X-ray Phase Contrast Imaging And CT Technology

Ever since the first X-ray photo was taken by Wilhelm Conrad Rontgen in 1896, X-ray imaging technique has been developing rapidly.A wide range of applications including clinical diagnosis,biology,material engineering,and information science et al. have benefited from the availability of such imaging technique.As the advanced field of X-ray imaging technique,X-ray Phase Contrast Imaging technique is well recognized for the capability of detecting the phase change associated with the sample structure. Especially in the case of investigating bio-medical samples which are typically composed of low Z elements,the real part of the refractive index is much larger than the imaginary part,consequently X-ray phase contrast imaging technique is of considerable advantage and is a hot research topic.The main contributions of this thesis are summarized as follows:1.An extensive theoretical investigation,computer simulation,and experimental research,performed at Beijing Synchrotron Radiation Facility Beamline 4W1A, allows a detailed investigation on the basic principles of Diffraction Enhanced X-ray Phase Contrast Imaging technique.A new DE-XPCI experimental scheme and corresponding phase recovery algorithm are proposed,which makes DE-XPCI technique more convenient and more reliable.We have also established close cooperation relationships with scientists in various research fields,many valuable experimental results are acquired at Beamline 4W1A BSRF.2.We investigated Grating based X-ray Phase Contrast Imaging technique by means of computer simulation.The G-XPCI method is extremely impressive because it is applicable with a laboratory x-ray source without the requirement of a coherent intense X-ray source.We propose a novel Reverse-Projections Grating-based X-ray Phase Contrast Imaging(RP-GXPCI) method,which offers important improvement over existing G-XPCI techniques.The proposed method simplifies the experimental setup and reduces significantly the radiation dose delivered to the object.Our method is confirmed by experimental results with both synchrotron source and Laboratory X-ray source. 3.Considering the development of the next generation of X-ray source,i.e.the Free Electron Laser(FEL),we also investigated X-ray imaging systems under coherent illumination.As a first step,we explored Coherent Diffraction Enhanced X-ray Phase Contrast Imaging(CDE-XPCI) technique by means of computer simulation.A novel phase retrieval algorithm based on nearfield Hybrid Input-Output method is proposed,which extracted quantitative phase map from a single intensity distribution recorded by CCD in the CDE-XPCI setup.The capability of extracting both enhanced contour and quantitative phase map makes CDE-XPCI specially useful for structural investigation.It is anticipated that CDE-XPCI will become more and more popular with the further development of FEL.4.We have also investigated the in-line imaging system under coherent illumination. A different x-ray phase contrast imaging technique based on the combination of structured illumination and an optimized hybrid input-output algorithm for phase and amplitude retrieval is presented and discussed.Based on a modified and flexible experimental setup,compared to standard propagation-based x-ray imaging setups,the method we propose here represents a real advance in the phase-contrast imaging technique relating to the determination of the phase and amplitude distribution.Moreover,in coherent diffractive imaging applications, the proposed technique may yield high spatial resolution with currently available imaging detectors.5.A systematic analysis on Computed Tomography algorithm suggested the introduction of the first iterative CT reconstruction algorithm for X-ray Phase Contrast Imaging technique,which is later confirmed by experimental results.Our CT algorithm allows shortened experimental time and minimized radiation dose,without reducing image quality.The proposed algorithm is applicable for a wide range of XPCI technique with minor revision.We have already acquired a series of valuable results from such algorithm.