PATIENT DOSE AND IMAGE QUALITY FOR COMPUTED-TOMOGRAPHY IN SEVERAL DUTCH HOSPITALS

In several Dutch hospitals a survey of computed tomography (CT) techni ques was performed at 14 CT scanners. In this survey the computed tomo graphy dose index (CTDI) was measured free-in-air with a pencil type i onisation chamber. These measurements yield dose values related to a s ingle CT scan of one slice whilst radiation exposure of patients due t o a complete CT examination should preferably be expressed in terms of organ and tissue doses or effective dose. Organ and effective doses w ere derived by application of published organ dose conversion factors. Effective doses varied from 0.7 mSv to 2.2 mSv for head scans, from 6 .0 mSv to 13 mSv for chest scans and from 7.1 mSv to 21 mSv for standa rd abdomen scans. The survey also included the assessment of parameter s related to image quality, i.e. high contrast resolution and noise (s tandard deviation, sigma, of Hounsfield units) associated with the CT scanners and protocols at the different locations. Image quality in te rms of noise or resolution and effective dose did not reveal a signifi cant correlation for the different CT scanners.