• Vasily L Yarnykh, Alena A Kisel, and Marina Y Khodanovich.
• Department of Radiology, University of Washington, Seattle, Washington, USA.
• J Magn Reson Imaging. 2020 Jun 1; 51 (6): 1789-1798.

BackgroundSingle-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.PurposeTo assess scan-rescan repeatability and a value of B0 and B1 field inhomogeneity corrections in single-point synthetic-reference MPF mapping.Study TypeProspective.PopulationEight healthy adult volunteers underwent two scans with 11.5 ± 2.3 months interval.Field Strength/Sequence3T; whole-brain 3D MPF mapping protocol included three spoiled gradient-echo sequences providing T1 , proton density, and magnetization transfer contrasts with 1.25 × 1.25 × 1.25 mm3 resolution and B0 and B1 mapping sequences.AssessmentMPF maps were reconstructed with B0 and B1 field nonuniformity correction, B0 - and B1 -only corrections, and without corrections. Mean MPF values were measured in automatically segmented white matter (WM) and gray matter (GM).Statistical TestsWithin-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.ResultsMaximal relative local MPF errors without correction in the areas of largest field nonuniformities were about 5% and 27% for B0 and B1 , respectively. The effect of B0 correction was insignificant for whole-brain WM (P > 0.25) and GM (P > 0.98) MPF. The absence of B1 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 ConclusionThe single-point method enables high repeatability of MPF maps obtained with the same equipment. Correction of B0 inhomogeneity may be disregarded to shorten the examination time. B1 nonuniformity correction improves accuracy of MPF measurements at 3T. Reliability of whole-brain MPF measurements in WM and GM is not affected by B0 and B1 field corrections.Level Of Evidence2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:1789-1798.© 2019 International Society for Magnetic Resonance in Medicine.

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