X射线光栅相衬成像像质评估、优化和实验验证研究

Grating-based X-ray phase contrast imaging can detect the substance composed of light elements that can’t be detected by traditional X-ray absorption imaging, which has important potential applications in the field of medical and material science in the future. However, the fabrication of the grating is still very difficult, so it is very important to evaluate the influence of grating quality on the imaging quality. With the increase of X-ray energy and the expand of field of view, it becomes even more critical. Based on this issue, we plan to establish a theoretical model to study the impact mechanism of grating quality on imaging quality, and carry out a research on the evaluation and optimization of imaging quality. First, the transfer function model is build, and the evaluation system of imaging quality will be established after introducing the impact of the source coherence, detector resolution and grating parameters; The second is to study the impact of grating quality and fringe visibility on the imaging quality, and then a method would be proposed to optimize imaging quality and reduce the difficulty of device fabrication; Third is to develop a phase-type resolution panel by the femtosecond laser micromachining, and construct an imaging platform for the experimental validation of the proposed method. Implementation of this project will contribute to the development of theory and technology in grating-based X-ray phase contrast imaging, and promote the practical process of this technique.

X射线光栅相衬成像对轻元素物质具有传统吸收成像无法比拟的衬度优势，在医学和材料科学等领域具有巨大的应用潜力。目前成像使用的X射线光栅的制作仍然十分困难，评估光栅质量对成像质量的影响对器件制作非常重要，随着X射线能量提高和视场扩大，这个问题就更为关键。本项目基于这一问题，拟建立理论模型研究光栅质量对相衬成像质量的影响机制，开展其像质评估和优化方法的理论和实验研究：一是构建光栅相衬成像的传递函数模型，引入光源相干性、探测器分辨率和光栅参数等影响因素，建立像质评估体系；二是基于传递函数模型重点研究光栅质量及条纹对比度对成像质量的影响，提出优化成像质量和降低器件制作难度的方法和途径；三是利用飞秒激光微加工技术研制一种相位型分辨率板，构建成像平台对像质优化方法进行实验验证，探索更具实用价值的成像实现方案和技术。本项目的实施将有助于发展和完善X射线光栅相衬成像理论和技术，推动该技术的实用化进程。

X射线光栅相衬成像技术可同时获得轻元素物质的吸收、相衬和散射图像，在材料科学、生命科学和医学等领域有巨大应用潜力。相比传统X射线吸收成像技术而言，该成像技术仍然处于起步阶段，其成像灵敏度和图像分辨率尚有待评估和优化。本项目针对这一问题，建立了基于传递函数的相衬成像系统理论模型，引入光源焦斑在像面上的投影函数、转换屏的点扩散函数和探测器像素函数等影响因素，分析了光栅参数及位移误差对成像系统的影响，并设计制作了一种用于像质评估验证的相位灵敏度分辨率板，通过分辨率板样件的成像结果评估得到了实验系统不同空间分辨率情况下可探测的折射角灵敏度。在此基础上，提出了基于纳米颗粒填充制作吸收光栅的途径以降低光栅制作难度，初步实验探究了铋纳米颗粒填充制作24μm周期吸收光栅的结果；提出了一种X射线级联光栅相衬成像系统以提高成像视场和成像质量，验证了对称型级联光栅相衬成像系统的实验结果，分析了样品位置对成像灵敏度的影响规律，并利用基于空间滤波的傅里叶变换恢复算法得到了样品的吸收、相衬和散射图像。本项目传递函数模型的建立和相位灵敏度分辨率板的研制，从理论和实验两方面为光栅相衬成像系统提供了像质评估和验证机制；本项目纳米颗粒填充制作吸收光栅和级联光栅相衬成像系统的实施，从器件和系统两方面为光栅相衬成像系统提供了像质提升和优化方案。