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5 June 2003 Effect on DQE of screen energy weighting in mammography
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Our work investigates the effect on the zero-spatial-frequency DQE of indirect mammographic image receptors of the combined effects of x-ray beam hardening and light photon transport within the x-ray sensitive medium of the image receptor. Beam hardening, in this context, refers to the preferential absorption of low-energy x-ray photons at the surface of the detector on which the x-ray beam is incident, with deeper layers of the detector absorbing higher and higher average energies. The light photon transport properties of both powder and crystalline/columnar phosphors favor the collection at the light-sensitive element of the detector of light photons generated closest to that element. The net result of these two effects is to perform a weighting of the detected x-ray spectrum. For the standard back-screen configuration used in conventional mammography, low-energy x rays are more heavily weighted, matching the energy dependence of the signal to be detected. For a front-screen configuration, used in all existing indirect-detection digital mammographic systems, just the opposite is true. We have used the optical Monte Carlo simulation code DETECT-II to determine average light collection efficiency and optical pulse distributions for a Min-R screen in both front- and back-screen configurations, and for two thicknesses of CsI, as a function of x-ray energy. These data, along with appropriately hardened x-ray spectra for several anode and filter combinations and a range of tube voltages, were used as input to the task-dependent DQE theory of Tapiovaara and Wagner.
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Robert J. Jennings and Aldo Badano "Effect on DQE of screen energy weighting in mammography", Proc. SPIE 5030, Medical Imaging 2003: Physics of Medical Imaging, (5 June 2003);

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