Mapping fat-water separated R1, R2*, and fat fraction with bipolar multi-echo MP2RAGE

Motivation: Multi-Echo Magnetization Prepared Two Rapid Acquisition of Gradient Echoes (ME-MP2RAGE) can be combined with chemical shift-encoded fat-water separation to simultaneously map fat and water-specific R1. However, long echo times in the multi-echo portion of the technique can lead to poor fat-water separation and compromised accuracy and precision of the estimates. Goal(s): Simultaneous mapping of fat and water-specific R1, R2*, and proton density fat fraction with bipolar ME-MP2RAGE. Approach: Unipolar and bipolar ME-MP2RAGE sequences were compared in simulation and phantom experiments. Results: Numerical simulations and phantom experiments showed that bipolar readouts produce more accurate and precise estimates than unipolar alternatives. Impact: We propose a technique for simultaneous measurement of PDFF, fat and water-specific R1, and R2* combining multi-echo MP2RAGE and fat-water separation. Moreover, we show that bipolar readouts produce more accurate and precise estimates of these parameters using multi-echo MP2RAGE.