Radiographic mottle and patient exposure in mammography

Radiographic mottle has been analyzed in mammography using a comprehensive theory that takes into account fluctuations in absorbed x-ray energy and in phosphor light-photon yield, as well as film granularity and random variations in phosphor coating. Density fluctuations, signal-to-noise ratios, and quantum-efficiencies are presented for two screen/film systems as functions of density and viewing-aperture size. For sampling apertures of less than 500 micrometers in diameter, film granularity is the dominant source of noise for a Kodak Min-R screen/film system. This implies that quantum mottle can be increased and patient exposure reduced with little or no loss in imaged information. Such is the case for the second combination, a Min-R screen combined with Ortho-M film.