Perfusion computed tomography thresholds defining ischemic penumbra and infarct core: studies in a rat stroke model

BackgroundPerfusion computed tomography is becoming more widely used as a clinical imaging tool to predict potentially salvageable tissue (ischemic penumbra) after ischemic stroke and guide reperfusion therapies. AimsThe study aims to determine whether there are important changes in perfusion computed tomography thresholds defining ischemic penumbra and infarct core over time following stroke. MethodsPermanent middle cerebral artery occlusion was performed in adult outbred Wistar rats (n=6) and serial perfusion computed tomography scans were taken every 30 mins for 2h. To define infarction thresholds at 1h and 2h post-stroke, separate groups of rats underwent 1h (n=6) and 2h (n=6) of middle cerebral artery occlusion followed by reperfusion. Infarct volumes were defined by histology at 24h. Co-registration with perfusion computed tomography maps (cerebral blood flow, cerebral blood volume, and mean transit time) permitted pixel-based analysis of thresholds defining infarction, using receiver operating characteristic curves. ResultsRelative cerebral blood flow was the perfusion computed tomography parameter that most accurately predicted penumbra (area under the curve=0698) and also infarct core (area under the curve=0750). A relative cerebral blood flow threshold of <75% of mean contralateral cerebral blood flow most accurately predicted penumbral tissue at 05h (area under the curve=0660), 1h (area under the curve=0659), 15h (area under the curve=0636), and 2h (area under the curve=0664) after stroke onset. A relative cerebral blood flow threshold of <55% of mean contralateral most accurately predicted infarct core at 1h (area under the curve=0765) and at 2h (area under the curve=0689) after middle cerebral artery occlusion. ConclusionsThe data provide perfusion computed tomography defined relative cerebral blood flow thresholds for infarct core and ischemic penumbra within the first two hours after experimental stroke in rats. These thresholds were shown to be stable to define the volume of infarct core and penumbra within this time window.