Research Of X-ray Phase Contrast Imaging Technology And Method

In the hard X-ray band,the phase cross section of the low atomic number element is at least two orders of magnitude higher than that of the absorption cross section.Therefore,it is possible to obtain a higher image contrast and higher image sensitivity by using a phase contrast imaging mechanism to image soft tissues.For weakly absorbed samples,compared with the traditional X-ray absorption contrast imaging,the phase contrast has a higher sensitivity,can better reflect the internal structure of the object information.Therefore,this new imaging method in the field of materials,biology,medicine and other fields have a wide range of applications.With the continuous development of X-ray imaging technology,X-ray phase contrast imaging has been developed as a new imaging method,and many imaging methods have emerged.It can be roughly divided into the following categories:The first is interfering based imaging in which phase shift is transformed into interference intensity.The phase contrast microscopy invented in 1934 by Dutch physicist Frits Zernike and the crystal interferometer based imaging can be attributed to this method.The second is angular filtering based imaging in which the first derivative of phase is transformed into intensity.The differential interference contrast microscopy invented in 1952 by Polish physicist Georges Nomarski,diffraction enhanced imaging,grating based imaging,and abrasive paper based imaging can be attributed to this method.The angular filtering based imaging is generally called as differential phase contrast imaging.The third is phase propagating based imaging in which the second derivative of phase is transformed into intensity.The phase propagation based imaging and the defocus microscopy can be attributed to this method.X-ray Zernik phase contrast microscope technique is to introduce a phase ring in a full-field transmission X-ray microscope(TXM).The phase ring is located at the back focal plane of the objective lens to cause the phase shift of the pass-through light.The interference of the pass-through light and the scattering light on the detector converts the phase information into intensity information which detected by the detector.X-ray Zenik phase contrast microscopy using X-ray full-field transmission microscope's high-resolution ability,directly to convert the phase information into intensity information is a high-resolution and high contrast imaging method.Then it has a wide range of applications in cell,biological tissue and organic material imaging.In the field of X-ray projection imaging,the introduction of X-ray Talbot-Lau grating interferometer,make the X-ray phase contrast imaging technology from the synchrotron radiation source extended to the conventional light source.This method can simultaneously obtain attenuation,phase Lining and dark field of three kinds of information,but this technology has a high demand for coherence,requiring a small grating cycle,and high X-ray energy required grating enough to meet a certain diffraction efficiency.This large aspect ratio of the grating manufacturing difficulties,and difficult to achieve large field of view,high energy imaging.The X-ray grating phase contrast imaging method based on projection fringes has the low coherence and low grating period requirement,which can reduce the manufacturing difficulty of grating,and it is expected to obtain larger imaging field and higher imaging energy.The main contents are summarized as follows:Build the experimental platform,introduce the experimental platform to adjust the process,introduce the experimental operation process.Discuss data acquisition and processing methods,and use Matlab-GUI to write data processing software.Analysis of the factors that affect the imaging quality of the Hefei experimental platform:the drift of the intensity of the light source will affect the displacement curve and thus the result of the separation of the information.The instability of the mechanical system will cause drift between the gratings and lead to serious Ring artifacts.In this regard,we completed the correction of the drift of the light source,and proposed a method of image matching to find the background image of the same position as the sample image and improve the image quality.The feasibility of the experimental platform is verified by the experimental analysis,and the correctness of the imaging method is proved.Combined with the experimental results,analyze the factors that affect the sensitivity of the device,and provide support for future experiments and device improvements.A method of elemental resolution using X-ray Zernike phase contrast imaging technique is discussed.In the same way as the method of distinguishing the conventional absorption contrast,the method utilizes the real part of the refractive index of the metal element to reduce the amount of the refractive index in the vicinity of the absorption edge,and the X-ray Zernike phase contrast imaging technique is used before and after the absorption edge of the target element The image is imaged separately,and then the two images are subtracted to obtain the distribution of the target elements.Through the numerical simulation of the method,the correctness of the method is proved.The relationship between the number of incident photons and the image signal-to-noise ratio is analyzed.By comparison,it is concluded that the element resolution method of Zernike phase contrast has higher photon utilization than the traditional absorption contrast element method.The main contents of this paper include the following five parts:1.Overview of X-ray phase contrast imaging technology;2.Details of the development of Hefei experimental platform;3.Details of the data analysis and alignment;4.Analyze the factors that affect the quality of the image;5.Discuss the X-ray element resolution method using Zernike phase contrast imaging;6.Finally,summarizes and prospects.