Andrew Alexander, PhD – Slide of the Week

Andrew Alexander, PhD - Slide of the Week

Title: Demonstration of Motion Corrected MRI for Studies in Children

Legend: Demonstration of the ability of MPnRAGE to correct for severe motion artifacts in a 7 year old girl.  Retrospective motion correction greatly reduced motion-induced blurring in both  structural T1-weighted images and quantitative T1 maps.  The correction greatly improves the reliability of brain imaging measurements in children.  The plots indicate the estimated amount of head motions that were corrected.

Citation: Kecskemeti SR & Alexander AL; Three‐dimensional motion‐corrected T1 relaxometry with MPnRAGE. Magnetic Resonance in Medicine, Volume: 84, Issue: 5, Pages: 2400-2411, First published: 17 April 2020

Abstract: 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.

About the Lab: Alexander’s research focuses on the use of magnetic resonance imaging (MRI) for mapping and measuring the functional and structural organization of the human brain. These techniques are used to investigate the brain in both typically developing individuals and subjects with developmental disorders including autism. Functional MRI (fMRI) is used to assess brain regions associated with cognition and affect and their dysfunctions in these populations. Diffusion tensor MRI (DT-MRI) is used to study the patterns of structural connectivity between brain activity regions. Anatomic imaging methods are used to assess longitudinal structural changes in brain regions. These measurements are ultimately compared with measures of affect, behavior and cognition in specific population groups.

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