Inclusion Criteria:  Patients presented with clinical signs of acute ischemic stroke between 4.5 and 24 hours of stroke onset or awakening with stroke (if within 24 hours from the midpoint of sleep). Patient's age is >18 years. NIHSS 4 to 26. Imaging inclusion criteria: infarct core volume ≤ 70 mL and penumbra ≥ 10 mL with at least 20% mismatch (as evaluated by CTP). Patient, family member or legally responsible person depending on local ethics requirements has given informed consent.  Exclusion Criteria:  CT shows intracranial hemorrhage or lesions larger than one third of the territory of the middle cerebral artery. Pre-stroke mRS score of more than 1 (indicating previous disability); Contraindication for alteplase. Plan to receive endovascular treatment. A life expectancy of less than three months. Any condition that could impose hazards to the patient if study therapy is initiated or affect the participation of the patient in the study (this applies to patients with severe microangiopathy such as hemolytic uremic syndrome or thrombotic thrombocytopenic purpura). The judgment is left to the discretion of the investigator.