Stroke: neuroimaging in acute stroke-where does MRI fit in?

摘要

Noncontrast CT (NCCT) remains the current standard of care in the initial diagnosis of patients with stroke and provides valuable information, particularly with regard to the presence of intracranial hemorrhage. NCCT has variable accuracy in detection of early ischemic changes, however, and provides limited information on hypo-perfused brain tissue at risk of infarct. Conventional T2-weighted MRI and NCCT detect similar underlying pathophysiological parameters, but both modalities are inferior to diffusion-weighted imaging (DWI) in the early ischemic stages. In DWI, restriction of proton (water) motion, following ion-pump failure in ischemic regions, is responsible for the high signal that develops within the first hour after the ischemic insult. Ischemic infarct is the result of inadequate circulation through the capillary bed. Perfusion imaging (CT or MRI perfusion) depicts cerebral hemodynamics at the microvascular level and, therefore, offers an opportunity to study the pathophysiological events that lead most directly to ischemic damage.