QUALITY-CONTROL IN COMPUTED-TOMOGRAPHY PERFORMED IN PORTUGAL AND DENMARK

Quality Control (QC) in Computed Tomography is often performed by the representative of the manufacturer, usually under a service contract. This is the situation for 97% in Portugal and for 90% of all systems i n Denmark. This paper monitors relevant image and dose parameters befo re and after monthly service with the aim of evaluating the necessity of additional QC tests to be carried out by the user's operator. For t his purpose two parallel series of QC have been carried out in Portuga l and in Denmark. The CT systems studied are different models and have service and maintenance once a month. The QC tests were performed by phantom and dose measurements before and after each monthly maintenanc e. It is concluded from both series that the constancy of the scanner performance is high, and that the monthly service practised by most ma nufacturers seems sufficient and that extra QA tests would not improve performance. A daily check of the noise level should be recommended a nd a registration of this parameter should be performed. For compariso n it is important that the parameters measured are well defined. Speci al concern should be given to the proper use of the dose descriptor to avoid confusion. The various dose descriptors in use have been tested , and discrepancies are registered when shaped filters are presented i n a scanner system. This is in accordance with earlier findings.