Differences between gray matter and white matter water diffusion in stroke: Diffusion-tensor MR imaging in 12 patients

PURPOSE: To investigate differences in water diffusion between white matter and gray matter in acute to early subacute stroke with diffusion- tensor magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twelve patients with unilateral middle cerebral arterial infarcts were examined with diffusion tensor-encoded echo-planar MR imaging 17 hours to 5 days after stroke onset. Isotopic diffusion coefficient (D) and diffusion anisotropy (A(σ)) images were computed. D values were measured in ischemic and contralateral gray matter and white matter by using A(σ) images to differentiate white matter from gray matter. D images were compared with unidirectional and directionally averaged diffusion-weighted images. RESULTS: In all patients, D images showed two distinct levels of diffusion reduction in the infarct; more severe reduction occurred exclusively in white matter. D values were significantly less in infarcted white matter than in infarcted gray matter, whereas D values in the contralateral white matter and gray matter were not significantly different. Relative to the contralateral side, D values in the infarct were reduced by 46% in white matter and by 31% in gray matter (P < .001). Diffusion-weighted imaging caused underestimation of the magnitude and, in some cases, the spatial extent of the white matter diffusion abnormality. CONCLUSION: Isotropic diffusion is more reduced white matter in gray matter in acute to early subacute middle cerebral arterial stroke. Diffusion-tensor imaging may be more sensitive than diffusion- weighted imaging to white matter ischemia.