New Devices

Motivation: Float cable trap has gained widespread adoption in RF coil owing to its unique advantages. However, conventional float trap requires considerable dimensions to achieve an excellent performance.

Goal(s): This study is aiming to propose a novel float balun that can achieves high performance but with a compact size.

Approach: It was inspired by the well-established solenoid trap. The solenoid structure leverages strong inductive coupling between the cable shield and float resonator, ensuring high efficiency and enabling a compact design.

Results: With a compact size of 1.5x3cm², solenoid float balun shows a measured CMRR of -31 dB (vs. -5 dB using conventional float trap). 

Impact: The novel, compact and float balun offers significant advantages in the field of MRI RF coil and RF safety. It reduces the overall bulkiness of the RF coil, enables the incorporation of a greater number of elements in receive arrays.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Wireless MRI signal transfer reduces the need for physical cabling that can complicate patient table design and impede local coil preparation. Proposed techniques to eliminate cabling can involve complex subsystems for clock synchronization, high-fidelity ADC, low EMI, and high-speed data transfer. 

Goal(s): Our goal was to implement a short distance contact-free signal and power transfer system without complex circuitry. 

Approach: We designed a system to eliminate coil-to-scanner connections by transferring coil signals and preamplifier power over short distances using inductively coupled loops. 

Results: SNR in images acquired with the contact-free and traditional (wired) systems were within 3-5%. 

Impact: The proposed contact-free signal and power transfer system eliminated the physical connection between the coil and scanner while maintaining SNR, which opens the door to wireless coils and more robust and low-cost, detachable patient tables.

Keywords: New Devices, New Devices, In-bore electronics

Motivation: Due the noise emission of switch mode power supplies, linear regulators are often present in electronics in and around the MR bore, with the related thermal challenges. 

Goal(s): In this work we present a switched capacitor converter witch is capable of providing high output currents without emitting noise in the MR RF band. 

Approach: The goal was achieved by controlling the slew rate of the gate source voltage of the switching GaN FETs. 

Results: High efficiency, low output ripple and no unexpected transient behavior could be measured on the bench.

Impact: The presented 10A switched capacitor converter can provide efficiently power to electronics without emitting RF noise around the MR RF band. Enlarging the integration possibilities of high density electronics in and around the MR bore.

Keywords: New Devices, New Devices, Force Measurement

Motivation: Conventional load cells are not MRI-compatible, and MRI-compatible fiber optic force sensors are expensive and require specialized data collection systems.

Goal(s): Our goal was to develop and test a low-cost, MRI-compatible device for continuous force measurement.

Approach: We developed a hydraulic-based system for measuring continuous compressive forces within the magnet bore during scans.

Results: Pre-cycling increased the measurement repeatability of the device. The device was completely MRI-compatible and measured continuous compressive forces while simultaneous MRI data was acquired.

Impact: Our newly developed device is an inexpensive option for measuring continuous compressive forces during simultaneous MRI scans and is particularly useful for researchers who want to use a conventional electronic data acquisition system.

Keywords: Signal Representations, Signal Representations

Motivation: Point-of-Care Low Field MRI scanners are predominantly stifled by generic time-varying EMI, engendered by adjoined scanner electronics, environmental interference & radiation close to the lamor frequency and extraneous , creating decreased signal-to-noise ratio and artifacts on images.

Goal(s): Passive Faraday Shielding & Effectiveness Testing, EMI Detection, Cancellation using a single RF coil.

Approach: Passive Faraday Shielding using Aluminium and Copper sheets, Shielding Effectiveness testing using calibrated transmitters and receivers, EMI detection & cancellation using a single RF coil.

Results: Faraday Passive Shielding done and upto 74dB EMI attenuation effective. Active EMI detection & cancellation showed  EMI reduction up to approximately 53% in signal strength and 46%  image quality.

Impact: Broadband and Structured EMI elimination using passive faraday shielding with additional suppression techniques like system grounding, detection and elimination using a single coil will significantly improve signal strength by curbing signal loss and consequently better image quality. 

Keywords: RF Arrays & Systems, RF Arrays & Systems, X-nuclear array coil

Motivation: ³¹P MRSI provides a valuable tool for metabolic imaging of human brain, and is crucial for studying neuroenergetics and neurological diseases, however, faces the low SNR challenge. 

Goal(s): To construct a dual-tuned 8-channel ³¹P/¹H transceiver array head coil with excellent performance for both proton structural MRI and ³¹P MRSI at 7T.

Approach: We constructed an 8-ch ³¹P/¹H transceiver array coil based on the novel double tuned and double matched (DODO) coil element, and compared its performance with the ³¹P/¹H TEM volume coil.

Results: The 8-ch ³¹P/¹H transceiver array coil shows significantly higher performance compared to ³¹P/¹H TEM volume coil.

Impact: We developed an 8-ch ³¹P/¹H transceiver array coil with excellent performance based on the DODO coil design. This technology has broad applications for in vivo human brain ³¹P MRSI studies and can be adapted to other multinuclear array coil designs.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: The poultry industry utilizes MRI to assess egg quality, especially to identify fertilized eggs. Image quality across eggs should be similar and with efficient filling factor.

Goal(s): The goal is to design a specialized coil for MRI that can efficiently and accurately scan multiple eggs , providing the same image quality for each egg.

Approach: The proposed coil has a multiloop structure. We used electromagnetic simulations to compute the magnetic field and compared the proposed coil with a volume and individual loop coils.

Results: Validated through simulations and MR images, the coil displayed the scalability and, enabling the imaging of multiple eggs

Impact: The proposed coil design  shows better egg per area filling factor efficiency and uniform image quality for each egg and also scalability for high-throughput egg screening. This design promises to enhance multiple egg imaging quality control in the poultry industry.

Keywords: High-Field MRI, High-Field MRI, Flexible coils, SAR efficiency, Coupling, Non-uniform current distribution

Motivation: At Ultra-High-Field, non-uniform currents have the potential to boost efficiency of loop coils at depth. However, possible advantages of non-uniform current naturally arising from short wavelength at Ultra-High-Field have not been investigated yet.

Goal(s): To characterize the impact of non-uniform currents on SAR efficiency for different coil geometries and coil orientations relative to the main magnetic field, and evaluate the feasibility of using such coils

Approach: Analysis was performed using simulations and experiments

Results: A 62x280mm elongated loop provided higher SAR efficiency than a conventional loop, or a dipole, at depth, with flexibility. low coupling, similar SNR and transmit efficiency than a dipole.

Impact: An elongated design of loops provided higher performance than conventional loops and dipoles in terms of SAR efficiency at depth, with flexibility, and low coupling. Results in this work provide a new avenue to explore in flexible coil design.

Keywords: RF Arrays & Systems, High-Field MRI, non-human primate, RF antenna, Dipole

Motivation: Imaging the brains of non-human primates (NHPs) at ultra-high field (UHF) is challenging, especially for whole-brain functional imaging in awake NHPs where high SNR is needed.

Goal(s): To design a dedicated system that overcomes challenges associated with UHF imaging and enhances signal-to-noise ratio (SNR) for high-quality NHP brain imaging.

Approach: We developed a 6-dipole parallel-transceive array, and a 16-loop receive array, optimized through electromagnetic simulations. We implemented preamplifier-decoupled dipoles to reduce coupling issues.

Results: The system showed good preamplifier-decoupling levels. Our dipoles’ implementation reduced experimental noise matching issues and EM simulations shows an SNR improvement.

Impact: Our 6pTx/22Rx antenna should improve awake NHP brain imaging at UHF, including transceive preamplifier-decoupled dipoles, designed for a specific imaging setup.

Keywords: RF Arrays & Systems, RF Arrays & Systems, g-factors

Motivation: Driven by the potential of the highly flexible twisted pair coil in creating unique sensitivity patterns for optimal acceleration.

Goal(s): To compare geometry factors of the twisted pair and conventional copper coils, exploring effective arrangements for various coil shapes.

Approach: Simulations of eight-element arrays containing circular and elongated coils; assessing geometry factors and the impact of random coil placements.

Results: Findings emphasize similar geometry factors between the twisted pair and conventional coils. Moreover, random coil setups around a phantom do not inherently improve geometry factors.

Impact: A comparison between twisted pair and conventional coils shows similar performance in g-factors. The flexibility of the twisted pair can be used to improve the g-factor but more work is required in finding the optimal shape of these coils.

Keywords: RF Arrays & Systems, RF Arrays & Systems, 3T 13C applications, low field transmit array design

Motivation: Tackle the coupling issue among the coil elements in phased array design at low field, so as to use phased array as transceiver at low fields for good transmit efficiency, receive sensitivity profile, and acceleration performance.

Goal(s): Design and build a 3T ¹³C/¹H 8-channel array for hyperpolarized ¹³C MRSI and steady-state ¹³C MRS after oral uptake of ¹³C labelled glucose

Approach: Use a novel cable trap decoupling mechanism to decouple the coil elements in the 3T ¹³C 8-channel array

Results: Workbench and experiment results show that the coil elements are decoupled very well with each other.

Impact: This innovative research on mitigating coil element coupling in low-field phased array designs empowers low-field MRI applications. Enhanced transmit efficiency, receive sensitivity and acceleration performance offer improved diagnostic quality, benefiting scientists, clinicians, and patients.

Keywords: New Devices, Spectroscopy

Motivation: Quantification of magnetic resonance spectroscopy (MRS) spectra requires sufficient SNR to detect changes in metabolic state. At ultra-high field, low concentration metabolite require length scan times to obtain sufficient SNR.

Goal(s): To use a novel metasurface design to enhance the B₁^- receive sensitivity in phantom and in vivo brain proton spectroscopy data at 7T, resulting in increased SNR without additional scan time.

Approach: Receive sensitivity enhancement was measured in phantom and in vivo experiments with and without the metasurface present.

Results: The metasurfaces enhanced phantom spectral SNR by an average of 58%, while in vivo spectral SNR was improved on average by 38%. 

Impact: The work impacts 7T spectroscopy techniques by improving the inherent receive sensitivity, yielding higher SNR spectra. Future work will focus on demonstrating this application in patent populations to reduce scan times and enhance the signal from low concentration metabolites.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: Simultaneous functional imaging of the brain and spinal cord can offer valuable insights into the interactions and processing pathways between these organs

Goal(s): The goal is to build an transmit array and receive array for 7T the brain and spinal cord MRI.

Approach: The approach uses corner-fed self-decoupling for transmit array and center-fed self-decoupling for receive array.

Results: A 20-channel modular self-decoupled transmit array and 32-channel overlapped receive array were fabricated. Both arrays exhibit excellent matching performance, acceptable decoupling, and high detuning ability. Thanks to the self-decoupling technology, both arrays are splitable which simplifies the setup and allows for easier access by subjects.

Impact: The proposed device will solve the hardware issue and permit studies of healthy subjects to improve our understanding of the resting-state connectivity and interaction between the brain and spinal cord, compensating impaired sensory, motor, or autonomic functions in neurological disorders.

Keywords: RF Arrays & Systems, High-Field MRI, Hybrid & Novel Systems Technology, RF Array, Parallel Imaging

Motivation: Increased sensitivity and sufficient image coverage is demanded for more efficient and comprehensive extremity imaging. 

Goal(s): Our goal is to exploit multiple-row quadrature RF coil array configuration to increase detection/transmission sensitivity and image coverage for human knee imaging at 7T. 

Approach: Due to the increase of the channel count in a multiple-row configuration, it is technically challenging to attain adequate decoupling between quadrature elements of the array. We address this issue by using a double cross magnetic wall decoupling.

Results: The use of double cross magnetic wall decoupling have proven to be an efficient decoupling method. 

Impact: The feasibility of this work is a substantial achievement in the multichannel RF hardware engineering, poised to enhance MR imaging technology, especially in high-field applications, where multiple-row quadrature RF coil array configuration can significantly impact image quality and overall efficiency.   

Keywords: RF Arrays & Systems, MSK, Sodium, Ultra-High Field, Knee

Motivation: Overcome the limitations of current sodium/proton knee coil configurations using a flexible RF coil array system

Goal(s): Acceptance testing of a 32 channel (16 proton and 16 sodium) RF coil array and demonstrate applicability for sodium and proton MRI of the knee.

Approach: 8 hexagonal modules (4 coils each) were assembled in a volumetric configuration, with sodium and proton MRI quality assessed for phantom and human knee imaging.

Results: High quality sodium volumetric images of the knee were obtained while anatomical proton images were achieved using a standard TSE sequence with additional GRAPPA acceleration and without repositioning

Impact: A 32 channel modular array has been demonstrated to be an effective and flexible solution for both proton and sodium MRI of the knee. Sodium sensitivity was optimised while maintaining proton performance sufficient to acquire accelerated high quality anatomical images.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: The use of MLCs has shown the potential to improve the SNR at short distance as compared to an equivalent SLC.

Goal(s): Evaluation of the performances of a 8-channels MLC-array for head imaging at 7T.

Approach: Electromagnetic simulation was used to evaluate and compare the SNR, noise-covariance matrix and g-maps obtained with the MLC-array and with an equivalent array of SLC.

Results: As compared to the SLC-array, the MLC-array achieves an increased SNR in a relatively large peripheral ring and a reduced maximum g-factor.

Impact: Array of MLC represents a valuable strategy for array developpement at high field that can be employed to improve the SNR or reduce the number of  channels.

Keywords: RF Arrays & Systems, New Devices

Motivation: Advancements in array coil technology may not yield proportional gains in temporal SNR when physiological fluctuations are the primary noise source.

Goal(s): We constructed a highly dense array covering the visual cortex and evaluated its noise characteristics and performance as a function of resolution.

Approach: We evaluated image SNR and temporal SNR in vivo at 7 Tesla and produced BOLD activation maps using a visual paradigm.

Results: The improvement in image SNR with decreased resolution was significantly higher than the improvement in temporal SNR. This suggests physiological noise dominance at the lower resolution.

Impact: The image and temporal SNR offered by the visual coil allows for sub-millimeter resolution. Insight into the transition between thermal and physiologically noise dominated regimes will aid in reducing the risk of false positives in fMRI using this dense array.

Keywords: RF Arrays & Systems, RF Arrays & Systems, RF Rx array, Hybrid RF and shimming, Multi-coil shimming

Motivation: Multi-coil (MC) B0 shimming provides unrivaled brain shimming, yet early proof-of-concept implementations with preexisting RF hardware suffered from coupling and reduced sensitivity.

Goal(s): The design and realization of integrated MC/RF hardware for dynamic MC technique (DYNAMITE) B0 shimming of the human brain at 3T at full RF sensitivity.

Approach: We experimentally validate previously derived theoretical strategies for the minimization of MC-to-RF coupling and design integrated MC/RF hardware for MRI of the human brain.

Results: Great agreement was found between direct coupling measurements and simulated magnetic field flux, which was used in our previous work as a proxy of coupling due to mutual inductance.

Impact: Once the hardware construction and implementation with clinical MRI protocols is complete, the novel MC/RF setup is expected to improve diagnostic imaging in brain areas suffering from inhomogeneous B0 conditions.

Keywords: Safety, Safety

Motivation: Brain MRI with shoulder implants are often contraindicated at 7T with head coils due to possibility of radiofrequency (RF)-induced heating. Such implants are not uncommon in older adults; contraindication results in increasing proportion of elderly to be denied high-field scans. Assessing heating safety of MRI at 7T with implants is of significance.

