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Background and Purpose -In acute ischemic stroke, the hypoperfused but viab le tissue is the main therapeutic target. In clinical routine, time-to-peak (TTP) maps are frequently used to estimate the hemodynamic compromise and to cal culate the mismatch volume. We evaluated the accuracy of TTP maps to identify pe numbral flow by comparison with positron emission tomography (PET). Methods -M agnetic 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 del ay of >2, >4, >6, >8, and >10 seconds) were compared with the volume of hypoperf usion ( < 20 mL/100 g per min) assessed by 15O-water PET. In a volumetric anal ysis, each threshold’ s sensitivity, specificity, and predictive values were ca lculated. Results -The median hypoperfusion volume was 34.5 cm3. Low TTP thres holds included large parts of the hypoperfused but also large parts of normoperf used tissue (median sensitivity/specificity: 93% /60% for TTP >2) and vice ve rsa (50% /91% for TTP >10). TTP >4 seconds best identifies hypoperfusion (84 % /77% ). The positive predictive values increased with the size of hypoperfus ion. Conclusion -This first comparison of quantitative PET-CBF with TTP maps in acute ischemic human stroke indicates that the TTP threshold is crucial to r eliably identify the tissue at risk; TTP >4 seconds best identifies penumbral fl ow; and TTP maps overestimate the extent of true hemodynamic compromise dependin g on the size of ischemia. Only if methodological restrictions are kept in mind, relative TTP maps are suitable to estimate the mismatch volume.
Background and Purpose -In acute ischemic stroke, the hypoperfused but viab le tissue is the main therapeutic target. In clinical routine, time-to-peak (TTP) maps are frequently used to estimate the hemodynamic compromise and to cal culate the mismatch volume. We evaluated the accuracy of TTP maps to identify pe numbral flow by comparison with positron emission tomography (PET). Methods-M agnetic 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 del ay 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 anal ysis, each threshold ’s sensitivity, specificity, and predictive values were ca lculated. Results -The median hypoperfusion volume was 34.5 cm3. Low TTP thresought included large parts of the hypoperfuse TTP> 4 seconds best identifies hypoperfusion (84%), but also large parts of normoperf used tissue (median sensitivity / specificity: 93% / 60% for TTP> % / 77%). The positive predictive values increased with the size of hypoperfus ion. Conclusion -This first comparison of quantitative PET-CBF with TTP maps in acute ischemic human stroke that the the TTP threshold is crucial to eliably identify the tissue at TTP> 4 seconds best identifies penumbral fl ow; and TTP maps overestimate the extent of true hemodynamic compromise depend on g on the size of ischemia. Only if methodological restrictions are kept in mind, relative TTP maps are suitable to estimate the mismatch volume.