Body composition profiling at 0.55T: Feasibility and precision.PURPOSE
 Body composition MRI captures the distribution of fat and lean tissues throughout the body, and provides valuable biomarkers of obesity, metabolic disease, and muscle disorders, as well as risk assessment.  Highly reproducible protocols have been developed for 1.5T and 3T MRI.  The purpose of this work was to demonstrate the feasibility and test-retest repeatability of MRI body composition profiling on a 0.55T whole-body system.


 Healthy adult volunteers were scanned on a whole-body 0.55T MRI system using the integrated body RF coil.  Experiments were performed to refine parameter settings such as TEs, resolution, flip angle, bandwidth, acceleration, and oversampling factors.  The final protocol was evaluated using a test-retest study with subject removal and replacement in 10 adult volunteers (5 M/5F, age 25-60, body mass index 20-30).


 Compared to 1.5T and 3T, the optimal flip angle at 0.55T was higher (15°), due to the shorter T1 times, and the optimal echo spacing was larger, due to smaller chemical shift between water and fat.  Overall image quality was comparable to conventional field strengths, with no significant issues with fat/water swapping or inadequate SNR.  Repeatability coefficient of visceral fat, subcutaneous fat, total thigh muscle volume, muscle fat infiltration, and liver fat were 11.8 cL (2.2%), 46.9 cL (1.9%), 14.6 cL (0.5%), 0.1 pp (2%), and 0.2 pp (5%), respectively (coefficient of variation in parenthesis).


 CONCLUSIONS
 We demonstrate that 0.55T body composition MRI is feasible and present optimized scan parameters.  The resulting images provide satisfactory quality for automated post-processing and produce repeatable results.
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