Research: Imaging repair

Brown et al. Segmentation of magnetization transfer ratio lesions for longitudinal analysis of demyelination and remyelination in multiple sclerosis. Neuroimage. 2012 Oct 27. doi:pii: S1053-8119(12)01062-2.

These investigators' demonstrate a new technique to quantify longitudinal changes in magnetization transfer ratio (MTR) magnetic resonance imaging (MRI). These changes are indicative of demyelination and remyelination. This technique comprises a definition of ΔMTR lesions, which are identified directly from the MTR images, and an automatic procedure for segmenting these lesions. We used this technique to analyze MTR changes in lesions of subjects with rapidly progressing multiple sclerosis before and after treatment with immunoablation and stem cell transplant. Subjects who experienced clinical improvement after treatment showed significantly improved MTR recovery in lesions that were recovering during treatment (p<0.0001) while those who were clinically stable after treatment showed significantly poorer MTR recovery (p=0.002). The statistical power of this technique to detect treatment effects on MTR recovery was shown to be considerably better than previous methods. These results suggest that longitudinal measurements of MTR in ΔMTR lesions may be an important technique for the assessment of treatment effects on remyelination in clinical trials.

A representative slice of an MTR image from two timepoints (left and middle) and a ΔMTR map (right). The ΔMTR map is obtained by taking the difference between the MTR images at timepoint 2 and timepoint 1. Two new MTR lesions (blue arrows) are evident at timepoint 2 but not at timepoint 1. One MTR lesion apparent at timepoint 1 (red arrow) has partially recovered by timepoint 2. MTR lesions with increasing and decreasing MTR are segmented using the ΔMTR map and are called ΔMTR lesions

One important area to investigate repair is to work out how it may be monitored. This study suggests one such imaging modality. Although changes in MTR may be a good indicator of changes in myelin, MTR change is not completely specific for myelin. As with any imaging technique, possible confounding effects should be considered. MTR changes rapidly at the time of lesion formation, making measurements in this period dependent on the phase of lesion formation/resolution at the time of imaging. However if it does represent remyelination it is a useful tool.

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