Abstract: Projection coefficient has crucial effect on reconstruction speed and quality of Algebraic Reconstruction Technique.In this paper an efficient method based on ray to compute projection coefficient is presented，which classifies different situations of grids intercepted by ray.The coefficient matrix can be calculated fast and efficiently as the correlation and symmetry of the parallel lines.The experiments using Shepp-Logan phantom show that the result of this method are fast and effective.

Key words: algebraic reconstruction technique, image reconstruction, projection coefficient, base on ray

摘要： 针对ART（Algebraic Reconstruction Technique）算法重建图像中投影系数是影响重建速度和重建质量的主要因素，提出一种快速计算投影系数的方法。该方法由射线出发，根据射线与网格相交的不同情况，分类快速求解投影系数。同时利用平行射束下射线的相关性与对称性，避免大量重复计算，节省了计算时间。仿真实验选用Shepp-Logan模型，结果表明该方法快速有效。

关键词: 代数重建算法, 图像重建, 投影系数, 基于射线