Boone J M, Fewell T R, Jennings R J
Department of Radiology, University of California, Davis, UC Davis Medical Center, Sacramento 95817, USA.
Med Phys. 1997 Dec;24(12):1863-74. doi: 10.1118/1.598100.
Computer simulation is a convenient and frequently used tool in the study of x-ray mammography, for the design of novel detector systems, the evaluation of dose deposition, x-ray technique optimization, and other applications. An important component in the simulation process is the accurate computer-generation of x-ray spectra. A computer model for the generation of x-ray spectra in the mammographic energy range from 18 kV to 40 kV has been developed. The proposed model requires no assumptions concerning the physics of x-ray production in an x-ray tube, but rather makes use of x-ray spectra recently measured experimentally in the laboratories of the Center for Devices and Radiological Health. Using x-ray spectra measured for molybdenum, rhodium, and tungsten anode x-ray tubes at 13 different kV's (18, 20, 22, ..., 42 kV), a spectral model using interpolating polynomials was developed. At each energy in the spectrum, the x-ray photon fluence was fit using 2, 3, or 4 term (depending on the energy) polynomials as a function of the applied tube voltage (kV). Using the polynomial fit coefficients determined at each 0.5 keV interval in the x-ray spectrum, accurate x-ray spectra can be generated for any arbitrary kV between 18 and 40 kV. Each anode material (Mo, Rh, W) uses a different set of polynomial coefficients. The molybdenum anode spectral model using interpolating polynomials is given the acronym MASMIP, and the rhodium and tungsten spectral models are called RASMIP and TASMIP, respectively. It is shown that the mean differences in photon fluence calculated over the energy channels and over the kV range from 20 to 40 kV were -0.073% (sigma = 1.58%) for MASMIP, -0.145% (sigma = 1.263%) for RASMIP, and 0.611% (sigma = 2.07%) for TASMIP. The polynomial coefficients for all three models are given in an Appendix. A short C subroutine which uses the polynomial coefficients and generates x-ray spectra based on the proposed model is available on the World Wide Web at http:/(/)www.aip.org/epaps/epaps.html.
计算机模拟是乳腺X线摄影研究中一种便捷且常用的工具，可用于新型探测器系统的设计、剂量沉积评估、X射线技术优化及其他应用。模拟过程中的一个重要组成部分是精确地通过计算机生成X射线光谱。已开发出一种用于生成18 kV至40 kV乳腺摄影能量范围内X射线光谱的计算机模型。所提出的模型无需对X射线管中X射线产生的物理过程做任何假设，而是利用了最近在设备与放射卫生中心实验室通过实验测量得到的X射线光谱。利用在13个不同千伏值（18、20、22、……、42 kV）下对钼、铑和钨阳极X射线管测量得到的X射线光谱，开发了一种使用插值多项式的光谱模型。在光谱的每个能量点，X射线光子注量使用2、3或4项（取决于能量）多项式拟合为施加管电压（kV）的函数。利用在X射线光谱中每个0.5 keV间隔处确定的多项式拟合系数，可生成18至40 kV之间任意千伏值的精确X射线光谱。每种阳极材料（钼、铑、钨）使用不同的一组多项式系数。使用插值多项式的钼阳极光谱模型简称为MASMIP，铑和钨光谱模型分别称为RASMIP和TASMIP。结果表明，在能量通道以及20至40 kV的千伏范围内计算得到的光子注量平均差异，MASMIP为 -0.073%（标准差 = 1.58%），RASMIP为 -0.145%（标准差 = 1.263%），TASMIP为0.611%（标准差 = 2.07%）。附录中给出了所有三个模型的多项式系数。一个使用这些多项式系数并基于所提出的模型生成X射线光谱的简短C语言子程序可在万维网http:/(/)www.aip.org/epaps/epaps.html上获取。
