Inclusion Criteria- Age, 18 to 85 years inclusive
- Brain MRI findings consistent with early stroke onset
- Clinical diagnosis of acute ischemic stroke with disabling neurological deficit
- Stroke symptoms present for at least 30 minutes with no significant improvement before treatment
- Be last known well (without stroke symptoms) within 24 hours of triage
- Be able to receive IV rt-PA within 4.5 hours from the time the symptoms were discovered.
- MRI diagnostic of acute ischemic stroke and consistent with clinical syndrome
- Time between completion of qualifying MRI studies to treatment initiation ≤ 1 hour
Exclusion Criteria- History of intracranial hemorrhage
- Symptoms rapidly improving or only minor before start of study drug.
- Severe stroke as assessed clinically (e.g., NIHSS score >25) or by appropriate imaging techniques (lesion volume > one-third of MCA by visual inspection or >100 cm3 using the ellipsoid estimation formula of ABC/2)
- Stroke or serious head trauma within the previous 3 months
- Administration of heparin within the 48 hours preceding the onset of stroke, with an activated partial-thromboplastin time at presentation exceeding the upper limit of the normal range
- Platelet count of less than 100,000 per cubic millimeter
- Uncontrolled hypertension defined as systolic blood pressure > 185 mm Hg or diastolic blood pressure > 110 mm Hg that cannot be controlled except with continuous parenteral antihypertensive medication
- Blood glucose less than 50 mg per deciliter or greater than 400 mg per deciliter
- Symptoms suggestive of subarachnoid hemorrhage, even if CT/MRI scan was normal
- Oral anticoagulant treatment, regardless of INR.
- Major surgery or severe trauma within the previous 3 months
- Other major disorders associated with an increased risk of bleeding
- Eligible for rt-PA therapy per institutional protocol as part of routine clinical practice
- Non-ischemic etiology demonstrated by neuroimaging
- Neuroimaging (CT or gradient echo MRI) evidence of acute or chronic ICH (non-microbleed)
- Presence of 10 or more microbleeds on GRE (suggestive of amyloid angiopathy)
- Any contraindication for MRI, e.g. presence of a pacemaker, ferromagnetic aneurysm clip, etc, pre-menopausal women with a positive pregnancy blood test, or severe claustrophobia.
- Poor quality MRI- images are not interpretable
- In the opinion of the investigator, the patient is not an appropriate candidate for IV rt-PA
- Women known to be pregnant, lactating or having a positive or indeterminate pregnancy test.