显微CT的锥束重建技术

Cone-beam Reconstruction for Micro-CT

显微CT技术一直是Iowa大学CT/显微CT实验室研究的焦点。这篇文章报告了我们在锥束显微CT方面最近取得的一些进展。我们利用Feldkamp类算法进行了多X光源和检测器偏置条件下的近似图象重建;解释了Grangeat精确重构框架下的图象伪影。最后重点介绍了最近有关一般分块迭代Landweber格式的收敛性结果;给出了模拟和实验结果,探讨了进一步的研究方向。

X-ray micro-CT has been a focus in the CT/Micro-CT Lab, the University of Iowa. In this paper, some recent progress we made on cone-beam micro-CT is described. First, we address approximation reconstruction using Feldkamp-type algorithms with multiple X-ray sources and displaced detector configurations. After an appropriate fan-beam weighting function on the rectangular redundant region for equi-angular data is derived for multiple imaging chains, we can insert it into a general Feldkamp algorithm for cone-beam reconstruction with multiple sources and obtain a reconstruction formula. Then, we explain three types of artifacts associated with exact reconstruction in the Grangeat framework as applied to the circular scanning locus, which are thorn, wrinkle, and V artifacts. The thorn pattern is due to inappropriate extrapolation into the shadow zone in the Radon domain. Hence, the zero padding technique should be avoided in this context. The wrinkle texture arises if interpolation needed to compute the first derivatives of the Radon data is not smooth between adjacent detector planes. In particular, the nearest neighbor interpolation method should not be used in general. If the number of projections is not small, the bi-linear interpolation method is effective to suppress the wrinkle artifacts. The V shape on the meridian plane comes from the line integrations through the transition zones where derivative data change abruptly, and are very unstable. Two immediate remedies are to increase the sampling rate and suppress data noise. Finally, we report our recent convergence results of a generalized block-iterative Landweber scheme, which includes the SART and some other well-known algorithms and their ordered-subset versions as special cases. The iterative approach has been important in image reconstruction for reducing image noise and artifacts in the cases of noisy and/or incomplete data. It is shown that block-iterative schemes can greatly speed the reconstruction process and produce satisfactory image. Representative images from simulation and experiments are also given .