The purpose of this multiple-center study are: 1) To establish the ultrasound criteria for evaluating vulnerable plaques by comparing the plaque echo characteristics before CEA (carotid artery endarterectomy) and plaque specimen after CEA.

2) To establish the carotid artery recanalization strategies based on the evaluation results of carotid artery and intracranial artery by color doppler flow imaging and TCCS/TCD (transcranial color coded sonography/transcranial doppler).

3) To compare the success rate and the incidence of restenosis between CEA and carotid artery stenting.

In this study, a total of 1000-1200 patients with carotid artery moderate (50-69%, with symptoms), severe (70-99%) stenosis (with or without symptoms) or occlusion who received either CEA or stenting are to recruited. Before carotid artery recanalization, CDFI (color duplex flow imaging) and TCCS/TCD are used to evaluate the structures and hemodynamic of carotid artery and intracranial artery. In addition, patients are to be followed up by ultrasound 1 week, 3 month, 6month and 1 year after recanalization.

1. Ultrasound examinations procedures: According to the guidelines of vascular ultrasonography published by the Stroke Prevention Engineering Committee, the National Health Commission of China in 2015. The plaque characteristics, stenosis degrees of carotid artery and intracranial arteries, and collateral circulation are evaluated by CDFI and TCCS/TCD.
2. Radiology examination procedures: Before recanalization, enrolled patients receive MRI examinations to determine the presence and the location of cerebral infarction. If necessary, patients receive CT angiography (CTA) , MRI angiography (MRA) or Digital subtraction angiography (DSA) to confirm the degrees of vessel stenosis and occlusion. One week after recanalization, CT and MRI are used to identify the cerebral hemorrhage and newly cerebral infarction.
3. The data collected in this study including:

1) The general information of enrolled subjects, which include age, gender, resident address and telephone number, the history of hypertension, coronary artery diseases, dyslipidemia, diabetes mellitus and smoking.

2. The primary endpoints are: The combination endpoints events of death, cerebral hemorrhage , newly cerebral infarction, hyperperfusion syndrome, residual sternosis≥50% within 30-day after recanalization. The secondary endpoints are the re-current cerebral artery events and the occurence of restenosis during the at least 1 year follow-up period.

4. Statistical analysis plans: The Statistical Package of Social Sciences (SPSS version 22.0) software are used for statistical analysis.

1) Diagnostic test are used to test the sensitivity, specificity and accuracy of ultrasound for evaluating vulnerable plaque by using plaque specimen after CEA as the "gold" standard.

2) The Chi-square test are used to compare the success rate of stenting and CEA. The Cox regression analysis are used to compare the restenosis rate of stenting and CEA.

3) A P<0.05 was considered statistically significance. 5. Quality assurance plan:

1. The medical centers implement the projects are the stroke center awarded by the Stroke Prevention Engineering Committee, the National Health Commission of China. The medical centers have the instruments required in this study.
2. Neurologists, neurosurgeons and vascular ultrasound physicians have received standard training hosted by the Stroke Prevention Engineering Committee, the National Health Commission of China and obtained excellent records.
3. All the centers conduct the project followed the uniform implementation plans and each center guarantee the data input in time and accurately.
4. The project has the unique database and data input in uniform format.
5. There are specific staffs to check the accuracy and completeness of data.

Inclusion Criteria:

• 1) Patients with carotid artery moderate (50-69%, with symptoms), severe (70-99%, with or without symptoms) stenosis or occlusion diagnosed by CDFI and confirmed by CTA or DSA.

  2) Patient has the indications for carotid artery stenting or CEA according to the guidelines published by the Stroke Prevention Engineering Committee, the National Health Commission of China.

  3) Patient with complete imaging evaluation and can be followed up to at least 1 year.

Exclusion Criteria:

- 1) Patients with non-atherosclerotic carotid artery stenosis or occlusion, such as dissection, aneurysm, arteritis, cardiac embolism and et al.

2) Patients with cerebral hemorrhage. 3) Pregnant

Patients with carotid artery moderate (50-69%), severe (70-99%) stenosis or occlusion, who needs recanalization by CEA or stenting.