Prospectively Gated Coronary CT Angiography in Bypass Grafts: Dramatic Reductions in Radiation Dose

Abstract

Background: Coronary CT Angiography (CCTA) for the evaluation of disease in coronary artery bypass grafts (CABG) is classified as “uncertain” with a score of 5 in the 2010 Appropriate Use Criteria. A significant limitation is the high radiation dose, due to the large z-axis to cover the entire heart and CABG vessels. We proposed that using a prospectively gated “step-and-shoot” technique there would be significant reductions in radiation, with preservation of diagnostic image quality. Method: Patients undergoing CCTA for CABG patency using a Siemens dual-source scanner were retrospectively reviewed. Prospectively gated studies (group 1, n = 29) were compared to retrospective tube-current-modulated “min-dose” studies (group 2, n = 229), and to a historical cohort of “auto-dose” non-modulated studies (group 3, n = 73). z-Axis scan range was from the diaphragm to the left subclavian artery. Effective radiation dose (mSv) was calculated, and diagnostic image quality assessed by two expert observers. Results: Effective dose in prospectively gated studies was significantly lower (5.5 ± 1.9 mSv, p < 0.01) compared to tube-current-modulated studies (10.8 ± 5.6 mSv), and dramatically lower than full-dose (21.4 ± 10.7 mSv). Image quality was similar in all groups, with no difference in number of non-diagnostic segments. Prospectively gated studies could not assess LV function, a limitation of this technique. Heart rate in group 1 (54 ± 5 bpm) was significantly lower than in groups 2 and 3 (64 ± 9, 65 ± 11 bpm), reflecting the choice of acquisition technique for individual patients. Conclusions: Prospectively gated “step-and-shoot” CCTA is suitable for CABG patients, with dramatic reductions in radiation dose. This is suitable for selected patients with low and stable heart rates, and can be recommended in appropriate patients for the non-invasive evaluation of CABG graft patency.