New ultrasound tool could spare heart attack patients a second procedure

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age \>18 years, any sex. * The participant is able to understand the study procedures and provides voluntary written informed consent. * Diagnosed with Acute Coronary Syndrome (ACS) and meets the criteria for one of the two pre-specified cohorts: * STEMI Cohort: Symptom onset \< 12 hours with ECG findings of ST-segment elevation myocardial infarction. * High-Risk NSTEMI Cohort: Meets at least one of the following: GRACE score \> 140, dynamic ECG changes (ST-T), or significant Troponin elevation. * Has undergone successful emergency PCI of the Culprit Vessel (CV), with post-PCI TIMI flow Grade 3. * Coronary angiography confirms Multi-vessel Disease (MVD), defined as: at least one Non-Culprit Vessel (NCV) with a moderate stenosis (visual diameter stenosis 50-90%). * The target NCV (50-90% stenosis) is deemed by the investigator to be anatomically suitable for IVUS and pressure-wire assessment. * The participant agrees and is confirmed to be willing and able to strictly adhere to the protocol and complete all required invasive procedures, CMR scans, and follow-ups at the four timepoints (T0, T-CMR, T1, T2). Exclusion Criteria: * Presence of cardiogenic shock on presentation, or persistent hemodynamic instability despite successful PCI of the culprit vessel. * Known severe allergy to iodinated contrast media or gadolinium-based contrast agents (used for CMR). * Female participants who are pregnant, breastfeeding, or planning pregnancy within the 1-year study period.Unprotected left main coronary artery disease (stenosis \<50%) requiring intervention. * Prior history of Coronary Artery Bypass Grafting (CABG) surgery.The target NCV has received prior PCI (e.g., existing stent) or surgical revascularization. * The target NCV is a Chronic Total Occlusion (CTO). * Severe renal insufficiency (eGFR \< 30 ml/min/1.73m²) or currently undergoing chronic dialysis. * Standard contraindications to CMR examination (e.g., claustrophobia, non-MRI-compatible metallic implants/pacemakers). * Known presence of a severe non-cardiac comorbidity with an expected lifespan of \< 12 months (e.g., advanced malignancy). * Known severe hematological disease (e.g., severe anemia, active bleeding, thrombocytopenia \< 70 x 10⁹/L) rendering the participant unsuitable for multiple invasive procedures. * Inability to provide informed consent or comply with the complex longitudinal follow-up protocol due to psychiatric, cognitive, or other reasons. * Currently participating in another interventional (drug or device) clinical study. * Any other condition which, in the investigator's opinion, makes the participant unsuitable for enrollment (e.g., severe valvular heart disease, cardiomyopathy).