The brain is supplied with blood by a total of four large vessels, the internal carotid artery and vertebral artery on both sides, and the blood supply from both sides of the internal carotid artery accounts for about 80% to 90% of the total blood supply to the brain. When one of the arteries is narrowed and the collateral circulation is poor, the cerebral blood flow to the local or whole brain will be reduced, and when the critical level is exceeded, the clinical symptoms of cerebral ischemia will occur. When the narrowing of the inner diameter of the artery exceeds 50% of the original diameter, which corresponds to a 75% narrowing of the lumen area, it is considered a degree of stenosis sufficient to affect cerebral blood flow, that is, a stenosis with surgical significance.