Harding G, Armstrong R, McDaid S, Cooper M J
Philips Research Laboratory, Technical Systems Department, Hamburg, Germany.
Med Phys. 1995 Dec;22(12):2007-14. doi: 10.1118/1.597497.
The ratio method involves forming the ratio of the elastic to inelastic x-ray scatter signals from a localized region of a scattering medium to determine its mean atomic number. An analysis is presented of two major error sources influencing the ratio method: firstly statistical (photon) noise and secondly multiple scattering and self-attenuation of the primary and scatter radiations in the medium. It is shown that a forward scattering geometry minimizes errors of both types for substances composed of elements with low and medium atomic number. However, owing to the small energy separation (approximately 100 eV) of coherent and Compton scatter for this geometry, they cannot be distinguished directly with semiconductor (e.g., Ge) detectors. A novel K edge filter technique is described which permits separation of the elastic and Compton signals in the forward-scatter geometry. The feasibility of this method is demonstrated by experimental results obtained with Ta fluorescence radiation provided by a fluorescent x-ray source filtered with an Er foil. The extension of this technique to the "in vivo" measurement of low momentum transfer inelastic scattering from biological tissues, possibly providing useful diagnostic information, is briefly discussed.
比值法涉及形成来自散射介质局部区域的弹性与非弹性X射线散射信号的比值，以确定其平均原子序数。本文分析了影响比值法的两个主要误差源：一是统计（光子）噪声，二是介质中初级辐射和散射辐射的多次散射及自吸收。结果表明，对于由低原子序数和中等原子序数元素组成的物质，前向散射几何结构可使这两种类型的误差最小化。然而，由于这种几何结构下相干散射和康普顿散射的能量间隔较小（约100电子伏特），使用半导体（如锗）探测器无法直接区分它们。本文描述了一种新颖的K边滤波技术，该技术可在前向散射几何结构中分离弹性信号和康普顿信号。用铒箔滤波的荧光X射线源产生的钽荧光辐射所获得的实验结果证明了该方法的可行性。本文还简要讨论了将该技术扩展用于“体内”测量生物组织低动量转移非弹性散射的可能性，这可能会提供有用的诊断信息。
