Optimization and evaluation of reference region variable flip angle (RR-VFA) B1+ and T Mapping in the Prostate at 3T.

PURPOSE

To optimize and evaluate the reference region variable flip angle (RR-VFA) technique for simultaneous B1+ and T 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 ) and a signal fat-fraction threshold (r ), and the relative flip angle (FA) was characterized using an effective fat T (T ) within the fat region. Optimal values of t , r , and T were chosen by comparing relative FA maps using RR-VFA (A ) with a reference relative FA maps (A ) 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 , r and T were optimized as 0.5, 90%, and 320 ms, respectively. Prostate A showed differences of 30% among volunteers on one scanner, with no significant differences between A and A (P = 0.41). Prostate T after B1+ correction was 1998 ± 113 ms with significantly (P = 0.004) lower standard deviation than T before B1+ correction. The average coefficient of variation of prostate T across multiple scanners decreased from 15% to 5% after B1+ correction.

CONCLUSION

The optimized RR-VFA can simultaneously measure B1+ and T in the prostate without the need for an additional scan and improve T consistency within and across MRI scanners at 3T.

LEVEL OF EVIDENCE

3 J. Magn. Reson. Imaging 2017;45:751-760.