Floyd C E, Jaszczak R J, Harris C C, Greer K L, Coleman R E
Med Phys. 1985 Nov-Dec;12(6):776-8. doi: 10.1118/1.595663.
In single photon emission computed tomography (SPECT), Compton scattering produces a background that degrades the image quality and contributes erroneously to quantitative measurements. A clinically implementable compensation algorithm has previously been reported that subtracts a Compton scatter image, acquired in an energy window set below the energy of the photopeak, from the primary image acquired in the photopeak window. We present an evaluation and justification of the assumptions made in the previous empirical development of the subtraction algorithm. A Monte Carlo model of the SPECT system in which the Compton scattered vents may be followed independently of the nonscattered events was used to evaluate this subtraction technique. Simulation shows that the assumptions made in the experimental application of this algorithm were valid. Specifically (1) the "scatter" energy window used in the experiment (91-125 keV for imaging Tc-99m) contains only scattered events, (2) the shape of the line spread function (LSF) for the events in the scatter window is a reasonable approximation to the shape of the scatter in the photopeak window, and (3) the ratio of the number of scattered events in the photopeak window to the number of events in the scatter window is 0.57, close to the value of 0.5 derived heuristically. Thus, Monte Carlo simulation validates the basic assumptions underlying the empirical implementation of the scatter subtraction algorithm.
在单光子发射计算机断层扫描（SPECT）中，康普顿散射会产生背景，降低图像质量，并对定量测量产生错误影响。此前已报道了一种可临床应用的补偿算法，该算法从在光电峰窗口获取的主图像中减去在低于光电峰能量设置的能量窗口中获取的康普顿散射图像。我们对先前减法算法经验性开发中所做的假设进行了评估和论证。使用一个SPECT系统的蒙特卡罗模型来评估这种减法技术，在该模型中康普顿散射事件可以独立于非散射事件进行跟踪。模拟表明，该算法在实验应用中所做的假设是有效的。具体而言：（1）实验中使用的“散射”能量窗口（对于Tc-99m成像为91 - 125 keV）仅包含散射事件；（2）散射窗口中事件的线扩展函数（LSF）形状是对光电峰窗口中散射形状的合理近似；（3）光电峰窗口中散射事件数量与散射窗口中事件数量的比值为0.57，接近通过启发式方法得出的0.5的值。因此，蒙特卡罗模拟验证了散射减法算法经验性实现背后的基本假设。