Goal(s): To measure shoulder implant heating during MRI at 7T with pTx head coils and assess safety thereof.

Approach: Temperature of a reverse total shoulder implant was measured with fluoroptic sesnors during MRI at Siemens 7T Terra with pTX head coil.

Results: No significant heating (>1°C) of the implant was observed.

Impact: Findings from this study may enable brain scanning individuals with shoulder implant at 7T, thus making improved image quality a possibility.

Keywords: High-Field MRI, RF Arrays & Systems

Motivation: Labeling efficiency in pCASL suffers from an inferior drop-off in B1+ leading to low SNR perfusion-weighted images which can affect CBF quantification.

Goal(s): To assess the feasibility of pCASL in healthy volunteers using a custom-built head and neck coil at 7T.    

Approach: Volunteers were scanned with pCASL on two coils: a normal head coil and a head and neck coil with circularly polarized shim weights, and the results were compared in terms of CBF and tSNR.

Results: pCASL in healthy volunteers using a novel neurovascular coil at 7T gave an average GM/WM CBF ratio of 1.51, comparable to a conventional head coil.

Impact: This proof-of-concept study shows the feasibility of pCASL using a novel 8TxRx56Rx neurovascular (head and neck) coil at 7T and compares the performance against a conventional 8Tx64Rx head coil.

Keywords: High-Field MRI, Modelling, 9.4T RF coil LFMS TMS

Motivation: Recently, The research methods of transcranial magnetic stimulation(TMS)/fMRI in ultra-high fields are receiving increasing attention.

Goal(s): However, as the magnetic field strength increases, the interference problem between the TMS coil and the radio frequency（RF） coil will also become increasingly apparent.

Approach: We designed two types of TMS coils and 9.4T human RF  coil using the target field method, and evaluated the impact between the TMS coil and the RF coil using electromagnetic simulation based on the human head model.

Results: We have established a method for evaluating the interaction between RF coils and TMS coils in ultra-high fields.

Impact: Our work explores the combined use of TMS/fMRI in ultra-high fields, providing a non-invasive and precise approach for the microscopic study of brain nerve activity under  TMS, and also providing a basis for the regulation of brain nerves.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: To explore the SNR performance of Loop and Sleeve antennas for multi-channel human head imaging at 10.5T.

Goal(s): Validation of achievable receive performance of loop and sleeve antennas with same number of channels. 

Approach: Simulation based analysis of SNR between loop and sleeve antennas with same channels.

Results: We obtained and compared simulated SNR data of loop and sleeve antennas. For the same number of channels (1, 3, 5, and 32-channels), each SNR map was compared with similar imaging coverage. Our experimental data indicates an enhancement of SNR achieved with the 32-channel sleeve antenna array compared to the 32-channel loop array.

Impact: Our simulations indicate that a high-density sleeve antenna array compared to a classical loop array can achieve enhancement of SNR for human head imaging at 10.5T.

Keywords: Non-Array RF Coils, Antennas & Waveguides, High-Field MRI, Split Ring Resonator; Metamaterial surface; Loop Array

Motivation: Metasurfaces are conceptually appealing for enhancing RF coil performance due to added degrees of freedom for shaping electromagnetic fields. 

Goal(s): This work focuses on  development and validation of a novel split ring resonator (SRR) based metasurface for improving the performance of a two-channel surface loop array at 7.0 T.  

Approach: Application of a magnetic field perpendicular to SRR induces electromotive force, forming an LC circuit with resonance frequency as currents circulate between the rings. This property benefits MRI transmission field enhancement. 

Results: Our simulations and experimental results demonstrate that  wireless metasurfaces enhance transmission efficiency of a two-channel surface loop coil array at 7T.

Impact: Our approach provides technical foundation for development, implementation and validation of novel metasurfaces for RF arrays customized for UHF-MRI. Our metasurface offers customizable resonance properties by adjusting unit cells, periodicity, or structure placement to enhance transmit field efficiency and uniformity.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Challenges, Materials

Motivation: In MRI of tissues with short T₂, materials of RF coils may be detected and can cause background artefacts. Current solutions to this problem either compromise sequence performance or impose restrictions on coil design.

Goal(s): Making RF coils MR-invisible.

Approach: The material used for constructing the coil housing is filled with ferrimagnetic material, leading to effective signal spoiling. Coil formers are created by additive manufacturing using custom filaments made from magnetite-filled polymer.

Results: Unwanted signals from the RF coil are eliminated by using coil formers made from magnetically filled polymer. Hence, background-free short-T₂ imaging is enabled.

Impact: RF coils made MR-invisible by using magnetically-filled materials simplify coil design and manufacturing, and improve the performance of MRI of tissues with short T₂, such as bone, tendon, lung, or myelin.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: Wave-impedance-match is key to ensure maximized power transmission in travelling-wave (TW) MRI. Currently, only coaxial waveguide method has been proposed. It requires adding metallic cylinder inside magnet and gradient coils, which introduces risks of mechanical instability and patient safety due to eddy current.

Goal(s): Propose a novel wave-impedance-match method for TW excitation with non-metallic materials.

Approach: Dielectric cubes made up of easy-accessible distilled water were modelled and placed between feed and the load. Power-flow-density and power-loss results were used to evaluate wave-impedance-match.

Results: Wave-impedance-match varies with length and width of dielectric cube. The well-matched conditions with dielectric cube and coaxial waveguide are similar.

Impact: Non-metallic wave-impedance-match method was proposed for TW excitation. This has the potential to accelerate maturity of traveling-wave excitation method in UHF MRI.

Keywords: Non-Array RF Coils, Antennas & Waveguides, RF Arrays & Systems

Motivation: To develop a new generation of head coils for ultrahigh field MRI using loop-dipole combined dielectric resonator antenna arrays.

Goal(s): To construct and evaluate an 8-channel loop-coupled dielectric resonator antenna array for brain MRI at 7T.

Approach: Electromagnetic field simulations in a spherical phantom and Duke for different types of RF feeds were performed. An 8-channel, loop-coupled dielectric resonator antenna array was constructed using 8 ceramic, rectangular dielectric blocks (ε_r=275, σ=0.068 S/m).

Results: An 8-channel loop-coupled dielectric resonator antenna array was successfully constructed and evaluated at the bench as well as in preliminary phantom experiments at 7T using pTX system.

Impact: This study is an important step to improve transmit and receive performance of head coils for neuroimaging at 7T.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: Metamaterial-based designs have the potential to locally increase the RF field and to serve as resonators in MRI. However, many of the structure either include a high dielectric layer substrate or require large amount of lumped elements.

Goal(s): Our goal was to design a metamaterial without the need for either.

Approach: A novel metasurface was constructed from concentric split-rings alternatingly rotated by 90° - generating a maze-like configuration - which allowed to lower the resonant frequency.

Results: The novel maze-like metasurface achieved an RF field increase in the range of x1.5-2 compared to using a surface-coil of the same dimensions.

Impact: We demonstrated a new metasurface geometry that provides an efficient resonator at 298 MHz for 7T MRI. This design does not require high dielectric or lumped elements, which offers a simple implementation, a flexible setup and a high efficiency resonator.

Keywords: Non-Array RF Coils, Antennas & Waveguides, RF Arrays & Systems, stretchable

Motivation: Most commercial MRI coil designs are rigid, prohibiting optimal SNR and patient comfort. Flexible coils conform to anatomies varying in size/shape and significantly improve image quality in applications such as breast imaging.

Goal(s): We optimize manufacturing of our previously developed stretchable coils by direct integration of liquid metal within the polymeric coil substrate to allow for rapid one-step fabrication of multi-element arrays in the future.

Approach: Liquid metal is directly 3D printed on the substrate to expedite/integrate fabrication.

Results: A stretchable single element is fabricated and resonance at the 3T Larmor frequency is demonstrated.

Impact: Our novel 3D printing technique simplifies the production of stretchable liquid metal MRI coils, ensuring consistent quality and efficiency. With reduced fabrication time and elimination of manual injection steps, this technology facilitates seamless construction of multi-channel stretchable coil arrays.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Software Tools, Birdcage Coil Design

Motivation: Currently the well-known BirdcageBuilder software tool for providing a first prediction of capacitor values for Birdcage Coil design is available only as an app for Android devices.  

Goal(s): We introduce an Open-source version of BirdcageBuilder available for the MR community to use and improve on GitHub.

Approach: From Java code for BirdcageBuilder Mobile, we developed a version in JavaScript. The GUI is an HTML web page, so the webapp runs in any modern web browser on any device. Outputs were validated against the original publication and the Mobile version.

Results: The software and code are available to all for use and improvement. 

Impact: A freely-available open-source version of the BirdcageBuilder software facilitates rapid design of birdcage coils and allows improvement by the MR community. Additional functionalities could include prediction of all resonances of a coil, noncylindrical coils, and output of a CAD model.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, High Temperature Superconductor

Motivation: Multi-Loop Coils (MLCs) allow to reduce the sample-induced noise while achieving a large Field Of View. Their sensitivity would be improved with the use of superconducting materials.

Goal(s): We aim to develop a superconducting MLC achieving both a large Field Of View and high quality factor.

Approach: An initial design is modified to render a MLC self-resonant and optimized using electromagnetic simulations.

Results: The HTS Multi Loop Transmission Line Resonator coil characterizations are presented. Q-factor and resonance frequency decline in presence of the static magnetic field or of a conductive sample but the coil still exhibits higher performances than copper MLCs.

Impact: Multi Loop Transmission Line Resonator represents a promising design strategy to increase the Field Of View of HTS reception coils without compromising with the coil sensitivity.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: The DHD coil in the previous study had a narrow sensitivity region. We developed a DHD coil with improved sensitivity region and B1 uniformity to image large samples while maintaining SNR.

Goal(s): Imaging of all organs, especially the brain of a human embryo, using a coil with a wider sensitivity region.

Approach: We performed electromagnetic field simulations to find the shape that would give the best performance, and fabricated the coil.

Results: The imageable area was widened by 30% and the insensitive area was reduced. Not only the brain of a human embryo, but also organs could be imaged at the same time.

Impact: The DHD coil's geometry was determined by electromagnetic field simulation, which allows a 30% wider range in the z-axis than conventional coils. The human embryonic brain and organs such as the heart could be simultaneously imaged with sufficient SNR.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, Metamaterial, Metasurface

Motivation: Although lower B₀ field strength generally lead to lower SNR, metasurface resonators can greatly increase the sensitivity of scanner-integrated coils to practically perform wireless imaging.

Goal(s): This work investigates the dependence of the resonance frequency on metasurface enhancements and evaluates the potential towards developments designed for low-field applications.

Approach: The capabilities of three geometrically identical metasurfaces were experimentally compared at field strengths of 0.55T, 1.5T and 3T. Images were acquired using the table-integrated spine-coils.

Results: The achieved SNR enhancements beneath the metasurface increased with lower field strength and were highest at 0.55T with 27-fold gain.

Impact: The significant SNR gain achieved at low-field paves the way for further development and implementation of wireless metasurface technologies in MRI. As flexible and cost-effective alternatives or additions to conventional coils, they can additionally ease patient postitioning.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: The demand for improving RF coil designs to maximize the potential of high-field MRI continues to grow. Exploring innovative RF coil elements holds the potential to improve RF coil performance and diagnostic image quality.

Goal(s): Our goal is to investigate the performance of a cycloid dipole antenna as a possible RF coil element for high-field MRI.

Approach: FDTD simulations were performed to compare the performance of a standard half-wavelength dipole at 7 T with two variations of the cycloid dipole.

Results: Cycloid dipole exhibits a shorter resonance structure, higher B₁⁺ and  B₁⁺/√SAR_{10g_max} efficiencies when compared to the standard dipole antenna.  

Impact: The study introduces cycloid dipoles as potential MRI coil elements. This opens opportunities for future investigations to optimize cycloid antennas within specific MRI coil designs, improving clinical imaging quality.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Simulations, High Permittivity Materials, Fetal, RF shimming, Specific Absorption Rate

Motivation: Performing MRI on fetus at 3T can be clinically valuable but often encounters difficulties in transmit field inhomogeneity and SAR increase. 

Goal(s): Determine dominant designing factors for optimal dielectric pad configurations to improve B₁ homogeneity and reduce SAR for fetus imaging at 3T.

Approach: B₁ field distributions of transmit body coil with dielectric pads of various designs in different positions around a pregnant woman model were evaluated using computer simulations.

Results: The placement of dielectric pad could significantly improve B₁ field homogeneity (up to 84%) in the fetus brain. A generalizable routine can be developed for optimization of B₁ shimming using dielectric pads.

Impact: Passive RF shimming with HPM is a viable ancillary approach for reduction of transmit field inhomogeneity artifacts for body imaging in high field MRI (≥3T), which affect the quality and safety of fetal MRI at 3T.

Keywords: Analysis/Processing, Safety, Quality Control

Motivation: RF coil failures are often not visually recognizable. Quality control is only done weekly or monthly, leading to days to weeks where diagnostic images may be negatively impacted.

Goal(s): Identify RF coil failures on patient images using deep transfer learning.

Approach: >10,000 passed and failed images from 50 patients were used to train 4 pre-trained deep learning models using 2 different pipelines: (1) shuffled all images into train and test, and (2) shuffled by each patients’ images.

Results: EfficientNet V2 (L) was the highest performing model, achieving 99% accuracy for pipeline 1, and 55% for pipeline 2. Other models showed similar results.

Impact: Introducing a deep learning model that can identify radiofrequency coil failures on patient images would avoid costly rescans of patients whose images were only determined to be poor after a failure was detected on a later quality control scan.

Keywords: Low-Field MRI, RF Arrays & Systems, Wireless, Low-Field, Portable, Cellular

Motivation: Wireless transmission of MRI data acquired with low-field portable MRI scanners within EMT vehicles over cellular/satellite networks drastically decreases time between stoke onset and imaging for improved patient outcomes. 

Goal(s): Our goal is to enable wireless communication with an iRFW coil design for simultaneously imaging and wireless cellular/satellite data transfer from within the scanner and an EMT vehicle.

Approach: iRFW-Cellular simulations within a portable 70 mT scanner are performed to evaluate its SNR and far-field gain patterns for wireless communication.  

Results: The iRFW-Cellular simulations showed a uniform SNR in the head and gain patterns appropriate for the wireless transmission of MRI data. 

Impact: The iRFW-Cellular spiral coil design potentially enables wireless MRI data transfer from a low-field portable MRI scanner inside, or out, of an EMT vehicle for better stroke onset to imaging times. 

Keywords: RF Arrays & Systems, Parallel Imaging

Motivation: Dual-tuned cable traps, instead of two separate single-tuned ones in series, are preferred in multi-nuclear MRI and MRS.

Goal(s): We introduce a frequency-independent dual-tuned cable trap. For proton nuclear, standard solenoid cable trap was employed. For X-nuclear, an additional solenoid resonator was employed to block the common-mode signal.

Approach: The dual-tuned cable trap was analyzed in electromagnetic simulation, fabricated and its performance is evaluated by bench test.

 

Results: The dual-tuned trap exhibits exceptional common-mode current suppression abilities at both frequencies. And two frequencies of dual-tuned trap can be adjusted independently without mutual interference.

