Objective: To report our clinical experience with a 256-slice multidetector computed tomography (MDCT) with a 270-ms gantry rotation system in performing CT coronary angiograms (CTCA) using both prospectively gated step and shoot (PGSS) and retrospectively gated helical (RGH) techniques.

Materials and Methods: We studied 252 patients who received CTCA; 126 patients having mean heart rate (HR) of 72.1 were imaged with RGH CTCA and 126 patients having mean HR of 58.7 were imaged with PGSS CTCA. For patients with a prescan HR <= 70 beats/min, a PGSS acquisitions trigger was used, whereas patients whose prescan HR was >70 beats/min were imaged using an RGH acquisition. The blood vessel accessibility of both PGSS and RGH techniques was evaluated by grading the image quality score from 1 (no motion artifacts) to 4 (severe motion artifacts preventing diagnosis) for each coronary artery segment. Radiation doses of the techniques were also compared.

Results: In both groups, more than 50% of segments received the best imaging score. The overall image quality scores for RGH and PGSS groups were 1.522 +/- 0.317 and 1.500 (+/-) 0.374, respectively. There was no significant difference in right coronary artery, left anterior descending artery, and left circumflex artery image quality between the two groups. Only 0.1% of segments were nonevaluative with the PGSS technique and all segments were evaluative with RGH. PGSS was associated with a 62% reduction in effective radiation dose as compared to RGH (PGSS, 5.1 mSv; RGH, 13.2 mSv).

Conclusions: There is no significant difference in image quality between PGSS and RGH in this study. Although providing similar image quality as RGH, PGSS was associated with a 62% reduction in effective radiation dose. Further study to confirm the diagnostic accuracy as compared to coronary artery angiography is warranted.