Temporal evolution of Diffusion / Perfusion Mismatch in a Rat Stroke Model
Background and Purpose: Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) can rapidly detect lesions in acute ischemic stroke. Studies show that lesions by PWI are sometimes larger than those of DWI in patients with acute ischemic stroke, suggests that the mismatch between DWI and PWI is potentially predictive of tissue at high risk for evolving into infarction. The aims of this study were to detect the evolution of the DWI/PWI mismatch in permanent focal experimental ischemia and transient focal experimental ischemia. Methods: Rats were subjected to permanent (n=8) and 60 minutes of temporary ischemia (n=8) using the intraluminal middle cerebral artery occlusion method and then underwent DWI and PWI after occlusion. Rats in the transient ischemic experiments were reperfused 60 minutes after occlusion. An apparent diffusion coefficient map and a cerebral blood flow index map were used to calculate the percent hemispheric lesion volume (%HLV) for each MRI parameter. Results: In permanent ischemia, %HLVs by DWI were 21%, 45%, 60%, 87%, and 101% of %HLV by PWI at 15, 30, 60, 90 and 120 minutes after ischemia, respectively. The ratio did not change after 120 minutes. With 60 minutes of temporary ischemia, the changes were almost the same as those in permanent ischemia before reperfusion. After reperfusion the lesions on PWI were smaller than those on DWI. The DWI lesion did not increase after reperfusion, and was the almost the same size as just before reperfusion. Conclusions: The DWI/PWI mismatch disappears at 2 hours after permanent ischemia, and the region of DWI/PWI mismatch can be saved from ischemic damage if reperfused early, but ischemic lesions seen on DWI can not be reduced by reperfusion after 60 minutes of temporary ischemia in this rat stroke model.