Impact: This novel dual-tuned cable trap fills an important gap in dual-tuned MRI hardware for multi-nuclear magnetic resonance studies, potentially enable next-generation dual-tuned coils.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, Tirple-tunable, Stacked end-ring, Birdcage coil, Uniformity

Motivation: The PET insert can be used with MRI systems of different magnetic field strengths; however, a radio frequency(RF) coil cannot be used with different tesla.

Goal(s): Our goal is to generate uniform RF transmit magnetic fields at 3T, 7T and 11.74T MRI system using single RF coil.

Approach: Based on electromagnetic(EM) simulation, we proposed a new geometry of birdcage coil, which has 6 end-rings and 4 legs for triple resonance frequencies.

Results: In EM simulation, the proposed coil showed higher than 90% uniformity in the central axial plane. In bench measurement, proposed coil clearly showed triple resonance frequencies at 123.2, 297.2 and 500MHz.

Impact: Our proposed RF coil, named triple tunable birdcage coil, can generate uniform RF transmitted magnetic fields in 3T, 7T and 11.74T MRI systems. Therefore, it can be used for frequency selection in PET/MRI systems.

Keywords: High-Field MRI, High-Field MRI, Small-Sample Imaging

Motivation: Investigate potential uses for solenoidal dipoles, such as in human finger imaging.

Goal(s): The purpose is to evaluate how well the solenoidal dipole works for imaging the finger.

Approach: Comparison to alternative coil configurations for finger imaging.
 

Results:  Evaluate the inter-element coupling, Q-factor, H-field, E-field efficiency, and SNR of the solenoidal dipole in relation to the solenoid coil and LC loop.

Impact: The proposed solenoidal dipole design, despite less efficient H-fields, holds substantial potential for ultra-high-field MRI. It reduces crosstalk, enhances SNR distribution, and improves field homogeneity, making it a promising choice for high-resolution imaging of small samples.

Keywords: New Devices, New Devices, MRI, SNR enhancement, flux-focusing elements, Lenz lens, Lenz Resonator, Signal Amplification

Motivation: Despite numerous developments since MRI’s invention, low sensitivity remains the main limitation.

Goal(s): We aimed to improve upon the Lenz lens design for passive signal amplification in MRI, ultimately improving the signal-to-noise ratio. 

Approach: We created a first-in-kind Lenz resonator, a passive frequency selective flux-focusing circuit, to isolate and enhance the signal from a desired nucleus. 

Results: Performing RF testing with a vector network analyzer there was a 60 times signal amplification for the proton resonance frequency. At 3.0T, MRI demonstrated an experimental amplification of the signal-to-noise ratio by 3.9 times using an MRI insert of two coaxial Lenz resonators.

Impact: The substantial SNR boost produced by our Lenz resonators has a paramount importance for the field of MRI. The superior increase in SNR allows quicker scans, higher resolution scans, and precise disease detection.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, Double-resonance coil, non-proton, skeletal and simulations

Motivation: Metabolic bone disease is a prevalent health concern affecting more than 200 million individuals worldwide. MRI has the potential to noninvasively characterize bone quality. 

Goal(s): The goal was to custom-build a double-resonance RF coil capable of proton and phosphorus solid state MRI on a 1.5 T extremity scanner intended for arms, legs, and tissue specimen imaging. 

Approach: A double-resonance RF coil was constructed based on a double-tuning single solenoid configuration, employing quarter-wave transmission lines to isolate the two channels.

Results: ZTE ¹H and ³¹P MRI of bone specimens demonstrated the feasibility and effectiveness of this coil.

Impact: The constructed single-solenoid double-resonance RF coil is capable of acquiring solid state 1H and 31P MRI of bone specimens. With this coil, MR information on the organic matrix (1H) and mineral (31P) can be obtained to assess metabolic bone diseases.

Keywords: RF Arrays & Systems, RF Arrays & Systems, Balun and RF traps

Motivation: Baluns and RF traps are resonant structures and coupling among each other, as well as to receive and transmit coils must be avoided. This is a particular challenge for the efficient and compact class of wound inductor traps.

Goal(s): Wound inductor trap that is isolated from external fields, does not require metallic shielding surfaces and can be wound compactly also for cables with limited bending radius.

Approach: Employing the method of active shielding known from gradient coil design to RF trap inductors.

Results: RF traps with shielding properties comparable to metal sheath shielded versions with very low eddy current profile.

Impact: Compact and efficient RF traps can help to design better and safer RF coils. Requiring no metal sheath for shielding of the trap can help to reduce gradient-switching-induced vibrations and heating.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, Active catheter, Interventional Devices, Flexible Coils

Motivation: ¹⁹F-MRI can be used to monitor immune cell response to myocardial infarction, yet the low signal-to-noise ratio in the myocardium must be compensated by long measurement times and low spatial resolution.

Goal(s): To enable high spatial and temporal resolution ¹⁹F-MRI using an intraventricular expanding RF coil that can be introduced via a catheter.

Approach: A superelastic, self-resonant shielded-loop-resonator was developed to fit into a guiding catheter and the SNR was measured for different coil shapes.

Results: The expandable coil does not require re-tuning even at extreme shape deformations, and it can even be used as an active marker for real time ¹H guidance.

Impact: Intraventricular MRI of 19F-labeled immune cells will enable effective monitoring at myocardial infarction after fluorine labeling. The expandable SLR coil can be inserted via guiding catheters and used as 1H tracking coil without tuning or additional adjustments.

Keywords: Non-Array RF Coils, Antennas & Waveguides, RF Arrays & Systems

Motivation: Potassium(³⁹K) imaging provides an opportunity to probe cellular processes and has recently been demonstrated in human calf muscle at 7T

Goal(s): Developing an in-house birdcage resonator for potassium imaging, enabling simultaneous imaging with proton/sodium using previously developed dipole/loop array.

Approach: A low-pass eight-rung birdcage resonator was constructed using copper strip, chosen for its high Q factor. The resonator was optimized for maximum power efficiency and phantom images were acquired at 7T.

Results: The birdcage resonator demonstrated exceptional tuning and matching on the bench, with a homogeneous phantom image acquired in around 6 minutes. The findings suggest significant potential for in-vivo potassium quantification.

Impact: A birdcage resonator was designed and constructed in-house to create a capability for enhanced potassium imaging for neurological, musculoskeletal and oncology research. Potential integration with ¹H/²³Na array would allow simultaneous acquisition with three nuclei.

Keywords: New Devices, New Devices, flexible coils, broadband matching, elastic coils, textile coils, stretchable coils

Motivation: Fixed-volume copper coils fail to accommodate volume changes and flexing of the imaging region, therefore spoil MR signal and hamper the diagnosis.

Goal(s): To design a flexible surface coil for breast MR imaging.

Approach: A 2-ch stretchable knitted textile coil and a 2-ch reference copper coil, which were compatible with three different sized phantoms were compared in terms of their sensitivity profiles and SNR results.

Results: A three-stage broadband matching network could compensate for 15MHz of frequency shift. Although the textile coil was 31-81% more lossy compared to the copper coil, it only resulted in 10-26% SNR decrease.

Impact: Despite loss of the WEAR coil, a textile-based coil can sustain a sample-loss-dominated behavior and a broadband matching network can compensate for the frequency shift without compromising on SNR.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, Novel RF coil

Motivation: Great potentials arise from multinuclear imaging modalities of ²H, ¹⁷O, ³¹P and ¹H, which could depict the complexity of tissue and physiopathology related to the disease progression from multiple dimensions.

Goal(s): To develop a triple-tuned RF coil which can operate at three resonant frequencies of interest (²H, ¹⁷O, and ¹H) or (²H, ³¹P and ¹H).

Approach: A triple-frequency tuned RF coil was developed and simultaneously tuned and match to three resonant frequencies, and evaluated using a head-size phantom at 7T.

Results: We demonstrated a novel triple-frequency tuned coil design with robust imaging results for all three imaging frequencies.

Impact: As deuterium MRS imaging (DMRSI) is gaining more attention for brain tumor imaging, this triple-frequency tuned coil design can help add another X-nuclear frequency to the current DMRSI coil design, thus creating additional contrast for the brain tumor diagnosis. 

Keywords: Non-Array RF Coils, Antennas & Waveguides, RF Arrays & Systems

Motivation: The occipital lobe is the site of a variety of brain diseases. ³¹P MRS can noninvasively detect the metabolites to monitor and diagnose related diseases timely.

Goal(s): To collect ³¹P MRS signals in the occipital lobe at 3T, the dedicated RF coil setup is designed as a double-channel transceiver integrated surface coil.

Approach: The coil was designed as a "pillow” and verified by finite element simulation, physical production, bench tests and phantom experiments.

Results: The coil showed good uniformity and strong magnetic field intensity at the imaging region. Scanning with phantom, the spectral lines had a smooth baseline, high peaks, and excellent SNR.

Impact: we propose a transceiver and transmitter integrated surface coil for 31P magnetic resonance spectroscopy in the occipital lobe, which provides an excellent signal-to-noise ratio for excitation and acquisition of 31P spectral signals at 3T.

Keywords: Low-Field MRI, Low-Field MRI, X-nuclei

Motivation: Our project aims to refine MRI technology for a specific clinical purpose, focusing on a double-resonant coil design. This innovation bridges knowledge gaps and enhances diagnostic precision.

Goal(s): Our goal during the current semester is to create a double-resonant coil for MRI experiments on fluorine and protons. Achieving this involves circuit design and hardware construction.

Approach: Our approach includes capacitor and inductor integration, two separate output channels, and the development of essential hardware for signal acquisition using a didactic low field MR system.

Results: The design allows us to measure T₁ and T₂ relaxation times and enables us to perform imaging as well. 

Impact: With the coil we performed proof-of-principle fluorine and proton measurements in a didactic low MR-system. It can be used to investigate samples with 1H and 19F without moving the sample. The non-proton channel can be tuned to other x-nuclei frequencies.

Keywords: Analysis/Processing, Brain, Optical position tracking

Motivation: Deep learning methods are popular for head pose tracking in many applications; however, most models focus on large motions that are not applicable to the sub-millimeter accuracy required for motion correction in magnetic resonance imaging.

Goal(s): We aim to create a deep neural network capable of “markerlessly” tracking incremental changes in head pose in 6 degrees of freedom (DOF) with sub-millimeter/degree accuracy. 

Approach: We pre-trained a network on simulated images of a face in our expected environment as preparation for real-world data collection and training.

Results: Initial test results show a low average mean squared error of 0.0588 mm/degrees across the 6DOF. 

Impact: A deep neural network for sub-millimeter head pose tracking for motion correction was successfully pre-trained on simulated face data, with a test mean MSE of 0.0588 mm/degrees. This method shows potential towards motion correction applications in MRI.

Keywords: RF Arrays & Systems, RF Arrays & Systems, preamplifiers, preamplifier decoupling, power matching, noise matching, matching networks

Motivation: While preamplifier decoupling is a widely accepted technique, based on impedance mismatching, it appears counter-intuitive and still introduces confusion in the MRI community and scientists, who are not electrical engineers by training.

Goal(s): This work aims to develop a simulation setup, which clearly illustrates the signal-to-noise ratio (SNR) in preamplifier decoupled and power matched receive coils.

Approach: Circuit simulations are used to compare SNR at the output of power matched and preamplifier decoupled coils in 3T MRI systems.

Results: The networks yield similar SNR, despite having significantly different input reflection coefficients; demonstrating that preamplifier decoupling and power matching approaches lead to equivalent SNR.

Impact: The developed demonstrator is useful in understanding properties of preamplifier decoupling and breaking down a range of associated misconceptions. This can facilitate mastering a proper use of this decoupling method.

Keywords: Non-Array RF Coils, Antennas & Waveguides, RF Arrays & Systems, signal-to-noise ratio, high-resolution, cryogenic, RF coils.

Motivation: The signal-to-noise ratio of high-field RF surface coils decays with distance, and we propose cryogenic coils to compensate for the SNR of MR Imaging.

Goal(s): The cryogenic coil in our work aims to significantly improve the SNR of the images at long distances while guaranteeing a large imaging FOV.

Approach: We design a large size RF coil and cool it down for rat imaging.

Results: The experimental results show that the cryogenic coil obtained a SNR of 1.8-fold higher than a room-temperature coil and 1.1-fold higher than that of a commercial multi-channel rat coil.

Impact: The designed coil can help to improve the quality of MR imaging in some scenarios where the object to be measured is far away from the RF receive coil.

Keywords: RF Arrays & Systems, RF Arrays & Systems, matching networks, baluns, common-modes, noise matching, preamplifier decoupling

Motivation: Lattice baluns are traditionally used in receive arrays to achieve common mode rejection and preamplifier decoupling. They, however, are limited to real impedance transformations only.

Goal(s): New matching networks are sought that achieve noise matching and preamplifier decoupling, as well as common-mode rejection.

Approach: In this abstract, new network topologies are introduced and their bandwidths are studied.

Results: In addition to being more compact, the new networks offer a wider bandwidth as well as higher common-mode rejection. Thus, it is expected that the new networks are more resilient to component tolerances and loading effects, and they may enable multinuclear imaging.

Impact: New topologies of preamplifier decoupling networks with integrated balun functionality are introduced. They offer wider bandwidth and higher common-mode rejection compared to traditional networks.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, wireless coils, inductive coupling

Motivation: MRI is a highly preferable but also an expensive modality mainly due to 1)high operational cost, 2)staff cost, 3)long scan and preparation times.

Goal(s): Reducing costs and simplifying MRI scans.

Approach: A wired coil and a wireless coil which was inductively coupled to a receiver loop were compared in terms of their efficiency and SNR results.

Results: On the bench, a 0.8 dB+/-0.5dB of decrease was observed in the efficiency of the wireless coil over a range of 3 cm. The SNR of the wireless coil was practically identical to the wired coil both in phantom and in vivo MR images.  

Impact: The efficiency obtained by a wired coil decreased by 0.8 dB when an inductively coupled wireless coil was used. Phantom and in vivo measurements show a practically identical sensitivity profile and SNR for both coils.

Keywords: New Devices, New Devices, Orientation-dependent MRI, Post-mortem MRI, Temperature control, Temperature-dependent MRI, Tiltable Coil

Motivation: Systematic variation of external parameters can provide insight into whether theoretical models appropriately describe MRI contrast.

Goal(s): Our goal was to develop a cost-effective setup for comprehensive temperature- and orientation-dependent relaxation and magnetization-transfer experiments in post-mortem tissue on a clinical scanner. 

Approach: A remotely tiltable Helmholtz coil was integrated into a thermally insulated box, where the temperature can be adjusted by a heated airflow. 

Results: Robust coil performance, accurate adjustment of the sample orientation relative to B₀  (±1°), and stable temperature conditions (±0.5 °C) were achieved. Theoretically expected temperature dependencies of T₁ and diffusivity in agarose were experimentally reproduced.

Impact: Well-defined variations of the temperature (between ambient temperature and 45 °C) and sample orientation (between 0 and 90° relative to B₀) in MRI experiments with small post-mortem tissue specimens were achieved on a clinical scanner with a cost-effective setup.

Keywords: New Devices, Brain, wireless coil

Motivation: The bulky cables of the MRI RF coil not only complicate the coil replacement procedure but also lead to a waste of examination time. 

Goal(s): In order to achieve a lightweight and user-friendly wireless RF coil with high-resolution imaging capability.

Approach: In this study, we made a wireless coil and compared its SNR and high-resolution imaging performance with the rat coil RAC and the knee coil alone, using the knee coil as the pickup coil.

