inclusion criteria:  Patient age ≥ 18 years old and life expectancy of 5 years or more. Symptomatic sNA-ICAO defined as:diagnosed by CTA or MRA and confirmed by angiography; Vascular occlusion time more than 24 hours;TIA or ischemic stroke (confirmed by CT or MRI) related to the LCAO despite SMT < 90 days prior to enrollment. Modified Rankin scale score of 0 or 1 at the time of informed consent. More than one risk factor for atherosclerosis. For patients with ICA or MCA M1 segment occlusion, ipsilateral hypoperfusion confirmed by CTP or MRI perfusion imaging prior to enrollment and analysis by the RAPID system. For patients with intracranial segment occlusion of the vertebral artery, severe stenosis or occlusion of the contralateral vertebral artery. Among women, no childbearing potential; or if a woman with childbearing potential, a negative pregnancy test result prior to randomization. Agreement of the patient to comply with all protocol-specified follow-up appointments. Signature by a patient of a consent form that has been approved by the local governing institutional review board (IRB)/medical ethics committee (MEC) of the respective clinical site.  exclusion criteria:  Intolerance or allergic reaction to a study medication without a suitable management alternative. No atherosclerotic intracranial vasculopathies, such as dissection, moyamoya disease and vasculitis. Concomitant intracranial aneurysms or any bleeding disorder. Life expectancy <1 year due to other medical conditions. Large infarction core, defined as an ASPECTS < 6 in anterior circulation and pc-ASPECTS < 6 points in posterior circulation. For patients with MCA M1 segment occlusion, concomitant ≥50% stenosis of the proximal internal carotid artery or other intracranial arteries. For patients with intracranial segment occlusion of the vertebral artery, continuance of the occluded vertebral artery to the posterior inferior cerebellar artery with no stump. Incomplete clinical and imaging data. Coexistent cardioembolic source (e.g., atrial fibrillation, mitral stenosis, prosthetic valve, MI within six weeks, intracardiac clot, ventricular aneurysm and bacterial endocarditis). Occlusive lesions with severe calcification. Platelet count <100,000/ml or history of heparin-induced thrombocytopenia. Left ventricular ejection fraction <30% or admission for heart failure in the prior 6 months. Extreme morbid obesity that would compromise patient safety during the procedure or the periprocedural period. Coronary artery disease with two or more proximal or major diseased coronary arteries with 70% stenosis that have not or cannot be revascularized. Anticoagulation with Marcumar, warfarin or direct thrombin inhibitors or anti-XA drugs. Chronic atrial fibrillation. Any history of atrial fibrillation or paroxysmal atrial fibrillation in the past 6 months that is considered to require long-term anticoagulant therapy. Other high-risk cardiogenic embolisms, including left ventricular aneurysm, severe cardiomyopathy, aortic or mitral mechanical heart valve, severe calcified aortic stenosis (valve area < 1.0 cm2), endocarditis, moderate to severe mitral stenosis, left atrial thrombus or any intracardiac mass or known paradoxical embolism of unrepaired PFO. Unstable angina defined as rest angina with ECG changes that is not amenable to revascularization (patients should undergo planned coronary revascularization at least 30 days before randomization). Any major surgery, major trauma, revascularization procedure or acute coronary syndrome within the past 1 month. serum creatinine >2.5 mg/dl or estimated GFR <30 cc/min. Major surgery planned within 3 months after enrollment. Currently listed or being evaluated for major organ transplantation (i.e., heart, lung, liver and kidney). Participation in other trials and may affect the results of this study. Inability to understand and cooperate with research procedures or provide informed consent. Endarterectomy, bypass or stent implantation performed on the proximal end of the occlusion vessel.