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Abstract
Stroke is a leading cause of mortality and long term disability worldwide. The goals of an imaging evaluation of acute stroke are to diagnose as early as possible and to obtain accurate information about the intracranial vasculature and brain perfusion for guidance in selecting the appropriate therapy. This essay highlights the role of functional magnetic resonance imaging including both diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI) in diagnosis of acute cerebral ischemic stroke. PWI lesion estimates the region of acute dysfunctional brain tissue, whereas, the acute DWI lesion corresponds to the core of the early infarction. The mismatch between the acute PWI lesion and the smaller DWI lesion represents potentially salvageable brain tissue (an estimate of the ischemic penumbra). In patients with a PWI/DWI mismatch, early reperfusion is often associated with substantial clinical improvement and reversal or reduction of DWI lesion growth.