['Our purpose was to determine (1) the correlation between quantitative CT and MR measurements of infarct core, penumbra, and mismatch; and (2) whether the difference between these measurements would alter patient selection for stroke clinical trials.', 'We studied 45 patients with acute middle cerebral artery stroke imaged a mean of 3.8 hours after onset (range, 0.48 to 8.35 hours) who underwent CT perfusion and MR diffusion (DWI)/perfusion imaging within 3 hours of each other. The DWI and MR-mean transit time (MTT) abnormalities were visually segmented using a semiautomated commercial analysis program. The CT-cerebral blood volume) and CT-MTT lesions were automatically segmented using a relative cerebral blood volume threshold of 0.56 and a relative MTT threshold of 1.50 on commercially available software. Percent mismatch was defined as [(MTT-DWI)/DWI volume]x100. Pearson correlation coefficients were calculated.', 'There were significant correlations for DWI versus CT-cerebral blood volume lesion volumes (r2=0.88, P<0.001), for MR-MTT versus CT-MTT lesion volumes(r2=0.86, P<0.001), and for MR-MTT/DWI versus CT-MTT/CT-cerebral blood volume mismatch lesion volumes(r2=0.81, P<0.001). MR perfusion and CT perfusion agreed for determining: (1) infarct core < versus >or=100 mL in 41 of 45 (91.1%); (2) MTT lesion size < versus >2 cm diameter in 42 of 45 (93.3%); (3) mismatch < versus >20% in 41 of 45 (91.1%); and (4) inclusion versus exclusion from trial enrollment in 38 of 45 (84.4%) patients. Six of 7 disagreements were due to inadequate CT coverage.'] Are quantitative assessment of core/penumbra mismatch in acute stroke : CT and MR perfusion imaging strongly correlated when sufficient brain volume is imaged?