Research Of Information Extraction Methods On X-ray Differential Phase Contrast Imaging

X-ray phase contrast imaging does not only inherit the advantages of conventional absorption-based imaging,but also carries the advantages of phase contrast imaging and dark-field imaging.Theoretically,it may provide remarkably improved contrast over conventional absorption-based imaging for weakly absorbing samples,such as biological soft tissues and fibre composites.In these main methods,differential phase contrast imaging(including diffraction enhanced imaging and grating-based phase contrast imaging)has attracted a lot of attentions in the field of X-ray imaging recently.Both of them measure the first derivative of the phase shift of the object,Diffraction enhanced imaging is an effective method to characterize the internal structure of materials based on synchrotron radiation,and conventional X-ray tube sources can be efficiently used with a Talbot-Lau interferometer,it is the most promising X-ray imaging technology in clinical medicine.The image acquired by the detector is a projection image with mixed information including the absorption,phase and scattering of the object.Three contrast mechanisms correspond to different compositions and structures of objects,and three kind of independent signals can provide clearer results.Therefore,it is essential to extract independent information images from projected images.This paper systematically summarizes the information extraction methods of X-ray differential phase contrast imaging and proposes several new information extraction methods.This paper mainly carried out research work in the following aspects:1.Information extraction method based on high-order expansion of intensity function.In X-ray grating-based phase contrast imaging,the small angle information of the imaged object can be effectively extracted by Taylor expansion of the intensity function.When the intensity function is expanded to the second order,the information of absorption,refraction and ultra-small Angle scattering(USAXS)can be extracted at the same time.However,for objects with larger refraction angles and scattering widths,only expanding to the second order is insufficient.Based on previous work,this chapter explores the influence of higher-order expansion of intensity function on information extraction results.2.Three-image information extraction method for diffraction enhanced imaging.In diffraction enhanced imaging,gaussian function is used to fit the rocking curve,the analytical expression of intensity is derived,and information extraction formulas are given.The three-image method can separate the absorption,refraction and scattering information of an object at the same time.The results of the synchrotron radiation experiment showed that the new method was basically consistent with the traditional standard method MIR.Compared with MIR,our method only required three projection images,which greatly simplified the image acquisition process,reduced the imaging time and to some extent reduced the radiation dose,and was of great significance for clinical medicine and vivo imaging.