Results: The wireless coil achieved high-resolution imaging of up to 0.13 mm × 0.13 mm × 1mm on the 3T system.

Impact: The experiment demonstrated the potential of wireless RF coils for high-resolution imaging.

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides

Motivation: High performance RF coils are needed for better SNR so that higher resolution and spectral dispersion can be obtained in small animal MR imaging. 
 

Goal(s): To develop a surface coil with improved SNR over the conventional surface coil for small animal imaging at 7T.
 

Approach: A small animal surface coil is designed based on multimodal surface coil technique. The coil is investigated and compared with conventional surface coil using full-wave electromagnetic simulations.
 

Results: The multimodal surface coil shows superior B1 field efficiency and lower E field over standard coils, indicating a potential to gain SNR and resolution.

Impact: The proposed multimodal surface coil can operate at high frequency and provides improved SNR over conventional surface coils at 7T, opening avenues for highly efficient coil design in small animal imaging, ultimately enabling the detection of  previously indiscernible physiological details.  

Keywords: Non-Array RF Coils, Antennas & Waveguides, Non-Array RF Coils, Antennas & Waveguides, flexible coil

Motivation: Portable low-field MRI opens doors for low-cost and point-of-care imaging, but comes at the expense of decreased SNR, resulting in inferior image quality. 

Goal(s): We aim to increase SNR with stretchable, subject-adaptable, helmet coils for low-field, portable MRI brain imaging. Specifically, a single-channel Tx/Rx volume coil for brain imaging at 72 mT.

Approach: We use a flexible 3D printed former and elastic bands for stretchable coil former. To account for the coil’s variable inductance, we develop an MATLAB-controlled autotuning circuit, composed of 8 capacitor values that can be switched in/out via Reed relays. 

Results: We present a preliminary coil and autotuning system design.

Impact: To unlock portable MRI's full potential, we must boost SNR without sacrificing portability or safety. Our solution involves stretchable RF coil caps that mold to the subject's head in conjunction with an  auto-tuning system for optimal performance.

Keywords: New Devices, New Devices, Cryogenic coils; cryogenic preamplifiers; remote coils

Motivation: The MRI scanning procedure often relies on close-fitting RF coils to maximize signal-to-noise (SNR) ratio and assure image quality. Such an approach impairs patient comfort and requires qualified personnel, which increases the overall costs.

Goal(s): This study aims to avoid using close-fitting RF coils by integrating them in the bore of the scanner.

Approach: The coil is evaluated by developing a single element cryogenic coil prototype for a wide-bore 1.5T MRI system and with simulation to evaluate SNR and decoupling.

Results: Simulations indicate that the coil can achieve 15dB of preamplifier decoupling and that cooling results in a 3dB SNR improvement.

Impact: Avoiding close proximity and making RF coils invisible to a patient by integrating them into a bore of an MRI scanner will positively impact operating costs. While the signal strength is reduced, SNR can be partially regained by cryogenic cooling.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: There are growing interest in low field specialised MRI R&D but they are currently burdened by their low SNR images.

Goal(s): A novel 2-channel orthogonally arranged dual loop solenoid RF coil design has been proposed to improve low field MR image SNR.

Approach: Two transceive 2-Channel RF coil prototypes using the novel design and using conventional design were constructed and tested in a 0.35T MRI system.

Results: In comparing the acquired MR images, it is shown that the proposed novel design can improve low field MR  image SNR by ≥20% as compared to the conventional design.

Impact: A novel 2-channel orthogonally arranged dual loop solenoid transceive RF coil has been constructed and tested in a 0.35T MRI system. Using this new RF coil design it is shown that the acquired image SNR can be increased by ≥20%.

Keywords: Hybrid & Novel Systems Technology, Hybrid & Novel Systems Technology, Wireless

Motivation: MRI coil arrays are now burdened by cable and connector limitations that inhibit conformability.

Goal(s): We seek a low cost approach to wireless MRI coil data links that is easy to scale with multiple array subsections. We demonstrate feasibility of a FPGA-based short-range microwave wireless serial link.

Approach: A complete end to end link was constructed for link distances of 20cm. A low power FPGA sent scrambled serial data with embedded start/stop bits to a receiver with FPGA recovery of the data.

Results: This complete demo could achieve over 200Mbps with a simple FPGA, mixer and oscillator.

Impact: Cutting the cord of MRI arrays has been a long-term goal of MRI engineering. It would eliminate the mechanical and RF pitfalls of the cable, and enable more conformable and wearable receive arrays.

Keywords: In Silico, Simulations, X-Nuclei, RF, Coil, FDTD

Motivation: An untuned, non-resonant coil called the ADAPT Coil has recently been developed to excite any nucleus in high field, human-scale MRI. However, the coil’s nonlinear and time-varying characteristics render conventional simulation methods insufficient.

Goal(s): To develop an accurate simulation method for nonlinear and time-varying coils.

Approach: A finite-difference time-domain solver and a harmonic balance simulator were combined to simulate the linear components and the nonlinear and time-varying components, respectively.

Results: Nonlinear and time-varying coil operation was simulated and the resulting magnetic fields for five harmonics were visualized. The fundamental frequency magnetic field resembles that of an ideal current loop.

Impact: If validated for use with humans, the ADAPT Coil would significantly reduce barriers to clinical translation of X-nuclei research. The simulation method presented here represents a major step towards validation of the ADAPT Coil or any other nonlinear coil.

Keywords: High-Field MRI, High-Field MRI, B1+ Mapping, SatTFL, AFI, DREAM, Sandwich, SA2RAGE

Motivation: To benefit from all the advantages that ultra-high field MRI offers, knowledge of the RF transmit field (B₁⁺) is required. Many B₁⁺ mapping methods have been developed, but no single method has become the ‘gold-standard’, with many sites opting for their own implementations.

Goal(s): To evaluate five promising sequences and understand their sensitivity to B₀, T₁, flow and SNR on the accuracy and dynamic range of the measured B₁⁺.

Approach: SatTFL, Sandwich, SA2RAGE, AFI, and 3DREAM were investigated in MATLAB using open-source EPG and Bloch simulations.

Results: A simulation framework to compare B₁⁺ mapping sequences was developed.

Impact: This simulation framework is beneficial for understanding the impact of various factors on the accuracy of B₁⁺ mapping sequences and can help to inform better pulse sequence design and parameter optimisation.

Keywords: RF Arrays & Systems, RF Arrays & Systems, TMJ, MRI, wireless coil, SNR, detune, RF coil

Motivation: Most imaging facilities lack specialized coils, resulting in suboptimal TMJ MRI scans using head receive array.

Goal(s): Developing flexible, cost-effective and efficient accessories to enhance TMJ MRI image using existing facilities. 

Approach: Improve TMJ MRI scans by incorporating an inductive wireless resonator insert into a head array. evaluating its performance against the head array alone using phantom and in vivo imaging.

Results: The SNR increases by 5.3-fold times at the TMJ's articular fossa area and remains 2.4-fold at a 4cm depth, using a wireless resonator insert and head array combination, compared to a phased array.

Impact: Combining wireless RF resonators and phased arrays transformed MRI coils technology. It enhancing SNR in specific regions like the thyroid and carotid artery, allowing parallel imaging . This advancement ensures affordability, well-workflow, and the adaptability to various magnetic field strengths.

Keywords: RF Arrays & Systems, RF Arrays & Systems, Knee, MRI, wireless coil, SNR, Tx/Rx, RF coil.

Motivation: The conventional Tx/Rx knee coil optimizes transmission and reception using a complex dual-layer structure with multiple components, requiring local transmit power and a limited diameter.

Goal(s): Developing a  knee coil for that offers superior performance, patient-comfort, and affordable, without the need for a local transmit connection.

Approach: Design a wireless Tx/Rx knee coil incorporating system body coil in transmit phase and a flex phased array during receive phase, evaluating its performance against the flex phased array alone using phantom and in vivo imaging.

Results: Enhanced SNR is achieved when compared to a 13-channel flexible phased array, effectively eliminating wrap-around artifacts in knee image.

Impact: The advancement of inductive RF resonator technology with a wireless birdcage resonator incorporating a Figure-of-Eight (Fo8) conductor design is aiming to achieve cost-effective and improved performance for knee MRI which improves the way of designing MRI coils and their applications

Keywords: RF Arrays & Systems, Animals, Marmoset, High Field MRI, 7T

Motivation: 7T promises a high SNR for high-resolution imaging of the small marmoset brain, which requires a custom RF coil.

Goal(s): To develop a robust marmoset coil for 7T with an efficient volume transmit and receive array with a very high density and high filling factor.

Approach: The coil was constructed, consisting of a volume transmit coil and receive array of 8 receive-only loops. The coil was tested with a phantom and a single anesthetized marmoset.

Results: The transmit coil along with the optimized receive array for imaging the whole marmoset brain has been shown to produce images of high resolution and high SNR. 

Impact: A shielded, band-pass birdcage transmit coil was designed and fabricated for marmoset brain imaging at 7T. An 8-channel receive array consisting of eight overlapped loops covering the whole brain of the marmoset was also built and applied for signal reception.

Keywords: RF Arrays & Systems, Simulations, Antenna array

Motivation: The multi-channel RF coil scheme for 14T head imaging has not been defined yet.

Goal(s): Our goal was to optimize the number of elements in the dipole antenna array in order to achieve optimal performance at 14T.

Approach: We obtained the  $$$\text{B}_{1}^{+}$$$   field distributions and SAR distributions of dipole antenna arrays with 8, 12, 16, and 20 channels through electromagnetic simulation, and compared their performances.

Results: The results showed that the 12-channel dipole antenna array exhibits superior performance.

Impact: The number of channels in an RF coil at ultrahigh fields requires a trade-off between RF field uniformity and inter-cell coupling; 12-channel dipole antenna array serves as a suitable reference coil for 14T head imaging.

Keywords: High-Field MRI, High-Field MRI, Head & Neck/ENT, coil arrays

Motivation: Covering the head-neck region in UHF MRI is challenging due to the limited number of only 8 parallel transmission (pTx) channels available in most UHF MR systems.

Goal(s): Our goal was to design and simulate an 8-channel pTx coil for combined head/neck imaging at 7T.

Approach: A geometrical setup for MR imaging with modified stripline elements was investigated by simulating the B₁⁺ efficiency in a heterogenous  tissue model.

Results: B₁⁺ efficiency maxima of 0.31 μT/√W for head region and 0.13 μT/√W for neck region with SAR_10g maximum of 1.21 W/kg for 1W stimulated input power per channel could be achieved.

Impact: Meander stripline elements can be overlapped while showing only low coupling, allowing a good coverage of the head-neck area while only using 8 pTx elements in total.

Keywords: RF Arrays & Systems, High-Field MRI, carotid array

Motivation: Ultra-high field MRI is popular in brain imaging research. However, high-res imaging of carotid vessels and walls is not possible due to the lack of a carotid array.

Goal(s): High-resolution imaging of the neck position at ultra-high fields

Approach: In this study, carotid array with two wireless resonators insert was developed at 5T. 

Results: SNR was significantly improved using the novel coil in comparison with the only carotid array at 5T.

Impact: An 8-channel carotid array with wireless resonators was designed for 5T magnetic resonance imaging. Water model imaging provides sufficient signal-to-noise ratio and resolution for high-field imaging, meeting the requirements for detailed neck artery disease feature descriptions.

Keywords: Low-Field MRI, Low-Field MRI, cardiovascular,aortic imaging

Motivation: Bright-blood and black-blood imaging are relevant for assessing aortic pathologies. Research on aortic imaging at 0.55T which could potentially make MRI more accessible and affordable is scarce.

Goal(s): To evaluate the feasibility of a novel non-contrast enhanced simultaneous bright- and black-blood aorta imaging at 0.55T at systole and diastole.

Approach: Five healthy volunteers were scanned at 0.55T with the proposed accelerated and non-rigid motion-compensated sequence (iT2prep-BOOST). Adiabatic, MLEV4 and MLEV8 T2-preparation pulses were compared.

Results: Good image quality was obtained for simultaneous acquisition of 3D bright- and black-blood aorta imaging at 0.55T at systole and diastole with the proposed iT2prep-BOOST and MLEV8 T2-preparation.

Impact: The proposed approach enables 3D simultaneous bright- and black-blood aorta imaging at 0.55T during a fast free-breathing scan and thus shows promise for the detection of different aortic diseases, potentially making aortic MRI more accessible and affordable.

Keywords: Low-Field MRI, Low-Field MRI, Heart, Cardiovascular, Pulse sequence design

Motivation: CMR has not seen widespread adoption beyond large urban academic centers. The reasons for this limited uptake include the cost and time-intensive nature of CMR. 5D Free-Running CMR using self-navigation (5D CMR) implemented on a low-field clinical scanner may help bridge this gap.

Goal(s): Investigate the feasibility of cardiac function measurements using 5D CMR on a 0.55T system.

Approach: 5D CMR data were collected in 10 adult subjects and compared to results from reference 2D cines. Right- and left-ventricular ejection fraction and left atrial volume were ascertained.

Results: 5D CMR allowed for time-efficient and concordant measurements when compared to the 2D reference method.

Impact: 5D Free-Running whole-heart CMR without the need for ECG, breath-holding, navigators, or complex scan plane planning enables a highly simplified and time-efficient assessment of myocardial function on a 0.55T clinical system in under 8 min.

Keywords: Low-Field MRI, Low-Field MRI, Lung, Tissue Characterization, Reader Performance Study

Motivation: Although MRI has had low adoption in lung imaging due to susceptibility artifacts, limiting its utility in pulmonary parenchymal imaging, low-field MRI (0.55T) has potential to address those limitations.  

Goal(s): However, its thoracic diagnostic capabilities remain indeterminate, so our goal was to compare its ability to detect common lung pathologies to chest CT and provide comparable quantitative measurements.

Approach: Structures and pathologies were measured with both modalities, and two radiologists identified lung pathologies with MRI only.

Results: Results indicated that readers were able to detect pathologies using 0.55T MRI, serving as a first step in exploring 0.55T MRI as an alternative modality.

Impact: Our study revealed potential for 0.55T MRI as an emerging tool for MR-based anatomic evaluation of the lung, and its limitations. This can expand lung imaging options and potentially provide better tissue characterization for diagnoses like lung cancer.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: 0.55T MRI may be a promising platform for quantitative multiparametric liver imaging with improved cost-effectiveness and robustness.

Goal(s): This study demonstrates the feasibility of rapid free-breathing 3D MRI of the liver with simultaneous quantification of PDFF, R2*, and water-specific T1 at 0.55 Tesla.

Approach: We tested free-breathing GraspT1-Dixon sequence with in vivo experiment and the quantitative maps are validated using R2* and PDFF phantoms.

Results: We show that (1)the estimated parameters are accurate; (2)the influence of fat on liver T1 mapping can be effectively mitigated to ensure accurate and robust T1 quantification; and (3)R2* mapping may be insensitive to respiratory motion at 0.55T.

Impact: 0.55T MRI offers a cost-effective platform for quantitative multiparametric MRI of the liver to improve the management of various chronic disease conditions. In particular, the improved magnetic field homogeneity at 0.55T may enable more robust estimation of R2* maps.

Keywords: Low-Field MRI, Lung

Motivation: Parametric mapping may enable early detection and monitoring of pulmonary diseases but is hampered by low signal levels, short T₂/T₂* values, and susceptibility artifacts.

