光线投射算法是一种应用广泛的体绘制技术的基本算法，其存在的主要问题是绘制速度较慢。为了提高光线投射算法的绘制速度，以满足医学图像三维重建的应用需求，在深入研究和比较各种光线投射加速算法的基础上，提出了以接近云算法为核心的、适用于医学图像三维重建的综合性加速算法，并在PC机平台上实现了该算法，在保证图像质量的同时绘制速度提高了一个数量级左右，为医学图像三维重建的实用化提供了有效的手段。

Medical image 3D reconstruct is an important application filed for volume rendering, for it special using, it required fast interactive speed and high image quality. Ray casting is a widely used basic volume rendering algorithm. It can get high quality image but the rendering speed is very slowly. In order to improve its rendering speed and apply it to medical image 3D reconstruct, a synthesized accelerate algorithm is proposed in this paper. Firstly, accelerate algorithms for ray casting are fully studied and compared. Secondly, proximity clouds algorithm has been selected and extended to continuous ray casting. Then the synthesized accelerate algorithm base on ray coherence has been proposed. Finally, the algorithm is realized on PC platform. Four data sets are used for test at two different image resolutions. The result shown that compare with standard ray casting algorithm, the accelerate algorithm not only improve the rendering speed for nearly ten times but also bring no depress on image quality. At 512×512 image resolution, a nearly real time interactive speed has been get. It gives a more capability method for the application of medical image 3D reconstruct.