| Film graininess can be measured by providing air spaces between the screen and film in the screen-film system. In this study, the necessary air spaces were investigated to measure mammographic film graininess by using a mammography unit at the low tube voltage of 28 kV. Wiener spectra were measured with the screen held 1, 3, 6, 9,15, 21, and 30 mm from the film at densities of 0.8 and 1.3. Konica New CM film with a Konica M-150 screen was employed in this investigation. Results showed that Wiener spectral values were almost constant at densities of 0.8 and 1.3 when the air spaces were 9 mm or more. That is, it was considered that film graininess was evaluated independently by blurring quantum mottle, and 15 mm air spaces were used to provide a safety margin. Furthermore, film graininess of three mammographic films, Fuji UM-MA HC(with a Fuji UM MAMMO Fine screen), Kodak Min-R 2000(with a Kodak Min-R 2000 screen), and Kodak Min-R M(with a Kodak Min-R Medium screen)were measured with 15 mm air spaces. Min-R 2000 film had the lowest Wiener spectral values for film graininess at low spatial frequencies. |
