The AAPM/RSNA physics tutorial for residents. Measures of screen-film performance.

The choice of screen-film combination, combined with film-processing conditions, substantially affects radiographic image quality (contrast, blur, and noise) and radiation dose. Film type (single or double emulsion, silver halide content, grain morphology, and spectral sensitivity), processing conditions (chemicals, temperature, time, and agitation), fog level (storage, safelight, light leaks), and characteristics (gradient) determine how the x-ray intensity pattern will be related to the optical density pattern in the radiograph. The type of screen (phosphor layer thickness, light-absorbing dyes and pigments, phosphor particle size), speed of the screen-film processing system (sensitivity), film granularity, screen uniformity, and film contrast affect radiographic noise. Detective quantum efficiency is the basic measure of the efficiency of an imaging system and takes into account the contrast, image blur, speed, and image noise of the system. For radiologists, residents, medical physicists, and technologists involved in medical imaging, it is important to have a basic understanding of the characteristics of screen-film and film-processing systems.