Magnetic resonance perfusion-weighted imaging is a more sensitive method than conventional CT and MR imaging. While the latter can detect acute intracranial hemorrhage, they are not sufficiently sensitive to evaluate acute ischemic stroke immediately after it occurs.
Traditional scanning methods may initially be negative – for the first 24–36 h for CT and for the first 6–12 h for MR. Given that most new acute stroke therapies must be implemented during the first 3–4 h after onset, two important objectives of imaging are to define early and quickly the area of brain infarction and perfusion deficit and to identify any ischemic tissue that can be salvaged by medical, surgical, or endovascular therapy. Perfusion imaging is positive immediately following an acute stroke.
The difference between diffusion and perfusion abnormalities provides a measure of the ischemic penumbra or the brain tissue that has been injured but has reversible ischemia. This...
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