Performance assessment of X-ray image intensified television fluoroscopy systems in New Zealand

The protocol for image intensifier (II) quality assurance recommended by the UK Hospital Physicists' Association (HPA) and the UK Department of Health and Social Security has been adapted for use in New Zealand for assessment of such systems. Test objects were constructed at the National Radiation Laboratory to match the specifications of those recommended by the HPA. Over 100 individual surveys have been made and, in a few cases, machines have been surveyed several times. Results are summarized in terms of key parameters: II input dose rate, low-contrast detectability, contrast-detail performance and limiting resolution. These are given as mean and standard deviation, and also as good, average or poor. Video waveforms, conversion factors and modulation transfer functions have also been determined on a number of systems. In several cases, video voltages were found to be seriously maladjusted. During routine protection visits to radiology depart- ments in New Zealand hospitals, National Radiation Laboratory (NRL) staff had often encountered dissatis- faction among radiological staff with the performance of their image intensifier (II) systems. As such equipment is expensive, decisions regarding servicing or replacement should be based on objective criteria. However, dissatisfaction could only be expressed in vague subjective terms and hence, remedial action was difficult and poorly adjusted or inadequate equipment could continue in service. The NRL therefore became involved in establishing methods of evaluating image intensifier system performance, so that optimum image quality and dose levels could be maintained during the life of the equipment and so that replacement could be recommended on a sound basis. Both direct physical measurements (Le Heron &