Reversible Focal Ischemic Injury Demonstrated by Diffusion‐Weighted Magnetic Resonance Imaging in Rats

Background and Purpose: Diffusion-weighted magnetic resonance imaging (DWI) can quantitatively display focal brain abnormalities within minutes after the onset of ischemia. We performed the present study to determine the effects of 1 and 2 hours of temporary ischemia on DWI. Methods: We examined DWI and T2-weighted magnetic resonance images (T2WI) during and after 1 and 2 hours of temporary middle cerebral artery occlusion in rats (n=10 for each group). In a subgroup of four animals from each group, we employed perfusion magnetic resonance imaging to monitor cerebral perfusion. Neurological outcome and infarct size after survival for 24 hours were compared between the groups and correlated with DWI and T2WI studies. Results: Perfusion studies qualitatively documented hypoperfusion and reperfusion during and after temporary occlusion. Lesion size on DWI during reperfusion was significantly less than that during ischemia for 1 (55% decline, p<0.02) but not 2 hours of occlusion. The DWI signal intensity ratio (intensity compared with that in the contralateral homologous area) just before withdrawal of the occluder was significantly less in regions where the hyperintensity disappeared after withdrawal than in regions with persistent hyperintensity (p<0.002). The T2WI studies revealed few or no abnormalities, except after 2 hours of occlusion. The neurological outcome was significantly better in the 1-hour than in the 2-hour group (p<0.05). Postmortem infarct volume was significantly smaller in the 1-hour group than in the 2-hour group (p<0.05). The postwithdrawal DWI accurately predicted infarct size (R=0.96, p<0.0001). Conclusions: The present study indicates that DWI can rapidly display not only irreversible but also reversible ischemic brain damage and enhances the importance of DWI as a diagnostic modality for stroke.