A black and white silver halide photograph is developed to form a visible image. In medical radiography, an illness is diagnosed by the density of a silver image. When a trouble area in which the difference in transmittance of an X-ray is small is observed, an image having a high gradation and a sharp outline is required. In recent years, as diagnosis becomes more precise and there are more cases in which a soft tissue such as a breast is observed, the requirement for high gradation and sharp outline increases.
In diagnosing a breast cancer, the system of a screen on one side and a film on the other side is preferably used because there is a serious need for a sharpness. However, that system shows a low sensitivity when subjected to standard processing as compared to those systems in which screens and emulsion layers are on both sides. Therefore, there are some cases in which the developing temperature must be raised and the developing time prolonged in order to obtain the needed characteristics of high sensitivity and gradation.
Fog caused in such processing results in worse image contrast and a deterioration of visible sharpness. Fog is likely to increase, especially when a light-sensitive material is processed at a high temperature where the KBr amount in a developing solution is decreased.