AN EXPERIMENTAL INVESTIGATION OF THE EFFECT OF LIGHT-BOX LUMINANCE ONTHE DETECTION OF LOW-CONTRAST OBJECTS IN MAMMOGRAPHY

It has been hypothesized that light-box luminance is an important fact or in the detection of objects on radiographs. In this work, existing psychophysical data relating to the measurement of visual thresholds a t various scene luminance levels are applied to the problem of the obs ervation of radiographs on a light-box. These data suggest that for a given stimulus size; the threshold contrast varies little over several orders of magnitude of scene luminance. In a series of contrast detai l experiments performed over a wide range of light-box luminances it h as been demonstrated that the detection of low contrast objects on mam mographic film is dominated by external noise, that is noise on the fi lm, rather than the internal visual noise of the observer. It is there fore suggested that in mammography it is inappropriate to base recomme ndations for optimal values of light-box luminance on psychophysical s tudies of visual noise. It has been shown that commonly used light-box luminances are suitable for viewing mammograms at the higher average optical densities now being recommended, provided that precautions are taken to avoid glare and reflection.