Research On Grating Based X-ray Phase-contrast Imaging

X-ray is widely used in the fields of clinical medicine,material science and homeland security.In order to detect the material composed of light elements,X-ray phase-contrast imaging is proposed.X-ray phase-contrast imaging technology got rapid development in the past twenty years and a series of X-ray phase-contrast imaging techniques have been developed.Grating based X-ray phase-contrast imaging technology no longer has strict requirements for light source.It can realize the refraction information extraction on the conventional X-ray source and has the possibility of clinical application.Therefore it has been paid more attention and the research on this technology develops rapidly.In order to improve the grating based X-ray phase-contrast imaging technology,this dissertation is carried out mianly on the following work of the construction of the experimental platform,the development of the grating and the research of phase contrast imaging method:1.Design and set-up of grating based X-ray phase contrast imaging platform and optimization of image acquisition systemSet up grating-based X-ray phase contrast imaging platform in NSRL in the University of Science and Technology of China.This imaging system combines the traditional Talbot-Lau interferometer with the geometric projection imaging principle.lt mainly has the following advantages:the grating is easy to fabricate and is easy to realize high-dose phase-contrast imaging;the imaging device is more compact and requires less mechanical stability to the imaging system;more selection for imaging energy,a wider range of applications.Through Labview programming,the required operation during experiment is integrated to an interface.We can simultaneously realize the setting of the X-ray source parameters,the operation of the grating displacement motion,the image acquisition and image post-processing.It is convenient for the operator and reduces the experimental time.In the aspect of image acquisition,we introduce an image acquisition method called integral bucket method.Compared with the traditional phase stepping method,its main advantages are:the continuous movement of the analyze grating,which is beneficial to the mechanical stability of the imaging system;the continuous image acquisition of the X-ray detector,which redues unnecessary radiation recieved by the sample.2.Fabrication of the important components of grating based X-ray phase-contrast imaging system.As the important component of the grating based X-ray phase-contrast imaging system,the quality of the grating has a decisive effect on the imaging results.In the fabrication process of high aspect ratio grating,the grating structure failure often occurs.To solve this problem,we propose optimization processing technic on the grating fabrication.High aspect ratio grating can be fabricated to meet the imaging requirements.3.Research on the background correction methods in grating based X-ray phase-contrast imaging.Through the comparison of the two commonly used background correction methods,we find that when there is a large inhomogeneity in the background image,one of the methods will appear error.To solve this problem,we propose the optimization scheme.We propose the use of cyclic shift in the phase stepping process to find the correct starting position.Finally,the feasibility and correctness of the proposed optimal methods are verified by simulation and experimental data.