Stroke is the first cause of death and disability among Chinese residents, and stroke screening and prevention is a major national health intervention project in China. With the aging of our society, the incidence of stroke is increasing, and early detection and intervention to achieve primary and secondary prevention will bring great economic and social benefits. Layer by layer analysis of ischemic stroke risk factors, carotid atherosclerosis is one of the main risk factors. Carotid artery intima is damaged by physical (hypertension, vasospasm, or chemical (smoking, hyperlipidemia, diabetes, etc.) factors, causing lipid infiltration and deposition in the damaged local vessel wall, and activating monocytes in the blood, smooth muscle cells in the arterial mesothelium, phagocytosis of lipid substances, and then focal thickening, which is covered with smooth muscle cells and some matrix secreted by them to form a fibrous cap, forming a plaque, thus leading to arterial These are closely related to ischemic stroke. For carotid artery stenosis caused by atherosclerotic plaque, early diagnosis and treatment are advocated in clinical practice. Ultrasound has the advantages of being dynamic, noninvasive, economical, convenient and reproducible compared with other imaging examinations, and can play an important role in the early diagnosis of carotid atherosclerotic disease by early detection. For those with intima-media thickening, plaque and lumen stenosis rate below 50% detected by ultrasonography, drug therapy is generally recommended to prevent and control further intima-media thickening, fix the plaque or make the plaque shrink or even disappear; for those with lumen stenosis rate above 50% and frequent transient ischemic attack (TIA), or lumen stenosis rate above 70%, carotid artery surgery should be performed. Carotid surgery should be performed in order to obtain good results of early treatment. Currently, there are several surgical options available in carotid surgery, including carotid endarterectomy (CEA), carotid stenting (CAS), and percutaneous transluminal angioplasty (PTA). The standardized application of ultrasound technology in the perioperative period can assist vascular surgeons to successfully complete preoperative evaluation, intraoperative monitoring, postoperative follow-up and other related tasks. With the rapid development of new ultrasound technology, ultrasound equipment has changed from single gray-scale imaging to a rich variety of imaging modes, including 1, two-dimensional ultrasound (2DUS,: to observe the vascular anatomy; 2, color Doppler flow imaging (CDFI,: to understand the blood flow in the lumen; 3, pulsed Doppler (PW,: to study the flow field characteristics and detect the hemodynamic parameters; 4, ultrasonography (CEUS) ): to study the microcirculatory perfusion characteristics; 5, three-dimensional ultrasound (3DUS): to observe the spatial three-dimensional structure; 6, elastic ultrasound (EI): to evaluate the degree of softness of the texture. The use of these advanced examination means can help clinicians enrich the ultrasonic diagnostic information of carotid surgical diseases and improve the diagnostic confidence. I. Application of ultrasound in preoperative evaluation of carotid surgery 1. Preoperative screening: Ultrasound plays an important role in preoperative patient screening and is the most sensitive method for examining carotid arteries in extracranial segments. Routine ultrasonography not only clearly shows the intima-media thickness (IMT), the site and extent of stenosis, and the nature of the plaque, but also can more accurately determine the degree of stenosis and the relationship with its adjacent structures. Studies have shown that the indication for carotid stenosis surgery is not only related to the degree of arterial stenosis due to atherosclerotic plaque, but also closely related to the pathology of the atherosclerotic plaque; unstable plaques (thin or ruptured fibrous cap, ulcer formation, more lipid components within the plaque, or bleeding) are more likely to produce symptoms than stable plaques; cortical or subcortical cerebral infarction is associated with microemboli formed in unstable plaques, and surface Plaques with ulcers are prone to accompany thrombus attachment, resulting in rapid plaque enlargement in the short term, lumen narrowing, and increased cerebral blood supply deficiency. Therefore, ultrasound examination of the size and echogenicity of the plaque is particularly important. The nature and degree of carotid artery stenosis determine the timing of surgery. Generally speaking, plaques with hypoechoic and mixed echogenicity dislodge or develop, easily leading to cerebral infarction, and should be treated surgically in time; smaller, softer hypoechoic atheromatous plaques have poor adhesion to the canal wall, easily dislodged and embolized, and should be surgically intervened in time. The nature of the plaque also determines the appropriate surgical approach. According to clinical experience, plaques with ulceration, bleeding or calcification are not suitable for PTA and CAS; while centripetal soft plaques have less complications for PTA; hard plaques with ulceration, bleeding and calcification are suitable for CEA. 3. Specific assessment indicators and clinical significance: 1. IMT thickening: It is the initial manifestation of atherosclerotic plaque, which thickens with age and is also the trend of early plaque formation. Studies have shown that IMT can be used as an indicator for clinical evaluation of cardiovascular disease risk, but there are geographical and racial differences, and a normal IMT ≥ 1.0 mm is used as an abnormal criterion. Measurement should be noted: 1. Measurement site: measure the common carotid artery, internal carotid artery and carotid bulge respectively, and try to measure the IMT of the posterior wall. 2. The vessel wall of non-carotid plaque should be measured. 