SWAD: Large-Area Photon Counting X-Ray Imager using Amorphous Selenium

摘要 医用x射线成像领域在本世纪初经历了一场“数字革命”， 基于面板有源矩阵成像器(AMFPI)的数字射线成像系统的推广。 从那时起，我们看到了基于非晶硅有源矩阵技术的大面积AMFPI的快速发展和临床移植。然而，他们有一个主要的困难需要克服：生产 X射线量子噪声在非常低的剂量下限制了图像。AMFPI的先进应用，包括断层合成和锥束计算机断层扫描，推动了下一代的发展 探测器，主要是AMFPI生成受量子噪声限制的高质量图像的能力 并且在低X射线曝光和高帧速率下没有伪影。另一种方法是运营 脉冲模式的探测器用于光子计数，通过高效地提供更高的剂量效率 噪声抑制、量子噪声限制性能和最佳能量权重。光子计数 系统也不容易受到内存伪像的影响。虽然用于计算机层析成像的光子计数探测器的发展已经非常有前途，但还没有商用的光子计数2D传感器 由于同时需要高分辨率，所以存在用于X光照相或乳房X光照相 而且面积很大。我们的假设是，一种单极直接转换非晶态硒探测器 时差(UTD)电荷传感和雪崩增益可以产生经济高效的大面积光子 具有光谱功能的计数成像仪。光子计数的真正影响是提供高光谱成像(通过多能量阈值)，以实现对比度增强的广泛应用 (Ce)具有快速采集和无运动伪影的乳房成像(通过同时采集 单次X射线曝光期间的高能量和低图像)。因此，这项提议的目标是 利用所提出的电场整形多井制作和测试光子计数成像仪样机 雪崩探测器(SWAD)。从概念上讲，拟议的Swad成像仪使用四个主要组件： (1)光子计数芯片；(2)多井象素几何结构；(3)非晶态硒(a-Se)光导体 沉积在多井衬底上，用于UTD电荷传感和雪崩增益，最后(4)和 SWAD芯片将要连接到的图像采集电路板。我们希望表明， 所提出的光子计数SWAD成像器具有量子噪声受限的性能、对能量加权的高光谱灵敏度和高帧速率。SWAD的成功开发将带来有史以来的第一次 用于X射线成像的高性价比大面积光子计数探测器。尽管这似乎是一种 高成本的方案，我们开发的技术创新将导致广泛的临床应用 用于乳房X光检查的更有效和更低剂量的对比剂增强癌症筛查系统。

Abstract The field of medical x-ray imaging experienced a "digital revolution" in the early 2000s, with the spreading of digital radiography systems which are based on active matrix at panel imagers (AMFPI). Since then we have seen rapid development and clinical translation of large-area AMFPI based on amorphous silicon active matrix technology. However they have one major difficulty to overcome: producing x-ray quantum noise limited images at very low dose. Advanced applications of AMFPI, including tomosynthesis and cone-beam computed tomography have fueled the development of the next generation detectors, mainly in the ability of AMFPI to generate high quality images that are quantum noise limited and free from artifacts at low x-ray exposures and high frame rates. An alternative approach is to operate the detector in pulse mode for photon counting which provides higher dose efficiency through efficient noise rejection, quantum-noise limited performance, and optimal energy weighting. Photon counting systems are also not susceptible to memory artifacts. While the development of photon counting detector for computed tomography has been very promising, no commercial photon counting 2D sensors exists for radiography or mammography due to the simultaneous requirement for both high resolution and large area. Our hypothesis is that a direct-conversion amorphous selenium detector with unipolar time-differential (UTD) charge sensing and avalanche gain can yield a cost-effective and large-area photon counting imager with spectroscopic capabilities. The true impact of photon counting is to provide hyperspectral imaging (via multi-energy thresholding) to enable widespread application of contrast enhanced (CE) breast imaging with rapid acquisition and without motion artifacts (via simultaneous acquisition of high energy and low images during a single x-ray exposure). The objective of this proposal is therefore to fabricate and test a prototype photon counting imager using the proposed eld-Shaping multi-Well Avalanche Detector (SWAD). Conceptually the proposed SWAD imager employs four major components: (1) a photon counting chip, (2) multi-well pixel geometry, (3) amorphous selenium (a-Se) photoconductor deposited over the multi-well substrate for UTD charge sensing and avalanche gain, and finally (4) an image acquisition circuit board where the SWAD chip will be connected to. We expect to show that the proposed photon counting SWAD imager has quantum-noise-limited performance, high spectral sensitivity for energy weighting, and high frame-rates. Successful development of SWAD will lead to the first ever cost-effective and large-area photon counting detector for x-ray imaging. Although this is seemingly a high cost proposal, the technological innovation we develop will lead to the widespread clinical application of a more efficient and lower dose contrast-enhanced cancer screening system for mammography.