基于迭代重构算法改进晶体衍射分光X射线鬼成像的图像质量研究

Improving quality of crystal diffraction based X-ray ghost imaging through iterative reconstruction algorithm

X射线鬼成像是一种低剂量、非定域成像方法,对医疗诊断和生物成像具有重要意义.在基于晶体劳厄衍射分光的X射线鬼成像中,晶体振动会造成衍射光路上散斑的模糊,进而导致利用关联方法重构图像衬度和空间分辨的降低.本文系统分析了衍射光路上散斑图像的模糊程度对归一化二阶关联函数g^((2))的最大值和半高全。宽的影响.模糊程度的增强会导致g^((2))最大值的减小和半高全宽的展宽,在理论上证明了模糊程度会引起重构图像的衬度和分辨能力的降低.为解决上述问题,本文在衍射光路和直通光路的直接关联方法(CLH)的基础上提出G_(LH)E方法(CLH enhanced method).模拟实验表明G_(LH)E算法能同时改善图像衬度和提高重构分辨率,并且模糊程度增强时,G_(LH)E算法重构图像的峰值信噪比与先对直通光路的散斑图像进行高斯滤波处理再进行双光路关联计算方法(G_(LL))的差距扩大,同时保证其对噪声的鲁棒性.本文为晶体衍射分光的X射线鬼成像的实际应用提供可行的思路.

X-ray ghost imaging is a low-dose,non-localized imaging method,which is of great significance in medical diagnosis and biological imaging.In crystal diffraction based X-ray ghost imaging,the blurring patterns in the diffracted beam,caused by the crystal vibration,can result in a reduction in the contrast and spatial resolution of the reconstructed imaged by ensemble average.In the paper,we systematically analyze the influence of the blurring degree of the speckle patterns from the diffracted beam on the normalized second-order intensity correlation function g^(2)numerically and theoretically.Both demonstrates that as the blurring degree increases,the maximum value of g^(2)decreases and the full width at half maximum broadens,which theoretically proves the blurring degree relating to image quality.In order to solve the above problem,in the paper we propose a G_(LH)enhanced(G_(LH)E)method to optimize the image quality based on the scheme(G;)which directly correlates the bucket signals in diffracted beam with the high-definition patterns in transmitted beam.The simulation experiments exhibit that the G_(LH)E method can improve both the image contrast and the spatial resolution simultaneously.As the blurring degree increases,the difference between the peak signal-to noise ratio of the reconstructed image by the iterative method and that by the scheme(G_(LL))which preprocess the speckle patterns in the transmitted beam through Gaussian filtering,becomes greater.Furthermore,the G_(LH)E is almost immune to the additive noise.In summary,the present study provides a feasible idea or the practical application of X-ray ghost imaging based on crystal diffraction.