 1. Successful completion of screening procedures inclusive of cerebral blood flow velocity greater than or equal to 200 cmsec measured twice or at least one measurement greater than or equal to 220 cmsec in the middle cerebral artery, internal carotid, or both vessels with non-imaging or imaging technique and greater than or equal to 180 cmsec in the middle cerebral artery with non-imaging or imaging technique performed by two study personnel; 