Bipolar Readouts Improve Quantitative Performance of Motion-Robust, Flip-Angle Modulated PDFF and R2* Mapping at High R2*

Motivation: Flip-angle modulation (FAM) for motion-robust fat and iron quantification has been previously proposed with monopolar readouts, but may have poor performance in high R2* patients. Implementing bipolar readouts may shorten scan times and improve performance. Goal(s): Development of bipolar-FAM and evaluation in patients with liver steatosis and/or iron overload. Evaluation of breath-held bipolar-FAM, which remains artifact free in failed breath-holds. Approach: Prospective phantom and in vivo studies in adult liver steatosis/iron overload patients, and children with normal and elevated BMI. Results: Free-breathing and breath-held bipolar-FAM both show reduced bias and artifacts and improved repeatability in the R2*=300-500s-1 range. Impact: Bipolar-FAM may facilitate free-breathing FAM-based fat and iron quantification in patients with elevated R2*. The faster bipolar readouts improve motion robustness and enable breath-held FAM, which provides consistently-registered slices with good breath-holds, and remains motion-artifact free with poor breath-holds.