Study On Differential Phase Extraction In Phase-contrast Imaging

Hard X-ray phase-contrast imaging is a newborn non-destructive testing and diagnostic technology in medicine, biology and materials science. In order to reveal the internal structure of objects, this technology is adopted to capture the X-ray phase-shift information to observe the electron density of objects. Theoretically, the transmitted beam will change along its direction of propagation slightly because of the refractive index's gradients of the sample.In Diffraction Enhanced Imaging and Grating phase-contrast imaging technology .The key problem of these technologies is how to extract phase information which is expressed by refraction angle images from a series of original images measured in different position of the rocking curve (RC) or displacement curve.Study on the DEI technology and the modality of rocking curve, based on the extension method which is presented by Maksimenko, we provide the analytic formula of GEDEI in case of the rocking curve which can be fitted by Gaussian function approximately. Furthermore, in order to make the GEDEI formula can be solved in a nutshell, we present a predigest process on the DEI images. In the end, the extraction results on simulation data and columnar model proved that the GEDEI algorithm with a pretreatment approximation is accredited. And the extraction results of GEDEI are better than the GOA method.GCF method in DEI provides the most approximate refraction-angle values in exist methods, but it has a high computational complexity due to the nonlinear multiplex iterative process. So the enormous calculation time obviously limits the practical applications of GCF method. In order to speed up the computation time, this paper presented a theoretical and experimental study on polynomial curve fitting (PCF) method for refraction-angle extraction in DEI. In conclusion, PCF method can obtain most approximate refraction-angle values and its computational speed is 10 times faster than GCF method. Study on the traditional grating phase-contrast imaging technology based on the Talbot self-imaging principle in the third part of this paper, we introduce a new grating phase-contrast imaging system based on the Moirés deflection principle. Based on this system, we presented a theoretical and experimental study on the sine curve fitting (SCF) method and polynomial curve fitting (PCF) method for refraction-angle extraction in the experimental system. Then we tried to apply the fringe scan method to extract the refraction-angle in this new experimental system. In conclusion, the comparisons of PCF SCF and FS methods proved that the FS method is the fastest and the best exaction method for this moirés deflection-based grating phase-contrast imaging system.