Viability thresholds of ischemic penumbra of hyperacute stroke defined by perfusion-weighted MRI and apparent diffusion coefficient

Background and Purpose-The penumbra of ischemic stroke consists of hypoperf used, but not irreversibly damaged, tissue surrounding the ischemic core. T he purpose of this study was to determine viability thresholds in the ische mic penumbra, defined as the perfusion/diffusion mismatch in hyperacute str oke, by the use of diffusion- and perfusion- weighted MRI (DWI and PWI, res pectively). Methods-DWI and PWI were performed in 11 patients less than or equal to6 ho urs after the onset of symptoms of acute ischemic stroke. Regions of intere st (ROIs) were placed covering the ischemic core (ROI 1), the penumbra that progressed to infarction on the basis of follow-up scans (ROI 2), and the penumbra that recovered (ROI 3). The ratios of relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), mean transit time (MTT), an d apparent diffusion coefficient were calculated as lesion ROIs relative to the contralateral mirror ROIs. Results-The post hoc analysis showed that the penumbra progressed to infarc tion at the following cutoff values: rCBF <0.59 and MTT >1.63. Higher sensi tivity and accuracy in predicting outcome of the penumbra were obtained fro m the rCBF maps compared with the rCBV and MTT maps. The initial rCBV and a pparent diffusion coefficient ratios did not differentiate between the part of the penumbra that recovered and the part that progressed to infarction, The mean rCBF ratio was optimal in distinguishing the parts of the penumbr a recovering or progressing to infarction. Conclusions-The thresholds found in this study by combined DWI/PWI might ai d in the selection of patients suitable for therapeutic intervention within 6 hours. However, these hypothesized thresholds need to be prospectively t ested at the voxel level on a larger patient sample before they can be appl ied clinically.