Perfusion Computed Tomography for the Evaluation of Acute Ischemic Stroke

Ischemic stroke results from occlusion of a cerebral artery, and it is the leading cause of disability and the fifth leading cause of death in the United States.1 Cerebral artery occlusion results in irreversible death of a component of cerebral tissue, which is referred to as the core infarction. There is an additional component of brain tissue that is ischemic, but viable, which is commonly referred to as the penumbra. The penumbra is at risk of irreversible infarction if timely restoration of blood flow is not achieved, and the preservation of the penumbra by restoration of arterial blood flow is the target of reperfusion therapy in the treatment of ischemic stroke.Increasingly, perfusion computed tomography CT (PCT) is performed for physiological evaluation of the brain parenchyma in the setting of cerebral ischemia, and this technique may be used to determine volume of core infarction and of the penumbra. The physiological data derived from PCT is typically displayed in perfusion maps, including cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT; Figure 1). Regions of brain with severely reduced CBV or CBF correspond to the region of core infarction.2 Regions of brain with prolongation of the MTT or its derivatives, the time-to-peak and time-to-maximum (Tmax) of the residue function, have been shown to accurately measure the penumbra in patients with acute ischemic stroke.2Figure 1. Matched and Mismatched perfusion computed tomography (PCT) imaging in a patient with middle cerebral artery (MCA) occlusions. Noncontrast head CT (NCCT) and PCT images in a patient with a matched core and penumbra (patient 1) and in a patient with a mismatch between the core and penumbra (patient 2). Patient 1: NCCT images demonstrate evidence of acute ischemia within the left MCA territory, including loss of the left insular ribbon (NCCT, …