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3D isotropic dual-phase whole-heart MRI with interleaved cardiac-triggered acquisition at 3.0T: Initial clinical experience1Philips GmbH Market DACH, Hamburg, Germany, 2Philips, Best, Netherlands, 3Philips Japan, Tokyo, Japan, 4Diagnostic and Interventional Radiology, University Hospital Bonn, Bonn, Germany, 5Quantitative Imaging Laboratory Bonn, Bonn, Germany, 6Department of Pediatric Cardiology, University Hospital Bonn, Bonn, Germany
Synopsis
Keywords: Cardiovascular, Data Acquisition, congenital heart disease, morphology, function
Motivation: 3D dual-phase whole-heart MRI has shown advantage for simultaneous morphological and functional cardiac imaging but is so far not available at 3.0T due to bSSFP susceptibility artifacts and specific absorption rate limitation at high field.
Goal(s): Our goal was to develop a new sequence to circumvent the problems and allow 3D dual-phase whole-heart MRI for high-field cardiac imaging.
Approach: We implemented an interleaved cardiac-triggered acquisition with non-balanced readout and applied it in patients with congenital heart disease at 3.0T.
Results: 3D dual-phase whole-heart MRI at 3.0T successfully depicted morphological and functional changes within one single scan in concordance with standard techniques.
Impact: 3D isotropic dual-phase whole-heart MRI with interleaved ECG-triggered acquisition and non-balanced readout now permits visualization and assessment of cardiac morphology and function with high resolutions within one single scan at 3.0T and promises wider clinical applications in congenital heart disease.
Introduction
Cardiovascular MRI is a powerful tool for assessing cardiac morphology and function. The advent of 3D dual-phase whole-heart (3D DP WH) MRI has allowed simultaneous morphological and functional imaging within a single scan, offering considerable advantages in clinical practice1-5, particularly in congenital heart disease (CHD). However, the implementation of this technique at 3.0T has been hindered by susceptibility artifacts associated with balanced steady-state free precession (bSSFP) readout and specific absorption rate (SAR) limitations at high field strengths. In response to these challenges, we set out to develop a novel sequence that would overcome these issues and make 3D DP WH MRI available for high-field cardiac imaging.Methods
The proposed technique is based on previously introduced Relaxation-Enhanced Angiography without ContrasT (REACT)6-9. In short, it consists of magnetization preparation pulses of non-selective T2-prep and inversion recovery (IR), followed by data acquisition using 3D dual-echo turbo-field echo (TFE) modified Dixon (mDixon) with semi-flexible echo times. Three important technical components to allow for dual-phase whole-heart MRI at 3.0T are:(1) Interleaved cardiac-triggered acquisition, which avoids quick build-up of SAR energy and permits longitudinal magnetization recovery between every IR pulse;
(2) 3D non-balanced readout, which avoids high sensitivity to susceptibility differences at high field strength;
(3) T2prep with shorter refocusing interval (“MLEV16”, TE = 50 to 60 ms, 16 refocusing pulses, interval = 3.125 to 3.75 ms), which is less sensitive to ΔB0 and flow to minimize signal loss10,11.
A schematic diagram of the imaging pulse sequence is shown in Figure 1. Compressed sensing reconstruction in combination of wavelet transformation and sensitivity encoding (SENSE) coil information (compressed SENSE) was applied with an acceleration factor of 6 for scan reduction. Other imaging parameters are summarized in Table 1.
Two healthy young adult volunteers and five patients aged under 18 years regardless of the type of CHD or previously performed surgical procedures were scanned on a 3.0T clinical MRI system (Philips Elition, Best, the Netherlands). Standard imaging sequences in the routine clinical scan protocol included cine in multiple clinically aligned anatomical views such as coronal and short-axis views for comparison. In addition, steady-state contrast-enhanced MR angiography (ss CE-MRA) was performed during administration of gadobutrol (0.1 mmol/kg body weight) with slow flow rate and ECG triggering for end-diastolic single cardiac phase acquisition. This was followed by the 3D DP WH MRI sequence. Both scans were respiratory navigator gated. The proposed pre-pulse modifications increase SAR on 3T but fall within acceptable limits. Average SAR for MLEV16 was below 2.0 W/kG. Vascular structures were visually inspected and evaluated. Cardiac function was analyzed and compared to the cine scans.
Results and Discussion
3D DP WH MRI was successful in all subjects. Overall image quality was found good, and visualization of important anatomical structures was possible. Images acquired at the end-diastolic (ED) and end-systolic (ES) phases from the same single scan provided complementary information for observation of intra- and extra-cardiac morphology. One representative clinical example is shown in Figure 2 in a pediatric patient with sub-valvular stenosis (arrows), which was well depicted at ES but not visualized at ED. This was in good concordance with findings from conventional 2D bSSFP cine (only 4 selected cardiac phases were shown) in the same coronal orientation. Figure 3 demonstrates another selected clinical case in a young child, where coronary arteries were better visualized at ES (arrow) comparing to ED. In the same case local signal void (arrowhead) was seen at ES due to intra-voxel phase dispersion very likely induced by turbulent flows. Noteworthy, in some other cases such signal loss can be observed at ED but not ES, primarily due to turbulent flow associated with severe pulmonary insufficiency during the diastolic phase, particularly at higher field strength. Left (LV) and right (RV) ventricular cardiac volumes obtained with the 3D DP WH technique were in good agreement with those obtained with the standard 2D bSSFP technique (data not reported here due to low sample size and statistical power). The study is continued to investigate the clinical performance of the proposed method in detailed comparison with the standard techniques.Conclusion
The successfully implemented 3D isotropic DP WH MRI sequence with interleaved ECG-triggered acquisition and non-balanced readout at 3.0T demonstrated the ability to visualize and assess cardiac morphology with high resolutions. Further studies are needed to investigate its clinical performance in larger cohorts.Acknowledgements
N.A.References
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Figures
Table 1. Imaging parameters of the pulse sequences used in the study including the proposed 3D dual-phase whole-heart (3D DP WH) MRI.
ssCE-MRA = steady-state contrast-enhanced MR angiography; TFE = turbo field echo; ELT = echo-train length; SENSE = sensitivity encoding; C-SENSE = compressed SENSE.
Figure 1. Schematic pulse sequence diagram of the dual-phase whole-heart MRI proposed in this work. (a) Interleaved cardiac-triggered acquisition based on REACT using 3D non-balanced readout on 3.0T. (b) REACT acquisition with T2prep and inversion recovery and mDixon non-balanced TFE readout. (c) Optimized MLEV16 pre-pulse for reduced sensitivity to off-resonance and flow effects.
REACT = Relaxation-Enhanced Angiography without ContrasT, TFE = Turbo field echo; mDixon = modified Dixon.
