Further acceleration of the visualization process used in virtual colonoscopy

We present a novel technique to accelerate the volume ray casting process used in virtual colonoscopy. Virtual colonoscopy is a less invasive alternative to colonoscopy with potential for wide use in the early detection of colorectal cancer. The idea of our method is to find the exact distance from each image plane pixel to the closest colon wall (boundary) voxel and use this distance information to start ray integration directly from the colon boundary. Our method also improves the rendering time by exploiting the fact that only a small part of the colon is visible from any internal viewing point. We apply a preprocessing visibility determination algorithm to identify the potentially visible part of the colon at each internal view point. The algorithm only projects the potentially visible boundary voxels on to a distance buffer. Using this distance it is possible to skip the space and start the ray casting integration directly from the colon wall. We have used parallel projection and a generic projection template to achieve more acceleration in our implementation. The method has been implemented on an IBM compatible personal computer and tested with a synthetic colon data set.