High-Flux Multi-Spectral X-Ray Imaging for Accurate and Early Cancer Diagnosis

传统的医学X射线成像系统配备有：i）安装在快速旋转机架上的强大的X射线管，其产生以宽能量谱为特征的多色辐射，以及ii）X射线检测器，其记录透射通过患者身体的所有X射线的总能量。X射线束在穿过患者身体时的衰减取决于光子能量，并且这种能量依赖性对于不同的材料、组织和元素是不同的。因此，每个探测到的光子的能量包含关于被扫描物体的元素组成的附加有价值的信息。当前的X射线检测器大多对该光谱信息不敏感，因为它们的信号输出与沉积在检测器的有效区域内的总能量成比例，而具有能量辨别能力的检测器可以通过记录所有这些不同能量的光子并将它们布置到相应的光谱箱中来提供用于增强利用该附加光谱信息的解决方案。直接转换CdZnTe（CZT）半导体探测器具有高灵敏度、高阻止本领、高空间分辨率和优异的能量分辨率，在光谱和成像领域有着广泛的应用。最近，人们越来越关注将CZT探测器用于下一代高通量多能量X射线成像系统，特别强调计算机断层扫描（CT）和3D X射线乳腺成像。这两种成像方式都有共同的目标，能够进行定量测量，因此，在低患者剂量下提高诊断能力。然而，这些应用需要非常快速的数据采集，因此，需要能够以高光子通量（几乎每秒每平方毫米1亿个光子）有效操作的探测器。设计和制作基于能量敏感CZT探测器的高通量光子计数多光谱X射线成像扫描器是本方案的重点。这项工作的主要动机是调查在何种程度上光子计数，能量鉴别CZT探测器能够克服基本的性能限制，并进行定量成像揭示额外的光谱信息，因此，改善传统的X射线医学成像。如果能量信息与强度一起记录，则X射线医学成像模式可以通过软组织分化、材料分解、肿瘤表征、目标量化和疾病特异性靶向造影剂和药物的开发来提高诊断准确性。后者可以在显著降低辐射剂量的情况下提高低对比度分辨率和整体图像质量，并以较低的成本获得上级诊断性能。光谱X射线成像可以成为一种重要的成像技术，结合高空间分辨率成像提供特定材料的定量信息，因此，导致X射线医疗诊断的范式转变。

Conventional medical x-ray imaging systems are equipped with: i) a powerful x-ray tube, mounted on a fast rotating gantry, which generates polychromatic radiation characterised by a broad spectrum of energies, and ii) an x-ray detector, which records the total energy of all the x-rays that transmitted through the body of the patient. The attenuation of the x-ray beam, as it passes through the patient's body, depends on the photon energy and this energy dependence is different for different materials, tissues and elements. Therefore, the energy of each detected photon contains additional valuable information about the elemental composition of the scanned object. The current x-ray detectors are mostly insensitive to this spectral information, because their signal output is proportional to the total energy deposited within the active area of the detector, while a detector with energy-discrimination capabilities can provide the solution for enhanced exploitation of this additional spectral information by recording all these different energy photons and arranging them into respective spectral bins. Direct conversion CdZnTe (CZT) semiconductor detectors with high sensitivity, high stopping power, high spatial resolution and excellent energy resolution have emerged as the dominant solid-state room temperature detectors in a wide range of spectroscopic and imaging applications. Most recently, there has been a growing interest in using the CZT detectors for the next generation of high-flux multi-energy x-ray imaging systems, with a particular emphasis on Computed Tomography (CT) and 3D x-ray breast imaging. Both these imaging modalities have common goals, the ability to make quantitative measurements, and therefore, the enhancement of diagnostic capability at low patient doses. However, these applications require very fast data acquisition, and hence, there is a need for detectors that can efficiently operate at a high photon flux, almost 100 million photons per second per square millimetre. The design and fabrication of energy-sensitive CZT detector based scanner for high-flux photon-counting multi-spectral x-ray imaging is the focus of this proposal. The main motivation of this work is to investigate to which extent photon-counting, energy discriminating CZT detectors are capable of overcoming fundamental performance limits and carrying out quantitative imaging revealing the additional spectral information, and therefore, improving conventional x-ray medical imaging. If energy information is recorded alongside the intensity, x-ray medical imaging modalities could increase diagnostic accuracy through soft-tissue differentiation, material decomposition, tumour characterisation, target quantification and development of disease-specific targeted contrast agents and drugs. The latter could improve low-contrast resolution and overall image quality at significantly reduced radiation doses and lead to superior diagnostic performance with lower cost. Spectral x-ray imaging can become an important imaging technique providing material-specific quantitative information in combination with high spatial resolution imaging, and therefore, leading to a paradigm shift in x-ray medical diagnostics.