Which Time-to-Peak Threshold Best Identifies Penumbral Flow?

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Abstract
Background and Purpose— In acute ischemic stroke, the hypoperfused but viable tissue is the main therapeutic target. In clinical routine, time-to-peak (TTP) maps are frequently used to estimate the hemodynamic compromise and to calculate the mismatch volume. We evaluated the accuracy of TTP maps to identify penumbral flow by comparison with positron emission tomography (PET). Methods— Magnetic resonance imaging (MRI) and PET were performed in 11 patients with acute ischemic stroke (median 8 hours after stroke onset, 60 minutes between MRI and PET imaging). The volumes defined by increasing TTP thresholds (relative TTP delay of >2, >4, >6, >8, and >10 seconds) were compared with the volume of hypoperfusion (<20 mL/100 g per min) assessed by 15O-water PET. In a volumetric analysis, each threshold’s sensitivity, specificity, and predictive values were calculated. Results— The median hypoperfusion volume was 34.5 cm3. Low TTP thresholds included large parts of the hypoperfused but also large parts of normoper...