Brief Summary: Intracranial atherosclerotic disease (ICAD) is an important cause of ischemic stroke. The occurrence of stroke caused by symptomatic ICAD is significantly different compared with asymptomatic ICAD (19% vs 3.5%), suggesting that plaque vulnerability may be responsible for the difference. Based on the previous high-resolution magnetic resonance vessel wall imaging (HR-MRI) results, the investigators hypothesis that the feature of intracranial plaque enhancement is an important imaging biomarker of plaque instability, which is closely related to stroke. The investigators will establish the ICAD cohort and use HR-MRI to investigate the composition, morphology and the enhancement pattern of symptomatic ICAD plaques. These findings will correlate with biochemical markers, and stroke recurrence, in order to explore: 1. plaque characteristics and the enhancement features between symptomatic ICAD and asymptomatic ICAD 2. the relationship between plaque enhancement and the composition of plaques; 3. relationship among enhancement features of symptomatic ICAD plaques, biomarkers with different clinical significance, 4. evolution of enhancement features of symptomatic ICAD plaques under intensive medical therapy. The investigators aim to explore the correlation between vulnerable plaque stratification and clinical outcomes, to explore the value of vascular responses in the pathogenicity of ICAD vulnerable plaques, as well as to provide objective basis for the establishment of the evaluation criteria of intracranial atherosclerotic vulnerable plaques.