Research On Phase-contrast Imaging With Micro-focus X-ray Source

Conventional X-ray imaging is based on amplitude-variable absorption attenuation imaging,and has better resolution for substances with larger atomic number,and poor resolution for light substances with smaller atomic number.However,for light-element substances,the change of phase produced by X-rays is three orders of magnitude larger than the change of amplitude,so phase-contrast imaging can be used to achieve better resolution of light-element substances imaging.Today,there are about four main methods of X-ray phase contrast imaging.In-line imaging has a very strong practical prospect because the imaging device is simple and can be built in an ordinary laboratory.So the imaging algorithms and algorithms of phase information retrieval of this method were studied in the paper.Firstly,the paper explained the basic model of X-ray in-line phase contrast imaging based on Fresnel-Kirchhoff scalar diffraction integral.And then several phase retrieval algorithms including TIE(Transport of Intensity Equation),CTF(Contrast Transfer Function)and IASA(Iterative Angular Spectrum Approach)were emphasized.Secondly,the paper simulated X-ray phase contrast imaging of a phase-only sample under the condition of ideal parallel light source and the obvious edge enhancement effect was observed by changing the imaging distance which proved the phase contrast imaging is directly proportional to the second derivative of phase.Through the simulation of these phase algorithms,some conclusions were found: for the TIE algorithm,the closer the imaging distance is,the better he retrieval phase quality is;for the IASA algorithm,the longer the imaging distance is,the better the phase quality is.Through combining the TIE algorithm and IASA algorithm,better results were obtained regardless of the imaging distance.The CTF algorithm requires at least two imaging planes and it was found that the CTF algorithm is greatly influenced by the distance between two imaging planes.When the distance between two imaging planes meets certain conditions,the change of the first imaging position has little effect on the phase recovery.At the end of the paper,with micro-focus X-ray source,phase-contrast imaging and phase recovery of phase-only samples were studied.Through the simulation,it was found that the quality of phase-contrast imaging and recovery is related to the pixel?imaging distance and the magnification.The effect of imaging distance on the quality of phase-contrast imaging was verified by real experiment.At the same time,the phase recovery was realized by using TIE algorithm.