This study evaluates the diagnostic accuracy and limitations of photon-counting computed tomography (PCCT) in characterizing coronary plaque, with comparisons to optical coherence tomography (OCT) and intravascular ultrasound (IVUS). The objective is to assess whether cardiac ultra-high resolution (UHR) PCCT -with its improved spatial resolution and superior soft tissue contrast relative to conventional CT- can serve as a reliable, non-invasive alternative for coronary plaque assessment and support clinical decision-making. A total of 100 patients with either acute or chronic coronary syndrome will be enrolled, including 40 individuals with suspected in-stent restenosis and 10 patients one year post-percutaneous coronary intervention (PCI) for chronic total occlusion (CTO). All participants will undergo invasive coronary angiography based on current European Society of Cardiology guidelines. Cardiac PCCT imaging will be conducted shortly before the angiographic procedure, accompanied by invasive OCT evaluation. Additionally, a subgroup of 10 patients will undergo both OCT and IVUS, allowing for direct comparison across imaging modalities. OCT, regarded as the gold standard for plaque characterization, offers near-histological resolution for identifying plaque features, while IVUS is particularly effective in evaluating plaque burden and volume.

Inclusion criteria:

Participants eligible for inclusion in this study must meet all of the following criteria:

1. Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures.
2. At least 18 years of age at the time of signing the Informed Consent Form (ICF).
3. Patients presenting with suspected acute coronary syndrome (UA or NSTEMI) or chronic coronary syndrome (stable angina or silent ischemia).

Exclusion criteria:

Participants eligible for this study must not meet any of the following criteria:

1. Patients presenting with STEMI.
2. Haemodynamically unstable patients.
3. Unstable ventricular arrhythmias.
4. Killip class III-IV heart failure.
5. Creatinine clearance <30 ml/min/1.73 m2 (as calculated by CKD-EPI formula 2009 for estimated GFR) and not on dialysis. Note: patients dependent on long-term dialysis are eligible for enrolment irrespective of their creatinine clearance levels.
6. Severe coronary vessel tortuosity.
7. Subject has known hypersensitivity to radiocontrast dye or that cannot be adequately pre-medicated.
8. Female who is pregnant or breast-feeding.

The study aims to enrol 100 patients with acute or chronic coronary syndrome, including 40 participants with suspected in-stent restenosis and 10 participants one year after a CTO PCI.