Coronary angiography has been considered the main method and standard for the diagnosis of coronary artery stenosis and is considered the “gold standard” for the diagnosis of coronary heart disease. However, coronary angiography has great limitations in evaluating the characteristics of the vessel wall and plaque: First, angiography can only reflect the contour of contrast filling in the vessel lumen, and when the degree of coronary stenosis is below 40%, the angiography cannot detect coronary artery abnormalities; second, because the lesions in the coronary arteries are often biased to one side of the lumen or have an irregular shape, the limitations of the angiographic projection also affect the assessment of the degree of stenosis. Third, the accuracy and reproducibility of coronary angiography have been questioned since the 1960s. However, coronary atherosclerosis is often diffuse, and the so-called “normal” reference vessel segment may not be the normal standard, and coronary angiography may underestimate the extent of the lesion. The extent of the lesion may be underestimated by coronary angiography. Furthermore, in the early stages of coronary artery disease, compensatory dilatation of the diseased vessel may occur, and coronary angiography may also underestimate the extent of the lesion at this time. In 1983, Marcus et al. developed a coronary artery Doppler catheter. In 1988, Hodgson, Pandian and Yock applied intracoronary Doppler catheters to show the detailed changes in arterial wall structure and atherosclerotic components and to reveal the deficiencies of angiography. 1990, Doucette et al. were the first to apply Doppler guidewires to measure coronary blood flow. The guidewire can be inserted into severely stenosed coronary arteries and can measure flow rates while interventional treatments are being performed. The clinical application of coronary ultrasound has opened up new ideas for interventional treatment, making traditional coronary angiography a great challenge. The main characteristics of vulnerable plaques include eccentric distribution, large lipid nuclei, thin fibrous cap, and positive vascular remodeling at the plaque site. Yamagishi et al. applied IVUS examination and found that eccentric plaques in the left anterior descending branch of the coronary artery have a greater dilatability, and the dilatability of each segment of the wall at the eccentric plaque varies, and the increase in local stress leads to plaque rupture. Histopathology has confirmed this view and found that rupture is mostly located at the junction between the eccentric plaque and the normal intima of the canal wall. In addition, the eccentric distribution of plaques predisposes to plaque fissure formation. ivus examination also revealed that plaques in patients with acute coronary syndrome contain large hypoechoic areas that are prone to rupture, with significant differences compared to plaques in patients with stable angina. ge et al. proposed intravascular ultrasound of vulnerable plaques after quantitative analysis of ruptured plaques in 114 patients with angina based on the results of the ivus study Quantitative indexes were proposed for lipid nuclei > 1 mm2, lipid nucleus/plaque ratio > 20% and fibrous cap thickness < 0.7 mm as susceptible to rupture. In 1987, Glagov first proposed the concept of vascular remodeling: as atherosclerosis progresses, the outer elastic membrane of the vessel expands outward to accommodate the plaque, at which time the lumen area can remain constant, and only when the plaque area is greater than 40% does the lumen become narrowed. Since then, the concept of positive remodeling has been further proposed by Losoodo et al. Fussl et al. applied the IVUS study to confirm that the remodeling index (RI) of soft plaques was significantly higher than that of fibrous and calcified plaques, and found that soft plaques were mainly positively remodeled, while the latter two were negatively or systerically remodeled. By multiple regression analysis of clinical data, coronary angiographic indexes and IVUS variables in patients with unstable angina, positive remodeling, minimum lumen area of pre-interventional IVUS and post-dilatation lumen diameter were found to be independent predictors of major cardiac events in patients with unstable angina. The above study demonstrates that intravascular ultrasound (IVUS) is capable of showing the size, composition and distribution of plaques, and has advantages in the diagnosis of plaque vulnerability that coronary angiography cannot match. Comparison of coronary ultrasound and coronary angiography in the evaluation of vascular entrapment Interventional treatment often produces vascular entrapment by squeezing or tearing the plaque by mechanical force or by forming an entrapment to enlarge the lumen. The criterion for coronary angiography to evaluate vascular entrapment is linear filling defect in the lumen or extravasation of contrast, whereas the criterion for IVUS to evaluate entrapment is the presence of an anechoic zone between the plaque and the middle layer, usually > 0.3 mm in width or the fluctuation of plaque with blood flow near the lumen and the presence of a traffic tear with the lumen, which can be confirmed by contrast injection. Therefore, when the contrast agent enters into the fragmented plaque or in the interstitial layer after the intervention, it creates the illusion of contrast filling the lumen and the result can often overestimate the effect of the intervention. Comparison of coronary ultrasound and coronary angiography in the evaluation of critical coronary artery disease A clinical study at the Chinese Union Medical College found that 400 patients with clinically pending or confirmed coronary artery disease were studied and intracoronary ultrasound (ICUS) was performed at the same time as coronary angiography. The results showed that 135 of the 400 patients had normal coronary angiograms, 91 men and 44 women, aged 31-77 years (55.5±11.1 years), whereas ICUS showed normal in 28 cases, intimal thickening in 38 cases, and the presence of plaques of different nature in 69 cases (51%), including 19 cases (14%) with ≥50% coronary stenosis, of which 6 cases had angina The clinical symptoms were significantly relieved after PTCA and stenting. In a study by Nishioka et al. 70 patients with only one coronary lesion were studied, and dynamic and static isotope myocardial perfusion imaging was used as a criterion for determining myocardial ischemia. The results showed that the sensitivity and specificity of coronary angiography for the diagnosis of myocardial ischemia were 49% and 90%, respectively, when a 75% internal diameter stenosis was used as the criterion for ischemia, and 96% and 52%, respectively, when a 50% internal diameter stenosis was used. Thus, the use of both imaging criteria for ischemia-related lesions was inaccurate and varied greatly; when IVUS results were analyzed, the sensitivity and specificity of using the minimum CSA 4 mm2 at the coronary lesion site as a criterion for ischemia was 88% and 90%, respectively, which greatly improved the accuracy of the diagnosis of ischemic lesions compared with imaging. In another study by Bech et al, 325 patients with critical lesions on coronary angiography were included, and those with FFR < 0.75 received intervention (reference group), while those with FFR > 0.75 were divided into two groups, with or without intervention (intervention and non-intervention groups). All patients were followed up for 24 months. The results showed that the 24-month event-free survival rates were similar in the intervention and non-intervention groups, and both were significantly higher than the reference group; the incidence of angina was also similar in the intervention and non-intervention groups, and both were significantly lower than the reference group. Therefore, for patients with critical lesions on coronary angiography, using FFR0.75 as the cut-off value can also be a good guide for clinical decision making. IVUS provides more complete information on vascular lesions than coronary angiography, thus providing a basis for determining critical lesions and guiding clinical decision making from a vascular physiology perspective. In addition to this, IVUS has been used to guide the staging of coronary X syndrome in patients with normal coronary angiography, and the presence of plaque can be detected in most of these patients when examined with IVUS. In the diagnosis of myocardial bridges, IVUS has a higher sensitivity, which can lead to a much higher rate of myocardial bridge diagnosis, as well as help to study the pathophysiological characteristics of myocardial bridges and guide the treatment of myocardial bridges. In conclusion, coronary ultrasound provides richer clinical information than coronary angiography in vulnerable plaque, vascular entrapment, and critical coronary artery disease, thus providing a better basis for studying the pathophysiological features of coronary artery disease and guiding clinical practice, and has been called the new “gold standard” for coronary artery disease.