| 题名 | 硬X射线位相衬度成像及荧光全息成像的实验与理论研究 |
| 作者 | 谢红兰 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 |
| 关键词 | X射线 全息术 层析术 位相衬度 |
| 其他题名 | Theoretical and experimental study on phase-contrast imaging and fluorescence holography with hard X-rays |
| 中文摘要 | X射线成像技术因为其光源波长比可见光短得多，因而在理论上可以达到更高的成像分辨率。此外，X射线与物质相互作用时的性质也与可见光有所不同，因此用X射线成像可以获得许多丰富的信息。近年来，随着高亮度同步辐射光源及X射线激光的迅猛发展，X射线成像技术已经成为国际上成像领域的一个研究热点，在医学诊断、生物和材料研究等领域有显著的优越性，极具推广应用的潜力，但在我国尚处于起步阶段。本论文分别对X射线层析成像技术、硬X射线位相衬度成像技术和硬X射线荧光全息成像技术进行了理论模拟和实验研究，取得了若干具有创新性的研究成果：一、X射线层析成像的理论研究1．进行了X射线层析成像技术的理论模拟研究，用两种代数迭代算法对模拟的投影图进行了重构，讨论了投影角度范围不完全、投影的角度步长、样品的疏密程度及迭代次数的多少对重构结果的影响，为实验研究提供了有用的指导。2．在国际上首次提出了预放大X射线全息层析成像方法和X射线像面全息层析成像方法，利用微波带片在记录全息图前对干涉场进行预放大，可将干涉条纹间距放大至1000倍左右，大大降低对记录介质的分辨率要求，因此可以直接用CCD记录全息投影图，实现实时的三维重构。3．在国际上首次在X射线荧光层析成像装置中引入一种新型的双聚焦模式晶体单色器来消除背景透射光和散射光，通过调节晶体单色器的位置来选择和聚焦所需的特定能量的X射线荧光，大大提高了信噪比。在此基础上提出了一种新的实验方案，可同时进行X射线荧光层析成像和传统的X射线层析成像实验研究，为待测样品提供更全面的信息。二、硬X射线位相衬度成像的理论与实验研究4．根据X射线干涉仪位相衬度成像原理，对单次干涉成像过程和多次干涉成像过程进行了数值模拟研究并用相应的数值方法进行了位相恢复，发现虽然单次干涉成像的实验过程比较简单，但其位相恢复结果不及多次干涉成像的位相恢复结果好，为实验研究提供了理论依据。5．在北京同步辐射实验室成功地进行了生物样品的X射线衍射增强的位相衬度成像的实验研究，得到了非常清晰的成像结果，其衬度大大高于传统的X射线吸收衬度成像结果，其成像分辨率可达10微米左右。6．进行了X射线同轴位相衬度成像的数值模拟研究，采用强度传输方程位相恢复算法对模拟结果进行了数字重构，分别讨论了成像距离及测量噪声对位相衬度像及其位相恢复像的影响。这些理论结果将指导实验研究，其重构程序可对实验数据进行处理。并在北京同步辐射实验室成功地进行了生物样品的X射线同轴位相衬度成像的实验研究，获得了图像衬度比较高的成像结果。三、硬X射线荧光全息成像的理论研究7．自行编制了硬X射线荧光全息成像的数值模拟程序及其原子像的重构程序。重构了国外的研究小组发表在美国物理评论快报上的实验结果，证实了该重构程序的正确性。对体心立方的Fe单晶进行了数值模拟研究，分别在（001）、（010）、（100）晶面上得到了与晶格模型一致的原子重构像，表明运 用这种成像技术，能够得到晶体内部的原子的三维排列信息。8．详细讨论了记录X射线荧光全息图的角度范围对原子像的影响，发现角度 范围不完全将导致原子像畸变。研究了全息图上的衍射线的性质，提出利用衍射线的性质拓展全息图来消除角度范围不完全对原子像的影响。9．详细讨论了单能量全息图重构中的孪生像对原子像的影响。自行编制了消除孪生像的多重能量全息图重构程序和双能量全息图重构程序。通过详细的理论推导和数值模拟研究，在国际上首次提出了既能消除孪生像又能提高原子像分辨率和原子像位置的准确性的方法：可进一步地指导实验研究。10．通过数值模拟研究详细讨论了入射光源的偏振性对重构的原子像的影响，发现水平线偏振光和垂直线偏振光对不同位置的原子像有不同的影响。在国际上首次将双能量全息图重构算法和消除偏振效应的修正算法结合起来，提出了一种能同时消除孪生像和入射光源的偏振效应的方法，并通过数值模拟研究验证这一方法是可行的。这些理论上的结果将在以后的实践中指导实验研究，编制的重构程序可直接用来处理实验结果。 |
| 英文摘要 | X-ray imaging techniques can obtain a higher image resolution in theory because the wavelength of X-rays is much shorter than that of visible light. Moreover, the interaction between X-rays and matter is different from that between visible light and matter and therefore much more information can be obtained by X-ray imaging. With the rapid development of high-brightness synchrotron radiation and X-ray laser, researches on X-ray imaging techniques become very active for years in international imaging field and have a widely applied potentiality and obvious advantages in medical diagnosis, biology and material science. However, the study on X-ray imaging techniques just begins in China. This dissertation includes theoretical simulation and experimental study of X-ray tomography, phase-contrast imaging and fluorescence holography with hard x-rays and some important results are obtained as below: Part 1: Theoretical study on X-ray tomography 1. A theoretical simulation study of X-ray tomography is carried out. The reconstruction is obtained from simulated projects by using two kinds of Algebraic Reconstruction Techniques (ART). The influences of the range and the step length of projected angles, the density of a sample and times of iteration on reconstructed results are discussed and the results will direct experimental study. 2. Two new methods of X-ray holographic tomography are first proposed in the world including Pre-amplified X-ray holographic tomography and X-ray image holographic tomography. The interference field is pre-amplified by a micro-zone plate before recording a projected hologram and then the requirement on resolution of recording medium is degraded greatly. Therefore, the hologram can be directly recorded with a CCD camera andihejreal-time reconstruction can be realized. 3. A kind of new center-stopped sagittally focusing crystal monochromator is first introduced in X-ray fluorescence tomography for removing scattered andtransmitted X-rays in the world. With the monochromator normal to incident X-rays, the required X-ray fluorescence signals can be focused on the detector surface by adjusting distance between the monochromator and a test sample and can improve signal-to-noise ratio. On the basis, a new experimental system is proposed, which can perform experimental study of X-ray fluorescence tomography and traditional X-ray tomography at the same time and provides much more information of test samples. Part 2: Theoretical and experimental study on phase-contrast imaging with hard x-rays 4. Based on the imaging principle of phase-contrast imaging with an X-ray interferometer, simulations of a single interference imaging and multiple interference imaging are performed and phase retrieval results from the simulated data are obtained with two methods. The results indicate that a single interference imaging is simpler in experiment that multiple interference imaging, but the phase retrieval result is not better than that of the latter. The simulated results will provide theoretical direction. 