Long-Term Magnetization Transfer Ratio Evolution in Multiple Sclerosis White Matter Lesions

BACKGROUND AND PURPOSE: Magnetization transfer ratio (MTR), a magnetic resonance imaging technique used to assess tissue integrity, correlates with demyelination and axonal loss in multiple sclerosis (MS) lesions. In acute white matter lesions, short-term MTR changes mainly reflect demyelination and remyelination, in addition to edema and axonal and glial changes. Long-term MTR changes in MS lesions have not been studied extensively. METHODS: A new quantitative image analysis method was developed to measure long-term MTR changes in MS lesions. The method was applied to a group of 59 patients and 14 healthy control subjects followed for 4 years. MTR changes in white matter lesions were analyzed, where lesion voxels were classified into six categories based on starting MTR and change over time. For each patient, the proportion of lesion voxels in each MTR-change category was calculated. Correlations between long-term MTR evolution, disability progression, and brain atrophy were investigated. RESULTS: The proportion of lesion voxels in the high stable category correlated with less atrophy progression, while the proportion with low and increasing MTR correlated with increased atrophy. The proportion of lesion voxels in the high and stable MTR lesion category was significantly different between MS disease subgroups. The group with disability progression had a higher proportion of lesion voxels with low and increasing MTR. CONCLUSIONS: These results suggest that long-term changes in MTR in white matter lesions can be used to distinguish lesion subtypes associated with MS disease progression and improve understanding of the temporal evolution of MS pathology.