Robarts Research Institute and Department of Medical Biophysics, Western University, London, Ontario N6A 5C1, Canada.
Med Phys. 2013 Apr;40(4):041913. doi: 10.1118/1.4794499.
Single-photon counting (SPC) x-ray imaging has the potential to improve image quality and enable new advanced energy-dependent methods. The purpose of this study is to extend cascaded-systems analyses (CSA) to the description of image quality and the detective quantum efficiency (DQE) of SPC systems.
Point-process theory is used to develop a method of propagating the mean signal and Wiener noise-power spectrum through a thresholding stage (required to identify x-ray interaction events). The new transfer relationships are used to describe the zero-frequency DQE of a hypothetical SPC detector including the effects of stochastic conversion of incident photons to secondary quanta, secondary quantum sinks, additive noise, and threshold level. Theoretical results are compared with Monte Carlo calculations assuming the same detector model.
Under certain conditions, the CSA approach can be applied to SPC systems with the additional requirement of propagating the probability density function describing the total number of image-forming quanta through each stage of a cascaded model. Theoretical results including DQE show excellent agreement with Monte Carlo calculations under all conditions considered.
Application of the CSA method shows that false counts due to additive electronic noise results in both a nonlinear image signal and increased image noise. There is a window of allowable threshold values to achieve a high DQE that depends on conversion gain, secondary quantum sinks, and additive noise.
单光子计数 (SPC) X 射线成像具有提高图像质量和实现新的先进能量相关方法的潜力。本研究的目的是将级联系统分析 (CSA) 扩展到 SPC 系统的图像质量和探测量子效率 (DQE) 的描述中。
点过程理论用于开发一种通过阈值处理阶段（用于识别 X 射线相互作用事件）传播平均信号和 Wiener 噪声功率谱的方法。新的传递关系用于描述包括入射光子随机转换为二次量子、二次量子汇、附加噪声和阈值水平影响的假想 SPC 探测器的零频率 DQE。理论结果与假设相同探测器模型的蒙特卡罗计算进行了比较。
在某些条件下，可以将 CSA 方法应用于 SPC 系统，附加要求是通过级联模型的每个阶段传播描述形成图像的总量子数的概率密度函数。在考虑的所有条件下，包括 DQE 的理论结果与蒙特卡罗计算非常吻合。
CSA 方法的应用表明，由于附加电子噪声而导致的错误计数会导致图像信号非线性和图像噪声增加。存在一个允许的阈值窗口，可以实现高 DQE，这取决于转换增益、二次量子汇和附加噪声。
