Prediction of delayed ischemic injury with diffusion-weighted MRI following temporary middle cerebral artery occlusion in rats.

Early reductions in the apparent diffusion coefficient of water (ADC) during focal cerebral ischemia are often reversible with reperfusion. With sustained ischemia, the magnitude of the ADC reduction generally increases with time, which could reflect increased severity of ischemic damage. Thus, a threshold in ADC reduction may exist beyond which damage can not be reversed with reperfusion. The goal of this study was to determine if such a threshold exists that is independent of the duration of ischemia in a rat model. Rats were subjected to either 30, 60, or 90 min of temporary middle cerebral artery occlusion. ADC maps acquired just before and 30 min after reperfusion were compared to histology performed after a 72 h survival period to determine the relationship between ADC reduction and final ischemic injury. Significant variability in tissue recovery was observed for the 30 min group. Regions with ADC reductions of up to 45% often recovered, while some regions not exhibiting any change in ADC during occlusion showed ischemic injury at 72 h. Similar observations were made in cortical regions of the 60 min group. In the caudate-putamen, reduced ADC was often associated with ischemic injury. For the 90 min group, results for the caudate-putamen were similar to those for the 60 min group, while reduced ADC was a much better predictor of final ischemic injury in cortical regions than it was in both the 30 and 60 min groups. Thus, no single threshold of ADC reduction that was independent of the duration of ischemia was associated with irreversible injury.