The Lipid-Rich Plaque Study

General Inclusion Criteria: * Subjects presenting for coronary angiography in whom IVUS imaging is likely to be performed for clinical purposes. * Greater than 18 years of age. * Clinical presenting symptoms meeting one of the three criteria below: 1. Subjects presenting with an acute coronary syndrome (ACS) including at least one of the following: 1. Elevated cardiac biomarkers with CK-MB or troponin greater than upper limits of normal; 2. ST depression or ST elevation \>1mm in 2 or more contiguous leads in the absence of LVH, paced rhythm, BBB or early repolarization; 3. A stabilized patient 24 to 72 hours post STEMI; 2. Unstable angina pectoris; 3. Stable angina pectoris and/or a positive functional study with evidence of ischemia. Angiographic Inclusion Criteria * At least one Suspected Index Culprit Lesion requiring imaging with IVUS and/or NIRS for clinical indications. * At least two native epicardial coronary arteries (which may include the Suspected Index Culprit Artery) eligible for imaging with NIRS-IVUS. IVUS/NIRS Imaging Inclusion Criterion * A minimum of a total 50 mm of coronary artery not involved in a prior or Index Procedure PCI (including the 5mm borders on either edge of the site receiving PCI) must be scanned. This 50mm total length may include contributions from the Suspected Index Culprit Arteries and from Index Non-Culprit Arteries. This total length must include contributions from two or more native imaged arteries. Exclusion Criteria: * Unstable patients (STEMI within the prior 24 hours; cardiogenic shock, hypotension needing inotropes, hypoxia needing intubation, and IABP) and patients that had a procedural complication (coronary dissection, perforation or a complication that would necessitate immediate-unplanned revascularization) during index PCI procedure. * History of CABG or planned CABG within 6 months following NIRS-IVUS imaging. * Patient has additional lesion(s) that needs a staged PCI. * Subject life expectancy is less than 2 years at time of index catheterization. * Subject with ejection fraction (EF) \<30%. * Subject pacemaker dependent/paced rhythm. * Subject pregnant and lactating. * Any other factor that the investigator feels would put the patient at increased risk or otherwise make the patient unsuitable for participation in the protocol * Patients undergoing performance of PCI in all three major vessels during the index PCI.