Diffusion-weighted magnetic resonance imaging: rapid and quantitative detection of focal brain ischemia.

We examined serial changes of diffusion- (DWI) and T2-weighted (T2WI) magnetic resonance images 30 minutes to 3 hours after intraluminal suture occlusion of the middle cerebral artery (MCA) in eight rats and after sham occlusion in four. We correlated the abnormal areas on DWI and T2WI with postmortem areas of infarction determined by 2,3,5-triphenyltetrazolium chloride (TTC), 24 hours after the operation. The 30-minute DWI in each MCA-occluded rat demonstrated increased signal intensity in the ipsilateral MCA territory, while T2WI showed no changes. At 3 hours, the ipsilateral DWI signal intensity increased further and the area of abnormality slightly increased. In some animals, the 3-hour T2WI disclosed an area of hyperintensity significantly smaller than that seen on the 30-minute DWI. TTC staining demonstrated an extensive MCA infarction in all rats with permanent MCA occlusion, confirmed by hematoxylin and eosin staining. The percent infarcted area of coronal brain sections, as determined by TTC staining, correlated significantly with areas on similar DWI sections at both 30 minutes and 3 hours. Sham-occluded control animals did not display any changes on DWI, T2WI, or TTC staining. The present study suggests that DWI is a very sensitive modality for detecting early ischemic brain injury, being highly correlated with post-mortem area of infarction, and may be useful to assess pharmacologic intervention.