Post-CABG Coronary CT Angiography:

Rationale and Objectives

The aim of this study was to compare effective radiation doses between prospective and retrospective electrocardiographic gating during coronary computed tomographic angiography for coronary artery bypass grafting evaluation.

Materials and Methods

Fifty consecutive coronary computed tomographic angiographic exams for coronary artery bypass grafting evaluation, 25 prospectively gated and 25 retrospectively gated, were reviewed from January 8, 2008, to June 16, 2009. Body mass index and image quality were also compared between the two groups. To minimize the potential bias introduced by differences in torso length, the effective radiation dose from each exam was measured and normalized to a 24-cm z-axis scan length for all patients. Pooled t tests were used to compare the prospectively and retrospectively gated groups.

Results

The average effective doses delivered in the retrospective and prospective groups were 40.8 mSv (standard error [SE], 1.8 mSv) and 8.6 mSv (SE, 0.7 mSv), respectively. When normalized to the average z-axis scan length of 24 cm, the effective dose in the retrospective group, 38.4 mSv (SE, 1.3 mSv), was still >4 times greater than that in the prospective group, 9.1 mSv (SE, 0.7 mSv) (P < .0001). There was no significant difference in body mass index or image quality between the groups.

Conclusions

Effective radiation dose in coronary computed tomographic angiography for coronary artery bypass grafting evaluation is very high because of long scan lengths. Prospective electrocardiographic gating significantly reduces effective radiation dose by an average of 76% compared to retrospectively gated scans (9.1 vs 38.4 mSv). In the coronary artery bypass grafting population, prospective electrocardiographic gating should be used whenever ventricular functional assessment is not required.

Key Words: CT angiography, CABG, radiation dose