New imaging strategies for patient selection for thrombolytic and neuroprotective therapies.

Ischemic stroke trials have traditionally sought to limit the range of disease studied according to several dimensions based on clinical examination and CT scan results. It has been proposed that the optimal sample for stroke trials would include a positive imaging diagnosis of a pathology rationally linked to the drug's mechanisms of action and that this would improve the likelihood of positive results. This principle has been supported by the results of the Prolyse in Acute Cerebral Thromoembolism II (PROACT II) study. Whereas trials of iv thrombolysis between 3 and 6 hours after symptom onset in a general sample of patients were not positive, selection of a subgroup by angiography was an effective strategy in this time period for PROACT II. This study contradicted the hypothesis that treatment of stroke beyond 3 hours would not be successful. MRI with diffusion and perfusion has been an appealing imaging modality because it provides pretreatment angiography, perfusion, and lesion volume information during a brief, non-invasive assessment. Current literature supports the validity of MRI as a marker for clinical severity and clinical improvement. The diffusion-perfusion mismatch, the MRI marker for the ischemic penumbra, is a very strong predictor of lesion volume growth. Several acute trials in progress use a positive imaging diagnosis for the basis of selection. As the field of stroke clinical trials examines opportunities for improving trial design, positive imaging diagnoses in patient selection are likely to assume an increasingly useful role.