Concentric Retriever Device (CRD) in Acute Ischemic Stroke

Inclusion Criteria: 1(a) -Patients who present within 8 hours of stroke onset and are not candidates for treatment with t-PA who have clinical signs consistent with the diagnosis of ischemic stroke such as impairment of language, motor function, sensation, cognition, and/or gaze, or vision. 1(b). Patients who have had an acute ischemic stroke treated with intravenous thrombolytic therapy where vascular imaging (TCD, CTA, MRA, angiography) shows a persistent occlusion after the end of the infusion treatment. 2\. Patients \> 18 years of age. 3. NIHSSS \> 7 4. Angiogram shows a thrombotic occlusion originating in the internal carotid, middle cerebral (M1 or M2 segment), basilar, posterior cerebral, or vertebral arteries. 5\. Patient/patient guardian is willing to comply with the protocol requirements and return to the treatment center for all required clinical evaluations. Exclusion Criteria: 1. Patient is pregnant (if within child bearing age). 2. Patient has baseline glucose of \< 50mg/dL (\<50 mg/mM). 3. Patient has excessive arterial tortuosity that precludes the device from reaching the target area. 4. Patient has known hemorrhagic diathesis, coagulation factor deficiency, or oral anticoagulant therapy with INR \> 2.0. 5. Patient received Heparin within 48 hours with a PTT greater than 2 times the lab normal. 6. Patient has baseline platelets \< 30,000. 7. Patient has history of severe allergy to intra-arterial contrast medium. 8. Patient has severe, sustained hypertension (systolic blood pressure \> 185 mm Hg or diastolic blood pressure \> 110 mm Hg). NOTE: If the blood pressure can be successfully reduced and maintained at the acceptable level using medication (i.e. Nipride), the patient can be enrolled. 9. CT Scan or MRI reveals significant mass effect with midline shift. 10. Patient's angiogram shows an arterial stenosis (\>50%) proximal to the embolus. 11. Patient's anticipated life expectancy is less than 3 months.