Purpose: To test the performance of the MPnRAGE motion-correction algorithm on quantitative relaxometry estimates.
Methods: Twelve children (9.4 ± 2.6 years, min = 6.5 years, max = 13.8 years) were imaged 3 times in a session without sedation. Stabilization padding was not used for the second and third scans. Quantitative T1 values were estimated in each voxel on images reconstructed with and without motion correction. Mean T1 values were assessed in various regions determined from automated segmentation algorithms. Statistical tests were performed on mean values and the coefficient of variation across the measurements. Accuracy of T1 estimates were determined by scanning the High Precision Devices (Boulder, CO) MRI system phantom with the same protocol.
Results: The T1 values obtained with MPnRAGE agreed within 4% of the reference values of the High Precision Devices phantom. The best fit line was T1 (MPnRAGE) = 1.02 T1 (reference)-0.9 ms, R2 = 0.9999. For in vivo studies, motion correction reduced the coefficients of variation of mean T1 values in whole-brain tissue regions determined by FSL FAST by 74% ± 7%, and subcortical regions determined by FIRST and FreeSurfer by 32% ± 21% and 33% ± 26%, respectively. Across all participants, the mean coefficients of variation ranged from 0.8% to 2.0% for subcortical regions and 0.6% ± 0.5% for cortical regions when motion correction was applied.
Conclusion: The MPnRAGE technique demonstrated highly accurate values in phantom measurements. When combined with retrospective motion correction, MPnRAGE demonstrated highly reproducible T1 values, even in participants who moved during the acquisition.
Keywords: MPnRAGE; R1; T1; motion correction; relaxometry.
© 2020 International Society for Magnetic Resonance in Medicine.