Numerical Simulation And Method Study Of In-line Phase Contrast X-ray Computed Tomography

X-ray phase contrast imaging is a kind of imaging technology that uses the phase change of X-ray as it passes through the object and transforming its phase shift into the intensity that can be observed in the detector plane.Among the developed X-ray phase contrast imaging methods,in-line phase contrast imaging is considered to be the most promising clinical methods owing to no other optical devices are needed.In X-ray phase contrast imaging,contrast is a mixture of absorption,phase contrast and scattering,therefore how to develop a feasible and effective phase retrieval algorithm is an important research content in the field of phase contrast imaging.In this paper,two-dimensional phase retrieval algorithm and three-dimensional phase retrieval algorithm were studied respectively.For two-dimensional phase retrieval algorithm,we studied the single material phase retrieval algorithm and multi-material phase retrieval algorithm respectively:(1)In the research of single material phase retrieval algorithm,the PAD-PA algorithm and PAD-WA algorithm were further studied separately.In order to apply the PAD-PA algorithm to the phase retrieval of multi-material objects,the spatial domain expression of the kernel function in the frequency domain was derived in this paper.The value of the phase shift-absorption coefficient of a single material in the formula was replaced by a phase shift-absorption function related to the spatial position of a plurality of materials,and a new kernel function was obtained.In order to eliminate the influence of non-ideality imaging system,this paper developed a PAD-WA phase retrieval algorithm based on system transfer function compensation model,and combined this algorithm with Tw IST iterative method to further develop Tw IST-PAD-WA phase retrieval algorithm.Both methods were tested using simulated phantoms.(2)In the research of multi-material phase retrieval algorithm,this paper developed a multi-material phase retrieval method which can be applied to the phase retrieval of objects containing both strongly absorbing and weakly absorbing materials.For three-dimensional phase retrieval algorithm,based on the traditional two-dimensional phase retrieval algorithm,this paper derived the Born approximation three-dimensional phase extraction algorithm.The algorithm can perform three-dimensional phase retrieval on the reconstructed phase contrast image and retrieved the three-dimensional phase distribution of the object directly.Based on the derived algorithm,the in-line phase contrast XCT imaging of single material and multi-material phantoms was carried out,and the imaging result was compared with the imaging results based on the traditional two-dimensional phase retrieval algorithm and TIE three-dimensional phase retrieval algorithm.