5. An experiment of diffraction enhanced imaging with hard X-rays is successfully performed at Beijing Synchrotron Radiation Facility and a clear image of inside structures of the sample is obtained. The image contrast is higher than absorption image contrast by traditional X-ray radiography and the spatial resolution is about 10 micrometer. 6. A simulation study of in-line phase-contrast imaging with hard x-rays is performed. Phase retrieve from the simulated data is obtained with Transport Intensity Equation (TIE) algorithm. The influences of the distance between a sample and a detector, measuring noise on the imaging results and reconstructed results are discussed. An experimental study of in-line phase-contrast imaging with hard x-rays of biological specimens is successfully performed at Beijing Synchrotron Radiation Facility. An Image with high phase contrast is obtained at a suitable distance between the specimen and the detector. Part 3: Theoretical study on X-ray fluorescence holography 7. A simulation program of X-ray fluorescence holography and a reconstruction program to obtained atomic images from an x-ray fluorescence hologram are written. The atomic images are reconstructed from the experimental results performed by a foreign research group published at PRL with the reconstruction program. The result proves that the reconstruction program can treat experimental results. An X-ray fluorescence hologram of an iron single crystal with a body-centred cubic lattice is numerically simulated with the simulation program and the Fe atomic images are reconstructed from the simulated hologram. The atomic images of the (001), (010), (100) crystallographic planes are consistent with the corresponding atomic positions of the lattice. The results indicate that three-dimensional atomic arrangement information can be obtained by X-ray fluorescence holography. 8. The influences of the angle ranges for recording X-ray fluorescence holograms on reconstructed atomic images are discussed in detail. It is found that incomplete ranges of azimuth and polar angels for recording holograms can lead to distorted reconstructed atomic images. The character of diffraction lines on holograms is discussed and the character of diffraction lines can be used to remove the influences of incomplete ranges of angles for recording hologram. 9. The influence of twin images effects on the reconstructed images in single-energy holographic reconstruction is discussed in detail. Two reconstruction programs including multiple-energy and two-energy holographic reconstruction for removing twin images are written. With detailed theoretical derivation and numerical simulations, a new method of removing twin images and improving resolution and site accuracy of atomic images is first proposed in the world. 10. The influence of polarization of incident X rays on the reconstructed images is also discussed in detail. It is found that the influences of horizontally and vertically polarized incident radiation on reconstructed atomic images are different for the atoms at different sites. The two-energy holographic reconstruction algorithm is first combined with correction algorithm of polarization in the world and a new reconstruction algorithm is proposed for removing twin images and the influence of polarization of incident X rays on the reconstructed atomic images. The results of numerical simulation verify it feasible. These theoretical results will direct experimental study in future and the reconstruction program can be directly used to treat experimental results. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15574]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 谢红兰. 硬X射线位相衬度成像及荧光全息成像的实验与理论研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
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