LANDMARK ADVANCES POISED TO SHIFT THE PARADIGM OF ACUTE STROKE IMAGING AND TREATMENT
The basic premise underlying acute stroke therapy is to salvage the ischemic region from evolving into infarction, thereby maintaining brain function and improving outcome. The concept of the ischemic penumbra concept envisions not only potentially salvageable or at-risk ischemic tissue but also nonviable tissue known as the “ischemic core”. The Stanford Stroke Center has been at the forefront of developing acute imaging and image processing techniques that provide immediate and accurate visualization of both core and penumbra. These techniques, which involve MRI with diffusion weighted imaging (DWI) and perfusion weighed imaging (PWI), have proven to identify patients who can benefit from both intravenous and intra-arterial therapies well beyond established time frames.
A research collaboration coordinated at Stanford has helped establish that a lesion detected by DWI lesion is an extremely accurate surrogate for the ischemic core.
Furthermore, recent data from Stanford demonstrate that PWI, when optimally processed, can accurately identify critically hypoperfused penumbral tissue.
The DEFUSE Study
This Stanford study, sponsored by the NIH, demonstrated that patients with a favorable MRI profile, called Target Mismatch, have excellent outcomes following reperfusion, even when treated up to 6 hours after symptom onset with iv tPA. Other MRI profiles, including the No mismatch and Malignant profile failed to show any evidence of benefit from reperfusion.
RAPID Software
In order to automatically process DWI and PWI data quickly and accurately, Stanford Stroke Center faculty members developed a unique software program called RAPID. Using the databases from 2 international studies, this software program has been retrospectively demonstrated to identify patients who benefit from reperfusion following iv tPA therapy.
DEFUSE 2
This recently completed multicenter trial was designed and run by Stanford and funded by the NIH. The trial results demonstrated that using the RAPID software, selected patients can be identified who benefit for intra-arterial clot removal therapy up to 12 hours after symptom onset. These findings have the potential to substantially expand the number of patients eligible for successful stroke treatment and significantly improve the overall results of intra-arterial therapies.
Future Implications
The research findings described above imply that the paradigm for acute stroke treatment can now move away from arbitrary time windows. Identification of salvageable brain tissue and determining the site of vascular obstruction will become the focus of acute imaging. Treatment strategies can then be individualized to maximize reperfusion of viable tissue.
