MEASUREMENTS OF THE FREQUENCY-DISTRIBUTION OF OPTICAL-DENSITY IN SCREENING MAMMOGRAPHY

A method for obtaining histograms of the frequency of occurrence of op tical densities in mammograms has been implemented. Averaged optical d ensity distributions were produced for approximately 50 screening mamm ograms at each of two centres using different film-screen and processi ng chemistry combinations. Additional measurements were made on films of two commercially available anthropomorphic breast phantoms. The res ults show that screening mammograms, on average, exhibit a strongly pe aked optical density distribution which corresponds closely to the tar get optical density measured using the current recommended test protoc ol for automatic exposure control devices.