With the development of medical science and technology, the means of prevention and treatment of ischemic cerebrovascular disease have been developed greatly, and in the treatment of ischemic cerebral infarction, there are thrombolysis and thrombus extraction within the “time window” in the acute stage, which can achieve better efficacy with drug treatment; in the prevention of ischemic cerebral infarction, clinicians can provide stenting and endothelial debridement of stenotic vessels, which can achieve ideal results. In the prevention of ischemic cerebral infarction, clinicians can provide stenting and endothelial debridement to achieve the desired effect. Intracranial and extracranial vascular bypass surgery is one of the surgical procedures, which requires a rigorous preoperative evaluation to determine the need for cerebrovascular bypass surgery, which directly bypasses the scalp artery vasculature to the cerebral artery vasculature and immediately introduces scalp artery blood to the cerebral ischemic area to improve cerebral blood supply. The indications for this procedure are: 1. occlusion or stenosis of the internal carotid artery that cannot be reached by extracranial surgery, with symptoms of cerebral ischemia due to insufficient collateral circulation; 2. occlusion or stenosis of the middle cerebral artery, with symptoms of cerebral ischemia due to insufficient collateral circulation; 3. lesions involving the internal carotid artery or middle cerebral artery, requiring blockage of these vessels for treatment; 4. 4. Diffuse hypoperfusion syndrome, multiple cerebral artery stenosis or occlusion due to “unreachable” extracranial surgery; 5. Internal carotid artery stenosis on one side and internal carotid artery occlusion on the opposite side. The following clinical tests should be selected: 1. CT/MRI for local or extensive cerebral ischemia without fresh or large infarcts; 2. CTA/MRA/DSA for severe stenosis or occlusion of the internal carotid artery or middle cerebral artery with inadequate collateral compensation; 3. CTP for hypoperfusion status.