Theoretical considerations of effects of x-ray film-screen characteristics on threshold detectability of small low-contrast objects.

An expression is derived for visual contrast of a radiographed small object that takes into account the proportion of scattered radiation as well as the shape of the sensitometric curve of the film-screen combination. Based on this expression for visual contrast applied to two different film-screen systems, predictions are made for threshold perceptability of low-contrast objects radiographed with the two imaging systems in the presence of scattered radiation and at different points on the sensitometric curves.