Motion-compensated fat-water imaging for 3D cardiac MRI at ultra-high fields

Abstract

Purpose: Respiratory motion-compensated (MC) 3D cardiac fat-water imaging at 7T.

Methods: 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 $B_1^{+}$ 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.

Results: 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.

Conclusion: This work demonstrates the feasibility of 3D fat-water imaging at UHF for the entire human heart despite spatial and temporal $B_1^{+}$ and B₀ variations, as well as respiratory and cardiac motion.

Keywords: 7 Tesla; B0; Dixon; body imaging; fat-water imaging; parallel transmission; respiration.