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

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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. **