Cone-Beam Phase Computed Tomography Based On Grating Imaging

X-ray phase contrast imaging always provides high density resolution when images weakly absorbing material, which shows wide prospect of application in many fields such as medicine, biology and material science. However, due to the particular principle and structure of interferometic imaging method, diffraction enhanced imaging method and in-line imaging method, these methods need either highly coherent or highly monochromatic X-ray, and can not provide a large field of view. None of them is widely used. Grating imaging overcomes the limitations of above imaging methods and enables phase contrast imaging to develop into the form of cone-beam imaging. At present, there has been no cone-beam reconstruction algorithm based on this imaging pattern. However, grating imaging will be applied in cone-beam scanning and become a main phase contrast imaging method as long as theory is deeply investigated and the technique of fabricating grating is developed. At that time, cone-beam phase CT will draw more attention in CT theory and application fields. Therefore, research of cone-beam phase CT is significant and practical.This paper works on phase contrast imaging and phase contrast CT. In research of phase contrast imaging, diffraction enhanced imaging and grating imaging are discussed, which includes differences between these two imaging methods, advantages of phase contrast imaging, and the prospect of developing grating imaging into cone-beam imaging pattern; In research of phase contrast CT, reconstruction of phase item and its gradient in diffraction enhanced imaging is studied firstly, and then, with the foundation of phase item direct reconstruction algorithm of parallel-beam phase CT, characteristic of cone-beam phase imaging and the theory of FDK reconstruction algorithm, this paper derives reconstruction algorithm of cone-beam phase CT based on grating imaging, this method is filtered back-projection type and can reconstruct the phase item of object directly with the phase gradient as projection. Moreover, because present phase contrast imaging methods belong to parallel-beam imaging in nature, a projection simulation method of cone-beam grating imaging is provided as well, which can simulate refraction projection with phase item, this makes for the research of reconstruction algorithm.