Diffusion tensor imaging of lesions and normal-appearing white matter in multiple sclerosis

OBJECTIVE: To determine whether diffusion tensor imaging (DTI) can detect structural changes in normal-appearing white matter, and to distinguish between plaques of different pathologic severity, in patients with MS. BACKGROUND: Conventional MRI detects lesions sensitively in MS but has limited pathologic specificity. The diffusion of water molecules in brain tissue, most fully expressed mathematically by a tensor quantity, reflects its intrinsic microstructure. It is now possible to estimate the diffusion tensor noninvasively in the human brain using MR DTI. This method is unique in providing precise and rotationally invariant measurements of the amount and directional bias (anisotropy) of diffusion in white matter tracts relating to tissue integrity and orientation. METHODS: DTI was performed in six patients with MS and in six age-matched control subjects. Diffusion was characterized in normal-appearing white matter in both groups, and in lesions of different pathologic subtypes (inflammatory, noninflammatory, T1 hypointense, and T1 isointense). RESULTS: DTI identified significantly altered water diffusion properties in the normal-appearing white matter of patients compared with control subjects (p < 0.001), and distinguished between lesion types. The highest diffusion was seen in destructive (T1 hypointense) lesions, whereas the greatest change in anisotropy was found in inflammatory (gadolinium-enhancing) lesions. CONCLUSIONS: DTI detects diffuse abnormalities in the normal-appearing white matter of MS patients, and the findings in lesions appear to relate to pathologic severity. Its use in serial studies and in larger clinical cohorts may increase our understanding of pathogenetic mechanisms of reversible and persistent disability.