ABSTRACT
Several definitions of the ischemic penumbra have been proposed.1-3 Fundamental to any definition is that the penumbra is a region of reduced blood supply that has spatial characteristics (i.e. it is situated within the vicinity of irreversibly damaged ischemic tissue) and temporal characteristics (i.e. it is progressively recruited into the infarcted tissue with time).4
However, the penumbral tissue is potentially salvageable, if reperfusion occurs or tissue salvage therapy is initiated within a certain time period.4 Imaging of the penumbra, therefore, requires detection of ischemic tissue and measuring reduced regional blood flow below a certain functional threshold. Multimodal magnetic resonance imaging (MRI) techniques that combine diffusion-and perfusionweighted imaging and perfusion computed tomography (CT) have the potential capability to identify and separate brain tissue that is irreversibly injured (ischemic core), severely hypoperfused and at risk of infarction (the penumbra), mildly hypoperfused but not at risk (oligemia), and unaffected (normal).
