Inclusion Criteria:  Age ranging from 18 to 80, both genders Unilateral internal carotid artery (ICA) or M1 segment of middle cerebral artery (MCA) stenosis (rate of stenosis ranging from 50-99%) Acute ischemic cerebrovascular events (TIA or ischemic stroke) within cerebral stenotic artery supplying area Onset of disease <30 d before enrollment Modified Ranking Scale (mRS) ≤1 before stroke onset National Institutes of Health Stroke Scale (NIHSS) ≤20 Sufficient bilateral temporal bone windows for insonation of the middle cerebral artery Be conscious, and able to cooperate with CA assessment Willing to participate and sign the informed consent  Exclusion Criteria:  Vertebral artery (VA), basilar artery (BA), anterior cerebral artery (ACA), or posterior cerebral artery (PCA) stenosis; Bilateral internal carotid artery (ICA) or M1 segment of middle cerebral artery (MCA) stenosis(rate of stenosis ranging from 50-99%) Patients who have received or plan to undergo intravascular interventional treatment/endarterectomy Other intracranial diseases, including cerebral hemorrhage (primary or secondary), intracranial neoplasm, aneurysm, arteriovenous malformation, etc. Evidence for embolic stroke, such as atrial fibrillation, prosthetic valve surgery, and suspected endocarditis, etc. Arrhythmia, anemia and hyperthyroidism which may influence the stability of cerebral blood flow diagnosed by two physicians by electrocardiogram and laboratory tests. Dementia, severe anxiety, depression, and other mental diseases Malignant neoplasm and expected lifetime <2 years Enrolled in other clinical trails within 6 months