- Patients who have large areas (greater than one lobe) of obvious low density on the baseline CT scan will be presumed to have had ongoing cerebral ischemia for greater than 3 hours, and will, therefore, be excluded. Patients with subtle early signs of cerebral infarction (e.g., sulcal effacement, blurring of the grey-white junction, asymmetry of the basal ganglia, insular ribbon sign, and others) and the dense artery sign on baseline CT scan will be eligible. Similarly, evidence of previous remote cerebral infarction on baseline CT will not be exclusionary.