Continuous anatomical radiation modulation for the acquisition of coronary computed tomography angiography in difficult to scan patients: a prospective cohort study.

BACKGROUND: A novel continuous anatomically modulated (CAM) retrospectively-gated scan mode for coronary computed tomography angiography (CCTA) modulates tube current as a function of patient anatomy, offering potential for good image quality (IQ) and radiation dose reduction in patients undergoing CCTA on a traditional scanner with significant ectopy (SE) or high heart rate (HHR) who are not candidates for prospectively-triggered scanning. We evaluated the effect of CAM on IQ and radiation dose in a large group of patients. METHODS: Three hundred and twenty consecutive patients at a single center (Advanced Cardiovascular Imaging, New York, NY) undergoing CCTA were prospectively protocoled by clinicians to CAM retrospectively-gated scanning if they had SE/HHR or prospectively-triggered scanning if they had regular heart rates. IQ was graded on a 5-point scale by two readers and radiation dose-length product (DLP) evaluated. Radiation exposure was assessed using DLP, with effective dose estimated using a cardiac-specific conversion factor. Associations between patient weight and radiation dose were evaluated using log-linear regression models. RESULTS: Of 320 patients, 166 (52%) were assigned to prospective triggering (PT) and 154 (48%) to continuous anatomically modulated retrospectively gated (CAM RG). Patients in the CAM RG group had higher heart rates throughout the scanning process. Mean DLP was higher in the CAM RG group compared with the PT group (411.6±308.9 vs. 324.0±208.4 mGy·cm; P=0.03), corresponding to effective doses of 10.7±8.0 vs. 8.4±5.4 mSv, respectively. Despite these differences, IQ remained high across all groups, with mean composite scores exceeding 4.5. When diagnostic quality was defined as an overall IQ score ≥4, the proportion of diagnostic-quality studies did not differ significantly between groups (92.8% vs. 89.6%, P=0.42). In adjusted logistic regression models, scan protocol was not independently associated with diagnostic-quality imaging. Patient weight demonstrated a strong association with radiation dose, with DLP increasing by approximately 13-16% per 10-lb increase in weight, independent of scan protocol. CONCLUSIONS: On a standard single-source CT scanner, CAM-based retrospectively gated CCTA provides consistently diagnostic IQ in patients with more challenging heart rate profiles, at the cost of modestly higher radiation exposure that is largely driven by patient size. CAM RG represents a practical, software-based acquisition strategy for centers without advanced CT hardware, enabling effective imaging of complex patients while maintaining acceptable radiation dose.