Optimum x-ray spectra for mammography: choice of K-edge filters for tungsten anode tubes

Zirconium, niobium, molybdenum, rhodium and palladium are the only materials having K-edges in the range of energies considered optimum for mammography and available in foil form. To compare the effectiveness of the five filters for different breast thicknesses, the highest optimum energy indices obtained for each filter are plotted as a function of breast thickness. It was concluded that a tungsten anode tube with appropriate K-edge filtration can be used successfully for the entire range of breast thicknesses. Such a system would be preferred to a molybdenum-filtered, molybdenum-anode unit for breast thicknesses greater than 5 cm and may be appropriate for magnification mammography where the requirement for a fine focal spot size may demand the higher melting point of a tungsten anode. (author)