Photoconductors for radiation imaging detectors: materials issues and device designs

用于辐射成像探测器的光电导体：材料问题和器件设计

• 批准号: RGPIN-2014-06103
• 负责人: Kabir, MZahangir
• 金额: $ 1.82万
• 依托单位: Concordia University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612034
• 关键词: Photoconductors; radiation; imaging; detectors; materials

There is a huge demand for lowering irradiation dose in various medical radiation imaging modalities especially in general X-ray radiography and real-time radiation imaging. After last two decades of extensive research, amorphous selenium (a-Se) based direct conversion flat-panel digital X-ray detector (the incident X-rays directly generate charge carriers in the photoconductor layer) is recently commercialized for digital mammography. The a-Se detector is not perfect and the main drawback of the conventional a-Se detector under normal operation is its low sensitivity compared to other potential photoconductors such as polycrystalline lead oxide or mercuric iodide. Low sensitivity gives low signal to noise ratio in low-dose imaging and thus severely affects the diagnostic features of the image. Very low-dose medical X-ray imaging could be achieved by; (1) utilizing avalanche multiplication process at a very high electric field in a-Se layer for higher charge signal, and/or (2) replacing a-Se by other potential photoconductors that can provide higher collected charge. Low-cost X-ray imaging can be obtained by utilizing organic photoconductors in X-ray detectors. The research on avalanche a-Se solid state imaging detector is in a very premature level; it needs extensive research works to clearly understand the fundamental underlying physics of carrier generation, multiplication, and transport mechanisms, and to optimize the detector design by examining imaging performances. The PI's research program will endeavor to develop low-dose and/or low-cost medical X-ray/optical imaging detectors by extensively investigating charge carrier generation, transport, multiplication, and noise creation mechanisms in photoconductors, developing mathematical models for analyzing imaging detector performances such as dark current, sensitivity, DQE (detective quantum efficiency), and MTF (modulation transfer function) as a function of field, temperature, detector structure, X-ray induced effects, excess noise, and hence optimizing the detector designs. The proposed work is vital to understand the fundamental physics of X-ray/optical detector operations and photoconductor properties, and to identify the important factors that limit the detector performances, which can ultimately lead to finding the efficient materials and designs for low-cost and efficient radiation imaging detectors for various digital medical imaging applications. This research will advance scientific knowledge in high field transport mechanisms in amorphous and polycrystalline photoconductors. The mathematical models can be used as design tools by researchers in academia and industries. The proposed work has excellent scope for original and fundamental research for graduate students, which will advance fundamental scientific knowledge and transfer it to the next generation. This research will be beneficial to Canada’s R&D efforts in medical digital imaging, and the digital radiation image detector community (e.g., Analogic and Hologic).

在各种医学辐射成像方式中，特别是在普通X射线照相和实时辐射成像中，存在着降低辐射剂量的巨大需求。经过近二十年的广泛研究，基于非晶态硒(a-Se)的直接转换平板数字X射线探测器(入射X射线在光导层中直接产生载流子)最近被商业化，用于数字乳房X光成像。A-Se探测器并不完美，常规a-Se探测器在正常工作状态下的主要缺点是其灵敏度低于其他潜在的光电导体，如多晶氧化铅或碘化汞。在低剂量成像中，低灵敏度会导致低信噪比，从而严重影响图像的诊断特征。通过以下方法可以实现极低剂量医用X射线成像：(1)利用a-Se层中极高电场下的雪崩倍增过程来获得更高的电荷信号，和/或(2)用其他能够提供更高收集电荷的潜在光导体来取代a-Se。在X射线探测器中使用有机光导体可以获得低成本的X射线成像。雪崩a-Se固体成像探测器的研究还处于一个非常不成熟的水平，需要大量的研究工作来清楚地了解载流子产生、倍增和输运机制的基本物理基础，并通过检查成像性能来优化探测器的设计。 PI的研究计划将致力于开发低剂量和/或低成本的医用X射线/光学成像探测器，方法是广泛研究光导体中载流子的产生、传输、倍增和噪声产生机制，开发数学模型来分析成像探测器的性能，如暗电流、灵敏度、DQE(探测量子效率)和MTF(调制传递函数)随场、温度、探测器结构、X射线诱导效应、过剩噪声的函数，从而优化探测器设计。 这项拟议的工作对于理解X射线/光学探测器操作的基本物理和光导体特性，以及确定限制探测器性能的重要因素至关重要，这些因素最终可以导致为各种数字医学成像应用找到低成本和高效率的辐射成像探测器的有效材料和设计。这项研究将促进对非晶态和多晶光导体中高场输运机制的科学认识。这些数学模型可以作为学术界和工业界研究人员的设计工具。建议的工作对研究生具有很好的原创性和基础性研究的范围，这将促进基础科学知识并将其传递给下一代。这项研究将有益于加拿大在医疗数字成像和数字辐射图像探测器社区(例如，Analogic和HOLOGIC)的研发工作。