Study On Accelerated Algorithms Of Medical CT Image Visualization

The problems which3D reconstruction faces are the enormous data to process and the complexity of the medical images, so it is very crucial to optimize the3D reconstruction algorithms and to accelerate the processing speed. According to the certain sampling and rendering rules, Direct Volume Rendering algorithm directly render the volume data to get an image. DVR is one of the most important techniques in the field of information visualization which is widely used. The research on DVR is very significant in academia and practice.There are two different approaches of3D reconstruction from medical images, including surface rendering and volume rendering. Compared with surface rendering in3D reconstruction, volume rendering can concentrate on visualizing internal features of choice and surfaces at the same time. Volume rendering is the emphasis of the thesis. This thesis mainly studies two volume rendering algorithm:Ray-casting and Shear-Warp.Firstly, this thesis anatomizes the basic principles of ray-casting algorithm, deeply researches the key techniques such as data classification, distributing color and opacity value to each voxel, Phong illumination model, depth modulation, resample and trilinear interpolation, space transform, projection transform, composition etc. At last, refer to the disadvantage of the medical images, there are many empty voxels, an algorithm named jumping ray cast is presented in this thesis. For each empty voxel, recording the distance between it and its nearest non-empty voxel. In ray casting process, the distance can be the step. At this range of distance, the light will no longer encounter empty voxel in each directions, this is equivalent to skip the empty voxel. This algorithm can save the part of time that be cost in the calculation of empty voxels, and improves the speed.Secondly, the thesis deeply analyses the basic principles of shear-warp algorithm, in-depth studies emphatically the related problems such as the selection of main collimation axis, shear transformation, replacement, deformation matrix calculation, and factorization etc. The simplified illumination model, which can save a lot of time and improve the efficiency, is presented in this thesis; In order to improve the quality of image rendering, bilinear interpolation method was improved; After the comprehensive improvement, it is realized to improve the rendering speed while the quality of image is not been damaged.At last, an interactive medical3D-reconstruction system is designed by VC++6.0. The system can implement basic function of3D reconstruction, validate the correctness and high efficiency of the algorithms, and obtain the anticipate results.