Development of quality control system for digital mammographic x-ray units to aim reduction of patient dose

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The analysis of x-ray spectra is important for quality assurance (QA) and quality control (QC) of radiographic systems. The aim of this study is to measure the digital mammographic x-ray spectra under clinical conditions using a high-resolution Schottky, CdTe detector. Under clinical conditions, the direct measurement of a mammographic spectrum is difficult because of the high photon fluence rates that cause significant detector photon pile-up. An alternative way of measuring the output spectra from a tube is first to measure the 90-degree Compton scattered photons from a given sample. With this set-up detector pile-up is not a problem. From the scattered spectrum one can then use an energy correction and the Klein-Nishina function to reconstruct the actual spectrum incident upon the scattering sample. The verification of whether our spectra measured by the Compton method are accurate was accomplished by comparing exposure rates calculated from the reconstructed spectra to those measur … More ed with an ionization chamber. We used aluminum (Al) filtration ranging in thickness from 0 to 0.8 mm. The difference rates to the dosimeter of the half-value layers (HVLs) obtained for a 27 kV beam were 17.5 % for carbon scatterer and 16.5 % for acrylic resin scatterer. For a 32 kV beam we obtained 12.8 % and 11.4 %. The small differences in HVLs obtained by both techniques suggest that Compton scatter spectroscopy with a high-resolution Schottky CdTe detector is suitable for measuring the digital mammographic x-ray spectra and useful for QA and QC of clinical digital mammographic x-ray equipment.Evaluation standard of phantom images in mammography guideline (second edition) published on March, 2004 including film outcome of digital images was indicated and evaluation of physical imaging properties (digital characteristic curve, modulation transfer function, noise power (Wiener) spectrum, detective quantum efficiency, detectorbility of CDMAM phantom) of digital mammography was explained. Less