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Endovascular rescue patient selection: perfusion scanning

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(a) The "ideal" patient is one with a large mismatch between the ischemic core and the penumbra volume, particularly if the cerebral blood volume is maintained normal (i). Although this is the picture of the typical onset, as time elapses, cerebral blood volume will begin to decrease in the core, spreading centrifugally (ii) to span the entire area of ischemia. (b) A lesser degree of mismatch is seen later, as the ischemic core also expands, indicating a less than "ideal" situation for a beneficial reperfusion effect. The abnormally low cerebral blood volume will also spread (from ii to iii), suggesting the progressive loss of tissue to infarction. (c) Finally, unless the tissue is revascularized, all evidence of parameters mismatch is lost, suggesting irreparable damage and futility of intervention. NOTE: As a practical step, we have used the same color scheme typically applied by the RAPID software (iSchemaView) to display cerebral blood flow and mean transit time. (Contributed by Dr. Camilo Gomez.)