Modeling fat-water R1 relaxation in Fat DESPOT from complex signal

Motivation: Fat DESPOT, a fat and water R1 mapping technique, has been proposed to image tumor hypoxia through the oxygen-induced change in fat R1. Goal(s): Using the complex signal for Fat DESPOT doubles the usable data for each acquisition, reducing the total number of acquisitions required and scan time. Approach: The published magnitude approach to fat DESPOT was compared to the complex approach in simulations and phantom experiments. Results: Compared to the magnitude approach, the complex approach to Fat DESPOT increased the precision and accuracy of fat R­1 estimates in simulations and phantom experiments and increased the accuracy of PDFF in phantom experiments. Impact: This study suggests that the complex approach to fat DESPOT R1 measurements could reduce imaging time without compromising PDFF or R­1f estimates. It could therefore offer sensitive and versatile R1-based tumor hypoxia mapping in potentially clinically feasible scan times.