Inclusion Criteria1. Age 18 years and older
2. Clinical diagnosis of ischemic stroke and a score of 5 or more points in the NIHSS.
3. Planned to undergo intra-arterial (IA) therapy for acute hemispheric stroke (Either as primary therapy or as adjuvant therapy following intravenous tPA treatment)
4. Planned to have a standard MRI including perfusion imaging and MR angiography of the circle of Willis (MRA) prior to IA therapy
5. Intra-arterial thrombectomy can be started within 90 minutes of completion of MRI scan and within 12 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)
6. Able to obtain informed consent (informed consent should be obtained prior to the baseline MRI scan).
Exclusion Criteria1. Any pre-existing neurological illness resulting in a modified Rankin Scale Score of 3 or higher prior to the qualifying stroke