Diagnostic Accuracy for Hemodynamically ICAS of MR-FFR Comparing With Pressure-wire-based FFR.

Inclusion Criteria: 1. Patients aged 18 years or older. 2. Patients with transient ischemic attack (TIA) or nondisabling ischemic stroke caused by a focal ICAS lesion located in intracranial anterior circulation (intracranial internal carotid artery and their major branches). 3. 50% to 99% stenosis (calculated by modified WASID method) of responsible arterial occlusion, confirmed by digital subtraction angiography (DSA). 4. Informed of the study protocol and objectives. Exclusion Criteria: 1. Non-atherosclerotic MCA stenosis 2. Combined with moderate or severe stenosis of other extracranial and intracranial arteries 3. Previous endovascular treatment or surgery for cerebrovascular diseases 4. Large cerebral infarction (more than 1/2 MCA perfusion area) 5. Combined with other neurological diseases, such as aneurysm, arteriovenous malformation, tumor, hydrocephalus, cerebral trauma, cerebral hemorrhage, multiple sclerosis, epilepsy and intracranial infection. 6. Vascular abnormality or stunting, resulting in the impossibility of endovascular intervention 7. Liver and kidney dysfunction, or severe allergy to the contrast agent 8. Severe coagulation dysfunction 9. Pregnancy or in the preparation for pregnancy 10. Patients who cannot tolerate or do not allow MR screening, including metal implanting and claustrophobia 11. Patients with severe dementia or mental disorders, who cannot cooperate with examination