Radiation dose of coronary CT angiography with a third-generation dual-source CT in a "real-world" patient population.

OBJECTIVES: To assess radiation dose and image quality of coronary computed tomography angiography (cCTA) with a third-generation dual-source scanner in a real-world patient population.

METHODS: Scans of otherwise unselected, consecutive patients referred for clinically indicated cCTA between June 2015 and November 2017 were included for retrospective analysis. Scan protocol was based on heart rate: prospectively ECG-gated high-pitch spiral below 60 beats per minute (bpm), prospectively ECG-gated sequential scan between 61 and 70 bpm, and retrospective spiral above 70 bmp or at irregular heart rates. Objective image quality was measured as signal-to-noise (SNR) and contrast-to-noise ratio (CNR); subjective image quality was evaluated using a five-point Likert scale by two independent readers. For radiation dose analysis, effective dose, size-specific dose estimates, and volume CT dose index were assessed.

RESULTS: Two hundred seventy-eight patients (median age, 60 years; 155 men) with a median body mass index of 26.6 kg/m2 (range, 16.7-60.9 kg/m2 ; 180 (64.7%) overweight or obese) were included (122 in the high-pitch spiral group, 60 in the prospective sequence group, and 96 in the retrospective spiral group). Median effective dose was 0.63 mSv (interquartile range [IQR], 0.51-0.90 mSv) for high-pitch spiral, 1.32 mSv (IQR, 0.79-2.46 mSv) for prospective sequence, and 4.77 (IQR, 3.02-8.27 mSv) for retrospective spiral (p < 0.001). Most studies had at least very good image quality (91.4/88.8% R1/R2), with highest SNR and CNR in the high-pitch spiral group.

CONCLUSIONS: cCTA with sufficient image quality is achievable at reasonably low radiation exposure in a real-world patient collective with a high proportion of overweight or obese patients.

KEY POINTS: • Submillisievert radiation dose coronary CT angiography with good diagnostic image quality is feasible in the majority of cases in a real-world patient using high-pitch spiral. • Prospective sequence results in about double median effective dose compared to the high-pitch protocol. • To optimize individual radiation exposure, lowering the heart rate is paramount, as it allows for choosing a dose-optimized (high-pitch spiral) scan protocol.