Purpose: To optimize and evaluate the reference region variable flip angle (RR-VFA) technique for simultaneous B1+ and T1 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 (tF ) and a signal fat-fraction threshold (rF ), and the relative flip angle (FA) was characterized using an effective fat T1 (T1f ) within the fat region. Optimal values of tF , rF , and T1f were chosen by comparing relative FA maps using RR-VFA (ARR-VFA ) with a reference relative FA maps (AREF ) 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: tF , rF and T1f were optimized as 0.5, 90%, and 320 ms, respectively. Prostate ARR-VFA showed differences of 30% among volunteers on one scanner, with no significant differences between ARR-VFA and AREF (P = 0.41). Prostate T1 after B1+ correction was 1998 ± 113 ms with significantly (P = 0.004) lower standard deviation than T1 before B1+ correction. The average coefficient of variation of prostate T1 across multiple scanners decreased from 15% to 5% after B1+ correction.
Conclusion: The optimized RR-VFA can simultaneously measure B1+ and T1 in the prostate without the need for an additional scan and improve T1 consistency within and across MRI scanners at 3T.
Level of evidence: 3 J. Magn. Reson. Imaging 2017;45:751-760.
Keywords: T1 mapping; B1 + mapping; variable flip angle; dynamic contrast-enhanced MRI; multi-parametric MRI; prostate.
© 2016 International Society for Magnetic Resonance in Medicine.