Goal(s): This project aims to develop an MRF approach for simultaneous 2D T₁, T₂, and M₀ mapping in the lungs on a commercial 0.55T scanner.

Approach: MRF data were acquired in five healthy subjects during a 16s breathhold, repeated at end-inspiration and end-expiration, and reconstructed using a deep image prior.

Results: Feasibility of lung MRF at 0.55T was demonstrated in healthy subjects, with lung T₁ of 868±57ms (expiration) and 806±59ms (inspiration), and T₂ of 54.1±3.2ms (expiration) and 58.7±4.0ms (inspiration).

Impact: This study demonstrates the feasibility of MR Fingerprinting for 2D T₁, T₂, and M₀ mapping of the lung parenchyma at 0.55T in healthy subjects, which may have future clinical implications for various pulmonary diseases including asthma, emphysema, and cystic fibrosis.

Keywords: Low-Field MRI, Low-Field MRI, MR Fingerprinting, T1 Mapping, T2 Mapping, Fat-fraction Quantification

Motivation: Cardiac MRF is a powerful imaging-technique that allows for comprehensive myocardial tissue characterization in a single-scan and has been proposed at 1.5T and 3T. However, cMRF has not been demonstrated at lower-field yet.

Goal(s): Investigate the feasibility of a Dixon-cMRF sequence for simultaneous T1, T2 and fat-fraction quantification at 0.55T.

Approach: Dual-echo spoiled-GRE-acquisition with varying IR-T2-preparation pulses. Experiments were performed on standardized phantoms and with 5 healthy volunteers and compared with spin-echo references.

Results: T1, T2 and fat-fraction Dixon-cMRF at 0.55T was tested with phantoms and with healthy subjects, showing good agreement with reference values in phantom and promising results in healthy subjects.

Impact: The simultaneous quantification of T1, T2 and fat-fraction at 0.55T in a single cardiac-MRF of 15s could provide an alternative to higher field scanners, allowing for a more accessible way to assess cardiovascular disease.

Keywords: Non-Array RF Coils, Antennas & Waveguides, New Devices, Flexible Electronics, 3D-Write Technology

Motivation: MRI receiver coils are often rigid thus cannot conform to every anatomy. This motivates to create flexible, robust, and easy to manufacture coils.

Goal(s): To create scalable and low-cost MRI coils using direct-3D-writing. The coils should conform to different anatomies and be robust to bending and stretching.

Approach: We utilize a fast direct-3D-write method (~8 minutes print time per coil) that uses an easy to modify coil model, and compare performance against a rigid copper coil at 0.55 Tesla.

Results: The flexible printed coil provided 1.8 times higher SNR compared to the reference copper coil due to better form-fitting.

Impact: MRI receiver coils, printed with the direct-3D-write method, can be made flexible to conform to imaging anatomy, while offering scalability and lower cost. This simplifies manufacturing and improves SNR due to better form-fitting.

Keywords: Low-Field MRI, Low-Field MRI, Fat suppression, Dixon, bSSFP

Motivation: Fat suppression is challenging at low field strengths due to small fat frequency shifts. Dixon imaging with bSSFP offers an attractive solution by combining the robust fat-water separation performance of Dixon with the high SNR and scan speed of bSSFP sequence.  However, the distinctive spectral response of bSSFP signals was overlooked in existing Dixon implementations.

Goal(s): This study aims to improve fat suppression with bSSFP sequence at low field by incorporating bSSFP signal model in a two-point Dixon algorithm. 

Approach: Numerical simulations and phantom experiments were performed at 0.55T.

Results: Results suggest that integration of bSSFP signal model can improve fat suppression.

Impact: Our proposed bSSFP-based two-point Dixon method could improve imaging with fat suppression at low field, which has been a challenging task due to small fat frequency shift and low SNR.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: As assessment of liver metastases requires multiple imaging modalities, it is essential to compare diagnostic capabilities and patient experiences of the low-cost 0.55T MRI to conventional imaging techniques.

Goal(s): We analyzed the sensitivity for neuroendocrine tumor metastases detection of gadoxetate-enhanced 0.55T MRI to ⁶⁸Ga-DOTATATE PET/CT and 3.0T MRI while evaluating patient experience

Approach: Patients were imaged on 0.55T MRI with ⁶⁸Ga-DOTATATE PET/CT and/or 3.0T MRI for comparison. Sound pressure levels (SPLmax) were compared between 0.55T and 3.0T.

Results: Hepatobiliary phase imaging at 0.55T showed increased detection rates over ⁶⁸Ga-DOTATATE PET/CT. SPLmax of 0.55T was significantly lower. Patients found the 0.55T MRI less stressful.

Impact: Routine imaging of patients with neuroendocrine tumor metastases is feasible at 0.55T MRI. Low-field MR imaging has the potential to improve patient experience and accessibility without sacrificing diagnostic capability.

Keywords: Low-Field MRI, Low-Field MRI, resting-state, functional connectivity, resting-state network, test-retest reliability

Motivation: Resting state fMRI (rs-fMRI) provides vital neurological information in acute care.

Goal(s): To demonstrate the feasibility of rs-fMRI at 0.5T.

Approach: Repeated rs-fMRI acquisitions of two healthy volunteers (n = 6, n = 4) were acquired at 0.5T using a 31 min EPI based protocol.

Results: All eleven well-established resting state networks were identified. Sensorimotor and language networks were very reliable across scans for both volunteers with intersession intra-class correlation coefficient values > 0.5.

Impact: Resting state fMRI is feasible at 0.5T with an EPI acquisition technique. The functional connectivity detected resembles a 3T database for well-established resting-state networks.

Keywords: Low-Field MRI, Diffusion/other diffusion imaging techniques

Motivation: Single-shot diffusion weighted imaging at 0.5T has low SNR, increased blurring and is limited by spatial resolution.

Goal(s): We want to demonstrate image quality improvement in multi-shot DWI at 0.5T with MUSE DL reconstruction.

Approach: Multi-shot DWI is reconstructed using MUSE algorithm followed by ARDL.

Results: The qualitative DWI results show improved image quality and less blurring with MUSE ARDL reconstruction.

Impact: Using multi-shot DWI and the MUSE ARDL recon increases spatial resolution and image quality at 0.5T and provides reliable imaging for low SNR DWI acquisitions.

Keywords: Low-Field MRI, Data Acquisition, PROPELLER, Image Reconstruction, Compressed Sensing, NUFFT, Acceleration

Motivation: Mid-field MRI have lower SNR so data acquisition is associated with longer data acquisition time. Therefore, develop fast imaging technique with motion robust data acquisition with minimal SNR penalty due to fast imaging.

Goal(s): Develop a robust image reconstruction technique for compressed sensing (CS) accelerated PROPELLER acquisitions. 

Approach: A new iterative reconstruction technique based on NUFTT and CS for PROPELLER acquisitions. 

Results: MRI imaging of ISMRM-NIST phantom and volunteer scan were acquired and reconstructed with minimal under-sampling artifacts such as haze and streaks with PROPELLER acceleration.

Impact: Compressed sense accelerated PROPELLER can acquire high quality motion robust MRI images at mid-field MRI. Proposed MR image reconstruction technique for compressed sensing accelerated PROPELLER technique can enable acquisitions requiring longer scan time due to SNR.

Keywords: Low-Field MRI, Low-Field MRI, T2*,subcortical brain,SNR

Motivation: Accurate knowledge of T2* relaxation times is important for optimizing contrast and SNR in multi-echo gradient echo sequences.

Goal(s): To measure the nominal T2* relaxation parameter at 0.5 T over subregions in the brain.

Approach: A 2 mm isotropic 3D multi-echo GRE sequence was acquired in 5 healthy volunteers. T2* estimates were computed over regions of interest using a mono-exponential fit.

Results: T2* estimates of gray (86±8 ms) and white (78±5 ms) matter are in good agreement with previously published measurements in the mid-field. In the deep brain, average T2* values ranged between 70±2 ms to  89±5 ms.

Impact: For optimal T2* contrast in the brain at 0.5 T, echoes from multi-echo acquisitions should extend beyond 60 ms. For optimal SNR, echoes should be combined with a target T2* of ~80 ms.

Keywords: In Silico, Relaxometry, Low-Field MRI, Hepatic Steatosis and Iron Overload, HIC, Fat Fraction

Motivation: Multi-spectral fat water models fail to produce reliable fat fraction(FF) estimations for severe iron overload conditions at 1.5T and 3T. Low-field MRIs(<1T) may increase the accuracy in HIC and FF estimations at high iron overload by slowing signal decay but might suffer from lower signal-to-noise ratio(SNR).

Goal(s): Assess the accuracy and robustness of quantifying R2* and FF at 0.75T across various SNR conditions.

Approach: Realistic virtual liver models with concomitant presence of iron overload and hepatic steatosis were used to simulate MRI signals at 0.75T and 1.5T using Monte Carlo simulations.

Results: 0.75T showed improved FF and R2* estimation compared to 1.5T.

Impact: Low-field MRI can increase the accuracy and precision in simultaneous quantification of R2* and FF in the presence of mild-to-severe iron overload. With low-field MRI systems being less expensive and potentially increasing MRI accessibility, they can facilitate the reliable diagnosis.

Keywords: Low-Field MRI, Low-Field MRI, Hardware, Spine

Motivation: MR image quality concerns due to metallic implants may be addressed by preferentially scanning on 0.55T units.

Goal(s): To assess image quality, metallic artifacts, and diagnostic agreement secondary to spinal hardware at 0.55T compared to higher-field imaging.

Approach: Two blinded neuroradiologists independently reviewed 20 0.55T studies and 10 paired high-field studies. Diagnostic efficacy of 0.55T scans was assessed via pick-list, and image quality and metal artifact reduction were assigned scaled ratings.

Results: 0.55T produced studies with high diagnostic efficacy (16/20 studies had complete or near-complete agreement) and equivalent or improved image quality compared to higher-field images.

Impact: Commercial 0.55T MRI systems may improve the appearance of artifacts caused by spinal hardware compared to higher fields, and can be used in routine clinical practice without compromising image quality or diagnostic efficacy.

Keywords: Quantitative Imaging, Breast

Motivation: The fractional T1 differences between healthy and abnormal tissue are significant larger in the ultra-low-field (ULF) regime (<10 mT) compared to high field. 

Goal(s): Despite the challenges of imaging at ULF (predominately low SNR and spatial-temporal resolution), we demonstrate in vivo T1 mapping in the breast at 6.5 mT in 43 minutes.

Approach: A variable flip angle (VFA) method with B1 correction was used. 

Results: T1 mapping of CuSO₄ solutions showed an average T1 deviation <7% compared to reference T1 measurements. Breast phantom T1 mapping was also performed. Finally, this method was applied on two healthy female volunteers.

Impact: This work explores ultra-low field T1 mapping as potential biomarker for low-cost breast imaging. We demonstrate the feasibility of quantitative T1 mapping of the human breast in healthy female volunteers at 6.5 mT using a variable flip angle method.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Ultra-low-field (ULF) MRI technology holds significant promise for advancing medical imaging by offering low-cost and portable solutions for point-of-care applications. These advancements have the potential to improve access to medical imaging in resource-limited settings, thereby benefiting underserved populations and enhancing diagnostic capabilities to ultimately improve patient care. 

Goal(s): The implementation of a highly efficient protocol for ULF MRI.

Approach: A 3D bSSFP protocol was implemented and optimized. 

Results: The study successfully implemented bSSFP protocol at 0.05 T and demonstrated its utility for imaging the brain, cervical spine, and knee.

Impact: In this study, a bSSFP protocol was successfully implemented at 0.05 T by  demonstrating its utility for imaging the brain, cervical spine, and knee. These findings enable the potential of high-quality ULF MRI. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Magnetic resonance spectroscopy at ultralow-field (B₀ < 0.1T) on portable MRI scanner is challenging due to the low signal-to-noise ratio (SNR) and the impossible spectral separability.

Goal(s): To obtain spectroscopic images of lactate at different concentrations in a phantom on our 46mT Halbach point-of-care MRI scanner and maximize SNR with incorporation of composite refocusing pulses.

Approach: We modified a non-localized Carr-Purcell-Meiboom-Gill (CPMG) echo train sequence to perform 2D J-spectroscopic imaging in lactate phantom with composite refocusing pulses for improved SNR. 

Results: We showed the first steps towards lactate spectroscopic imaging at ultralow-field. 

Impact: The implementation of lactate spectroscopic imaging could add value to the growing list of biomedical applications of low field MR systems, for example in neonatal hypoxic ischemic encephalopathy.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Imaging with a single sided MRI allows for a smaller scanner footprint, making it possible to bring the scanner into the doctor's office.

Goal(s): An xSPEN pulse sequence capable of producing three dimensional images is presented here, allowing for rapid image collection in an inhomogeneous magnetic field.

Approach: An additional phase encode array is incorporated into the xSPEN pulse sequence, allowing for the excited slab to be resolved along the z axis.

Results: A two dimensional multislice technique was converted into a three dimensional volumetric imaging by adding a phase encode array to the spatiotemporal axis.

Impact: A method for rapidly collecting three dimensional images in an inhomogeneous magnetic field is presented here. This technique will help bring MRI into the doctor's office by allowing for higher quality images to be collected in less time.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Developing methods for rapidly imaging in an inhomogeneous magnetic field is necessary for the general adoption of single sided MRI, which would bring MR imaging into the doctor's office.

Goal(s): We aim to develop a fully spatiotemporal pulse sequence for collecting images with a single sided scanner.

Approach: A hyperbolic phase is imparted to the magnetization which results in a time domain signal that is a profile of the phantom. The angle of this profile is rotated to produce an image.

Results: Images with no Fourier encoding were produced and the images could be cropped without aliasing.

Impact: This novel technique allows for rapid imaging in an inhomgeneous magnetic field. Furthermore, this technique allows for improved resolution because the field of view of the images collected with it can be smaller than the object without aliasing.

Keywords: Low-Field MRI, Sparse & Low-Rank Models, Electromagnetic Interference

Motivation: Point-of-care MRI systems need electromagnetic interference (EMI) cancellation with limited passive shielding to improve cost and portability. Existing methods require external hardware or training, which increases costs and design complexity.

Goal(s): This novel solution targeting narrowband EMI is hardware-free, training-free, introduces no white-noise and can be used in conjunction with other methods.

Approach: Exploiting the sparsity, L1-regularized compressed sensing is used to extract EMI from a comb-shaped sampling window that consists of noise-dominated regions in acquisition.

Results: With proof-of-concept implementation, robust EMI cancellation is demonstrated on both simulated and experimental data, with comparable performance to collector-based method despite the lack of extra hardware.

Impact: Point-of-care MRI systems can further push SNR and save scan time by removing narrowband EMI without the cost of additional hardware or training data, enabling new design possibilities for fast, portable, and economically accessible MRI.

Keywords: Low-Field MRI, Low-Field MRI, Relaxometry

Motivation: Low-field MRI holds promise for efficient diagnostics. T₁ mapping is valuable in neuroscience for studying myelination and brain development. To reduce scan time, incoherent, variable density trajectories are often used. 

Goal(s): to reach high image quality and T₁ accuracy for fast T₁ mapping at 64 mT.