2.Plaque formation: Generally, IMT thickness greater than or equal to 1.5mm and protruding into the lumen is defined as plaque, but some scholars believe that if the thickness of the protrusion is more than 2 times of the surrounding normal IMT, it can also be considered as plaque formation, even if the thickness does not exceed 1.5mm. Plaque is divided into flat plaque, soft plaque, hard plaque and composite plaque (including calcification, ulceration, plaque bleeding, thrombosis, etc.) according to the echogenic characteristics; according to Homogeneity is divided into homogeneous plaque, inhomogeneous plaque; regular plaque (circular thickening, continuous and smooth intima, irregular plaque (eccentric thickening, discontinuous intima, uneven surface, including ulcerated plaque,) by regular shape; stable and unstable plaque by whether the plaque is stable or not. However, each classification criterion is not isolated, and there can be multiple classification names for the same plaque, for example, unstable soft plaque with uneven echogenicity and irregular morphology is seen in the inner wall of carotid artery. Two-dimensional gray-scale ultrasound can measure the length and thickness of plaque, and the trajectory method short-axis section can measure the lumen cross-sectional area at the plaque (calculate the area stenosis percentage,); color Doppler flow imaging (CDFI) shows that the plaque area is filled with blood flow signal defect. 3.Stability of atherosclerotic plaque: Neovascularization in the plaque is one of the factors of plaque instability. These neovascularization can aggravate the inflammatory reaction within the plaque, and these vessels lack the outer membrane of the vessel wall, which can easily rupture and bleed under the action of external force, causing a dramatic increase in plaque volume and finally leading to the rupture of the plaque. The existing studies have confirmed that CEUS can show the neovascularization in plaque in addition to the blood flow in the lumen, and CEUS shows that the neovascularization appears as dotted or thin strips of enhanced signal, and the neovascularization grows from the outer membrane and the lumen into the plaque, most of which comes from the outer membrane, and the neovascularization in the shoulder of the plaque is more than that in the body. Neovascularization was almost always seen in soft plaques, while neovascularization was less in strongly echogenic hard plaques. It has been reported in the literature that neovascularization within soft plaques of carotid arteries is significantly more in patients with cerebral infarction than in those without cerebral infarction, and the detection rate of neovascularization within unstable plaques can be significantly improved by CEUS. 4. Plaque volume or stenosis lumen volume: Intraluminal plaques can be single or multiple, and 2D ultrasound can only measure their area, but intraluminal plaques are three-dimensional structures that develop asymmetrically, and the area obtained using 2D ultrasound will underestimate or overestimate the actual size of the plaque. Using the existing three-dimensional ultrasound (3DUS, reconstruction technique, the luminal stenosis volume and plaque volume can be calculated, thus providing a more objective and realistic description of the size of the plaque and the degree of luminal stenosis. In addition, although ordinary CEUS can show the neovascularization within the plaque, each imaging can only understand the neovascularization in one section of the plaque, but not the distribution of neovascularization within the whole plaque. If the CEUS combined with 3DUS technology is used, it can show the overall distribution of neovascularization in the plaque more objectively. 5.Lumen stenosis degree: It is an important index to decide whether to operate or not and the specific operation method. The degree of stenosis on gray-scale ultrasound is graded by calculating the % internal diameter stenosis and % area stenosis: normal; < 50%; 50-69%; ≥ 70% but not close to occlusion; close to occlusion; occlusion. 2.The degree of stenosis on CDFI is graded by showing the presence or absence of turbulent flow at the stenosis: mild stenosis <50%, cdfi shows similar flow to normal lumen; stenosis >50%, turbulent floral flow signal is seen at the stenosis. 