<qa>  What is the primary purpose of the CRD?The primary purpose is to study the safety and effectiveness of the Concentric Retriever DeviceCRDin ischemic stroke patients who undergo clot retrieval with the CRD within 8 hours of stroke symptom onset. The CRD has been approved by the U.S. Food and Drug Administration to retrieve foreign bodies such as pieces of metal from blood vessels in the body. The CRD is a small metal wire with a loop at the end like a corkscrew that removes clots from arteries and thereby restores blood flow to the brain. Prior versions of the CRD may have been too soft to pull out clots, just as a corkscrew that is too soft would not pull out corks. The current version of the CRD is not as soft and may be more effective in retrieving clots. Hypothesis: By restoring blood flow to the brain, stroke symptoms may get better or the stroke may be prevented from getting worse. 