Should the automatic exposure control system of CT be disabled when scanning patients with endoaortic stents or mechanical heart valves? A phantom study

Objectives: To estimate the impact of endoaortic stents/mechanical heart valves on the output of an automatic exposure control (AEC) system and CT radiation dose. Methods: In this phantom study, seven stents and two valves were scanned with varying tube voltage (80/100/120 kVp), AEC activation (enabled/disabled) and prosthesis (present/absent), for a total of 540 scans. For each prosthesis, the dose-length product (DLP) was compared between scans with the AEC enabled and disabled. Percentage confidence levels for differences due to the prosthesis were calculated. Results: Differences between results with the AEC enabled and disabled were not statistically significant (p ≥ 0.059). In the comparison with and without the prosthesis, DLP was unchanged at 80 kVp and 100 kVp, while a slight increase was observed at 120 kVp. The radiation dose varied from 1.8 mGy to 2.4 mGy without the prosthesis and from 1.8 mGy to 2.5 mGy with the prosthesis (confidence level 37–100%). Conclusions: The effect of the prosthesis on the AEC system was negligible and not clinically relevant. Therefore, disabling the AEC system when scanning these patients is not likely to provide a benefit. Key points: • CT-AEC system is not impaired in patients with endoaortic prostheses/heart valves.• Negligible differences may be observed only at 120 kVp.• Disabling the AEC system in these patients is not recommended.