Experimental Techniques And Applied Research On X-ray Grating-based Phase Contrast Imaging

Over past two decades,several X-ray phase-contrast imaging techniques have been developed.Most of these phase-contrast imaging techniques are restricted to synchrotron radiation or micro-focus tubes,the X-ray from which posses high spatial and/or temporal coherence.However,grating-based X-ray phase-contrast imaging(GBPCI)technique can be operated with high-powered polychromatic conventional X-ray source with broad foci.Another advantage of GBPCI is its compatibility with a coarsely-pixelated commercial detector,resulting in the possibility of large field-of-view.Moreover,GBPCI is multi-modal X-ray imaging technique:it enables to retrieve differential phase,dark-field and conventional transmission images simultaneously.Through the efforts of many science groups in the world,GBPCI has experienced a great development and showed its potential pre-clinical and clinical applications.This thesis focus on GBPCI,after establishing the grating phase contrast imaging system,the experimental technique of GBPCI is explored in details.In order to solve the problem that appears,the core components of X-ray source,grating and detector are tested and optimized.The causes and the corresponding correction and improvement schemes are put forward.Through the actual experiment,the application of grating-based phase contrast imaging in biomedical imaging and food detection were initially explored.These efforts will greatly facilitate the wide application of GBPCI technology.The main contributions of this thesis are summarized as follows:1.Grating-based phase contrast imaging system experimental techniques:we completed the non-interferometirc GBPCI system,and then explored the experimental technology and data processing;Morevore,through performance testing results,this setup and traditional Talbot-Lau interferometer were compared to point out the characteristics of the system.2.Correcting intensity drift of X-ray source and correction methods:in actual experiments,we found that the photon intensity drift of the X-ray source would influence the final images,especially the refraction images.After analyzing the phase-stepping curve,we proposed a correction method to fix the problem due to the effect of intensity drift.The proposed correction method is successfully applied to GBPCI setup having un-stable X-ray source.The experimental results show that our method could solve this problem.3.The new imaging system of the optimal placement of the absorption grating:to reduce the thermal vibration and damage of the grating,after analyzing the grating structure and material,two grating placement schemes—normal incidence and back incident—are proposed and compared.The calculation and experiment results showed that the two schemes are consistent in imaging function,but the back incident method will reduce the grating vibration and deformation caused by the corresponding thermal effect,improve the stability of the system and prolong the service life of the grating.4.The advance detector image correction method in grating phase contrast imaging method:in order to simplify the complicated operation in the previous detector image correction process,we exploered the advance correction methods.Inspired by the multiline embedded X-ray targets,then a new gain correction mehods based on source grating is proposed which the X-ray tube and source grating used as a whole source,and verified by experiment.Furthermore,based on the analyzed theoretical influences of dark-current and inhomogeneity of detector on the results of GBPCI,a simplified image correction method without gain correction in GBPCI is proposed.Compared with conventional image correction method,the new image correction method can achieve same performance.Therefore,the new method simplifies the experiment and calculation procedure and is expected to be used widely in future.5.Exploration the application of biomedical imaging and food inspection:First,a new bone density measurement scheme combining absorption and refraction is proposed and verified by theoretical calculation and experiment.Then,based on the results of GBPCI of crucian carp,the effect of different sample treatments on the experimental results of phase contrast imaging was verified.Finally,the fresh cherry tomato and dried umeboshi were used as samples to explore the potential of phase contrast imaging in food inspection.