Computed tomography: Influence of exposure parameters and the establishment of reference dose values

The frequency and importance of CT in radiological diagnosis is still increasing; the concomitant increase in the radiation exposure of the population is a point of growing concern. Further efforts are demanded to determine patient dose values and their dependence on exposure factors, to establish demands on image quality and to provide the demanded level of image quality with minimal dose. The respective efforts and the underlying basic principles and considerations are reviewed. The influence of components, of scan types and parameters is briefly explained. A particular focus is on new technical approaches to reduce dose in CT. These include adequate use of spiral CT and anatomically adapted tube current modulation. It appears possible to reduce dose in CT through technical means by a factor of two in many cases without a loss in image quality. An automatic exposure control (AEC) for CT must be an aim for future CT developments to ensure that this goal will be achieved or even exceeded, based on technical advances and on the definition of quality criteria.