Periodic passive components (PPC) such as metamaterials can improve SAR efficiency and B₁ penetration. However, due to the shorter RF wavelength in MRI, the performance of PPC is confined by the limited number of unit cells. In this work, a novel PPC structure has been proposed to combine with a high permittivity pad (HPP), so a larger number of unit cells can be used. The designed structure is excited by a dipole coil and compared with the case when a single HPP is used. It is observed that more than 50% SAR reduction can be achieved.

Higher magnetic field strength leads to an increase of the SNR. On the other hand, the increase of magnetic field strength implies larger magnetic susceptibility inhomogeneities. Recently, 5.0T whole body magnetic resonance imaging system has been introduced into research and clinical settings. In this study, we evaluated the feasibility of abdominal imaging at 5T and compared the image quality and potential artifacts with 3T. Our results indicated that 5T MRI is able to acquire artifact-free anatomical images of the abdomen. Compared to 3T MRI, abdominal MRI at 5T resulted in comparable image quality and better contrast ratios.

Compared to clinical field strengths, MRI at ultra-high magnetic fields allows higher SNR. However, imaging at 7T remains challenging, especially in renal MRI. This study investigated the feasibility of renal MRI at 5T, with a brand new 5T MR scanner. Compared to 3T examination, 5T renal MRI demonstrated higher SNR and improved corticomedullar discrimination with diagnostic image quality. Functional imaging, including DWI and T2* mapping, was also feasible at 5T. Therefore, in vivo 5T renal MRI may better elucidate the renal diseases with both anatomical and functional imaging, compared to conventional clinical MRI scanners.

Moving to higher magnetic field strength (> 3 T) may have clinical advantages because of an intrinsic increase of the signal-to-noise ratio (SNR), while heterogeneity in the transmit radiofrequency (RF) field or B1 can cause signal voids throughout images. This study aimed to evaluate the development of prostate MRI at 5T by providing assessment of image quality on clinical sequences, including T1W, T2W and DWI images. According to current results about image quality, present of artifacts, visibility of anatomical structures of T2W images, and geometric distortion of DWI images, clinical prostate imaging is feasible at 5T MRI.

Imaging the hip cartilage using magnetic resonance imaging (MRI) is more challenging compared with other joints. The utilize of higher magnetic field strengths (>3T) is able to improve the assessment of cartilage structures in the hip. In this study we evaluated morphological 5T hip MRI in healthy subjects and compared image quality at 5T with 3T MRI. The results revealed that morphological 5T hip MRI in healthy subjects was superior to 3T MRI in image quality, visibility of the anatomical structures and contrast ratios.

An 8-channel shielded transmit/receive RF array has been designed and fabricated for imaging the carotid arteries at 7T. The array, similar to that presented in Ref. [1], consists of four overlapping surface loops per side. In addition to the Ref. [1], we have also added two RF shields per side with DC blocking capacitors to mitigate eddy currents. To ensure robust safety of the 7T pTx coil, local SAR matrices, and the commensurate virtual observation points (VOPs), were calculated for online SAR supervision [2,3]. Finally, the phase and amplitude of each channel have been optimized to achieve maximum B1+ homogeneity.

A thin (8mm) helmet-shaped shell of high-permittivity material (HPM) is seen to double transmit efficiency and increase SNR by 40% at the center of tissue equivalent head phantom when compared to the body coil alone, with little effect on B₁ homogeneity within the brain region. While evaluation of effects on receive arrays is ongoing, from the results shown here it seems an HPM helmet could be used at 3T in place of more electronically cumbersome head transmit coils.

This study aims to assess the feasibility of performing MRF in the liver and examine the feasibility of water-fat separation using rosette MRF at low field. MRF sequences using spiral and rosette trajectories were implemented on a 0.55T scanner. T₁ and T₂ quantification in the liver was achieved in a single breath-hold of <15s with in-plane resolution of 1.56×1.56mm² and slice thickness of 5mm. In addition, water-fat separation was achieved along with T₁ and T₂ quantification with no time penalty using rosette MRF.

Gradients in B₁ can be useful as a source of spatial encoding for low-field MRI. Here, an asymmetric spiral surface coil is introduced that generates an RF gradient around the coil. Simulations have shown that the shape of the B₁ field can be controlled by adjusting the spacing between the wires. The measured B₁ field of the asymmetric spiral coil shows that the RF gradient is generated near the coil as shown in the simulation results.

MR imaging has a significant role in medical diagnostics. Imaging quality depends on SNR levels. Higher B₀ field and consequently higher RF-field intensity increase SNR but it also elevates the total body SAR. This can be alleviated by local magnetic field enhancement. Metamaterial based structures have shown promising applications in this regard. Here we report a new metamaterial inspired resonant structure for local field enhancement in 3T MRI machine. We show field enhancement capabilities of our design in planar and cylindrical forms, each of which can be used based on the anatomical site under investigation. 

In this work a first human-sized Magnetic Particle Imaging (MPI) scanner designed and specifically engineered for experimental (cardio)vascular interventions is presented.

Based on a novel open design implementing the so called traveling wave MPI approach, the open iMPI system provides imaging of Tracers based on superparamagnetic iron oxide nanoparticles (SPIONs) with high sensitivity, optimal patient handling and would even allow hybrid imaging of magnetic tracers within gold standard x-ray based interventional angiography systems.

In initial experiments, the feasibility of a human-sized interventional MPI scanner with real-time data reconstruction and image visualization is demonstrated.

