and Purpose-Perfusion-weighted imaging maps are used to identify hypoperfusion in acute ischemic stroke. We evaluated maps of cerebral blood flow (CBF), cerebral blood volume, mean transit time, and time to peak (TTP) in acute stroke by comparison with positron emission tomography. Methods-Perfusion-weighted imaging and positron emission tomography were performed in 26 patients with acute ischemic stroke (median 18.5 hours after stroke onset, 65 minutes between MRI and positron emission

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... hy). The perfusion-weighted imaging-derived maps of CBF, cerebral blood volume, mean transit time, and TTP delay were compared with quantitative positron emission tomography CBF. A receiver-operating characteristic curve analysis identified the best perfusionweighted imaging map and threshold to identify hypoperfusion Ͻ20 mL/100 g/min, a widely used measure of penumbral flow. Results-Individual regression analysis of positron emission tomography CBF and perfusion-weighted imaging values were strong for CBF and TTP delay and weaker for mean transit time and cerebral blood volume, but the pooled analysis showed a large variance. Receiver-operating characteristic curve analysis identified TTP and CBF maps as most predictive (median area under the curveϭ0.94 and 0.93). Penumbral flow thresholds were Ͻ21.7 mL/100 g/min (CBF), Ͻ1.5 mL/100 g (cerebral blood volume), Ͼ5.3 seconds (mean transit time), and Ͼ4.2 seconds (TTP). TTP and CBF maps reached sensitivity/specificity values of 91%/82% and 89%/87%. Conclusion-In our sample, maps of CBF, TTP, and mean transit time yielded a good estimate of penumbral flow. The performance of TTP maps was equivalent to deconvolution techniques using an arterial input function. For all maps, the application of a predefined threshold is mandatory and calibration studies will enhance their use in acute stroke therapy as well as in clinical stroke trials. (Stroke. 2010;41:443-449.) Key Words: acute stroke Ⅲ cerebral blood flow Ⅲ cerebral ischemia Ⅲ perfusion-weighted magnet resonance imaging Ⅲ positron emission tomography Ⅲ penumbra