IMAGE QUALITY AND DOSE IN COMPUTED-TOMOGRAPHY

Radiation exposure to the patient during CT is relatively high, and it is therefore important to optimize the dose so that it is a low as po ssible but still consistent with required diagnostic image quality. Th ere is no established method for measuring diagnostic image quality; t herefore, a set of image quality criteria which must be fulfilled for optimal image quality was defined for the retroperitoneal space and th e mediastinum. The use of these criteria for assessment of image quali ty was tested based on 113 retroperitoneal and 68 mediastinal examinat ions performed in seven different CT units. All the criteria, except o ne, were found to be usable for measuring diagnostic image quality. Th e fulfilment of criteria was related to the radiation dose given in th e different departments. By examination of the retroperitoneal space t he effective dose varied between 5.1 and 20.0 mSv (milli Sievert), and there was a slight correlation between dose and high percent of ''yes '' score for the image quality criteria. For examination of the medias tinum the dose range was 4.4-26.5 mSv, and there was no significant in crement of image quality at high doses. The great variation of dose at different CT units was due partly to differences regarding the examin ation procedure, especially the number of slices and the mAs (milli am pere second), but inherent dose variation between different scanners a lso played a part.