Inclusion Criteria1. be 18 or older;
2. have a clinical diagnosis of ischemic stroke and a score of 5 or more points on the NIHSSS;
3. be scheduled to undergo intraarterial (IA) therapy for acute hemispheric stroke (either as primary therapy or as adjuvant therapy following intravenous tPA treatment);
4. be scheduled to have a standard CT including perfusion imaging and CT angiography of the circle of Willis (CTA) prior to IA therapy;
5. begin intra-arterial thrombectomy within 90 minutes of completion of the CT scan and within 18 hours of symptom onset. (Start of IA therapy is defined as the time of insertion of the femoral artery sheath; Time of brain scan is defined as the time that the scan is completed); and
6. have provided informed consent.
Exclusion Criteria1. have any pre-existing illness resulting in a modified Rankin Scale Score of 3 or higher prior to the qualifying stroke;
2. are pregnant.