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

x射线光谱分析是射线照相系统质量保证和质量控制的重要内容。本研究的目的是在临床条件下使用高分辨率肖特基CdTe探测器测量数字乳房x射线光谱。在临床条件下，由于高光子通量率导致检测器光子堆积，直接测量乳房x线摄影光谱是困难的。测量管输出光谱的另一种方法是首先测量给定样品的90度康普顿散射光子。有了这种设置，探测器堆积就不是问题了。从散射光谱中，可以使用能量校正和Klein-Nishina函数来重建散射样品上的实际光谱入射。通过将重建光谱计算的暴露率与电离室测量的暴露率进行比较，验证了康普顿法测量的光谱是否准确。我们使用铝（Al）过滤，厚度从0到0.8毫米。在27 kV光束中，碳散射体和丙烯酸树脂散射体的半值层与剂量计的差异率分别为17.5%和16.5%。对于32千伏的束流，分别得到12.8%和11.4%。两种技术获得的hvl差异很小，这表明康普顿散射光谱与高分辨率肖特基CdTe探测器适用于测量数字乳房x射线光谱，可用于临床数字乳房x射线设备的质量保证和质量控制。介绍了2004年3月出版的《乳腺摄影指南（第二版）》中数字影像成像效果幻象评价标准，并对数字乳腺摄影物理成像特性（数字特征曲线、调制传递函数、噪声功率（维纳）谱、探测量子效率、CDMAM幻象可探测性）的评价进行了阐述。少

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