Research On Synchrotron Radiation X-ray In-line Phase-contrast Imaging Algorithms And Its Biomedical Application

In traditional X-ray imaging, only the differences in radiation absorptionof different materials are exploited. For samples composed of light elementssuch as soft biological tissues, which demonstrate almost no difference inabsorption attenuation, it is difficult to acquire their compositions andstructures. Recently, the rapid development of synchrotron radiation makesX-ray phase contrast imaging become a research focus. The phase shift ofsoft tissue is three orders of magnitude larger than attenuation at photonenergies larger than10keV. So phase-contrast imaging can get moreinformation and increase the image quality. Among the phase contrastimaging methods, in-line phase contrast imaging needs no optical elements.So it is easy to realize and widely used. However, phase retrieval algorithmplays an important role in this kind of phase-contrast imaging. In this paper,the imaging principle and phase retrieval algorithms of in-line phase contrastimaging are studied, as well as the biomedical application of in-linephase-contrast imaging.In this paper, we first build a model of the interaction of X-ray andmaterials. Based on Fresnel-Kirchhoff scalar diffraction integral which is metby the free space propagation of X ray, we established the in-line phasecontrast imaging model based on wigner distribution. Then we deriveddifferent phase retrieval algorithms using different approximation condition,including CTF (Contrast Transfer Function), First Born Approximation, TIE(Transport of Intensity Equation, Bronnikov’s Algorithm and MBA (ModifiedBronnikov’s Algorithm). We compare and analysis the phase retrieval results of different algorithms with different imaging distances, absorptions andnoise varies, at last we draw conclusions that TIE and CTF are sensitive tonoise while MBA can restrain noise but only suitable for weak-absorptionobjects. The simulation results have important guiding significance forexperiments. Thus an improved phase retrieval algorithm based on iterationwhich uses phase retrieved by MBA as initial value is presented. Thisalgorithm can be applied to materials without requirement of weak absorptionwhich is the limitation for MBA. Simulation tests demonstrated the validityof this improved algorithm, and the computational complexity will not beincreased significantly. Because the actual samples are often complicated andthe absorption properties are unknown, the improved algorithm has animportant practical significance.We performed in-line phase contrast imaging experiments using standardphysical and biological samples at Shanghai Synchrotron Radiation Facility(SSRF). The phase retrieval algorithms derived in this paper was used to dophase retrieval and3D phase reconstruction. Compared to conventionalattenuation-based X-ray imaging, different compositions of soft tissue werebetter distinguished by in-line phase contrast imaging, and the reconstructionvalues of different tissue had a larger discrimination. So In-line phasecontrast imaging generated significantly greater image contrast whileradiation dose did not increase, which showed enormous potential inbiomedical applications.