When coronary angiography is performed, if the coronary artery stenosis exceeds 70%, direct stent implantation treatment is possible. It is now believed that if the stenosis of the coronary arteries exceeds 70%, it can cause clear ischemic symptoms that can lead to angina attacks during emotional stress and exercise, and severe coronary stenosis can increase the likelihood of acute myocardial infarction. In some patients with clear symptoms of unstable angina, but the stenosis does not exceed 70% during coronary angiography, intravascular ultrasound can be performed to assess plaque stability. Although the stenosis does not reach the level of stenting at this time, the patient may have acute myocardial infarction or other diseases at any time because of the unstable plaque, and stenting is also needed.