Approach: Using the 64-mT, Hyperfine Swoop scanner, we compared T₁ maps acquired with fully sampled and undersampled trajectories (with and without incoherence) and reconstructed them with locally low rank regularization at different regularization factors λ. 

Results: Our findings showed that the most effective approach involves the use of a customized trajectory with λ around 0.004. 

Impact: Since fast and accurate T₁ mapping in the context of low-field MRI is achievable, it would now be interesting to study brain developement in children, that present a unique challenge due to movement.

Keywords: Low-Field MRI, Elastography

Motivation: Magnetic resonance elastography can provided quantitative assessment of tissue mechanical properties, but requires large, expensive, in demand clinical MRI scanners, this motivates a more accessible portable MR technique. 

Goal(s): To develop robust experimental protocols for bulk assessment of tissue mechanical properties using portable magnetic resonance and explore clinical applications.

Approach: Effects of phase interference on the MR signal magnitude and phase are investigated to characterize the shear wave velocity for samples with differing mechanical properties under harmonic and transient excitation. 

Results: Preliminary measurements show that a portable MR instrument can be used to quantify the shear wave velocity in homogeneous samples. 

Impact: These results show the potential of a portable magnetic resonance instrument for quantification of  shear mechanical properties in biological tissues. This merits further investigation of applications to the diagnosis of specific diseases which could potentially improve patient outcomes. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Limited access to medical equipment makes low-field MRI an interesting option in many settings. One challenge is the prolonged scan time, especially for quantitative imaging. However, parallel imaging is typically not used due to the very high sensitivity of a single solenoid receive coil.

Goal(s): This study aims to accelerate T₁ mapping (used for estimating brain myelination) on a Halbach low-field system.

Approach: A locally low-rank reconstruction was applied to diminish undersampling artifacts from the variable-density random sampling trajectory.

Results: The study highlights the potential for both, fast lower-resolution (2.5mm² in-plane) and higher-resolution (1.5mm² in-plane) T₁ mapping with an acceleration factor of R=4.

Impact: Our study's advanced low-rank reconstruction approach for low-field MRI could transform imaging methods in regions where high-field MRI is inaccessible, enabling precise and fast T₁ brain mapping, which is critical for assessing myelination-related diseases with newfound speed and reliability.

Keywords: Low-Field MRI, Low-Field MRI, Diffusion

Motivation: DWI/DTI are very challenging in portable MRI system, while they play a pivotal role in timely triage, diagnosis and treatment for patients with suspected acute conditions such as stroke. 

Goal(s): To mitigate the effects of eddy currents and achieve multi-directional diffusion-weighted imaging and diffusion tensor imaging in portable MRI system.

Approach: With the three-axis gradient coil accompanied with anti-eddy plate and image-phase based eddy current correction, we applied multi-scaning average to suppress noise and adopted eddy correction to mitigate the motion blurring.

Results: We succeed obtain visible multi-direction diffusion-weighted imaging and DTI imaging in portable MRI system.

Impact: With the three-axis gradient coil accompanied with anti-eddy plate and image-phase based eddy current correction, we succeed in obtaining multi-direction diffusion-weighted imaging and  DTI images with the portable MRI system.

Keywords: Gray Matter, Segmentation, Analysis/Processing, Brain, Data Acquisition, Validation

Motivation: Ultra-low-field MRI scanners offer a cost-effective and portable alternative to high-field neuroimaging.

Goal(s): To quantify between-scanner test-retest reliability of 64mT brain scans, and their correspondence to 3T MRI.

Approach: We scanned 23 healthy participants on two Hyperfine 64mT scanners and a GE 3T scanner using T₁w and T₂w scans at multiple resolutions. We segmented images into 98 structures and estimated their volumes.

Results: We demonstrate excellent reliability of volumetric estimates from ultra-low-field MRI, and high correspondence to high-field scans. The highest reliability and high-field correspondence was obtained using T₂w ultra-low-field scans, super-resolved by combining three orthogonal acquisitions with low through-plane resolution.

Impact: Measures of brain volume from Hyperfine portable ultra-low-field MRI scans show excellent test-retest reliability across scanners, and excellent correspondence to similar estimates from high-field MRI. This enables quantitative analysis of cost-effective and portable neuroimaging in various contexts, including low-resource environments.

Keywords: Low-Field MRI, Simulations

Motivation: Due to its convenience and affordability, ultra-low field MR imaging is growing in popularity. However, poor SNR requires a solution.

Goal(s): This research aims to determine if superconducting coils or low temperature coils are still beneficial in terms of SNR in ultra-low-field MR.

Approach: Our method compares RF coils made from different conductivities. This comparison will help us determine superconductor importance in coil performance.

Results: The findings highlight the significance of superconductor materials and how they can be used to improve imaging performance at lower field strengths.

Impact: This study investigates signal-to-noise ratio (SNR) in superconducting, low temperature and room temperature RF coils for affordable ultra-low-field MR imaging and determines if superconducting or low temperature coils are still beneficial in SNR at 0.07T. It shows how superconductor materials improve imaging performance, especially at lower field strengths.

Keywords: Low-Field MRI, Magnets (B0)

Motivation: The current optimizations of permanent magnet array (PMA) designs are guided by checking field properties, not reflecting the quality of reconstructed images.

Goal(s): We aim to propose indicating parameters for the encoding capability of spatial encoding magnetic fields (SEMs) to guide PMA designs.

Approach: Local k-spaces are pushed to be point-wise. The coverage area of the point-wise k-spaces between the spokes of the maximum and minimum angles is calculated to indicate the encoding capability.

Results: The proposed method is fast, enlarging the optimization space, resulting in SEMs having superior encoding capability with stronger field, higher gradient, and lower NRMSE of the resultant images.

Impact: The proposed point-wise k-space evaluation enlarges the solution space for the PMA optimizations thus significantly improves the performances of the outcomes, i.e., SEMs having superior encoding capability with higher field strength and higher gradient compared to that from conventional approachs.

Keywords: Low-Field MRI, Magnetization transfer, Low Field MRI

Motivation: Here, we exploited the Low SAR in low-field MRI to study magnetization transfer (MT) , and potential to enhance brain tissue contrast, in particular between white and gray matter (challenging at low-field). 

Goal(s): The study aimed to identify suitable MT settings and explore MT contrast in-vivo at 46 mT.

Approach: MT settings were optimized to minimize direct saturation and maximize MT contrast. With this setup, we scanned five volunteers at 46 mT and acquired additional 3T scans for two participants

Results:  Optimal MT settings were defined in the phantom and in-vivo scans demonstrated the expected MT effects, and improved tissue contrast at 46 mT.

Impact: Magnetization transfer could be achieved off-resonance in-vivo at low-field MRI. It improves brain tissue contrast, in particular between white matter and gray matter, and has minimal direct saturation.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: To enable 2D phantom imaging using low-cost, handheld MRI for point-of-care and educational applications.

Goal(s): Optimize a handheld spokes-and-hub magnet for 2D imaging, focusing on cost-effective design to create a comprehensive imaging system with affordability, accessibility, and versatility.

Approach: This research extends prior studies focusing on a handheld spokes-and-hub magnet. Spin echo and turbo spin echo phantom imaging is enabled through optimization of magnet's design, RF pulses, and digitally-controlled H-bridge gradient coil drive.

Results: 64x64 pixel MR images obtained in seconds from 10 mm diameter phantoms using a duration-phase-encoded TSE sequence on our redesigned handheld imager (spokes-and-hub magnet, dithered-pulse RF, switch-driven gradients).

Impact: From magnet design and budget-friendly hardware constraints, we delve into 2D image acquisition in handheld spokes-and-hub MRI. Our tools aid iterative design, demonstrating viability for education and potential clinical use. Advancing low-field MRI, this work boosts MR accessibility and affordability.

Keywords: Low-Field MRI, Low-Field MRI, Magnets (B0), New Devices

Motivation: To build a truly portable MRI scanner for neurological and MSK applications, optimized for field homogeneity and FoV size compared to standard Halbach configurations.

Goal(s): To explore elliptic-bore magnets to improve the field homogeneity and remove constraints to the extent of the gradient coils typical of Halbach magnets.

Approach: We have optimized a tightly-packed distribution of magnetic Nd2Fe14B cubes with differential evolution algorithm, and a second array of shimming magnets with interior point and differential evolution methods.

Results: We have built a 10 & 14 cm radii elliptic magnet with 87.4 mT@5700 ppm in a 10 cm radius FoV.

Impact: Elliptic-bore Halbach magnets enhance the ergonomicity and field distribution of low-costportable MRI scanners, while allowing for full-length gradient support to increase the FoV. Thisgeometry can be  potentially adapted for a prospective low-cost whole-body technology.

Keywords: Low-Field MRI, Low-Field MRI, SQUID

Motivation: At Chipiron we strive to develop the first commercial portable ultra-low field MRI scanner based on SQUID detection.

Goal(s):  Here, we aimed to acquire a first 3D image using SQUID-MRI at 1 mT.

Approach: Using our own integrated SQUID-MRI system, we scanned a hand-made water based phantom using a GRE sequence.

Results: We successfully acquired a 3D image of a phantom in 6 h with a resolution of 5x5x40 mm³.

Impact: Aspiring to democratise MRI, we develop a portable ultra-low field scanner that leverages the high sensitivity of SQUID detection. Our first 3D image is just the first step that paves the way to achieving competitive image quality for clinical employment.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: The narrow bandwidth of RF coils for low field MRI means that coils often require re-tuning between subjects due to different loading conditions.

Goal(s): We compare the performance and loading effects of an elliptical solenoid and a dome helmet coil to see which coil is more sensitive to loading

Approach: The SNR and transmit efficiency  of the two coil types are compared in when lightly loaded (phantom) and normally loaded (in-vivo) settings

Results: The elliptical solenoid coil has a substantially smaller frequency shift when loaded (~1kHz vs ~13kHz) and has superior SNR in-vivo compared to a tight -fitting dome helmet coil.

Impact: We compare the performance of tight-fitting dome helmet coil to an elliptical solenoid coil and find that due to reduced loading the performance of the elliptical coil is superior in-vivo while having better frequency stability with differing loads.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Diffusion-weighted Imaging (DWI) at very-low fields like the 0.064 Tesla Hyperfine Swoop is limited by low signal-to-noise ratio (SNR), impeding clinical application.

Goal(s): This study aims to enhance DWI at such low fields by creating synthetic high-field images using pre-trained neural networks.

Approach: The Diffusion Probabilistic Model (DPM), an advanced generative AI, will be trained on high-quality 3T DWI images to learn their distribution. Low-field DWI images guide the DPM to conditionally synthesize high-quality images.

Results: With a well-trained DPM, we aim to produce high-quality, synthetic 3T-like DWI images that mirror the original low-field ones, bypassing the need for paired training data.

Impact: The method enhances DWI image quality at very-low field strength in an unsupervised manner, eliminating the need for paired high-field and low-field data, thus expanding training data availability. Zero-shot image reconstruction enhances its generalizability for diverse tasks.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Access to MRI worldwide could be improved by reducing cost and increasing portability of the system. This requires imaging to occur in unshielded rooms making them highly susceptible to environmental noise; therefore, low-cost alternatives are needed for noise mitigation

Goal(s): Here we have designed a self-shielded RF coil array, made of resonating coaxial cables, for low-field parallel imaging in unshielded environments.

Approach: The proposed coils were tested against copper loops through phantom and clinical studies in various noise environments.

Results: The results indicate the self-shield coils are robust to external noise and produce images with sufficient signal and contrast to distinguish anatomical features.

Impact: With the increased interest in the community towards developing accessible MR systems, the proposed coil design presents a low-cost and resource efficient method for noise mitigation, thereby allowing MRI to be portable and available to provide point-of-care screening.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Ultra-low field scanners can vastly improve access to neuroimaging, and implementing MRI techniques to quantify microstructure allows monitoring of both neurodegenerative diseases as well as myelination trajectories during development.

Goal(s): To assess the reliability of microstructure-sensitive methods at ultra-low field before large-scale deployment.

Approach: The reliability of recently developed magnetization transfer (MT) imaging and T₂ mapping sequences at 64mT was assessed in 5 healthy subjects through histograms, difference maps and correlation analysis in white matter.

Results: Both MT ratios and T₂ values were highly reproducible in the test cohort.

Impact: Techniques to measure microstructure, even semi-quantitatively, can be useful for tracking myelination/demyelination. Here we demonstrate the reproducibility of two such methods: magnetization transfer imaging and T₂ mapping, in a small cohort of healthy adults at ultra-low field (64mT).

Keywords: Low-Field MRI, Magnets (B0)

Motivation: By adjusting individual coil currents, a loop coil array can generate a uniform B₀ field and it offers the flexibility to control gradient field direction making it suitable for compact MRI systems.

Goal(s): The goal is to show that the loop coil array produces a uniform and/or gradient magnetic fields.

Approach: The current values of individual loops for a uniform magnetic field were determined by ptimization to achieve either uniform field strength, whose orientation can be rotated, or a linear field gradient

Results: A method for calculating required current values has been presented, and simulations validate its effectiveness.

Impact: Suggested coil arrays offer the potential for developing more compact and lighter MRI systems by substituting traditional magnets and 3-axis gradient coils in current low-field MRI setups.

Keywords: Low-Field MRI, Brain

Motivation: Very low-field MRI offers several benefits related to accessibility. However, electromagnetic interference (EMI) poses a significant challenge by degrading SNR. Hence, evaluating the effect of EMI on image quality is improvement.

Goal(s): The study aims to investigate the influence of EMI on image quality using 50mT.

Approach: We varied the distance and amplitude of the EMI producing coil from signal generator. We analyzed the effect of EMI on the image quality.

Results: As expected, the SNR decreases with an increase in amplitude. The standard deviation and RMS of the background increase as the increase in amplitude and decrease in distance.

Impact: Highlight the influence of EMI on image quality.The results indicate that as the amplitude of the coil increases or the distance between the transmitter and scanner decreases, the signal-to-noise ratio decreases, the standard deviation and RMS of the background increase.

Keywords: Low-Field MRI, Low-Field MRI, Permanent Magnets

Motivation: The building process of low-field scanners magnets, when composed of a large number of small permanent magnets, is time-consuming and error-prone due to the highly repetitive task.

Goal(s): To design a low-cost and open-source solution making the magnet building process faster and more reliable.

Approach: To use a Hall sensor to distinguish between working and defective permanent magnets. Furthermore, to take advantage of the attractive force between two permanent magnets to identify the polarization direction.

Results: A magnetic test station is designed. CAD drawings and scripts are made available on the GitHub repository.

Impact: A magnet test station allowing for an easy and straightforward testing of small permanent magnets is proposed. The test station makes the construction process of low-field scanner magnets, composed of a large number of permanent magnets, faster and more reliable.

Keywords: Low-Field MRI, RF Arrays & Systems

Motivation: Low field MRI using RF based gradients can reduce both its cost and bulk.  Multi-channel RF arrays can enable this. Effective methods to decouple these coils and mitigate EMI are necessary for building efficient RF encoding based systems.

Goal(s): To  improve multi-channel RF array performance for low field MRI and automatically reject EMI.

Approach: Develop an array of multi-turn surface coils with concentric shields. These are verified with an EMI rejection test and geometric decoupling tests.

Results: These coils automatically reject environmental noise and add two additional geometric coupling modes when used in an array, allowing for more array configurations.

