Optimizing coronary CT angiography in patients with delayed contrast arrival using a free-breathing, high-threshold bolus-tracking protocol.

OBJECTIVE: To investigate the performance of a free-breathing coronary computed tomography angiography (CCTA) protocol using a high-threshold bolus-tracking strategy in improving coronary enhancement and diagnostic visualization in patients with delayed contrast arrival. MATERIALS AND METHODS: In this prospective study, 159 patients undergoing CCTA were randomized to either a conventional bolus-tracking protocol (breath-hold, 100 HU trigger threshold, 6.8 s delay) or a modified high-threshold protocol (free-breathing, 300 HU trigger threshold, 2 s delay). Patients were stratified according to contrast arrival time (Tarr) into normal and delayed contrast arrival groups using a predefined operational cutoff (15 s), resulting in four subgroups. Coronary attenuation, enhancement uniformity as assessed by the coefficient of variation (COV), enhancement phase distribution, and image quality scores were compared among groups. RESULTS: Under the conventional protocol, patients with delayed contrast arrival demonstrated reduced enhancement uniformity and a higher proportion of late-phase acquisitions. Compared with the conventional protocol, the modified protocol significantly increased coronary attenuation and improved enhancement uniformity (COV: 11.28% vs 16.73%, p < 0.001), as well as the proportion of segments with excellent image quality in patients with delayed contrast arrival (94.2% vs 86.8%, p = 0.004). In this subgroup, the modified protocol yielded more optimal-phase scans (19.4% vs 9.4%) and fewer late-phase acquisitions (32.3% vs 65.6%). Visual quality scores and quantitative metrics were consistently higher with the modified protocol across all major coronary arteries (all p < 0.001). CONCLUSION: The free-breathing, high-threshold bolus-tracking CCTA protocol improves enhancement uniformity and facilitates optimal scan-phase acquisition in patients with delayed contrast arrival, providing a more reliable and patient-tolerant alternative to conventional breath-hold protocols. KEY POINTS: Question Can a free-breathing high-threshold bolus-tracking strategy improve coronary enhancement timing and image quality in CCTA patients with delayed contrast arrival? Findings The modified protocol increased optimal-phase acquisitions, improved coronary enhancement uniformity, and maintained diagnostic image quality in patients with delayed contrast transit. Critical relevance statement A free-breathing high-threshold bolus-tracking strategy may improve acquisition robustness and enhancement consistency in patients with unpredictable contrast transit, potentially expanding the clinical applicability of CCTA in individuals with impaired breath-hold capacity or delayed circulation dynamics.