Three-dimensional Motion-corrected T Relaxometry with MPnRAGE

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 T values were estimated in each voxel on images reconstructed with and without motion correction. Mean T 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 T estimates were determined by scanning the High Precision Devices (Boulder, CO) MRI system phantom with the same protocol.

Results: The T values obtained with MPnRAGE agreed within 4% of the reference values of the High Precision Devices phantom. The best fit line was T (MPnRAGE) = 1.02 T (reference)-0.9 ms, R  = 0.9999. For in vivo studies, motion correction reduced the coefficients of variation of mean T 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 T values, even in participants who moved during the acquisition.