双能谱CT的迭代重建模型及重建方法

摘要

Dual energy computed tomography (DECT) is used to reconstruct energy-selective images ,images of the electron density and the effective atomic number ,or material-selective images of the scanned object .Compared with traditional CT ,DECT has a better material distinguishability .The substantial difficulty for DECT image reconstruction is its nonlinearity .This paper pro-poses a Newton type iterative reconstruction method for DECT .The main feature of the proposed method is its flexibility .It fits for many commonly used scanning configurations and does not require geometrically consistent rays for different spectra .It is also valid for multiple energy CT and slow kVp switching CT .The method is verified with simulated data .Numerical results show that the proposed method can reconstruct the two basis material images correctly .Besides ,as a side-effect ,the beam hardening artifacts in the reconstructed images are reduced significantly .%双能谱 CT 能够重建被测物体的等效原子序数和电子密度或是基材料的密度图像。与传统的单能谱 CT相比，有更好的物质区分能力，有着广泛的应用前景。但是双能谱 CT 重建问题的非线性性给重建带来了困难。针对该问题，本文提出一种适于双能谱 CT 的 Newton 型迭代重建方法。该方法首先将双能谱 CT 对应的非线性问题线性化得到一个线性方程组，然后利用 SART 方法对该线性方程组进行求解，最后利用求得的方程组的解对图像进行更新。该方法的主要优点是其灵活性。它能够适用于常用的各种扫描模式，对于几何一致和不一致投影均有效。同时容易将该方法推广到多能谱 CT 和慢电压切换的 CT 系统。数值实验表明，该方法能够正确重建出基材料的密度图像。另外该方法能有效去除重建图像中的硬化伪影。