| Popis: |
The x-ray photon energies that give the highest signal-to-noise ratios per unit of exposure or average dose in mammography are significantly greater than those used in current film/screen systems. Optimum photon energies for detection of calcifications in a range of thicknesses of water and fat were calculated. Soft-tissue targets were also considered. Comparison of the theoretical results and those obtained experimentally with the Stanton mammography phantom indicate that operation at less than optimum photon energies is a major cause of inefficiency in film/screen mammography. On the other hand, electrostatic imaging systems, because of their processing flexibility, can operate at the optimum photon energy levels, thus minimizing either dose or exposure. |
