Lead Oxide (PbO) x-ray-to-charge transducer for direct conversion medical imaging detectors

点击翻译按钮获取中文摘要

X-ray imaging detectors rely on indirect or direct conversion of x-ray quanta to an electron signal. In the direct method, the x-ray quanta are absorbed in a photoconductor which is deposited directly on imaging electronics and acts as an x-ray-to-charge transducer. X-ray absorption creates electron hole pairs, which are subsequently separated by a bias field to generate a signal. The charges are moved by an electric field making it possible to create an image with a thick detector layer without significant loss of resolution. The conversion process can be up to ten times more efficient than for the indirect method, thus making it possible to improve both spatial resolution and dose efficiency down to the lowest required radiation exposure. This is only possible if the right photoconductor with an appropriate x-ray quantum efficiency, temporal performance, x-ray-to-charge conversion gain and good transport properties can be developed. Recently, my research group at Lakehead University synthesized a new photoconductor material for direct conversion x-ray imaging systems called, amorphous Lead Oxide (a-PbO). a-PbO has enormous potential for applications in radiographic and fluoroscopic imaging. It is a suitable high-Z (atomic number) material with distinct advantages over amorphous selenium (a-Se) - currently the only commercially viable x-ray photoconductor in direct conversion x-ray detectors - such as: it has higher x-ray detection efficiency than a-Se due to its higher atomic number, and thus permits effective absorption of higher energy x-rays with a thinner layer, (2) it has lower electron-hole pair creation energy, and hence a higher x-ray-to-charge conversion gain. This has a potential to reduce the radiation dose needed for medical X-rays to the fundamental quantum and spatial resolution limits. Although very promising, a-PbO layers are still experimental. More work on a-PbO photoconductor is now needed to assure technical feasibility to produce large area detectors with a photoconductive layer deposited directly on the imaging array, to optimize PbO technology and to enhance a-PbO properties as an x-ray-to-charge convertor. The objectives of this NSERC Discovery program are two-fold: to undertake comprehensive material science research into a new photoconductor material for x-ray imaging systems, namely amorphous Lead Oxide, and to develop functional prototypes of x-ray detectors based on this material for fluoroscopic and radiographic applications. The new a-PbO technology will achieve the theoretical limit of high detective quantum efficiency at low dose rates allowing the detector to be x-ray quantum noise limited at the low exposures. This in turn will allow the reduction of the incident x-ray dose to acquire an image and, thereby, to improve the overall safety of diagnostic and image-guided interventional procedures.