School of Mechanical Engineering, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan, Republic of Korea.
Med Phys. 2012 May;39(5):2478-90. doi: 10.1118/1.3702455.
This study investigates the fundamental signal and noise performance limitations imposed by the stochastic nature of x-ray interactions in selected photoconductor materials, such as Si, a-Se, CdZnTe, HgI(2), PbI(2), PbO, and TlBr, for x-ray spectra typically used in mammography.
It is shown how Monte Carlo simulations can be combined with a cascaded model to determine the absorbed energy distribution for each combination of photoconductor and x-ray spectrum. The model is used to determine the quantum efficiency, mean energy absorption per interaction, Swank noise factor, secondary quantum noise, and zero-frequency detective quantum efficiency (DQE).
The quantum efficiency of materials with higher atomic number and density demonstrates a larger dependence on convertor thickness than those with lower atomic number and density with the exception of a-Se. The mean deposited energy increases with increasing average energy of the incident x-ray spectrum. HgI(2), PbI(2), and CdZnTe demonstrate the largest increase in deposited energy with increasing mass loading and a-Se and Si the smallest. The best DQE performances are achieved with PbO and TlBr. For mass loading greater than 100 mg cm(-2), a-Se, HgI(2), and PbI(2) provide similar DQE values to PbO and TlBr.
The quantum absorption efficiency, average deposited energy per interacting x-ray, Swank noise factor, and detective quantum efficiency are tabulated by means of graphs which may help with the design and selection of materials for photoconductor-based mammography detectors. Neglecting the electrical characteristics of photoconductor materials and taking into account only x-ray interactions, it is concluded that PbO shows the strongest signal-to-noise ratio performance of the materials investigated in this study.
本研究探讨了在乳腺 X 射线摄影中常用的 X 射线能谱范围内，选定光电导材料（如 Si、a-Se、CdZnTe、HgI(2)、PbI(2)、PbO 和 TlBr）中 X 射线相互作用的随机性对基本信号和噪声性能的限制。
展示了如何将蒙特卡罗模拟与级联模型相结合，以确定每种光电导材料与 X 射线光谱组合的吸收能量分布。该模型用于确定量子效率、每次相互作用的平均能量吸收、Swank 噪声因子、二次量子噪声和零频率探测量子效率（DQE）。
原子数和密度较高的材料的量子效率对转换器厚度的依赖性大于原子数和密度较低的材料，除了 a-Se 以外。平均沉积能量随入射 X 射线谱平均能量的增加而增加。HgI(2)、PbI(2)和 CdZnTe 随质量负载的增加而沉积能量增加最大，而 a-Se 和 Si 则最小。PbO 和 TlBr 具有最佳的 DQE 性能。对于质量负载大于 100mg/cm(-2)，a-Se、HgI(2)和 PbI(2)提供与 PbO 和 TlBr 相似的 DQE 值。
通过图表列出了量子吸收效率、每次相互作用的平均沉积能量、Swank 噪声因子和探测量子效率，这些图表可能有助于设计和选择基于光电导的乳腺 X 射线摄影探测器的材料。在不考虑光电导材料的电学特性，只考虑 X 射线相互作用的情况下，得出结论 PbO 表现出研究中所涉及材料中最强的信噪比性能。
