Evaluation of a dichromatic X-ray source for dual-energy imaging in mammography

A novel X-ray system, providing dichromatic beams for dual-energy radiography, has been assembled. The source generates pairs of superimposed quasi-monochromatic beams, having energies E and 2E, with E tuneable in the 15–20 keV range. In this paper the characteristics of the radiation field in terms of energy resolution and fluence, for three dichromatic X-ray beams are reported. A study of the spectra attenuated by a 5 cm-thick phantom of breast equivalent tissue demonstrates that the optimal energy of the dichromatic beam for dual-energy application may be set as a function of the thickness of investigated tissue. A detailed topographic study of mean energy and flux shows the spatial superposition of the first and the second diffraction order beam, that is the main requirement for the application of a single exposure dual-energy radiography. The bidimensional mapping of the irradiated beam is also reported, showing the presence of energy and intensity gradients. We estimate that the observed gradients do not affect the results of dual-energy technique application in an appreciable way.