Plaque stability is an important criterion for selecting different treatment strategies (interventional and antithrombotic). High-risk plaque characteristics are also considered to be related to the overall incidence of Major Adverse Cardiovascular Events (MACE). Single-modality intravascular imaging has inherent disadvantages in identifying atherosclerotic plaques, while the combination of IVUS, OCT, and NIRS enables multimodal intravascular imaging techniques to complement each other in obtaining plaque information. There is currently a lack of research on the prognostic benefits of multimodal intravascular imaging in assessing atherosclerotic plaques. This study is a multicenter, prospective, observational clinical study that will be conducted at 11 hospitals, enrolling approximately 500 subjects. It will use intravascular ultrasound (IVUS) and optical coherence tomography-near-infrared spectroscopy (OCT) to assess the morphology and stability of non-culprit lesions in patients with acute coronary syndrome (ACS) after percutaneous coronary intervention (PCI), and will follow up at 1 month, 1 year, 2 years, and 5 years post-surgery. The aim is to compare the clinical outcomes between high-risk and non-high-risk patients, as well as between high-risk and non-high-risk plaques defined by multimodal intravascular imaging, and to explore the predictive value of high-risk plaque characteristics shown by multimodal intravascular imaging for adverse cardiovascular events in patients with ACS.