Demyelinating plaques in relapsing-remitting and secondary-progressive multiple sclerosis: Assessment with diffusion MR imaging

BACKGROUND AND PURPOSE: Conventional MR imaging does not provide specific i nformation that can be reliably associated with the pathologic substrate an d clinical status of patients with multiple sclerosis (MS), Our goals were 1) to determine whether the orientationally averaged water diffusion coeffi cient (<D>) can be used to distinguish between plaques of different severit y in these patients and 2) to assess possible correlations between <D> valu es and disease duration, Expanded Disability Status Scale (EDSS) score, and signal intensity on T1-weighted MR images. METHODS: Twenty patients (10 with relapsing-remitting MS and 10 with second ary-progressive MS) and 11 healthy volunteers underwent a combined conventi onal and diffusion-weighted MR study of the brain, <D>, a parameter that is proportional to the trace of the diffusion tensor, was computed by averagi ng the apparent diffusion coefficients measured in the x, y, and z directio ns, <D> measurements were obtained for selected areas of white matter plaqu es, Differences in <D> among the three groups were tested using analysis of variance. RESULTS: <D> was significantly higher (1.445 +/- 0.129 x 10 (3) mm(2)/s) in secondary-progressive lesions than in relapsing-remitting lesions (0.951 /- 0.08), and both values were higher than <D> in normal white matter (0.73 2 +/- 0.02). There was a significant negative correlation between <D> and t he degree of hypointensity on T1-weighted images, and a positive correlatio n between <D> and both EDSS score and disease duration. CONCLUSION: Our findings suggest that <D> is useful for distinguishing MS l esions of different severities, which are associated with different degrees of clinical disability.