SELECT is a multicenter, observational prospective study implementing a protocol to acquire imaging and clinical variables known to affect clinical outcomes after endovascular therapy in an effort to evaluate and compare the different selection methods and criteria currently used in practice for acute ischemic stroke patients in the anterior circulation with large vessel occlusion. The study aim is to evaluate prospectively different selection methodologies for endovascular therapy, to compare them against each other to identify which method provides the highest predictive ability in the selection of patients for IAT and to devise a formula that predicts patients' outcomes.

This study will enroll patients based on the recent AHA guidelines (July 2015) regarding treatment of patients with acute ischemic strokes and large artery occlusions in the anterior circulation.

Our goal is to collect complete imaging, clinical, and 90 day follow up data on 250 endovascular therapy patients as well as up to 250 concurrent medical management patients as a comparison group.

Improving reperfusion status is the most effective therapeutic approach for patients with acute ischemic strokes (AIS) due to large artery occlusion (LAO). Intra-Arterial Therapy (IAT) by means of mechanical thrombectomy and/or chemical fibrinolysis has been adopted worldwide to recanalize LAO strokes. IAT is now the standard of care for AIS patients with LAO based on the results of five randomized clinical trials. However, these trials implemented different imaging methodologies for patient treatment with IAT. Specially, these trials were designed to use one or another selection methodology without knowing which may be superior and more effective in selecting patients that may or may not benefit from the intervention.

Decisions to pursue IAT are clinician-dependent and rest upon a number of different factors that may differ from one center to another and even in the same center from one treating physician to another. The Alberta Stroke Program Early CT Score (ASPECTS) has demonstrated utility in selecting candidates for recanalization strategies using a simple noncontrast head CT (NCCT). Numerous other studies suggest the utility of magnetic resonance imaging (MRI), CT angiography (CTA) and CT perfusion in identifying patients who have poor outcome after thrombolysis.

However, the current widely practiced selection methodologies have never been tested against one another in the context of a prospective trial to evaluate their sensitivity, specificity and superiority, which is in our opinion (and shared by many treating vascular neurologists), a major question that is being asked on daily basis by the treating physicians. Furthermore, prognostication and informing stroke patients' families of their chances of having good outcomes after Intra-Arterial Therapy is crucial and depends to a large extent on the clinical and imaging variables utilized prior to IAT as well as on the success of the intervention itself.

Inclusion Criteria:

Eligible patients will be:

1. Adults (≥18years) with the final diagnosis of an acute ischemic stroke
2. CT-Angiogram proven, large artery occlusion (LAO) in the internal carotid artery (ICA), middle cerebral artery (MCA -M1 or M2 site) locations
3. NIH Stroke Scale ≥6 (NIHSS) OR proven LAO on imaging (must be from designated LAO listed on inclusion #2)
4. LSN (last seen normal) to groin puncture (≤ 8 hours) in thrombectomy arm; LSN to presentation to endovascular capable center (≤ 8 hours) in medical arm
5. Baseline modified Rankin Scale score of 0-1
6. Signed Informed Consent obtained
7. Subject willing to comply with the protocol follow-up requirements
8. Anticipated life expectancy of at least 3 months
9. IV-tPA eligible patients must meet AHA guidelines

Exclusion Criteria:

Patients are excluded if:

1. Inability to undergo CT-Angiography and/or CT-Perfusion imaging (e.g., renal insufficiency, iodine/contrast allergy)
2. Co-morbid psychiatric or medical illnesses that would confound the neurological assessments
3. Subject is participating in another mechanical neuro-thrombectomy device trial (intervention) or any other trial where the study procedure or treatment might confound the study endpoint.

Eligible patients will be adults (≥18 with the final diagnosis of an acute ischemic infarction and large artery occlusion in anterior circulation strokes). Given the observational design of the study there will be no stringent exclusion based on stroke severity or IV tPA treatment