A Study of Intravenous Thrombolysis With Alteplase in MRI-Selected Patients

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.