Study On Extending The Depth Of Focus In X-ray Microscopy

With the German scientist Roentgen found X-ray,the scientists quickly discovered the advantages of X-ray imaging in the micro-imaging,which could observe the three-dimensional internal structure with high-resolution and non-destructive.In recent years,due to the continuous progress of the X-ray source,elaborate micro-nano fabrication technology,X-ray high sensitivity detector,high precision mechanical platform and control systems,X-ray microcscopy based on the Fresnel zone plate has obtained the significant development.The hard X-ray microscopy has the many outstanding features,such as strong penetration ability,high depth of focus and high spatial resolution,and has been widely applied to the fields of microelectronics industry,energy and environmental science,materials science.Because of "water window",Soft X-ray microscopy could keep biology cell sample "fresh" with observation of the structure and morphology of the sample while obtains high contrast imagings.Soft X-ray microscopy has been applied to the study of cells mechanisms,and the action mechanism of the virus and drugs.X-ray microscopy filled gaps in spatial resolution between optical microscopes and electron microscopes.With the development of micro-nano fabrication technology and synchrotron radiation source,the spatial resolution of X-ray microscopy can reach 12 nm.The depth of the X-ray micro-imaging system is proportional to the spatial resolution of the imaging system.The higher the spatial resolution of the system lead to the smaller the focal depth.When the sample is larger than the focal depth,the projection will be defocus and blur,affecting X-ray 3D CT reconstruction data.Therefore,it is significant to extend the depth of focus of X-ray microscopy.Based on the X-ray microscopy extending depth of focus,the main work of this paper are described as follow:1.We summarized the advantages and characteristics of the X-ray microscopy.The working principle and the parameters of optical device are introduced.We selected a few typical examples to illustrate the unique advantages.The application of hard X-ray microscopy:the three dimensional porous structure of the anode of the solid fuel cell is imaged,and according to its structure,the lattice Boltzmann method is used to simulate the transportation process of the gas at the nanometer scale of the fuel cell,and to provide reference for optimizing the preparation of the solid fuel cell;the microscopic imaging ofthe mammary carcinoma cells of the epithelial cell transplants was carried out to provide a basis for the cell mechanism of the cancer cells;images the mitotic yeast cells,thanks to Zenik composites imaging and cell dyeing techniques,show X-ray microscopy can produce high contrast imaging of biological large samples.The application of soft X-ray:images mouse adenocarcinoma cells to observe the morphology and distribution of various organelles of adenocarcinoma cells,and even observe the details of various subcellular structures;combines with fluorescence imaging,the whole cell cycle at all stages of the various organelles and cell volume morphology changes were studied;combines with low-temperature fluorescence,confocal microscopy and electron microscopy,the transformation of peripheral chromosomes during herpes simplex virus type 1(HSV-1)infection was analyzed by three-dimensional soft X-ray tomography;the composition of cell subcomponents and the bulk density of each organelle were analyzed and the linear absorption coefficients of each organelle and the volume fraction of whole cells were calculated and analyzed.2.Aiming at the characteristics of X-ray microscopy,several fusion algorithms are applied to fusion projection images of hard X-ray microscopy and soft X-ray micrograph imaging respectively.And a variety of fusion algorithms are developed,including fusion algorithm based on discrete wavelet transform,fusion algorithm Laplacian pyramid transform,fusion algorithm based on sparse representation,fusion algorithm based on sparse representation-discrete wavelet transform,fusion algorithm based on sparse representation-Laplacian pyramid transform,And according to the image processing,prepared five evaluation functions to evaluate the fusion image.When the X-ray microscopy projection fusion,it can become a clear and focused projection,and when the projection image is clear and focused,the entire three-dimensional CT reconstruction data will be clear and focused.3.Aiming at the characteristics of X-ray microscopy projection image and the system optical path,a defocus projection image restoration based on optical transfer function is proposed.According to the parameters of the X-ray microscopy system and the characteristics of the Fresnel zone plate,the optical transfer function of X-ray microscopy is calculated according to the formula.Using the optical transfer function to restore the defocused fuzzy projection image,get rid of blur,get a clear projection and focused projection image.In order to verify our method,we have made the simulation and experimental analysis.The results show that the defocus recovery method based on the optical transfer function of the Fresnel zone plate is effective and reliable for recovering the defocused X-ray projection and the 3D reconstruction of the image.And proposed a method of segmentation in accordance with the distance from the focus area,a good solution to the sample does not agree with the focal plane of the problem,to overcome the X-ray imaging depth of the restrictions.4.The limitations of the method for extending depth of focus based on the projection image fusion and based on the optical transfer function projection image restore are analyzed.Especially,it is difficult to solve the problem of the depth of the large sample.So we studied the characteristics of X-ray microscopy,and proposed a extending depth of focus method based three-dimensional CT reconstruction slice image fusion,which solves the problem of the limitation of depth of focus of X-ray microscopy in a real sense.In order to validate our method,we simulate the projection of a sample the cylinder and a plurality of object samples larger than depth of focus.According to a pair of overlapping diatom frustules imaging,our method to obtain a clear three-dimensional reconstruction in-focus data,the results show that this method to solve the X-ray microscopy the limitation of depth of focus in a real sense.