Optimized efficient liver T1ρ mapping using limited spin lock times

T-1 rho relaxation has recently been found to be sensitive to liver fibrosis and has potential to be used for early detection of liver fibrosis and grading. Liver T-1 rho imaging and accurate mapping are challenging because of the long scan time, respiration motion and high specific absorption rate. Reduction and optimization of spin lock times (TSLs) are an efficient way to reduce scan time and radiofrequency energy deposition of T-1 rho imaging, but maintain the near-optimal precision of T-1 rho mapping. This work analyzes the precision in T-1 rho estimation with limited, in particular two, spin lock times, and explores the feasibility of using two specific operator-selected TSLs for efficient and accurate liver T-1 rho mapping. Two optimized TSLs were derived by theoretical analysis and numerical simulations first, and tested experimentally by in vivo rat liver T-1 rho imaging at 3 T. The simulation showed that the TSLs of 1 and 50 ms gave optimal T-1 rho estimation in a range of 10-100 ms. In the experiment, no significant statistical difference was found between the T-1 rho maps generated using the optimized two-TSL combination and the maps generated using the six TSLs of [1, 10, 20, 30, 40, 50] ms according to one-way ANOVA analysis (p = 0.1364 for liver and p = 0.8708 for muscle).