Stroke Imaging/Diffusion-Perfusion MRI
Diffusion-perfusion magnetic resonance imaging (D-P MRI) refers to the use of a pair of different MRI techniques to assess the status of brain tissue in patients with acute ischemic stroke and to guide subsequent therapy. Currently, intravenous tissue plasminogen activator (IV-tPA) has been shown to be effective in improving the clinical outcome up to 4.5. h. A method for selecting a subgroup of patients with ischemic stroke more than 4.5. h from onset in whom the overall benefit from instituting reperfusion therapy outweighs the risk would be valuable. The rationale behind D-P MRI is that the combination of the two different images can be used to identify the ischemic brain tissue in which the cells will die if untreated, but will live and regain function if quickly reperfused. The diffusion image is used to identify the tissue that is irreversibly infarcted. The perfusion image is used to identify an area of critically low perfusion that corresponds to the tissue that is still at risk. The D-P mismatch is the region of critically low perfusion that does not have restricted diffusion. Theoretically, this mismatch region corresponds to the cells will die if untreated, but will live and regain function if quickly reperfused. Until now, there have been only a few randomized controlled trials (RCTs) that have evaluated D-P MRI mismatch in acute ischemic stroke. They have failed to support the hypothesis that D-P MRI can be useful to identify patients who will benefit from instituting reperfusion therapy beyond the 4.5. h IV-tPA window. However, these studies are not sufficient to conclusively disprove the hypothesis. Nevertheless, as there are no RCT data to support the hypothesis, the clinical value of MRI D-P imaging in this setting remains only a theory worthy of further investigation.
