Optimization and Evaluation of Reference Region Variable Flip Angle (RR-VFA) B1+ and T1 Mapping in the Prostate at 3T

Purpose: To optimize and evaluate the reference region variable flip angle (RR-VFA) technique for simultaneous B-1(+) and T-1 mapping of the prostate at 3 Tesla (T). Materials and Methods: The fat region surrounding the prostate was first identified using a fractional fat segmentation constant (t(F)) and a signal fat-fraction threshold (r(F)), and the relative flip angle (FA) was characterized using an effective fat T-1 (T-1f) within the fat region. Optimal values of t(F), r(F), and T-1f were chosen by comparing relative FA maps using RR-VFA (A(RR-VFA)) with a reference relative FA maps (A(REF)) in the surrounding fat and evaluating interpolation errors within the prostate. The optimized RR-VFA was evaluated in volunteers at 3T on a single scanner (n = 10) and across three scanners (n = 4). Results: t(F), r(F) and T-1f were optimized as 0.5, 90%, and 320 ms, respectively. Prostate A(RR-VFA) showed differences of 30% among volunteers on one scanner, with no significant differences between A(RR-VFA) and A(REF) (P = 0.41). Prostate T-1 after B-1(+) correction was 1998113 ms with significantly (P = 0.004) lower standard deviation than T-1 before B-1(+) correction. The average coefficient of variation of prostate T-1 across multiple scanners decreased from 15% to 5% after B-1(+) correction. Conclusion: The optimized RR-VFA can simultaneously measure B(1)(+)and T-1 in the prostate without the need for an additional scan and improve T-1 consistency within and across MRI scanners at 3T.