Coronary artery disease (CAD) is the leading cause of mortality and morbidity worldwide. Coronary Computed Tomography angiography (CCTA) gained a pivotal clinical role for excellent sensitivity in rule-out CAD, but has limited specificity for a tendency to overestimate stenoses and for the lack of information about their hemodynamic impact. Fractional Flow Reserve derived from CT (FFR-CT) and stress CT perfusion (CTP) have been recently proposed to complement CCTA in the non-invasive assessment of myocardial ischemia, increasing the specificity and avoiding unnecessary catheterization. However, on energy-integrating (EID)-CT, FFR-CT has suboptimal performance, while CTP is affected by high radiation exposure. Both these approaches may benefit by the introduction of the new Photon Counting Detector (PCD)-CT technology, but data completely lacks. Aim of the study is to assess the performance of PCD-CT in the identification of significant CAD combining CCTA with FFR-CT and spectral CTP.

Inclusion Criteria:

• Patient referred to our hospitals for elective CCTA for ruling out CAD
• CCTA evidence of moderate stenosis (50-69%) requiring functional assessment according to ESC guidelines

Exclusion Criteria:

• hemodynamically unstable conditions,
• previous revascularization,
• myocardial infarction,
• obesity (BMI>40 kg/m2),
• renal insufficiency (GFR<30 mL/min),
• atrial fibrillation or other significant arrhythmias; and
• other overt cardiovascular diseases affecting CTP performance (e.g., heart failure, severe valvular regurgitation),
• pregnancy and breastfeeding,
• contraindications to iodinated contrast agents or regadenoson.

142 patients (age>18 years old) referred to our hospitals for elective CCTA for ruling out CAD and CCTA evidence of moderate stenosis (50-69%) requiring functional assessment according to ESC guidelines (1) because is known that not all anatomical stenosis in the range of moderate (50-69%) are haemodynamically significant (2) or induce myocardial ischaemia (3).