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 (&Dgr;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). &Dgr;ADC was strongly associated with reperfusion (P<0.0001) but not with initial ADC reduction (P=0.83). &Dgr;ADC in ROI (1)reperf_3hour and ROI (2)reperf_6hour was significantly larger than that of ROI (3)nonreperf (P<0.05). Positive &Dgr;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.