A Dual Detector for X-Ray Attenuation and Phase Imaging

描述(由申请人提供)： 目的：总体目标是开发一种新的诊断X射线成像技术，同时获取衰减图像和相位图像。挑战：使用具有高空间相干性的第三代同步辐射X射线源进行的开创性研究已经证明，相位对比度可以显著提高诊断成像的灵敏度。然而，同步加速器X射线源的成本、大小和可用性都不适合临床应用。因此，提出了一种具有高空间相干性和双探测器系统的新型场发射X射线源。方法：应用尖端纳米技术制作X射线源电子枪的超级针尖。针尖由纳米晶体材料制成，其零维电子结构和非欧姆跳跃导电将使电流密度高达2×107A/cm2而不会烧毁。通过电子束诱导沉积，超级针尖将与微型轨道真空泵和离子反射镜集成在一起，以避免污染和对电子发射体的离子轰击。预期的最终产品是具有小焦斑(小于0.025毫安)的X射线源，同时具有高管电流(大于25 mA)，从而提供具有高空间相干性的明亮源。基于同轴全息原理，利用这种新型光源，我们将研制一种双探测器系统来获取衰减像和相位差图像，并将开发一种算法从这两幅图像中重建出一幅位相图像。将进行全面的测量，以表征拟议系统在临床条件下的性能。这包括分辨率、对比度和量子效率的客观测量，以及基于观察者的主观测量。临床益处：该技术具有以下临床友好的特点：(1)系统的源到探测器的距离不超过1m；这是通过使用所提出的具有高空间相干性的场发射源来实现的；(2)在传统剂量水平的一次曝光中获得两幅图像，一个相位对比度和一个衰减图像，以实现相位恢复。(3)由于组织与病变之间的相位差是常规衰减对比度的数百倍，因此与常规X射线图像相比，重建相位图像提供了显著改善的组织-病变对比度。摘要：通过将基于纳米技术的场发射源、双探测器系统和位相重建算法相结合，该研究将为诊断X射线成像创造一种新的灵敏方式。

DESCRIPTION (provided by applicant): Objective: The overall objective is to develop a new diagnostic x-ray imaging technique that acquires both attenuation- and phase-images simultaneously. Challenges: Pioneer research performed with the 3rd generation synchrotron x-ray sources with high spatial coherence has proved that phase-contrast can significantly improve the sensitivity of diagnostic imaging. However, the costs, size and availability of a synchrotron x-ray source do not fit to clinical applications. A novel field-emission x-ray source with high spatial coherence and a dual-detector system is therefore proposed. Methods: Cutting-edge nanotechnology will be applied to fabricate a super tip for the electron gun of the x-ray source. The tip is made of the nanocrystal material, whose zero-dimensional electronic structure and non-Ohmic hopping conduction will allow a current density as high as 2 x 107 A/cm2 without burning out. By using the electron beam induced deposition the super tip will be integrated with a miniature Orbitron vacuum pump and an ion mirror to avoid contamination and the ion bombardment of the electron emitter. The anticipated end product is an x-ray source with a small focal spot (less than 0.025 ram), and at the same time, a high tube current (greater than 25mA), thus providing a bright source with high spatial coherence. With such a new source, a dual detector system will be developed to acquire both attenuation- and phase-contrast images based on the in-line holography principle, and an algorithm will be developed to reconstruct a phase-image from these two images. Comprehensive measurements will be conducted to characterize the performance of the proposed system under clinical conditions. That includes objective measurements of resolution, contrast and quantum efficiency, and observer-based subjective measurements. Clinical benefits: The proposed technique has the following clinically friendly features: (1) The source-to-detector distance of the system is no more than 1 m; this is achieved by using the proposed field emission source with high spatial coherence; (2) Two images, a phase-contrast and an attenuation image are acquired at one exposure at the conventional dose level to enable phase-retrieval. (3) The reconstructed phase-image provides a significantly improved tissue-lesion contrast as compared with conventional x-ray images, because the phase differences between tissue and lesion are hundreds times larger than conventional attenuation contrast. Summary: By combining the nano-technology-based field emission source, a dual-detector system, and a phase-reconstruction algorithm, the proposed research would create a new sensitive way in diagnostic x-ray imaging.