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 B1+ 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 B1+ and B0 variations, as well as respiratory and cardiac motion.

Motion‐resolved fat‐fraction mapping with whole‐heart free‐running multiecho GRE and pilot tone

“…Therefore, such measurements are limited in the number of echoes collected, or restricted in terms of organ coverage. Although free-breathing techniques have enabled whole-heart water-fat separation at 1.5T, 26,27 3T 28,29 and 7T, 30 they still relied on triggered acquisitions with N TE ≤4, and did not focus on quantification. Alternatively, approaches that combine fingerprinting [31][32][33] or deep learning 34 with ME-GRE have shown promising results for fat quantification with various N TE , but still required breath-holding and ECG-triggering with restricted organ coverage.…”

Respiration induced B1+ changes and their impact on universal and tailored 3D kT‐point parallel transmission pulses for 7T cardiac imaging

“…A potential extension of this work would be the inclusion of B 0 variations in the pulse design. Nevertheless, further investigation is required to implement and validate the impact of respiration resolved 3D B 0 ‐maps in the human body 26 …”

“…In addition to the aforementioned observations in 2D acquisitions, 14 FA variations across the respiratory cycle may further limit the flexibility and data efficiency of retrospectively binned and motion corrected 3D reconstructions. Therefore, homogeneous FAs across all respiration states in the 3D target region are essential to use the full potential of 3D free‐breathing cardiac imaging methods 25,26 …”

“…Therefore, homogeneous FAs across all respiration states in the 3D target region are essential to use the full potential of 3D free-breathing cardiac imaging methods. 25,26 Three-dimensional respiration-resolved (RR) B + 1 mapping was recently proposed in subjects performing SB and DB. 12 Such 3D RR B + 1 -maps enable analyzing and potentially correcting for the impact of respiration-related B + 1 changes with a dedicated pTx pulse design.…”

“…Nevertheless, further investigation is required to implement and validate the impact of respiration resolved 3D B 0 -maps in the human body. 26…”