The ischemic penumbra - Operationally defined by diffusion and perfusion MRI

Background: Identifying tissue at risk for infarction is important in decid ing which patients would benefit most from potentially harmful therapies an d provides a way to evaluate newer therapies with regard to the amount of i schemic tissue salvaged. Objective: To operationally define and characteriz e cerebral tissue at risk for stroke progression. Methods: We retrospective ly selected 25 patients with an acute onset of a hemispheric stroke from ou r database who had undergone a combination of two diffusion-weighted MRI st udies and a perfusion-weighted MRI study. We applied a logistic regression model using maps of the relative mean transit time and relative cerebral bl ood flow (rCBF) as well as three different maps of the relative cerebral bl ood volume (rCBV) to predict an operationally defined penumbra (region of m ismatch between the diffusion lesion on day 1 and its extension 24 to 72 ho urs later). Results: Maps of the rCBF and initial rCBV were significant pre dictors for identifying penumbral tissue. Our operationally defined penumbr al region was characterized by a reduction in the initial rCBV (47% of cont ralateral control region [CCR]), an increase (163% of CCR) in the total rCB V, and a reduction (37% of CCR) in the rCBF, whereas the operationally defi ned ischemic core showed a more severe reduction in the rCBF (12% of CCR) a nd in the initial rCBV (19% of CCR). Conclusion: These MR indexes may allow the identification and quantification of viable but ischemically threatene d cerebral tissue amenable to therapeutic interventions in the hyperacute c are of stroke patients.