3, Degree of stenosis on PW, graded by quantitative determination of hemodynamic parameters: a, Grade I Normal pvs<125cm/s, no plaque and IMT thickening, ICA/CCA peak systolic flow velocity <2.0 b, Grade II <50% pvs>125cm/s, visible plaque or IMT thickening, ICA/CCA peak systolic flow velocity <2.0, systolic band normal or widened c. Grade III 50-69% PVS at 125-230cm/s, significant plaque, ICA/CCA peak systolic flow velocity at 2.0-4.0, end-diastolic flow velocity at 40-100cm/s d. Grade IV ≥70% but not close to occlusion PVS ≥230cm/s, significant plaque visible, with luminal stenosis, the higher the PVS the more severe the stenosis, The higher the PVS, the more severe the stenosis, ICA/CCA peak systolic flow velocity >4.0, end-diastolic flow velocity >100cm/s. The PVS of the blood flow before stenosis is reduced, while the blood flow after stenosis is turbulent, and the PVS is also significantly increased. e. Grade V Near occlusion Hemodynamic parameters are not used for diagnosis, the flow velocity near occlusion may not be detected, and the diagnosis mainly relies on color Doppler, a fibrous blood flow is seen at the point near occlusion through the lumen near occlusion. Because gray-scale ultrasound does not detect the lumen, color Doppler does not detect significant flow signals. Because gray-scale ultrasound is difficult to show the small lumen in grade V near occlusion, it is often impossible to distinguish from grade VI complete occlusion, and the correct diagnosis of carotid lumen occlusion is directly related to the choice of treatment plan. For example, non-occlusion or incomplete occlusion can be selected with endarterectomy and stent placement. Therefore, it is especially important to use CDFI during the examination, which can show the flow signal in the tiny lumen left by incomplete occlusion, but CEUS can further improve the accuracy and sensitivity of diagnosis by enhancing the contrast image with contrast agent. The application of ultrasound monitoring in carotid surgery Ultrasound monitoring is applied during CEA to observe whether there is intimal separation and live flap formation at the end of endarterectomy, and to understand the scope of endarterectomy (length and depth) to avoid under resection or over resection; ultrasound monitoring is applied during CAS to understand the site, scope, and fixation of the built-in stent in order to make timely adjustment and ensure the success of surgery. A retrospective analysis of post-operative deaths after CEA was conducted, and it was found that the cause of death was the formation of a live flap by intimal peeling of the artery after surgery, which caused blockage of the internal carotid artery, resulting in acute ischemia of one side of the brain and large cerebral infarction. Therefore, during surgery, before the suturing of the vessel is completed, ultrasound examination should be performed to observe whether the endothelium separates from the vessel wall and forms a live valve, so as to prompt the operator to take timely measures to avoid the above-mentioned serious complications that endanger the patient’s life. Third, the application of ultrasound in postoperative follow-up of carotid surgery All along, the clinical evaluation of the efficacy of carotid surgery is often based on whether the patient’s symptoms are reduced and whether the limb function is restored, which is highly subjective and cannot be objectively evaluated. The in-depth application of ultrasound technology can play an objective evaluation role in the postoperative efficacy follow-up. 1.Evaluate the endoscopic resected end of CEA, lumen internal diameter and patency; observe the site, scope and fixation of the built-in stent after CAS (whether there are complications such as distortion, destruction, collapse, etc.); understand the improvement of the stenotic lumen (blood flow filling degree, hemodynamic changes. 2. Prevention of postoperative complications. Postoperative ultrasound can detect early local appendage thrombus and the presence or absence of slowed blood flow; sensitive detection of intimal structural changes in the carotid artery to prevent restenosis. 3.Simultaneous observation of whether there is thrombus formation in the internal carotid vein after surgery, and the application of elastic ultrasound to quantitatively evaluate the softness and hardness of the thrombus formed in different parts of the lumen, in order to guide the thrombolytic treatment in different periods. Carotid ultrasonography plays an important role in the perioperative period of carotid surgical diseases, but its application still has certain limitations, such as the limited spatial resolution and contrast resolution of ultrasound images compared with DSA and MRA; the display and judgment of ultrasound images can be affected by the operator’s skill and clinical experience. Especially when the carotid bifurcation is located too high, the subject is obese with a thick and short neck, and the blood vessel is congenitally abnormal or anatomically variant, it increases the difficulty of ultrasound examination. With the continuous development and improvement of new ultrasound techniques, the combined use of CDFI, CEUS, 3DUS and other new ultrasound techniques should be emphasized in the future, so that carotid ultrasound can play a greater role in vascular surgery applications.