Image quality and radiation exposure with prospectively ECG-triggered axial scanning for coronary CT angiography: the multicenter, multivendor, randomized PROTECTION-III study.

Objectives: The purpose of this study was to evaluate image quality and radiation dose using a prospectively electrocardiogram (ECG)-triggered axial scan protocol compared with standard retrospective ECG-gated helical scanning for coronary computed tomography angiography.

Background: Concerns have been raised regarding radiation exposure during coronary computed tomography angiography. Although the use of prospectively ECG-triggered axial scan protocols may effectively lower radiation dose compared with helical scanning, it is unknown whether image quality is maintained in a clinical setting.

Methods: In a prospective, multicenter, multivendor trial, 400 patients with low and stable heart rates were randomized to either an axial or a helical coronary computed tomography angiography scan protocol. The primary endpoint was to demonstrate noninferiority in image quality with the axial scan protocol, which was assessed on a 4-point scale (1 = nondiagnostic, 4 = excellent image quality). Secondary endpoints included radiation dose and the rate of downstream testing during 30-day follow-up.

Results: Image quality in patients scanned with the axial scan protocol (score 3.36 ± 0.59) was not inferior compared with helical scan protocols (3.37 ± 0.59) (p for noninferiority <0.004). Axial scanning was associated with a 69% reduction in radiation exposure (dose-length product [estimated effective dose] 252 ± 147 mGy · cm [3.5 ± 2.1 mSv] vs. 802 ± 419 mGy · cm [11.2 ± 5.9 mSv] for axial vs. helical scan protocols, p < 0.001). The rate of downstream testing did not differ (13.8% vs. 15.9% for axial vs. helical scan protocols, p = 0.555).

Conclusions: In patients with stable and low heart rates, the prospectively ECG-triggered axial scan protocol maintained image quality but reduced radiation exposure by 69% compared with helical scanning. Axial computed tomography data acquisition should be strongly recommended in suitable patients to avoid unnecessarily high radiation exposure.