Design principles for advanced new low-dose photon-counting x-ray detectors for medical radiography

自1895年Röntgen发现x射线以来，x射线成像方法已经发展了100多年，现代医学完全依赖于基于x射线的诊断放射学，这继续激励着研究，以提高成本、疗效、安全性以及筛查和早期诊断的潜力。然而，已知有与辐射照射有关的风险，据估计，每200例癌症死亡中就有1例可归因于诊断性x射线成像。这种以更少的辐射产生更好的图像的关键需求是该提案的驱动动机。****探测器在低患者暴露下产生高质量图像的能力由探测器的探测量子效率（DQE）来描述。DQE是一个介于0和1之间的数字，表示为空间频率的函数，给出相对于理想探测器的性能。低频DQE值描述了在给定暴露条件下能清晰地看到大病变的程度。高频值描述小结构和精细细节的可视化。DQE的改进可用于提高图像质量或减少患者暴露，这取决于临床偏好。****新一代探测器目前正在开发中，可以测量x射线光子的能量，用于包括CT在内的高级成像程序。虽然设计这些光子计数系统以确保对患者的低剂量是必要的，但开发最佳设计所需的工具是原始的，不足以完成这项任务。因此，我们认为目前一些探测器几乎没有成功的机会，而另一些则没有开发出先进应用的全部潜力。****这些新探测器的全部潜力只能通过开发数学工具来实现，这些数学工具将物理设计参数和材料与所产生的图像质量联系起来。我们将在先前的贡献和基于傅立叶的线性系统的成功基础上，开发与光子计数能量鉴别探测器相关的信号和噪声的级联系统描述。我们将在多维方法中引入x射线光子能量作为独立参数，这将首次适应由能量依赖的x射线相互作用产生的图像信号中的空间相关性。正是这些相关性降低了成像系统的DQE，并最终导致图像质量差，需要对患者使用更高的辐射照射。这项研究的结果将为开发这些先进应用的最佳探测器提供第一种手段，并评估和验证它们在保持患者低水平x射线暴露的同时产生高质量图像的潜力。********

X-ray imaging methods have been under development for over 100 years since the discovery of x rays by Röntgen in 1895, and the complete dependency of modern medicine on x-ray-based diagnostic radiography continues to motivate research to improve costs, efficacy, safety and the potential for screening and early diagnoses. However, there are known risks associated with exposure to radiation and it has been estimated that 1 in 200 of all cancer deaths can be attributed to diagnostic x-ray imaging. This critical need to produce better images with less radiation is the driving motivation for this proposal.****The ability of a detector to produce high-quality images with low patient exposures is described by the detective quantum efficiency (DQE) of the detector. The DQE is a number between 0 and 1, expressed as a function of spatial frequency, giving performance relative to an ideal detector. Low-frequency DQE values describe how clearly large lesions can be visualized for a given exposure. High-frequency values describe visualization of small structures and fine detail. An improvement in DQE can be used either to increase image quality or reduce patient exposure, depending on the clinical preference.****A new generation of detectors is currently under development that can measure the energy of x-ray photons for use in advanced imaging procedures including CT. While it is essential these photon-counting systems be designed to ensure low dose to patients, the tools required to develop optimal designs are primitive and inadequate for the task. As a consequence, we believe some detectors currently under have little chance of success, while others are not being developed to exploit the full potential of advanced applications.****The full potential of these new detectors can only be achieved by developing the mathematical tools that relate physical design parameters and materials to the resulting image quality. We will build on previous contributions and the successes of Fourier-based linear systems to develop a cascaded-systems description of signal and noise as it pertains to photon-counting energy-discriminating detectors. We will introduce x-ray photon energy as an independent parameter in a multi-dimensional approach that will, for the first time, accommodate spatial correlations in image signals that result from energy-dependent x-ray interactions. It is these correlations that degrade the DQE of imaging systems, and are ultimately responsible for poor image quality requiring the use of higher radiation exposures to patients. Results from this research will provide the first means to develop optimal detectors for these advanced applications, and to assess and verify their potential to produce high-quality images while maintaining low levels of x-ray exposure to patients.********