Signal Evolution and Infarction Risk for Apparent Diffusion Coefficient Lesions in Acute Ischemic Stroke Are Both Time-and Perfusion-Dependent

Background and Purpose-This study aimed to examine the temporal relationship between tissue perfusion and apparent diffusion coefficient (ADC) changes within 6 hours of ischemic stroke onset and how different reperfusion patterns may affect tissue outcome in ADC lesions. Methods-Thirty-one participants were sequentially imaged at 3 hours, 6 hours, and 1 month post-stroke. Three regions of interest (ROIs) were defined within initial ADC lesions: ROI (1)(reperf_3hour) hyperacute reperfusion (within 3 hours), ROI (2)(reperf_6hour) acute reperfusion (3 to 6 hours), and ROI (3)(nonreperf) no reperfusion (by 6 hours). For each ROI, changes in ADC (Delta ADC) from 3 to 6 hours and risks of infarction were examined. Results-The magnitude of initial ADC reduction was similar in all 3 ROIs (P=0.51). Delta ADC was strongly associated with reperfusion (P<0.0001) but not with initial ADC reduction (P=0.83). Delta ADC in ROI (1) (reperf_3hour) and ROI (2) (reperf_6hour) was significantly larger than that of ROI (3)(nonreperf) (P<0.05). Positive Delta ADC was obtained from 3 to 6 hours in ROI (1) (reperf_3hour) that had restored perfusion before 3 hours, demonstrating a temporal delay between reperfusion and ADC changes. Risks of infarction were significantly higher in ROI (3)(nonreperf) than those in ROI (1) (reperf_3hour) and ROI (2) (reperf_6hour). Conclusions-Improvement in ADC did not occur coincidently with reperfusion but showed a temporal delay. Regions with similar initial ADC reductions at 3 hours had different evolution of ADC and infarction risks depending on when or if tissue reperfused. These findings provide a physiological basis for the observation that a single ADC measurement at a fixed time after stroke onset may not accurately predict tissue outcome. (Stroke. 2011;42:1276-1281.)