The depth information of surface is introduced to volume rendering algorithmto reduce the computation time and the 3-D interpolation algorithm based on surface gradient is porposed to alleviate the strip artifacts due to anisotropic resolution of the original 3-D image data. By providing depth information using run-length code for each slices, the unnecessary sampling points can be is eliminated on the ray tracing and the rendering time is reduced by one-fourth compared with the conventional case. Anisotropic resolution of the volume data produces discontinuous gradient vectors which result in the artifacts on the 3-D image. Using the proposed surface orientationbased interpolation, these artifacts have been reduced drastically, which is confirmed by computer simulation.