Impact of luminance distribution in the visual field on foveal contrast sensitivity in the context of mammographic softcopy reading

For quality control in mammographic softcopy reading (SCR) a number of recommendations exists. Among them is a room illuminance of 10 lx. Moreover, the use of masks on the image seems to be advantageous, due to a reduction of scattered light in the focus of view. Room illuminance affects the global luminance adaptation and the maximal monitor contrast; masking decreases the luminance in the central and near-peripheral region. We investigated the effects of masking and illuminance on foveal contrast sensitivity. A study with eight observers was conducted in the context of mammographic softcopy reading. Using Gabor patterns with varying spatial frequencies, orientations and contrast levels as stimuli and an orientation discrimination task, the intraobserver contrast sensitivity was determined for foveal vision. Tested illuminances for a non-masked image were 10, 30, 50 and 90 lx, and for a masked image 10 lx. Major findings are: (1) Masking does not lead to improved contrast sensitivity. Instead, all observers reported a strong fatigue effect during the presentation of the masked image. (2) Among the illuminances tested, only half of the observers showed the best contrast sensitivity at 10 lx. For the other observers best results were achieved at illuminance levels of 50 or 90 lx, respectively. The results can be used to appraise the effects of viewing conditions with the aim of drawing conclusions for mammographic SCR, and to initiate further studies