Human acute cerebral ischemia: Detection of changes in water diffusion anisotropy by using MR imaging

PURPOSE: To determine the optimal choice of a scalar metric of anisotropy a nd (b) determine by means of magnetic resonance imaging if changes in diffu sion anisptropy occurred in acute human ischemic stroke. MATERIALS AND METHODS: The full diffusion tensor over the entire brain was measured. To optimize the choice of a scalar anisotropy metric, the perform ances of scalar indices in simulated models and in a healthy volunteer were analyzed. The anisotropy, trace apparent diffusion coefficient (ADC), and eigenvalues of the diffusion tensor in lesions and contralateral normal bra in were compared in 50 patients with stroke. RESULTS: Changes in anisotropy in patients-were quantified by using fractio nal anistropy because it provided the best performance in terms of contrast -to-noise ratio as a function of signal-to-noise ratio in simulations. The anisotropy of ischemic white matter decreased (P = .01). Changes in anisotr opy in ischemic gray matter were not significant (P = .63). The trace ADC d ecreased for ischemic gray matter and white matter (P < .001). The first an d second eigenvalues decreased in both ischemic gray and ischemic white mat ter (P < .001). The third eigenvalue decreased in ischemic gray (P = .001) and white matter (P = .03). CONCLUSION: Gray matter is mildly anisotropic in normal and early ischemic states. However, early white matter ischemia is associated with not only ch anges in trace ADC values but also significant changes in the anisotropy, o r shape, of the water self-diffusion tensor.