Background and Purpose - Magnetic resonance imaging (MRI)- based perfusion measures using dynamic susceptibility contrast are extremely useful for identification of ischemic penumbral tissue in acute stroke. However, errors in the measurement of cerebral blood flow (CBF) and mean transit time (MTT)- can occur. The aim of this study was to investigate whether bolus delay- corrected (BDC) perfusion measures enable better delineation of the ischemic penumbra. Methods - Diffusion weighted MRI (DWI) and perfusion- weighted MRI data were acquired from 19 acute stroke patients. Perfusion abnormalities were manually defined on BDC perfusion maps (corrected MTT[cMTTAbstract: and corrected CBF [cCBFAbstract:), and on maps derived from an arterial input function placed within the contralateral (CBF, MTT) and ipsilateral (ipsilateral CBF [iCBFAbstract: and ipsilateral MTT [iMTTAbstract:) middle cerebral artery. Perfusion lesion volumes were correlated with 30- day T2- weighted MRI lesion volumes and with clinical outcome using the National Institutes of Health Stroke Scale (NIHSS).Results - Spearman correlation coefficients for comparing lesion volumes delineated on DWI, CBF, iCBF, cCBF, MTT, iMTT, and cMTT maps with 30- day T2- weighted lesion volumes were 0.72, 0.87, 0.88, 0.90, 0.84, 0.92, and 0.96, respectively (all P < 0.001). The analogous correlation coefficients for comparing 30- day National Institutes of Health Stroke Scale (NIHSS) scores were 0.39 (NS), 0.69 (NS), 0.75 (P < 0.001), 0.62 (NS), 0.72 (P < 0.001), 0.78 (P < 0.001), and 0.83 (P < 0.001), respectively. Conclusions - Uncorrected perfusion lesion volumes overestimated the extent of ischemic injury. BDC perfusion measures (cMTT) correlated more accurately with final lesion volume and clinical outcome. Such measures offer an improved estimation of the final infarct size in acute stroke. Background and Purpose - Magnetic resonance imaging (MRI) - based perfusion measures using dynamic susceptibility contrast are extremely useful for identification of ischemic penumbral tissue in acute stroke. However, errors in the measurement of cerebral blood flow (CBF) and mean transit time (MTT The aim of this study was to investigate whether bolus delay-corrected (BDC) perfusion measures enable better delineation of the ischemic penumbra. Methods - Diffusion weighted MRI (DWI) and perfusion-weighted MRI data were acquired from 19 acute stroke patients. Perfusion abnormalities were manually defined on BDC perfusion maps (corrected MTT [cMTTAbstract: and corrected CBF [cCBFAbstract :), and on maps derived from an arterial input function placed within the contralateral (CBF, MTT) and ipsilateral CBF [ iCBFAbstract: and ipsilateral MTT [iMTTAbstract :) middle cerebral artery. Perfusion lesion volumes were correlated with 30-day T2-weighted MRI lesion volumes a nd with clinical outcome using the National Institutes of Health Stroke Scale (NIHSS). Results - Spearman correlation coefficients for comparing lesion volumes delineated on DWI, CBF, iCBF, cCBF, MTT, iMTT, and cMTT maps with 30- day T2- weighted lesion (all P <0.001). The analogous correlation coefficients for comparing 30-day National Institutes of Health Stroke Scale (NIHSS) scores were 0.39 (NS), 0.87, 0.88, 0.90, 0.84, 0.92, and 0.96, 0.69 (NS), 0.75 (P <0.001), 0.62 (NS), 0.72 (P <0.001), 0.78 (P <0.001), and 0.83 of ischemic injury. BDC perfusion measures (cMTT) correlated more accurately with final lesion volume and clinical outcome. Such measures offer an improved estimation of the final infarct size in acute stroke.