Abstract
Respiratory motion-compensated (MC) 3D cardiac fat-water imaging at 7T. Free-breathing bipolar 3D triple-echo gradient-recalled-echo (GRE) data with radial phase-encoding (RPE) trajectory were acquired in 11 healthy volunteers (7M\4F, 21-35 years, mean: 30 years) with a wide range of body mass index (BMI; 19.9-34.0 kg/m2 ) and volunteer tailored shimming. The bipolar-corrected triple-echo GRE-RPE data were binned into different respiratory phases (self-navigation) and were used for the estimation of non-rigid motion vector fields (MF) and respiratory resolved (RR) maps of the main magnetic field deviations (ΔB0 ). RR ΔB0 maps and MC ΔB0 maps were compared to a reference respiratory phase to assess respiration-induced changes. Subsequently, cardiac binned fat-water images were obtained using a model-based, respiratory motion-corrected image reconstruction. The 3D cardiac fat-water imaging at 7T was successfully demonstrated. Local respiration-induced frequency shifts in MC ΔB0 maps are small compared to the chemical shifts used in the multi-peak model. Compared to the reference exhale ΔB0 map these changes are in the order of 10 Hz on average. Cardiac binned MC fat-water reconstruction reduced respiration induced blurring in the fat-water images, and flow artifacts are reduced in the end-diastolic fat-water separated images. This work demonstrates the feasibility of 3D fat-water imaging at UHF for the entire human heart despite spatial and temporal and B0 variations, as well as respiratory and cardiac motion.
Highlights
Fat-water (FW) cardiac MR (CMR) imaging is an essential technique for assessing fatty infiltration of the myocardium.[1]
The differentiation of epicardial fat from intramyocardial fat remains difficult for the right ventricle with its thin structure, and overall small, affected areas in the myocardium compared to the limited resolution of current systems, and currently fail for the assessment of disease like arrhythmogenic right ventricular cardiomyopathy.[2,3]
No undersampling or motion artifacts were observed in the different respiratory phases, yielding high-quality ΔB0 maps that reflect only subtle changes of ΔB0,respiration resolved (RR) over the different respiratory phases
Summary
Fat-water (FW) cardiac MR (CMR) imaging is an essential technique for assessing fatty infiltration of the myocardium.[1]. In the presence of main magnetic field deviations (ΔB0), triple gradient-recalled echo (GRE) methods[8,9] were proposed. The latter enables direct estimation of the ΔB0 inhomogeneities, which can be used to resolve the ambiguity problem.10–12 Thereby, the separation of the images into fat and water content can be performed sequentially[13,14] or in a joint reconstruction.[15,16] To date, 3D multi-echo GRE FW imaging techniques have been applied to the entire human body[10] as well as to various organs[8,17,18] at field strengths up to 3T
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