Lubberts effect in columnar phosphors
Lubberts effect in columnar phosphors
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DOI：
10.1118/1.1796151
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发表时间：
2004-11-01
期刊：
影响因子：
3.8
通讯作者：
Myers, KJ
中科院分区：
文献类型：
--
作者：
Badano, A;Gagne, RM;Myers, KJ
当对于整个屏幕厚度考虑传递特性时，颗粒状X射线成像荧光屏中的噪声传递与信号传递的幅度的平方不成比例，除非在每个相互作用深度处适当加权。这种性质，被称为吕伯特效应，尚未在柱状结构屏幕中进行研究，因为缺乏对深度相关光传输的一般描述。在本文中，我们调查的信号和噪声传输特性的柱状荧光粉用于数字乳腺X射线摄影检测器使用DETECT-II，光学蒙特卡罗光传输模拟代码。我们首先验证我们选择的光学参数的描述颗粒和柱状屏幕使用出版的归一化调制传递（MTF）的实验数据。我们的MTF的计算匹配经验测量的MTF的颗粒膜/屏幕模拟系统，并与CsI的间接X射线数字成像系统：T1屏幕的数字乳腺X射线摄影系统的代表。使用深度相关的扩展函数和收集效率，我们计算的信号和噪声传递函数和Lubberts分数，这是信号传递函数的噪声传递函数的比率，对于不同的屏幕厚度的颗粒状和柱状荧光粉。我们发现，一个85微米的颗粒状屏幕模型对应于一个Gd 2 O2 S：Tb屏幕的Lubberts分数是类似的分数为100微米柱状CsI：T1屏幕。
Noise transfer in granular x-ray imaging phosphor screens is not proportional to the square of the magnitude of the signal transfer when the transfer properties are considered for the entire screen thickness, unless appropriately weighted at each depth of interaction. This property, known as the Lubberts effect, has not yet been studied in columnar structured screens because of a lack of a generalized description of the depth-dependent light transport. In this paper, we investigate the signal and noise transfer characteristics of columnar phosphors used in digital mammography detectors using DETECT-II, an optical Monte Carlo light transport simulation code. We first validate our choice of optical parameters for the description of granular and columnar screens using published normalized modulation transfer (MTF) experimental data. Our calculations of MTF match empirically measured MTFs for a granular film/screen analog system, and for an indirect x-ray digital imaging system with CsI:T1 screen representative of digital mammography systems. Using the depth-dependent spread functions and collection efficiencies, we calculate the signal and noise transfer functions and the Lubberts fraction, which is the ratio of the signal transfer function to the noise transfer function, for different screen thicknesses of granular and columnar phosphors. We find that the Lubberts fraction of a 85 mum granular screen model corresponding to a Gd2O2S:Tb screen is similar to the fraction for a 100 mum columnar CsI:T1 screen.