CT反演常采用“直线重构模型”，即认为射线在震源和接收器之间走直线，这一条件只有在介质基本均匀的情况下近似成立。当介质中存在缺陷，射线行走路径不再是直线而是空间曲线时，若仍然采用“直线重构模型”进行反演，必然引入误差。本文提出了改进的ART算法，并在迭代的过程中利用基于旅行时的线性插值（LTI）射线追踪正演射线的实际行走路径。该算法首先利用概率的方法预判缺陷单元，将预判的缺陷单元与非缺陷单元区别对待，赋予不同的初始波速，在每轮迭代之前利用LTI射线追踪重新计算投影矩阵，并在迭代的过程中给预判的缺陷单元与非缺陷单元赋予不同的松弛因子。计算机模拟实验及混凝土试件实验结果表明，基于LTI射线追踪的改进的ART算法有效提高了计算的精度和图像重建质量，但是相应地增加了反演时间。

Straight line reconstruction model is frequently used in concrete computerized tomography. It assumes the ray travels in a straight line between a sending transducer and a receiving transducer, which is valid for homogeneous medium. When there are defects in the medium, the ray will not travel in a straight line but in a spatial curve, and if still using straight line reconstruction model, error will be brought in. An improved algebraic reconstruction technique (ART)is put forward in the paper, and linear travel time interpolation (LTI)ray tracing is used during the iterations to obtain the real travel paths of rays. Firstly, defect meshes are ascertained by probability and mathematical statistic method, and then defect meshes and normal meshes are provided with different initial wave velocities. Secondly, the projection matrix is anew computed by LTI ray tracing before each iteration. And during each iteration, defect meshes and normal meshes are provided with different relaxation factors. The results of computer simulation and concrete model experiment show that the improved ART based on LTI ray tracing is effective to improve the accuracy of computation and the quality of image reconstruction on concrete，but takes more time.