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 information that can be reliably associated with the pathologic substrate and clinical status of patients with multiple sclerosis (MS). Our goals were 1) to determine whether the orientationally averaged water diffusion coefficient (<D>) can be used to distinguish between plaques of different severity in these patients and 2) to assess possible correlations between <D> values 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 secondary-progressive MS) and 11 healthy volunteers underwent a combined conventional and diffusion-weighted MR study of the brain. <D>, a parameter that is proportional to the trace of the diffusion tensor, was computed by averaging the apparent diffusion coefficients measured in the x, y, and z directions. <D> measurements were obtained for selected areas of white matter plaques. 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) mm2/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 (0.732 +/- 0.02). There was a significant negative correlation between <D> and the degree of hypointensity on T1-weighted images, and a positive correlation between <D> and both EDSS score and disease duration.
CONCLUSION: Our findings suggest that <D> is useful for distinguishing MS lesions of different severities, which are associated with different degrees of clinical disability.