Autoradiographic image intensification methods for recovering the images of underexposed step wedges, resolution targets and radiographs were investigated. The fog level of the intensified image was decreased by treating the film in a subproportional photographic reducer (mixture of potassium ferricyanide and sodium thiosulfate) prior to activation with S-35 thiourea. The fog level of intensified images of a step wedge decreased from a density of 1.32 to .12, the maximum contrast increased from 2.08 to 5.52, the relative speed increase calculated at 0.6 above fog level increased from 3.05 to 4.06 while resolution remained the same at 5.0 lines per millimeter.Radiographs of underexposed images were recovered by using this autoradiographic image intensification method. The underexposed radiograph was developed in the conventional manner using the Kodak X-Omat processor and treated in the subproportional photographic reducer to lower the fog density. The silver image of the underexposed radiograph was made radioactive with a solution of sulfur-35 thiourea, air-dried and exposed to another emulsion. The intensified image was also developed in the conventional manner. Its diagnostic usefulness was judged by experienced radiologists as optimal, adequate, poor but diagnostic, or totally unacceptable in comparison to optimally exposed radiographs. Of the six underexposed radiographs involving various body regions studied following intensification, five were consistently rated adequate. This technique, when fully developed and applied will result in reduced radiation dose to patients undergoing radiologic examinations. A significant difference exists between the intensified image of a double-coated and single-coated emulsion. When both emulsions are treated in a subproportional reducer prior to activation with S-35 thiourea, the intensified image obtained from a single-coated emulsion has less base plus fog density, higher gamma, and is more contrasty than that of a double-coated emulsion. These results indicate that to make deliberate underexposures, it is better to use a singlecoated than a double-coated emulsion
