THE AAPM RSNA PHYSICS TUTORIAL FOR RESIDENTS - MEASURES OF SCREEN-FILM PERFORMANCE/

The choice of screen-film combination, combined with film-processing c onditions, substantially affects radiographic image quality (contrast, blur, and noise) and radiation dose. Film type (single or double emul sion, silver halide content, grain morphology, and spectral sensitivit y), processing conditions (chemicals, temperature, time, and agitation ), fog level (storage, safelight, light leaks), and characteristics (g radient) determine how the x-ray intensity pattern will be related to the optical density pattern in the radiograph. The type of screen (pho sphor layer thickness, light-absorbing dyes and pigments, phosphor par ticle size), speed of the screen-film processing system (sensitivity), film granularity, screen uniformity, and film contrast affect radiogr aphic noise. Detective quantum efficiency is the basic measure of the efficiency of an imaging system and takes into account the contrast, i mage blur, speed, and image noise of the system. For radiologists, res idents, medical physicists, and technologists involved in medical imag ing, it is important to have a basic understanding of the characterist ics of screen-film and film-processing systems.