1.Doppler-ultrasound examination Doppler-ultrasound examination is an organic combination of Doppler flow measurement and real-time imaging of ultrasound, which is the preferred non-invasive means of carotid artery examination at present, with the characteristics of simplicity, safety and low cost. It can not only display the anatomical image of carotid artery and perform morphological examination of plaque, such as distinguishing intraplaque hemorrhage from plaque ulcer, but also display arterial blood flow, flow rate, flow direction and intra-arterial thrombus. With an accuracy of over 95% in diagnosing the degree of carotid stenosis, Doppler-ultrasound has been widely used in the screening and follow-up of carotid stenotic lesions. The shortcomings of ultrasonography include: (1) it cannot detect intracranial carotid artery lesions; (2) the results are easily influenced by the operator’s skill level. 2.Magnetic resonance angiography Magnetic resonance angiography (MRA) is a non-invasive vascular imaging technique, which can clearly display the three-dimensional morphology and structure of the carotid artery and its branches, and can reconstruct the intracranial arterial images. The carotid vessels have a linear profile and are particularly suitable for MRA, which can accurately visualize thrombotic plaques, the presence or absence of clotted aneurysms and intracranial arteries, and is extremely helpful for diagnosis and protocol determination. The prominent disadvantage of MRA is that slow or complex flow often results in signal loss and exaggerated stenosis. It also has limitations in showing sclerotic plaques. MRA is contraindicated in patients with metal retention (e.g., metal stents, pacemakers, or metal prostheses). 3.CT angiography CT angiography (CTA) is a non-invasive angiographic technique developed on the basis of spiral CT. The method is to inject contrast agent through the blood vessels, and perform volume scanning when the concentration of contrast agent in the circulating blood or in the target vessel reaches its peak, and then process it to obtain digital stereoscopic images. CTA is suitable for carotid arteries in the extracranial segment, mainly because the carotid artery course is perpendicular to the CT section, thus avoiding the disadvantage of relatively insufficient resolution for vessels with horizontal course during spiral CT scanning. the advantage of CTA can directly show calcified plaques. At present, 3D revascularization generally uses surface shaded display (SSD) and maximum intensity projection (MIP); MIP reconstructed images can obtain angiography-like images and show calcification and attached thrombus, but the 3D spatial relationship is not as good as that of SDD; however, SDD cannot directly show density differences. CTA technique has been used more often in the diagnosis of carotid artery stenosis, but the technique is not mature enough and needs to be improved by further accumulation of experience. 4.Digital subtraction angiography At present, although non-invasive imaging means have been more and more widely used in the diagnosis of carotid artery lesions, each method has definite advantages and disadvantages. High-resolution MRA, CTA, and Doppler-ultrasound imaging are of great value for initial diagnosis and follow-up. Although angiography is no longer used for screening, primary diagnosis and follow-up, digital subtraction angiography (DSA) remains the “gold standard” for the diagnosis of carotid artery stenosis in terms of accurate evaluation of lesions and determination of treatment options. DSA can provide detailed information about the location, extent and degree of the lesion and the formation of side branches; help determine the nature of the lesion such as ulcers, calcified lesions and thrombosis; and understand coexisting vascular lesions such as aneurysms and vascular malformations. Aneurysms, vascular malformations, etc. Arteriography can provide the most valuable imaging basis for surgical and interventional treatment. Arteriography is an invasive and expensive test, and the literature reports a complication rate of 0.3% to 7%. The main complications are cerebral vasospasm, dislodgement of plaque causing stroke, cerebral embolism and contrast allergy. Renal impairment, vascular injury and hematoma at the puncture site, pseudoaneurysm, etc. 5.Measurement methods of carotid stenosis Although non-invasive examinations such as ultrasound, computerized tomography (CT), and magnetic resonance imaging (MRI) are increasingly useful in the diagnosis of carotid stenosis, arteriography is still the However, arteriography is still the “gold standard” for the diagnosis of carotid stenosis. The determination of the degree of carotid artery stenosis is based on arteriography results. Different research departments have used different measurement methods, and there are 2 common measurement methods used internationally, namely the North American Symptomatic Carotid Endarterectomy Trial Collaborators (NASCET) criteria and the European Carotid Surgery Trial collaborators Group (ECST) criteria. NASCET stenosis = (1 – narrowest internal carotid artery flow width / normal internal carotid artery diameter distal to the stenosis) × 100% ECST stenosis = (1 – narrowest internal carotid artery flow width / simulated internal diameter of the enlarged internal carotid artery) × 100% Both methods classify the degree of internal carotid artery stenosis into 4 grades: ① mild stenosis, <30% reduction in the internal diameter of the artery; ② moderate stenosis, 30% to 30% reduction in the internal diameter of the artery. (2) moderate stenosis, where the internal diameter of the artery is reduced by 30% to 69%; (3) severe stenosis, where the internal diameter of the artery is reduced by 70% to 99%; and (4) complete occlusion.