Polycrystalline Lead Oxide (PbO) photoconductor: physics and application in direct conversion x-ray medical imaging detectors

以非晶态硒(a-Se)层作为X射线-电荷换能器的直接转换X射线探测器使放射医学成像发生了革命性的变化。事实上，a-se乳房X光照相探测器显示的乳房图像质量优于其他现有的商业探测器。*尽管a-Se的特性适合乳房X光照相能量范围内的应用，但对于一般的射线照相和透视应用，a-Se必须被更高的Z(原子序数)材料取代。因此，需要一种新的材料来实现直接转换方法在诊断能量范围内的优势。这一需求在这里得到解决：拟议的研究计划的目标是将直接转换X射线探测器的进展扩展到基于最有前途的光电导体材料--多晶氧化铅(PbO)的荧光和射线照相应用。新的氧化铅光导体技术将实现比现有商业间接转换方法更高的灵敏度和更高的空间分辨率。*PBO在射线照相和荧光成像方面具有巨大的应用潜力。与a-Se相比，它有两个明显的优点：*(1)由于其更高的Z，它具有比a-Se更高的X射线探测效率，从而允许用更薄的层有效地吸收更高能量的x射线；*(2)它具有更低的电子-空穴对产生能，因此更高的x射线-电荷转换增益。*然而，PbO光导层仍处于实验阶段-它们还没有达到理论极限的转换效率，并且在技术的现阶段，PbO层还没有表现出足够的时间特性来用于荧光应用。克服这些挑战需要一个关于PBO物理和材料科学的综合计划，以了解这种材料中的制备-制造-性能关系，并在此基础上优化PBO技术。拟议的计划旨在将改进的PBO技术转化为用于透视的有源矩阵平板成像器(AMFPI)和用于射线照相的低成本X射线光阀(XLV)探测器。*基于PBO的探测器技术的发展是数字X射线成像系统不断发展的重要科学和工程成就。特别是，基于PbO的探测器在较低的X射线曝光时具有更高的灵敏度。这具有以下核心好处：减少入射X射线剂量以获得诊断图像，从而提高普通射线照相和介入操作的总体安全性，或者提高在典型X射线暴露下的疾病可探测性。因此，拟议的计划最终将使加拿大和世界各地的医疗保健受益。**

Direct conversion x-ray detectors with amorphous selenium (a-Se) layer as x-ray-to-charge transducers revolutionized radiation medical imaging. Indeed, a-Se mammographic detectors show breast image quality superior to other existing commercial detectors. ***Although a-Se properties fit applications in the mammographic energy range, for general radiographic and fluoroscopic applications a-Se has to be replaced by higher Z (atomic number) material. Therefore there is a need for a new material to realize the advantages of direct conversion methods in the diagnostic energy range. This need is addressed here: the objective of the proposed research program is to extend the advances of direct conversion x-ray detectors to fluoroscopic and radiographic applications on the basis of the most promising photoconductor material, namely Polycrystalline Lead Oxide (PbO). The new Lead Oxide Photoconductor technology will achieve higher sensitivity and improved spatial resolution over existing commercial indirect conversion methods. ***PbO has enormous potential for applications in radiographic and fluoroscopic imaging. It has two distinct advantages over a-Se: ***(1) it has higher x-ray detection efficiency than a-Se due to its higher Z and thus permits effective absorption of higher energy x-rays with thinner layer, and ***(2) it has lower electron-hole pair creation energy, and hence a higher x-ray-to-charge conversion gain.***However, PbO photoconductive layers are still experimental-they have not yet achieved conversion efficiency as high as the theoretical limit, and at the present stage of the technology, PbO layers have not yet shown adequate temporal behavior for fluoroscopic applications. Overcoming these challenges requires a comprehensive program on PbO physics and material science to understand the preparation-?fabrication-property relationships in this material and to optimize PbO technology based on this knowledge. The proposed program aims to transfer an improved PbO technology into Active Matrix Flat Panel Imagers (AMFPI) for fluoroscopy and low-cost X-ray light valve (XLV) detectors for radiography. ***The development of PbO-based detector technology is an important scientific and engineering accomplishment in the continuing development of digital x-ray imaging systems. In particular, PbO-based detectors have greater sensitivity at lower x-ray exposures. This has the core benefit of either reducing the incident x-ray dose to acquire a diagnostic image, and thereby improve the overall safety of general radiography and interventional procedures, or to improve disease detectability at typical x-ray exposures. As such, the proposed program will ultimately benefit healthcare in Canada and worldwide. **