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

Experiments were performed to test threshold detectability of a small nylon bead radiographed with two different image receptors and under different scattering conditions. In another paper, the present authors predicted, on theoretical grounds, the visibility of small low-contrast objects radiographed in the presence of scattered radiation. The experiments discussed in this paper tested these predictions using an observer-testing method resulting in Receiver Operating Characteristic (ROC) curves. In addition to the rigidly controlled experiments from which the ROC curves were obtained, another experiment was performed in which a human phantom was used and the radiographs rated as to the visibility of small artificial lesions. By and large, the experiments confirmed the predictions made from the theoretical analysis, using visual contrast as a measure of detectability.