Impact: RF array decoupling and EMI mitigation are challenging at low-field. We develop a method to decouple RF coil arrays by leveraging counter-wound multiturn surface coils allowing for additional decoupling modes. These coils are also self-shielded, providing added EMI mitigation.

Keywords: Low-Field MRI, Low-Field MRI, Field-Cycling

Motivation: Field-cycling imaging is a new imaging technique that allows access to new imaging biomarkers. To allow investigation of clinical applications a high performance and patient acceptable scanner is needed.

Goal(s): We have constructed a new clinical-grade resistive field-cycling imaging system operating at 0.2 T with a 60 cm bore and high performance gradient and magnet amplifiers, with a custom made outer covering.

Approach: The system is in the late stage of commissioning. The field homogeneity and temporal stability have been assessed.

Results: The final system is visually attractive and has < 1 ppm temporal stability and < 8 ppm field homogeneity.

Impact: This system will allow us to investigate the clinical utility of field-cycling and low-field imaging in a much larger patient population. The high performance gradient amplifiers will enable much faster imaging, which will enable new possibilities for new sequence development.

Keywords: Low-Field MRI, Low-Field MRI, open-source, console, acquisition

Motivation: We challenge proprietary barriers in low-field MRI to enhance methodological integration. Our focus is on improving system versatility for advanced imaging.

Goal(s): To create a versatile, MRI console driven by open-source software, capable of integrating sophisticated low-field imaging techniques. This involves for instance additional sensors or real-time adaptions.

Approach: We implemented Spectrum-Instrumentation measurement cards with a high-performance reconstruction system. The open-source Python software, incorporating a Pulseq interpreter, allows to streamline flexible, fast, and transparent low-field imaging applications.

Results: Successful implementation evidenced by high-fidelity Pulseq sequence execution to image 3D printed brain phantoms on a system capable of in-vivo applications.

Impact: The open and versatile design of our proposed console paves the way for advanced techniques in low-field MRI, enabling widespread adoption in research facilities and fostering innovative MRI applications in resource-limited settings.

Keywords: Low-Field MRI, Simulations

Motivation: Inner-Shield in Halbach-array magnet effect RF coil transmit efficiency and signal-to-noise ratio(SNR). With this, finding a good trade of between magnet diameter and SNR is important.

Goal(s): Find the proper magnet diameter with respect to the RF coil transmit efficiency.

Approach: Simulations of the transmit efficiency of three RF coils used for neuroimaging on a 46 mT Halbach-array point-of-care MRI system have been performed in terms of analyzing the coil to RF shield distance located inside the magnet. 

Results: Results show that a distance of 1 cm results in a 50% lower transmit/receive efficiency than a 3 cm gap. 

Impact: This means that slightly larger magnets may have higher signal-to-noise even though the B0 field is lower. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: The 64mT Hyperfine Swoop (Hyperfine Inc. Guilford CT) is a first-of-kind point-of-care (POC) commercial system to allow ‘patient-to-scanner’ imaging.

Goal(s): We report an independent technical benchmark analysis of this system’s power consumption in this study (pass-through measures of W, kWh, and A).

Approach: Performance benchmarks of MR systems power consumption was measured per-pulse sequence using consumer-grade instrumentation under continuous monitoring. Custom acquisition protocol using two portable 120V_AC NEMA-standard power banks were examined.

Results: A look-up benchmark table of empirical surge current draw (with 120V_AC), its implicit advisory, and a potentially viable protocol run example without 'wall' i.e. via stand-alone power supply are reported. 

Impact: POC-MR Instrumentation power benchmark considerations on a per-pulse-sequence power consumption basis provide key insights into protocol deployment, scheduling, and optimal scan resource management considerations in resource-limited settings. Successful pulse sequence protocol implementation with under resource-limited setting was also demonstrated.

Keywords: Low-Field MRI, Brain, Small vessel disease

Motivation: Field-cycling MRI makes it possible to characterise the clinical potential of endogenous spin-lattice R₁ image contrast that arises at ultra-low-magnetic field strengths.

Goal(s): Our goal was to examine the extent translated motion correction and denoising approaches improve the utility of R₁ mapping performed at ultra-low field.

Approach: : Improvements in sensitivity to differences in R₁ between tissue types and fitting accuracy were determined across brain and head tissues. 

Results: Improvements in sensitivity and goodness of fit were observed. Significant difference in R₁ values between regions of white matter and confluent small vessel disease were observed between 0.2 - 200 mT. 

Impact: The improvement in sensitivity of R₁ mapping using translated motion correction and denoising approaches provides new opportunities to assess the clinical potential of new endogenous image contrast mechanism at ultra-low field strengths. 

Keywords: Low-Field MRI, Low-Field MRI, denoising

Motivation: Low-field MRI holds the promise of expanding access to healthcare. The low signal-to-noise ratio (SNR) poses a significant challenge to acquiring diagnostically useful information in a reasonable scanning time. 

Goal(s): To overcome the challenge of low SNR in low-field MRI, achieving fast, self-supervised denoising.

Approach: A rapid 4D-denoising method utilizing the Zero-Shot-Noise2Noise framework is proposed, without the need for intensive network training.

Results: This method provides fast denoising in just 10-20 seconds per case and significantly boosts SNR efficiency, reducing the number of measrued TIs and TEs needed for precise, high-quality T₁/T₂ mapping.

Impact: This study's fast 4D-denoising approach revolutionizes low-field MRI by enhancing SNR without extensive training datasets, enabling faster, more efficient imaging and broadening diagnostic accessibility in resource-limited settings.

Keywords: Low-Field MRI, Simulations

Motivation: Accurate and precise simulation of low field MR, as well as simulation of high field MR with arbitrary granularity.

Goal(s): To assess and address the limitations in the Magnetic Resonance Integral Equation (MARIE) suite that prevent successful low field simulation.

Approach: We achieved these goals using a number of numerical analysis techniques, such as Taylor series approximations and Kahan summation.

Results: We successfully identified and addressed the limitations of MARIE, which we attributed to catastrophic loss of numerical precision. In doing so, we enabled low frequency and fine mesh simulation.

Impact: Low field and detailed simulation of coils would enable many applications, such as coil optimization, synthetic generation of MR data for machine learning algorithms, computational pulse sequence optimization, accurate safety assessments in simulation, among many other applications.

Keywords: Low-Field MRI, Low-Field MRI, Spatial encoding field, Evaluation method

Motivation: For non-linear encoding technology for portable MRI, the evaluation of encoding capability is by checking the image quality, which is time-consuming and hard to integrate into an optimization process. 

Goal(s): Here, we aim to propose a fast evaluation method for the encoding capability of rotational spatial encoding magnetic field (rSEM). 

Approach: The filling factor of local k-spaces is proposed to evaluate the encoding capability of an rSEM with non-linear gradients. 

Results: The proposed evaluation of encoding capability is fast and agrees with the resultant image quality.  It was used for angle selections to accelerate imaging, showing improved image quality experimentally. 

Impact: A rapid evaluation method for the encoding capability of rSEMs with non-linear gradients is validated using simulation and experimental data. It allows fast evaluations of SEMs without checking the image quality in a design process, which accelerate the optimization. 

Keywords: Data Processing, Low-Field MRI

Motivation: Applying the component imaging method to low-field MRI systems will face a main problem: low-SNR image data.

Goal(s): An optimized inversion method is proposed, aiming to give better results for image data with low SNR.

Approach: This paper proposes an optimized inversion method with the formula of the optimization problem combining intra- and inter-voxel constraints.

Results: The optimized method shows a better convergence rate avoiding the fragmentation of component images and the appearance of pseudo peaks in the spectrum.

Impact: This multi-component imaging approach can provide sub-voxel characterization and be applied to numerous applications of popular portable low-field MRI systems.

Keywords: Low-Field MRI, Susceptibility, Routine Protocols

Motivation: To investigate the performance of modernized low-field MRI relative to traditional systems for imaging near metallic devices within the clinical context.

Goal(s): To evaluate whether low-field MRI can offer a significant reduction in artifacts when using routine clinical protocols.

Approach: The artifact characteristics of 0.5 T, 1.5 T, and 3 T MRIs are compared in this ASTM F2119-07-based phantom study of common passive metallic devices.

Results: Low-field MRI demonstrated the capability to reduce susceptibility artifacts when imaging near metal-containing medical devices. However, artifact produced by some pulse sequences diverged from the anticipated field-dependence, highlighting the sizable effects of clinical protocolling.

Impact: This phantom study demonstrates that low-field MRI can image metallic devices with reduced artifact relative to 1.5/3 T systems using routine clinical protocols, highlighting opportunities for future in vivo studies involving implants and imaging in areas with magnetic susceptibility distortions.

Keywords: Low-Field MRI, Low-Field MRI, denoising, self-supervised learning, zero-shot learning, low SNR

Motivation: Low SNR per unit-time in low-field MRI results in noisy images when targeting both clinically acceptable resolution and acquisition times which may limit their diagnostic effectiveness.

Goal(s): We seek to improve low-field MRI SNR by means of deep-learning while overcoming the limitations of traditional supervised learning and without compromising denoising performance.

Approach: We build on:1)self-supervised method enabling training without having to collect ‘noise-free’ data and 2)zero-shot concept to achieve dataset-free and scan-specific denoising.Additionally,we adopted simplified architecture for fast training times.

Results: Our method showed high denoising performance for different SNR levels and contrasts within few seconds of processing time competing with well-established BM4D.

Impact: Our proposed denoising method, based on self-supervised zero-shot deep-learning, enables high-performance denoising within short processing times. This approach shows promise for speedy acquisitions and enhanced imaged quality in low-field, point-of-care settings.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Commercially available open source electronics will help lower the cost and increase accessibility of MRI scanners.

Goal(s): Here we characterise the performance of a commercially available, partially open source RF amplifier designed for low field (<100 mT) MRI

Approach: We examine the gain linearity and frequency stability of the RF amplifier and examine the behaviour of the RF amplifier when transmitting in to a 50 ohm load and RF coil.

Results: The RF amplifier performs well and has sufficient power for low field applications, making it an attractive open source option for low field MRI systems.

Impact: Commercially available open-source electronics will help fundamentally address the cost and access issues hampering the wide step adoption of MRI in low resource settings. In this work we characterise a commercial, partially open-source RF amplifier for low field MRI.

Keywords: Low-Field MRI, Low-Field MRI, Short T2, hard tissue, extremity imaging

Motivation: We have previously demonstrated the versatility of a portable 72mT extremity MRI scanner. Hard tissue imaging would enhance the system’s potential, but this remains to be demonstrated in low-field systems (<0.1T)

Goal(s): To explore the possibility of imaging samples with T2*<1ms, comparable to those bone or ligament.

Approach: We programmed a PETRA sequence into the MaRCoS opens-source console, and we compared images of short and long T2* samples resulting from PETRA and Spin Echo. 

Results: Image reconstructions show that samples with T2* as low as 800us can be successfully imaged with PETRA in conditions where Spin Echo outputs mostly noise. 

Impact: By successfully capturing signals from short T2* tissues, our research enhances  our 72mT portable MRI scanner utility designed for extremity imaging.

Keywords: Low-Field MRI, Contrast Agent, Low-Field MRI

Motivation: Point-of-care MRI systems have the potential to increase access to imaging. Contrast agents could enhance tissue differentiation at the ultra-low fields of these devices.

Goal(s): To characterize the performance of Gadolinium contrast agents on an FDA cleared, point-of-care MRI system to inform sequence optimization for in vivo imaging. 

Approach: Longitudinal relaxivities of six FDA approved gadolinium contrast agents were characterized at 64 mT on a point-of-care MRI device and used to optimize T1 imaging of white matter and CSF. 

Results: Longitudinal relaxivities increased at 64 mT compared to their 3 T values. Simulations showed enhancement could be well visualized within feasible sequence parameters. 

Impact: Point-of-care MRI systems have the potential to impact patient care by increasing access to imaging. This work explores the feasibility of contrast-enhanced imaging with FDA-approved agents at ultra-low field on a point-of-care MRI. 

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Single-sided MRI offers flexibility for the movements of the field-of-view (FoV) with respect to the magnet. This adds a degree-of-freedom for signal encoding especially when the gradients are non-linear.

Goal(s): We aim to optimize the trajectory of the FoV within a non-linear magnet field, generated by a single-sided magnet array for good signal encoding.

Approach: Genetic algorithm was used for the optimization. The fitness function includes the filling area of local k-spaces, an indicator of the encoding capability of non-linear gradient field.

Results: The optimized trajectories result in improved signal encoding and thus improved image quality.

Impact: This work provides an additional degree of freedom to encode signals using single-sided magnet/arrays besides the gradients of field patterns, to improve image quality. It extends the possibility to use a moving single-sided magnet/arrays for imaging.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: The field cycling (FC) scanner introduces an extra degree of freedom for adjusting the B0 field strength during both polarization and readout. However, the ideal readout Larmor frequency remains unexplored.

Goal(s): To investigate the optimal readout Larmor frequency for the non-uniform B0 (NuBo) scanner regarding SNR, T2*, and T2 dephasing. 

Approach: Controlled experiments at two Larmor frequencies, 1MHz and 2MHz, were conducted. Echo trains at these two frequencies were acquired.

Results: Results show that readout at a lower Larmor frequency could benefit from a longer echo train, and longer T2*, but with the penalty of a smaller initial signal amplitude.

Impact: This research conducted a comparison of the trade-off between SNR, T2* and T2 decay across various readout Larmor frequencies, potentially offering insights for researchers in the field of field cycling in the future.

Keywords: Low-Field MRI, Low-Field MRI

Motivation: Low-Field MR (LF-MRI) offers greater accessibility and reduced sensitivity to susceptibility artifacts, but it suffers from low SNR. As a result, novel denoising techniques hold great promise to improve image quality and promote broader clinical applications of LF-MRI.

Goal(s): This work introduces a novel MRI denoising technique that is based on self-supervised deep learning without requiring high SNR references.

Approach: Our technique, called SNAC-DL, employs a Self-supervised Network for Adaptive Convolutional Dictionary Learning using a complex-valued coil-to-coil ($\mathbb{C}$C2C) training strategy.

Results: SNAC-DL has been tested for lung MRI denoising at 0.55T to demonstrate efficient denoising while preserving the underlying image structure.

Impact: The proposed denoising technique holds significant potential to improve image quality for LF-MRI. This is expected to facilitate the broad adoption of LF-MRI to improve cost-effectiveness and enable new clinical applications that are traditionally challenging at high field strengths.

Keywords: Low-Field MRI, Low-Field MRI, Elastography

Motivation: To our knowledge, concomitant field effects in MRE have not been investigated yet, which might become of importance when translating MRE to low field MR systems.

Goal(s): Propose a framework to investigate concomitant field effects on MRE, in particular Hadamard-encoded 3D MRE at 0.55T.

Approach: A 6x6 encoding scheme is proposed to study the effects of concomitant fields on 3D MRE at 0.55T in phantom experiments.

Results: Phantom experiments demonstrated that the effects of concomitant fields on 3D Hadamard-encoded MRE at 0.55T are negligible.

Impact: A framework to assess concomitant field effects in MRE, in particular Hadamard-encoded 3D MRE at 0.55T in phantom experiments.

Keywords: Low-Field MRI, New Devices, Feild mapping robot

Motivation:  Measurement of  parameters like magnetic field and temperature inside a magnet bore is of interest at all MR magnetic field strengths to characterize the system and use that information for downstream image quality improvement or to determine safety thresholds.

