Inclusion Criteria1. Acute ischemic stroke patients, within 24 hours of symptom onset. In cases where onset time can not be established, including symptoms upon waking, it will be considered to be the time when the patient was last known to be well.
2. All patients will be 18 years or older.
3. Baseline NIHSS must be 4-18 inclusive.
4. Blood pressure (BP) must be ≤180 mmHg systolic and ≤105 mmHg diastolic at the time of enrolment. Treatment of higher systolic BP is permitted, prior to enrolment.
5. Female patients of child-bearing potential will have a negative pregnancy test prior to enrollment.
6. NCCT Inclusion Criteria: ASPECT scores of the NCCT will be assessed prior to enrolment. An ASPECT score of >6 will be required for inclusion in the trial. Patients with an ASPECT score of ≤6 will be considered screening failures and no further imaging will be conducted.
7. MRI Inclusion Criteria: Patients will have an MR mismatch score of >2. This will be defined as a minimum of 3 ASPECTS regions with evidence of hypoperfusion visible on MTT maps, associated with normal diffusion as demonstrated by DWI. This will ensure that all patients have more than 20% mismatch by volume. In cases where PWI demonstrates oligemia in the ACA or PCA territories, patients will be treated only if diffusion abnormality volumes are 50% of the MTT deficits by visual inspection.
8. CTP Inclusion Criteria: Patients will have a CTP mismatch score of >2. This will be defined as a minimum of 3 ASPECTS regions with evidence of hypoperfusion, visible on MTT maps, associated with normal CBV. This will ensure that all patients have more than 20% mismatch by volume.
Exclusion CriteriaPatients with contraindications to both MRI and CT perfusion will be excluded. MRI Exclusion Criteria: Patients with metallic implants and any past sensitivity to gadolinium contrast media will be excluded from MRI. Due to recent reports of nephrogenic systemic fibrosis associated with gadolinium exposure in individuals with pre-existing renal failure, patients with Creatinine > 160 μmol/l or Glomerular Filtration Rate (GFR) <60 ml/min will also be excluded.72 Patients with metallic implants of any kind, pacemakers or other foreign bodies will be excluded from MRI, as will those with excessive claustrophobia.
CT Perfusion Exclusion Criteria: Patients with any past sensitivity to iodinated contrast media, serum creatinine >160 μmol/l or Glomerular Filtration Rate (GFR) <50 ml/min will be excluded from CT perfusion imaging. Patients taking metformin will be eligible, but metformin will be withheld for 48 hours after imaging to avoid possible metabolic acidosis.
Thrombolysis Exclusion Criteria: Patients who have suffered a prior ischemic stroke within 30 days of the presenting event or who have any history of intracranial hemorrhage will be excluded. Patients with a known secured or unsecured cerebral aneurysm or vascular malformation will be ineligible. An inability to control systolic BP > 180 mmHg, or diastolic BP > 105 mmHg with IV anti-hypertensive medications will result in exclusion. Patients with a known coagulopathy or evidence of active bleeding will be excluded. Surgical procedures, biopsy, subclavian venous or arterial puncture, trauma, gastrointestinal or genitourinary bleeding within 14 days of the event will all result in exclusion. Patients treated with IV heparin within the previous 24 hours and an abnormal PTT will be excluded, as will those taking oral anticoagulants, resulting in an INR >1.4. A platelet count <100 000, venous glucose either < 3 mmol/l or >18 mmol/l will all result in exclusion.