Prediction of secondary ischemic lesions with diffusion-weighted imaging after transient middle cerebral artery occlusion in rats
Background and Purpose: Previous studies demonstrated that secondary ischemic lesions documented by diffusion-weighted imaging might be smaller than, larger than or similar to initial lesions that occur during ischemia. The purpose of this study was to investigate if the size of secondary lesions can be predicted. Methods: Twelve rats underwent 30 minutes of transient middle cerebral artery occlusion with the intraluminal suture method. Diffusion- and perfusion-weighted images were performed just before reperfusion, 90 minutes and 24 hours after reperfusion. The ischemic lesion size was calculated by tracing visual abnormalities on the apparent diffusion coefficient (ADC) maps. Cerebral blood flow index (CBFi) ratio was calculated by dividing the ipsilateral CBFi by the contralateral CBFi. Based on difference between initial and secondary lesion volume, rats were assigned to reperfusion-benefit group (n=6) where secondary lesions were smaller than initial lesions (less than 85% of initial lesions) and reperfusion-nonbenefit group (n=6) where secondary lesions were similar to or larger than initial lesions (more than 85% of initial lesions). Results: At 90 minutes after reperfusion, the initial ischemic lesions almost disappeared in both groups. At 24 hours, secondary lesions were 54±11% (mean±SD) of the initial lesions in the reperfusion-benefit group and 100±14% of the initial lesions in the reperfusion-nonbenefit group (p<0.001). There was no difference in ADC values (47±2×10-5 mm2/s vs 46±5×10-5 mm2/s, p=0.7) and CBFiratio (0.62±0.06 vs 0.67±0.04, p=0.2) between the two groups before reperfusion. However, the initial lesion volume was significantly smaller in the reperfusion-benefit group than in the reperfusion-nonbenefit group (125±54 mm3 vs 195±36 mm3, p=0.037). Conclusions: Changes of ADC values and CBF before reperfusion are unable to predict if initial ischemic lesions will eventually shrink or not after reperfusion. Smaller size of initial lesions may suggest that secondary lesions will be smaller than initial lesions.