Interactive visualisation of a virtual colonoscopy by combining ray casting with an acceleration corridor

We present a novel acceleration technique for the volume ray casting process used in virtual colonoscopy. Our method exploits the information obtained from casting a ray to avoid redundant computations for neighbouring rays. A corridor from the image plane into the volume data set is examined whenever a ray is cast. All rays passing through this corridor reach the same cell as the first non-space intersected cell. We apply the distance information obtained from casting a ray to other rays in the same group. Using this distance it is possible to skip the space and start the ray casting integration from a nonspace cell. The group of rays is obtained by projecting the non-space cell intersected by the first ray in to the image plane. The method has been implemented on a personal computer and tested with the visible human data set and a synthetic colon data set. The amount of acceleration achievable using this method depends on the enlargement factor. There is some degradation in the quality of the image produced using this method, due to the approximation used to select the group of rays that reaches the same non-space cell.