Numerical Simulation And Experiment Study Of Hard X-ray In-line Phase Contrast Imaging

The hard X-ray in-line phase contrast imaging, owns to its advantage of simple optical layout, having no other optical components, allowing multicolor X-ray source and widely imaging area compared with other imaging methods, has been widely applied in many fields such as medicine, biology, mechanics and plasma physics. This paper is primarily devoted to the investigation of imaging principle, imaging layout optimizations and image processing of the in-line phase contrast imaging by theoretical analysis, numerical simulation and experiment, expect to provide a useful support for the applications. Following is the main content, conclusion and innovation points of this research:1. Layout optimization of the X-ray in-line phase contrast imagingThe source size, pixel size and space frequency of the measuring objects are considered for improving the simulation precision based on theoretical analysis. The contrast, signal-to-noise ratio (SNR), spatial resolution and sampling rate are employed as an integrated evaluation standard for the imaging quality of the X-ray in-line phase contrast imaging system. The optimization of the maximum contrast and SNR are built respectively for the commonly used objects which has the feature of one dimensional Gaussian distribution, two dimensional Gaussian distribution, or one dimensional step blurred edge distribution. The parameters for the imaging systems based on the sub-micrometer focus X-ray source, laser-based micrometer focus X-ray source and synchrotron radiation X-ray source are optimized by numerical simulation.The results show that each optimization method has its advantages and disadvantages. The maximum contrast optimization method has advantages of higher contrast and spatial resolution, while the SNR optimization method has the advantages of higher SNR and reasonable space distance. Which optimization methods should be adopted is according to the real conditions and requirements of the applications. It should be noted that the methods are based on the assumptions that the X-ray source is homochromatic and transmit in vacuum, but it still can provide us a useful introduction.2. Image processing method of X-ray in-line phase contrast imagingThe noise disposal and phase retrieval are combined based on analysis of noise feature of in-line phase contrast image. The effects for noise disposal of some classical methods are analyzed through numerical simulation. The influence of the noise disposal methods to phase retrieval effects is evaluated quantitatively and corresponding suggestions of noise disposal and phase retrieval methods are given.Firstly, for the image of SNR is very high or having no noise, it needs no noise disposal during phase retrieval, and the phase retrieval effect for the original image is the best. Secondly, for the image of SNR is a bit lower than that of the first condition, it needs to make simple noise filter before the phase retrieval. Thirdly, for the image of SNR is very low, the quality of the phase retrieval image cannot be fine whatever method is adopted. The quality of the phase retrieval image can be improved by the enhanced smoothness filter of original image. Moreover, the median filter can’t be used to filter the images before the phase retrieval although it is deemed to be an effective method to remove the poisson noise.3. Experiments and numerical simulation of X-ray in-line phase contrast imagingThe simple X-ray sources, receiving systems, and limited space are considered for the real applications of X-ray in-line phase contrast imaging. The investigation of the effective energy of micrometer focus X-ray source through air absorbing analysis method and imaging principle of multicolor X-ray in-line phase contrast imaging was firstly done by the combination of experimental observation, theoretical analyses and numerical simulations. Then the X-ray in-line phase contrast imaging quality of metal and detonator samples were investigated in detail by experiment. Lastly, the phase is retrieved for the experimental images.Firstly, the influence of imaging parameters to imaging quality is analyzed in the condition of homochromatic and multicolor X-ray transmits in air or vacuum, respectively. Some important results are obtained from the experimental results and numerical simulations.Secondly, the results of X-ray in-line phase contrast imaging of metal sample shows that the light metal can much easy to get a good phase contrast compared with the heavy metal. This indicated we can use the hard X-ray in-line phase contrast imaging to study the light metal sample.Thirdly, the results of X-ray in-line phase contrast imaging of detonator show that the changing of cracks of the detonator during compressing is demonstrated clearly on microscopic scale.Lastly, the phase retrieval for the insects sample show that its retrieval effect is approximately satisfied, which can reach the level of phase retrieval for the Lena image of the possion noise at the same level.