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: