Automatic exposure control in CT an investigation between different manufacturers considering radiation dose and image quality

Background: Data from 1998 showed that CT represents about 10% of all the diagnostic X-ray examinations and almost 70% of the total radiation dose from medical diagnostic examinations in Sweden. Because of this there is a strong need to minimize the radiation dose and adapt the dose to each patient’s examination area and anatomy. Today practically all-modern CT systems are delivered with automatic exposure control (AEC) systems that perform tube current modulation in 3D.Aim: The purpose of this work is to investigate the potential of dose reduction and the possibility to maintain adequate image quality using the AEC systems from four different manufacturers: Siemens Medical Solutions, Philips Medical Systems, General Electric (GE) Healthcare and Toshiba Medical Corporation. Material and methods: A general scanning protocol was created for each examination where as many as possible of the scanning parameters were set equal. The dynamic of each AEC system has been investigated by scanning an anthropomorphic thorax phantom and an anthropomorphichead phantom on 16- and 64-slice CT scanners for each manufacturer with the AEC system activated and non-activated. The image quality in the thorax phantom has been evaluated by measuring the image noise (standard deviation) by insert regions of interests.Results and discussion: The result for each AEC system is strongly dependent on the selected image quality parameters. Each system has different solutions of defining the image quality level; consequently it is not possible to make direct comparison between the manufacturers. The dynamic of the tube current modulation is rather similar between the manufactures AEC system and there is large potential for dose reductions (thorax ~50%). A common result is that the image noise increases, especially in regions where the tube current is greatly decreased by the AEC systems, e.g. in the lung region.Conclusion: There are large possibilities to attain large dose reductions. The AEC systems cause a general increase in the image noise but the noise becomes more consistent between different anatomic regions.