Perfusion Imaging Evaluation for Ischemic Stroke on 6-24 Hours Undergoing Endovascular Thrombectomy

Inclusion Criteria: Clinical Inclusion Criteria: 1. Clinical signs and symptoms consistent with the diagnosis of an acute ischemic stroke 2. Age ≥18 years 3. NIHSS ≥ 6 4. Endovascular thrombectomy can be initiated (femoral puncture) between 6 and 24 hours after time last know well 5. No significant pre-stroke disability (pre-stroke mRS must be ≤ 3 ) 6. Patient/Legally Authorized Representative has signed the Informed Consent form Imaging Inclusion Criteria: 1. ICA or MCA-M1 or MCA-M2 or BA occlusion (carotid occlusions can be cervical or intracranial with or without tandem MCA lesions) as evidenced by MRA or 4D-CTA 2. Target Mismatch Profile on CT perfusion or MR perfusion: ischemic core volume is ≤ 70 ml, mismatch ratio is \>/= 1.2 ) Exclusion Criteria: Clinical Exclusion Criteria: 1. Other serious, advanced, or terminal illness (investigator judgment) or life expectancy is less than 90 days 2. Subject with a co-morbid disease or condition that would confound the neurological and functional evaluations or compromise survival or ability to complete follow-up assessments 3. Unable to undergo a contrast brain perfusion scan with either MRI or CT 4. Pregnant 5. Known serious sensitivity to radiographic contrast agents 6. Treated with rtPA \>6 hours after time last known well 7. Known hereditary or acquired hemorrhagic diathesis, coagulation factor deficiency; recent oral anticoagulant therapy with INR \> 3 (recent use of one of the new oral anticoagulants is not an exclusion if estimated GFR \> 30 ml/min). 8. Seizures at stroke onset if it precludes obtaining an accurate baseline NIHSS 9. Current participation in another investigational drug or device treatment study 10. Known hereditary or acquired hemorrhagic diathesis, coagulation factor deficiency 11. Any other condition that, in the opinion of the investigator, precludes an endovascular procedure or poses a significant hazard to the subject if an endovascular procedure was performed. Neuroimaging Exclusion Criteria: 1. ASPECTS score \<6 on non-contrast CT (if patient is enrolled based on CT perfusion criteria) 2. Evidence of intracranial tumor (except small meningioma), acute intracranial hemorrhage, neoplasm, subarachnoid hemorrhage, or arteriovenous malformation 3. Significant mass effect with midline shift 4. Evidence of internal carotid artery dissection 5. Intracranial stent implanted in the same vascular territory, known history of arterial tortuosity, and/or other arterial disease that precludes the safe deployment/removal of the thrombectomy device