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Differences among models in the temporal evolution of ischemia after middle cerebral artery occlusion (MCAO) in rats may considerably influence the results of experimental stroke research. Using diffusion and perfusion imaging, we compared the spatiotemporal evolution of ischemia in Sprague Dawley rats after permanent suture MCAO (sMCAO; n=8) and embolic MCAO (eMCAO; n=8).Serial measurements of quantitative cerebral blood flow (CBF) and the apparent diffusion coefficient (ADC) were performed up to 180 minutes after MCAO. ADC and CBF values within 5 different brain regions were analyzed. ADC and CBF lesion volumes were calculated by using previously established viability thresholds and correlated with infarct volume defined by 2,3,5-triphenyltetrazolium chloride staining 24 hours after MCAO.Compared with sMCAO animals, the threshold-derived CBF lesion volume was significantly larger in eMCAO at all time points (P<0.01), remained relatively constant over time, and was highly correlated with the 2,3,5-triphenyltetrazolium chloride–defined infarct size. The ADC lesion volume did not differ between models at any time point. A diffusion/perfusion mismatch was present significantly longer in eMCAO animals (P<0.05), and these rats demonstrated larger absolute mismatch volumes that were statistically significant at 30, 60, and 90 minutes (P<0.05). In both models, CBF and ADC declines were highly correlated.This study demonstrated substantial differences in acute ischemic lesion evolution between the eMCAO and sMCAO models.