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. (Prospective Randomized Trial on Radiation Dose Estimates of CT Angiography in Patients Scanned With a Sequential Scan Protocol [PROTECTION-III]; NCT00612092) (J Am Coll Cardiol Img 2012;5:484-93) (C) 2012 by the American College of Cardiology Foundation