Goal(s): Build and test a simple 3D movement robot.

Approach:   we design, build and test a simple 3D movement robot with a sensor holder as a standalone system using a Raspberry Pi and a 16 channel ADC hat.

Results:   The robot is capable of sub-millimeter measurements. We demonstrate the 3D field mapping of a 50mT scanner as an example use of the robot.

Impact:  We designed and built a $2000 3D field mapping robot to map a very low field scanner’s magnet. The system is standalone exploiting Raspberry Pi’s system on a chip architecture and is scalable to include 16 analog inputs (sensors).

Keywords: Safety, Safety

Motivation: To develop a reliable method to predict heating around deep brain stimulation implants as a safety assessment prior to scanning patients.

Goal(s): To investigate the accuracy of a heating prediction workflow in-vivo.

Approach: We surgically inserted a DBS electrode into swine brains and predicted the heating around DBS contacts, with and without perfusion. Our heating prediction workflow uses a new MR-based current measurement, proposed for this work, as well as quasi-static electromagnetic and thermal simulations to predict heating around the electrical contacts of DBS electrodes.

Results: The predicted temperature around electrical contacts agreed with the measurements (NRMSE ≤ 0.09). 

Impact: Our workflow predicts heating around the electrical contacts in-vivo without complex modeling and simulations. The results demonstrate the reliability of the workflow to assess heating risk before scanning patients with DBS implants.

Keywords: Safety, Safety

Motivation: RF-induced heating for the partially-in and partially-out (PIPO) medical implants is the primary concern for patient’s safety under MRI. 

Goal(s): Winding the external portion of the PIPO medical electrodes is proposed to reduce the RF heating under 1.5T MRI. 

Approach: One commercial PIPO medical electrode and an insulated solid wire were used to demonstrate this concept. RF heating is measured inside the ASTM phantom under a 1.5T RF birdcage coil and evaluated from the in-vivo simulations using the transfer function (TF) approach. 

Results: The results showed a significant reduction of RF heating in the commercial lead and simplified wire.

Impact: The proposed method can reduce RF-induced heating significantly, mitigating the risk of tissue damage and improving the quality of care for patients with partially-in and partially-out (PIPO) medical devices under 1.5T MRI.

Keywords: Safety, Safety, Low Field, RF-induced heating, Interventional

Motivation: RF-induced heating of interventional devices is reduced at lower magnetic fields, but dangerous heating conditions can still occur during MR-guided interventions.

Goal(s): To investigate the effect of body coil drive mode on RF-induced heating of interventional devices at 0.55T and 1.5T.

Approach: Numerical simulations, E-field, transfer function and temperature measurements are used to evaluate the dependency of RF-induced heating of commonly used interventional devices on the phase and amplitude settings of body coil ports.

Results: RF-induced heating can be reduced using individually adapted body coil drive modes.

Impact: Dual-drive body coil technology can be used to generate implant-friendly electromagnetic fields, which can enable safe use of clinical intravascular devices during MR-guided interventions at 0.55T and 1.5T.

Keywords: Safety, Safety

Motivation: MRI of (biodegradable) passively conducting implants is challenged by potential elevation of RF power deposition (SAR) in the vicinity of an implant. Accidental implant fractures or fissures due to dynamic degradation of biodegradable implants alter the implants’ structure. This mechanical impact induces changes in the electromagnetic response of the system versus an intact implant. 

Goal(s): Recognizing this clinical and patient safety challenge, this work first examines the SAR magnification caused by implant fracture

Approach: The efficacy of an optimized parallel excitation vectors deduced from a multi-objective genetic algorithm is demonstrated.

Results: Reduction of SAR magnification in fractured implant using the optimized excitation vector.

Impact: Amplification of RF power deposition in MRI of fractured metallic implants constitutes a patient safety hazard. This risk can be mitigated with parallel transmission using GA-driven excitation. This approach provides a viable clinical alternative for MRI monitoring of implantation sites.

Keywords: Safety, Safety, dental MRI, RF safety, intraoral coil, simulation

Motivation: In dental applications intraoral coils (IOCs) offer higher SNR than external surface coils, but the details of RF-induced heating of an intraoral coil dependent on many factors such as coil size, shape, incident E-field, surrounding tissue, and acquisition protocol.

Goal(s): This study investigates the effect of anatomical model complexity on SAR simulations for IOCs.

Approach: Numerical simulations were compared to electric field mapping and temperature measurements to evaluate RF-induced heating of various IOCs.

Results: RF heating and SAR simulations of IOCs can be performed with limited tissue models, but the required complexity of the tissue model depends on the coil type.

Impact: The complexity of numerical simulations can be reduced to limited tissues while maintaining accuracy of SAR estimation to determine the safety of intraoral coils through hotspot detection.

Keywords: Safety, Safety, Deep Brain Stimulation; Parallel Transmission

Motivation: Bilateral deep brain stimulation (DBS) surgery would benefit from safe intraoperative 3T MRI using conventional scanners.

Goal(s): Our goal was to develop a method to determine patient-specific safety constraints to scan a bilateral lead configuration with minimal RF-heating, by minimizing RF-induced currents at maximal B₁.

Approach: We scanned a phantom with two leads in different configurations, measured local heating and determined the transimpedance. 

Results: We could determine the phantom-specific safety constraints and find a low-SAR sequence meeting the constraints, after optimizing the two channel RF-shimming to minimize RF-heating by minimizing RF-induced currents at maximal B₁.

Impact: The proposed method can be used to minimize heating of a bilateral lead configuration and estimate patient-specific safety constraints, but further research has to be conducted to be able to use it during deep brain stimulation surgery.

Keywords: Safety, Safety

Motivation: Electrically short fragmented leads are sometimes left behind in the human body after the extraction of an active implantable medical device (AIMD). When a new AIMD is implanted near the fragmented leads, the radiofrequency (RF)-induced heating of the newly implanted AIMD could be altered. 

Goal(s): Develop a method to evaluate the RF-induced heating of AIMD with fragmented leads in the vicinity.

Approach: We propose to use the electric field distribution which includes the presence of the fragmented leads with the AIMD transfer function model for RF-induced heating evaluation.

Results: The proposed method can effectively predict the RF-induced heating for AIMDs near fragmented leads.

Impact: It was observed that the RF-induced heating for AIMD system can be altered by the nearby fragmented leads.

Keywords: RF Arrays & Systems, RF Arrays & Systems

Motivation: To improve the design of pTx head coils intended to produce uniform RF fields while controlling local SAR levels for patients with DBS implants.

Goal(s): To evaluate the effect of extended coil length and increased number of rows on performance using simulations.

Approach: Comparison of SAR and RF homogeneity in 3-row and 4-row pTx head coil configurations using FDTD simulations on a human head model with an implanted DBS lead. 

Results: The 4-row coil offered the best SAR control for the whole brain, with length having a greater impact on local SAR than the number of rows.

Impact: The research indicates that the length of multi-row pTx coils affects local SAR in MRI for DBS patients, enhancing efficiency and safety, and broadening imaging possibilities, potentially advancing MRI-compatible devices and personalized imaging techniques.

Keywords: Multimodal, Multimodal, EEG, fMRI

Motivation: Evaluate the impact of EPI read-out gradient slew-rate on EEG amp heating, for EEG-fMRI experiments at 7T.

Goal(s): Identify slew-rates that will minimize heating of EEG amps, for EEG-fMRI experiments at 7T.

Approach: Test a range of EPI slew-rates while measuring the temperature of the EEG amp, during phantom tests at 7T.

Results: EPI read-out slew-rates of 120, 88, 61 and 46 T/m/s were tested and the slew-rates of 61 and 46 T/m/s were found to induce minimal heating of the EEG amp during EEG-fMRI experiments at 7T.

Impact: These results should help neuroscientists doing EEG-fMRI studies at 7T, to conduct their experiments without damaging the EEG amps.

Keywords: Safety, Safety

Motivation: To reduce radiofrequency (RF)-induced heating of abandoned implantable cardiac leads equipped with plastic caps, which remarkably increase heat generation around the lead tip. 

Goal(s): RF-induced heating with various electrical property of the cap was investigated to find optimal condition.

Approach: Tissue heating around the lead wire with caps of electrical conductivity ranging over 10^-6 to 10⁺⁶ S/m were compared in the ASTM phantom model by FDTD simulation, and validated by experiments. 

Results: Tissue heating around the lead tip clearly decreased and became similar to the uncapped case, when the conductivity was higher than 10^-1 S/m, which was approximately the same as the media. 

Impact: Simulations and experiments on abandoned cardiac leads revealed that the "electrically conductive cap" dramatically reduces RF-induced heating around the lead tip. Such cap may protect the lead from body fluid infiltration into the insulation material while also contribute to MR-safety.

Keywords: Safety, Safety, Low-Field MRI, B1+RMS, SAR

Motivation: The primary RF exposure metric used for MR Conditional labeling of medical devices is whole-body(wb) average SAR, which is typically overestimated by MRI scanners, leading to potentially overly restrictive labels.

Goal(s): The purpose of this study was to determine if B₁⁺RMS as an RF exposure limit can help prevent overly restrictive MR Conditional labels.

Approach: In-vivo RF-induced heating simulations in a 0.55 T MRI scanner were performed to compare potential labeling at the scanner-reported B₁⁺RMS and wbSAR with the driving voltage maximized.

Results: Results depicted a 7-13x decrease in maximum temperature rise when the RF exposure is limited by B1+RMS instead of wbSAR.

Impact: The use of B₁⁺RMS to limit RF exposure instead of SAR has significant potential to prevent unnecessarily restrictive MR Conditional labels for medical devices, especially in lower magnetic field strength MRI systems that are incapable of achieving high SAR levels.

Keywords: Safety, Safety, temperature rise

Motivation: Evaluating induced temperature rise (ΔT) in human tissue at a hot spot.

Goal(s): Comprehensive analysis of ΔT by examining cases where SAR_{0.1 g} (SAR, specifically averaged over a mass of 0.1 gram of human tissue) remains constant but the spatial distribution of SAR inside and outside the averaging volume is different.

Approach: Analytical solutions were obtained for estimating ΔT as a result of the SAR distribution exhibiting spherical symmetry with both uniform and Gaussian distributions.

Results: Using SAR_0.1g without consideration of the distribution of SAR within and outside the enclosed volume cannot be a reliable tool for estimation of ΔT.

Impact: We have obtained analytical results on the effect of the SAR distribution on the conservatively estimated ΔT in different RF exposure scenarios.

Keywords: Safety, Safety, VOP, SAR

Motivation: Compression of SAR matrices can take very long for large data sets and large channel counts when using non-clustering algorithms that show the highest compression efficiency.

Goal(s): The goal of this study was to develop an algorithm that performs the compression faster while maintaining the compression efficiency.

Approach: We use a hybrid method that combines different algorithms to form a hybrid algorithm with greatly increased calculation speed.

Results: The new compression algorithm outperforms the older non-clustering compression algorithms at all VOP counts while maintaining the compression efficiency.

Impact: VOP compression is important for local SAR supervision and constraint pulse calculation in parallel transmission. We propose a new algorithm for non-clustered compression that greatly increases calculation speed, which is important especially at large channel counts.

Keywords: High-Field MRI, Safety

Motivation: Acoustic noise can be a severe physiological barrier for acquisitions at high field.

Goal(s): To isolate the main source of acoustic noise in the NexGen 7T scanner and investigate ways to reduce it.

Approach: Vibration and acoustic noise measurements were performed. Sponge window seal materials were stuck on the RF coil to attempt altering its vibrations and decrease acoustic noise.

Results: The experimental data is consistent with noise induced by eddy-currents on the RF shield. Altering its vibrations allowed decreasing sound level by up to 10 dB at some EPI echo-spacings.

Impact: Identifying the main source of acoustic noise shall open new research avenues to mitigate acoustic noise 

Keywords: Shims, Shims, High-Field MRI, Simulations, Safety, New Devices

Motivation: The safety concerns of heating and torque in ultra-high field MRI easily become a problem in implementing local devices. As our designed brain shim coil with dense wire pattern can improve the B₀ homogeneity significantly, it is important to ensure safety before utilization. 

Goal(s): The study aims to minimize the power dissipation and torque in the designed shim coil. 

Approach: The study introduced regularization for power dissipation and torque, employs the wire interpolation method to enhance power efficiency, and simulates the impact of varying the number of turns in shim coils. 

Results: We found the optimal design parameters balancing safety and performance.  

Impact: We introduced a series of methods to design a safe and efficient shim coil for the brain in ultra-high field. The torque and heat results provide insight into the performance of the local shim coil.  

Keywords: High-Field MRI, High-Field MRI, RF coil testing hardware

Motivation: Parallel transmission (pTx) is a very useful method for minimizing peak SAR and RF field inhomogeneity at UHF. To simplify the design, individual elements of pTx RF arrays are connected directly to scanner plugs and not easily accessible. In addition, in the case of a Tx-only/Rx-only (ToRo) setup, safety regulations require testing the Tx-only array without Rx-array.

Goal(s): To develop testing hardware and procedure for adjusting and evaluating pTx 16-channel Tx/32-channel Rx 9.4T array coils.

Approach: Electronic hardware and procedure was designed, constructed, and tested.

Results: The hardware was constructed and successfully used in development of the pTx 16Tx/32Rx human head ToRo-array coil.

Impact: We developed testing hardware and procedure for pTx-coils and used them in development of the human head ToRo-array. The developed hardware allows testing any pTx 9.4T RF coil with Rx-channel count up to 32 and Tx-channel count up to 16.

Keywords: Safety, Safety

Motivation: The effects of flexible receive-only coils on Specific Absorption Rate (SAR) are understudied and poorly understood.

Goal(s): The goal was to examine, in the pediatric case, SAR effects in the presence of a receive coil with various blocking impedance characteristics.

Approach: Finite Difference Time Domain analysis was applied to evaluate SAR for pediatric human models wrapped in a flexible 16-channel coil with three blocking impedance configurations.

Results: Results demonstrated that local and whole-body SAR decreased upon inclusion of a wrapped surface coil when blocking impedance was resistive or inductive and increased when capacitive.

Impact: The demonstration of SAR effects in the presence of flexible receive-only coils and the indication of SAR configurability via blocking impedance control informs coil design to lower SAR and facilitate safety in high thermal-risk applications such as pediatric imaging.

Keywords: Safety, RF Arrays & Systems

Motivation: 7T MRI enables ²³Na MRI due to enhanced sensitivity. Combined with proton imaging, functional and anatomical information can be acquired to characterise brain status.

Goal(s): Establishing safe RF power limits for an in-house built ¹H/²³Na loop/dipole array for subsequent in-vivo experiments.

Approach: Phantom MR results at 7T and electromagnetic simulations were compared to evaluate consistency between experiments and simulations. Human models were simulated to demonstrate SAR_10g levels for different patients.

Results: Simulated and experimental B₁⁺fields showed high correlation for individual magnitudes and phases. Worst-case SAR_10g for human models all remain within safety limits, demonstrating the clinical potential of our proposed coil.

Impact: Towards in-vivo RF coil use, we validated simulated RF models of the coil at ²³Na/¹H frequencies using measured B₁⁺field magnitude and phase maps. Safe RF power limits can therefore be established for research coils to proceed to in-vivo experiments.