Comparison of sequential and helical scanning for radiation dose and image quality: Results of the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography (PROTECTION) I Study

OBJECTIVE. Concerns have been raised about the radiation exposure of coronary CT angiography (CTA). Recently, a prospective ECG-triggered sequential coronary CTA technique was developed to reduce exposure to ionizing radiation. The purpose of this analysis was to determine the impact of a sequential scanning technique on image quality and radiation dose in a prespecified subgroup analysis of the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography I (PROTECTION I) Study when compared with a standard helical scanning technique. MATERIALS AND METHODS. This analysis comprises 685 64-MDCT coronary angiography studies of 47 international study sites in which the image quality was assessed by an experienced coronary CTA investigator using a 4-point score (1 = nondiagnostic, 4 = excellent image quality). Image quality was analyzed in all patients studied with the sequential scanning mode (n = 99) and in randomly selected patients of the population studied with the helical acquisition mode (n = 586). Radiation dose estimates were derived from the dose-length product (DLP) and a conversion coefficient for the chest (0.014 mSv x mGy^-1 x cm^-1). RESULTS. Although the sequential scanning mode significantly reduced radiation dose estimates by 68% from 11.2 mSv for the helical mode to 3.6 mSv for the sequential mode (p < 0.001), the median diagnostic image quality scores were comparable in both groups. The median diagnostic score for both scanning modes was 3.5 (interquartile range: sequential vs helical mode, 3.25-3.75 vs 3.0-3.75, respectively; p = 0.62). CONCLUSION. The results of the PROTECTION I Study suggest that the prospective ECG-triggered sequential coronary CTA technique significantly reduces radiation dose without impairing image quality when compared with the standard retrospective helical data acquisition in patients with a low and stable heart rate.