Photographic unsharp masking in chest radiography.
A photographic unsharp masking technique for improving the latitude of chest radiographs without sacrificing image contrast or detail is described. An unsharp mask film, prepared from a scout film of the patient's chest, is placed between the film and the front (entrance) screen in the cassette. A second radiograph then is recorded using technique factors that provide a well-penetrated view of the central mediastinum, etc. The unsharp mask absorbs light from the screen in those areas of the chest that normally are well penetrated, preventing overexposure of these areas and resulting in an improved balance of densities across the chest image. Improvement of contrast by a factor of 2 is demonstrated for mediastinal and retrocardiac structures with no loss of contrast in the central lung fields. Nodule detection studies with a chest phantom and simulated nodules suggest that a single unsharp masked film provides higher nodule detection rates than a pair of films consisting of a normally penetrated and an overpenetrated view, possibly because of facilitation of visual search patterns and contrast/brightness adaptation mechanisms of the visual system. Initial clinical studies indicate that unsharp masking may provide additional useful clinical information.
D006801:Humans; D013902:Radiography, Thoracic / Q000379:methods*; D013679:Technology, Radiologic