基于穿越长度权重反投影重建算法的初步研究

目的：直接反投影是一种快速简便的CT图像重建方法，但由于星形伪影会使图像模糊。为有效地改善CT反投影重建图像的质量，提出一种新的基于穿越长度权重的反投影重建算法，为图像重建提供一种新算法；同时穿越长度的计算方法也能为代数重建算法中的投影系数的计算提供一种新方法。方法：采用VC＋＋6．0工具设计模拟软件，对Shepp-Logan模型进行计算机模拟扫描获得投影数据，同时计算各射线穿越各体素的长度．以穿越长度作为权重对获取的数据进行反投影重建图像。结果：开发出一个具有模拟X-CT扫描与重建功能的软件，该软件能直观地显示传统直接反投影和基于穿越长度权重的反投影重建算法得出的图像，并能对得到的图像进行定量评价和定性分析。结论：基于穿越长度的反投影重建算法能有效地减少星状伪影，提高重建图像的质量，且评价指标（归一化均方距离判据d，归一化平均绝对距离判据r，最坏情况距离判据e）都优于传统的插值法；同时开发出的软件具有可扩展性，为其他算法的实现及比较提供一个良好的平台。

A Preliminary of Back-projection Reconstruction Algorithm Based on Penetrating-Length Weighted for Computed Tomography

Objective:Direct back-projection is a kind of fast and simple method for computed tomography image reconstruction,which causes star artifacts that lead to image blur.To effectively improve the quality of computed tomography reconstruction images,a new back-projection reconstruction algorithm based on penetrating-length weighted is introduced,and the method of penetrating-length calculation also provides a new way for the calculation of projection coefficient of algebra reconstruction algorithm.Methods: Using Visual C++ 6.0 as the programming tool to develop a project that can realize the computer simulation of the back-projection reconstruction process,which applies penetrating-length weighted algorithm to the Shepp-Logan model by computing the X-ray penetrating-length of each voxel.Results: A software was developed that could simulate the scanning and reconstruction processes of X-CT,display the images reconstructed by both traditional direct projection and penetrating-length weighted reconstruction algorithms,and conduct quantitative evaluation and qualitative analysis to these images.Conclusions: Simulation result shows that penetrating-length weighted algorithm can effectively improve the image quality by reducing the star artifacts,and its evaluation indicates(the normalized mean square distance criterion d,the normalized average absolute distance criterion r,the worst distance criterion e) are better than the traditional interpolation algorithm.Meanwhile,the software can provide a platform for the realization of other algorithms.