Quasi-monochromatic X-ray source for mammography via crystal array

It has been demonstrated both theoretically and experimentally that mammographic X-ray imaging with monochromatic beams could help to improve subject contrast and to reduce the dose delivered to the patient. To this aim, quasi-monochromatic X-rays have been produced in the mammographic energy range by making use of a conventional W-anode, Be-window X-ray tube and a monochromator optical system based on an array of mosaic crystals. The mosaic crystals are highly oriented pyrolytic graphite (002) which provide a gain in flux as compared to perfect crystals because of their higher integrated reflectivity. The monochromator optical system consists of an array of three crystals (2.8 x 6.0 cm(2) of size) which has been assembled so as to produce in the image plane an irradiation field obtained with adjacent reflected beams. The field size reflected by each crystal on the image plane is limited by the desired energy resolution along the horizontal direction and by the crystal size along the perpendicular one. The energy spread of the reflected beams is about 10%, The characteristics of the system in terms of energy resolution and fluence rate are reported, Radiographs of test phantoms imaged with quasi-monochromatic beams in the energy range of 18-21. keV have been obtained with a conventional screen/film combination, To remove the spatial non-uniformities of the entire irradiation field a correction procedure has been applied. Large field quasi-monochromatic X-ray beams with the same flux of a standard Mo-anode tube for mammography can be produced by using a mosaic crystals array and a W-anode tube with an anode current of about 600 mA.