We present numerical optimization of variable winding pitch coil designs for miniature coils with respect to target field homogeneity. The optimization is based on a continuous coil winding layout that was used to simulate field homogeneity in the target volume via the Biot-Savart law. The example coil designs expand the range of applications for frequency adjustable field probes, as they increase the B₀ modification field’s homogeneity by factor of 7. Due to the specific requirements of miniature B₀ modification coils, the dimensions of the coil are restricted in length, width and wire diameter.

The potential of half-wave dipole antennas in MRI is primarily recognized. This study presents the dielectric material-coated half-wave dipole antenna design and compares it with the conventional half-wave dipole antenna. The design includes a high dielectric material coating around the length of each conductor. The dipole length primarily determines the resonant frequency of a dipole antenna; therefore, it is difficult to tune small half-wave dipole antennas less than 50 cm at 300MHz. Our design provides a solution to this problem and can tune smaller half-wave dipole antennas at 300MHz without meandering the dipole conductors. 

This study presents a method for the B1 field flattening and length control of the half-wave dipole antenna for MR imaging with discrete dielectric material coating. To demonstrate this method, we designed a half-wave dipole antenna to operate at 300MHz, including coating the ends of the dipole conductors with a high dielectric material, serving as a way to control the dipole length and electromagnetic field distribution. We also compare the proposed technique with the conventional half-wave dipole antenna and show how the new technique effectively tunes the shorter half-wave dipole antennas at specific frequencies and produces efficient field distributions.

Magnetic resonance imaging for Musculoskeletal imaging plays a vital role in the early detection of various abnormalities. New array systems designed explicitly for Musculoskeletal imaging at Ultra-high field strengths are being developed rapidly. In this study, we propose a new 8-channel array system consisting of High-permittivity dielectric material-coated half-wave dipole antennas for knee imaging at Ultra-high field 7 Tesla. 

There is no widely adopted clinical protocol for diffusion weighted imaging near metal since the commonly used EPI trajectory fails completely due to distortion from off-resonance. We combine the magnetization prepared, stimulated echo diffusion preparation with 3D MSI encoding to enable volumetric diffusion weighted imaging near metal in clinically feasible times. Imaging time is reduced by a factor of 2× with high RF bandwidth root-flipped Shinnar-Le Roux refocusing pulses since spectral coverage can be maintained with fewer excitations. Joint design of the excitation and refocusing pulses reduces B1 sensitivity.

We compared the B₁ efficiency of a newly developed dual-frequency surface coil operating at proton and low-g X-nuclei frequencies at 16.4T with that of traditional proton coil and X-nuclei coil, respectively. Both simulation and experimental results revealed that the B₁ field strength of the new coil was similar to that of traditional coil at deuterium or oxygen-17 frequency though was significantly reduced at proton frequency, while their B₁ distributions were identical for both proton and deuterium/oxygen-17 frequencies. The efficacy of the new coil for in-vivo deuterium metabolic imaging applications was demonstrated in normal and tumor rat brains. 

This study proposes a new 15-channel end-coated half-wave dipole antenna array system for foot/ankle/calf imaging at 7T. The ends of the dipole antennas, operating at 300MHz, are coated with a high-permittivity dielectric material to decrease their length and flatten the B1 field simultaneously. The end-coated dipole antennas are placed around the region of interest to gain the required B1 coverage in the imaging target.  

Wearable RF coils are receiving increasing attention since they can improve patient comfort and maximize SNR. For wearable coil arrays, however, the geometrical relationships between coils may change when they are bent and/or stretched. This in turn may decrease the performance of conventional decoupling methods such as overlapping and L/C network, especially for transmit/receive coil where the preamp decoupling is not feasible. In this work, we proposed a novel coaxial self-decoupled coil that has robustness decoupling performance versus coil distance and coil shapes. High isolations of <-15 dB can be achieved when the coils are gapped, overlapped, and/or stretched.

We have generated a numerical model of a 64-channel receive array at 7T and analysed its influence on SAR on an 8-channel transmit array. Simulations were conducted using a finite integration technique in CST Microwave Studio to create a model of the combined Tx/Rx system on both our phantom and the Duke human body model. Each receive element was actively detuned and implemented within our 8 channel transmit array model to provide us with an improved model from which we found that there was a negligible effect on the B₁⁺ field and a reduction in the SAR of ~20%. 

B₀ field inhomogeneity can reduce the effectiveness of RF pulses, result in signal voids, blurring and image artefacts. Integrated RF-shim coil arrays^1,2,3 offer capabilities for concurrent parallel RF reception and local B0 shimming, and is superior to spherical harmonic shimming. However, its performance may still be limited due to the lack of flexibility for shimming and limited depth penetration for signal reception. We simulated the B0 shimming performance of a range of integrated RF-shim coil arrays with 3D orthogonal loop coil geometry, and compared the results with standard 2D loop coil arrays.

TRASE is an MR imaging sequence that achieves k-space encoding through the use of phase gradients in the RF transmit field. The twisted solenoid is the most efficient RF transmit coil used for TRASE encoding; however, the geometry results in a long coil with a relatively short imaging volume. We introduce a new truncated design for the twisted solenoid to increase the usable imaging volume relative to the coil’s size. Simulation studies conducted indicate the truncated design can create similar imaging volumes to the untruncated version whilst significantly reducing the coils length by as much as a half.

This study investigates concomitant gradient field effects on gradient echo phase contrast imaging when visualizing very slow (<50 mm/s) flow. The impact of real-time concomitant field compensation and the consequence of uncompensated higher-ordered terms is shown.