The study is to attain early recognition of the unstable plaques which have an imminent embolic risk in patients with intracranial atherosclerotic disease (IAD).

Potential candidates will undergo a cranial MRI and MR angiography. Patients who are found signal void in a relevant intracranial internal carotid artery or middle cerebral artery will proceed to a 30-minute TCD monitoring for MES an angiograms will be analyzed by investigators blind to subjects' clinical information. All recruited patients will receive standard medical therapy throughout the investigation period.

Inclusion Criteria:

• Inclusion Criteria for the Symptomatic Group:

  1. Patient is 30 to 85 years of age, inclusive.
  2. Patients who have an acute infarct in diffusion-weighted MRI compatible with artery-to-artery thrombo-embolism, a relevant intracranial atherosclerotic stenosis ≥60%, and MES detected by TCD.
  3. Patient who has no contra-indication for the proposed imaging tests.
  4. Patient understands the purpose and requirements of the study, and has provided an informed consent.

• Inclusion Criteria for the Asymptomatic Group:

  1. Patient is 30 to 85 years of age, inclusive.
  2. Patient who has a high-grade (>60%) intracranial stenosis (signal void in MR angiography) but without infarct in the corresponding vascular territory in DWI or T2-weighted sequence.
  3. Patient has no MES detected on TCD examination.
  4. Patient who has no contra-indication for the proposed imaging tests.
  5. Patient understands the purpose and requirements of the study, and has provided an informed consent.

Exclusion Criteria:

Subject who meets one or more of the following criteria cannot be recruited in the study:

1. Stroke etiology uncertain or unrelated to intracranial atherosclerosis, such as cardioembolism, Moyamoya disease, small vessel disease, etc.
2. A tandem stenosis >50% at proximal internal carotid artery.
3. Bleeding propensity: active peptic ulcer disease, major systemic hemorrhage within 30 days, thrombocytopenia (platelets <100 x 109/L), coagulopathy (INR >1.5).
4. A medical condition that would not allow the patient to adhere to the protocol or complete the study.

Patients who admitted to Prince of Wales Hospital for acute stroke will be screened for eligibility.