Scan-Rescan Repeatability and Impact of B0 and B1 Field Nonuniformity Corrections in Single-Point Whole-Brain Macromolecular Proton Fraction Mapping

Background Single-point macromolecular proton fraction (MPF) mapping is a recent quantitative MRI method for fast assessment of brain myelination. Information about reproducibility and sensitivity of MPF mapping to magnetic field nonuniformity is important for clinical applications. Purpose To assess scan-rescan repeatability and a value of B-0 and B-1 field inhomogeneity corrections in single-point synthetic-reference MPF mapping. Study Type Prospective. Population Eight healthy adult volunteers underwent two scans with 11.5 +/- 2.3 months interval. Field Strength/Sequence 3T; whole-brain 3D MPF mapping protocol included three spoiled gradient-echo sequences providing T-1, proton density, and magnetization transfer contrasts with 1.25 x 1.25 x 1.25 mm(3) resolution and B-0 and B-1 mapping sequences. Assessment MPF maps were reconstructed with B-0 and B-1 field nonuniformity correction, B-0- and B-1-only corrections, and without corrections. Mean MPF values were measured in automatically segmented white matter (WM) and gray matter (GM). Statistical Tests Within-subject coefficient of variation (CV), intraclass correlation coefficient (ICC), Bland-Altman plots, and paired t-tests to assess scan-rescan repeatability. Repeated-measures analysis of variance (ANOVA) to compare field corrections. Results Maximal relative local MPF errors without correction in the areas of largest field nonuniformities were about 5% and 27% for B-0 and B-1, respectively. The effect of B-0 correction was insignificant for whole-brain WM (P > 0.25) and GM (P > 0.98) MPF. The absence of B-1 correction caused a positive relative bias of 4-5% (P < 0.001) in both tissues. Scan-rescan agreement was similar for all field correction options with ICCs 0.80-0.81 for WM and 0.89-0.92 for GM. CVs were 1.6-1.7% for WM and 0.7-1.0% for GM. Data Conclusion The single-point method enables high repeatability of MPF maps obtained with the same equipment. Correction of B-0 inhomogeneity may be disregarded to shorten the examination time. B-1 nonuniformity correction improves accuracy of MPF measurements at 3T. Reliability of whole-brain MPF measurements in WM and GM is not affected by B-0 and B-1 field corrections. Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019.