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An investigation into the effects of suboptimal viewing conditions in screen-film mammography

Regional Medical Physics Department, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne, NE4 6BE, UK

Correspondence: K J Robson, Regional Medical Physics Department, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne, NE4 6BE, UK. E-mail: kevin.robson{at}nuth.nhs.uk

The ability of an observer to detect objects on a radiograph is influenced by the conditions under which the image is viewed. Therefore, to ensure that as much diagnostically relevant information as possible can be extracted from the image, it is important that satisfactory viewing conditions for the task are established and maintained. Factors that are thought to be important are the luminance of the image, glare and ambient light. Together, these factors lead to the formation of reflection on the image, which may degrade the observer's performance. The purpose of this study was to explore, in a systematic manner, the effect of the factors outlined above on the performance of an observer conducting a threshold contrast–detail diameter test. Each factor was investigated separately with attempts made to minimize the confounding effects of other factors. When examined individually, viewing box luminance, ambient light and glare were found to have little effect on the contrast–detail performance of the observers. Reflection was found to have a significant effect, particularly non-uniform reflection, and the magnitude of the effect was related to the contrast degradation factor and reflection modulation. These quantities, which are derived from basic photometric measurements, may be used to develop a protocol to assess viewing conditions in screen-film mammography.