Phase Contrast X-ray Imaging With Field-Emission Source

描述（由申请人提供）： 目的：总体目标是开发一种具有高空间相干性的场发射X射线源，以及用于临床应用的相衬成像技术。挑战：目前的相衬X射线技术通常需要高度单色、基于同步加速器的平面波辐射和复杂的X射线光学器件，因此其临床应用受到限制。理论分析和实验研究已经证明了使用小但非常明亮的X射线源的同轴相位衬度成像的临床可行性。然而，这些要求不能通过常规源来满足。提出了一种新型场发射X射线源。方法：利用纳米尖端技术，研制出一种用于X射线源电子枪的超级针尖。超级尖端将与微型真空泵和离子镜集成，以避免污染和电子发射器的离子轰击。预期的最终产品是一种具有小焦斑（小于0.025 mm）的X射线源，同时具有高管电流（大于25 mA），从而提供高空间相干性。在本项目的早期阶段开发的场发射X射线源将用于促进新的相衬成像技术。创新性的系统设计是基于同轴全息原理，在大衰减下获取相位衬度（2）在20 Ip/mm时，相对相位衬度因子可达0.015;（3）相衬系统的探测器量子效率、辐射剂量和曝光时间与当前技术水平的系统的探测器量子效率、辐射剂量和曝光时间相等;以及（4）由于相衬引入的边缘增强，对比度细节可探测性显著提高。将进行全面测量，以表征申报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，以及基于分辨率的主观测量。所提出的研究的最终产品是用于临床应用的原型相衬成像系统。总结：拟议的研究，其创新的场发射源和一个新的在线x射线成像系统，克服了主要的技术“路障”在临床应用的相衬x射线成像。

DESCRIPTION (provided by applicant): Objective: The overall objective is to develop a field-emission x-ray source with high spatial coherence, and a phase-contrast imaging technique for clinical applications. Challenges: Current phase-contrast x-ray techniques generally require highly monochromatic, synchrotron-based, plane-wave radiation and sophisticated x-ray optics, so their clinical application is limited. Theoretical analysis and experimental studies have demonstrated the clinical feasibility of in-line phase-contrast imaging using a small, yet very bright x-ray source. However, these requirements cannot be met by the conventional sources. A novel field-emission x-ray source 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 super tip will be integrated with a miniature 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 mm), and at the same time, a high tube current (greater than 25mA), thus providing high spatial coherence. The field-emission x-ray source developed in the early phase of this project will be used to facilitate a new phase contrast imaging technique. The innovative system design is based on the in-line holography principle, acquiring phase contrast under large attenuation (a common clinical condition); therefore has the following clinically friendly features: (1) The source-to-detector distance of the system is no more than 1 meter; (2) the relative phase-contrast factor is up to 0.015 at 20 Ip/mm; (3) the detector quantum efficiency, radiation dose, and exposure time of the phase-contrast system are equivalent to that of the current state-of-art systems; and (4) the contrast-detail detectability is significantly improved due to the edge enhancement introduced by phase-contrast. 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. The end product of the proposed research is a prototype phase-contrast imaging system for clinical applications. Summary: The proposed research, with its innovative field emission source and a new in-line x-ray imaging system, overcomes the major technical "roadblocks" in clinical applications of phase-contrast x-ray imaging.