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White Matter Thresholds for Ischemic Penumbra and Infarct Core in Patients with Acute Stroke: CT Perfusion Study¹

¹ From the Department of Imaging, Lawson Health Research Institute, London, Ontario, Canada (B.D.M., T.Y.L.); Departments of Radiology (D.H.L., I.B.G., D.P.) and Clinical Neurosciences (V.B., R.K.C.), London Health Sciences Centre, London, Ontario, Canada; Departments of Radiology (A.J.F., R.I.A., S.S.) and Neurology (S.E.B., D.J.S.), Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Departments of Clinical Neurosciences (S.B.C., A.M.D.) and Radiology (M.G.), Foothills Medical Centre, Calgary, Alberta, Canada; and Department of Neuroscience, Ottawa Health Research Institute, Ottawa, Ontario, Canada (M.J.H.). Received April 19, 2007; revision requested June 13; revision received July 31; accepted August 28; final version accepted November 8. Supported in part by GE Healthcare and the Canadian Stroke Network. T.Y.L. is a consultant to GE Healthcare and is associated with Robarts Research Institute, which licenses software to GE Healthcare. Address correspondence to T.Y.L., Imaging Research Laboratories, Robarts Research Institute, 100 Perth Dr, London, ON, Canada N6A 5K8 (e-mail: tlee{at}imaging.robarts.ca).

Purpose: To prospectively determine the parameters derived at admission computed tomographic (CT) perfusion imaging admission that best differentiate ischemic white matter that recovers from that which infarcts, with the latter retrospectively defined at a CT examination performed without contrast material (unenhanced CT) 5–7 days after the event.

Materials and Methods: Ethics committee approval and informed consent were obtained. Thirty patients with stroke underwent unenhanced CT, CT angiography, and CT perfusion studies at admission. Additionally, CT angiography was performed 24 hours after the stroke, and an unenhanced CT study was performed 5–7 days after the stroke. Five patients were excluded; the remaining patients (10 men, 15 women; mean age, 70 years ± 13 [standard deviation]) were separated into those with recanalization (n = 16) and those without recanalization (n = 9) at 24 hours. For patients with recanalization, the final infarct was outlined on unenhanced CT images obtained 5–7 days after the event and was superimposed on coregistered maps from the CT perfusion study performed at admission. Ischemic white matter tissue (cerebral blood flow [CBF] < 14 mL/min/100 g) was identified at the admission CT perfusion study, and the penumbra was defined as the difference between the ischemic region and the infarct region.

Results: Infarct regions showed a matched decrease in CBF and cerebral blood volume (CBV) at admission, whereas penumbra regions showed a significant (P < .05) decrease in CBF but no change in CBV (P > .05) from contralateral values. A threshold CBF · CBV value of 8.14 was the most sensitive (95%, 20 of 21 regions) and specific (94%, 32 of 34 regions) parameter for differentiating between regions of ischemic white matter that recovered and regions of ischemic white matter that infarcted.

Conclusion: The product of CBF and CBV derived from CT perfusion data provided the best differentiation between regions of ischemic white matter that infarcted and regions of ischemic white matter that recovered 5–7 days after a stroke.

© RSNA, 2008

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