Low- versus high-concentration iodine contrast media for coronary computed tomography angiography and dynamic stress computed tomography perfusion: a study protocol for a prospective randomized trial

BACKGROUND: This prospective randomized study protocol is designed to determine whether low-concentration iodine contrast media can maintain coronary enhancement on coronary computed tomography angiography (CCTA) compared with high-concentration iodine contrast media under standardized acquisition conditions. Dynamic stress computed tomography perfusion (CTP)-derived myocardial blood flow (MBF) will be assessed as a key secondary quantitative endpoint. Exploratory diagnostic performance analyses using invasive coronary angiography (ICA) and fractional flow reserve (FFR) will be performed only in clinically indicated invasive testing subgroups. METHODS: The trial plans to enroll 258 adults (age ≥ 40 years) with known or suspected coronary artery disease referred for clinically indicated cardiac computed tomography, including CCTA with planned dynamic stress CTP. Participants will be randomized 1:1 to receive low-concentration iodine contrast media (270 mg I/mL) or high-concentration iodine contrast media (350 mg I/mL). The primary endpoint is quantitative coronary enhancement on CCTA. Dynamic stress CTP-derived MBF will be evaluated as a key secondary endpoint focused on quantitative comparability. ICA/FFR-based diagnostic performance analyses will be considered prespecified exploratory analyses in participants who undergo invasive testing as part of routine clinical care. The primary endpoint will be analyzed using linear mixed-effects models with a prespecified noninferiority margin, and MBF will be analyzed using mixed-effects models without claiming formal equivalence or noninferiority. DISCUSSION: This study protocol is expected to clarify whether low-concentration iodine contrast media can maintain CCTA coronary enhancement and support quantitative dynamic stress CTP assessment while reducing iodine exposure. Because ICA and FFR are clinically driven rather than protocol mandated, diagnostic performance analyses will be interpreted cautiously and regarded as exploratory. TRIAL REGISTRATION: CRIS identifier: KCT0011418. Registered on January 7, 2026.