Figure 2. Sampling and interpolation. The diagram shows the intersection of two B-scans and a reslice plane with a voxel array. The circles represent individual pixels on the various planes. Consider the shaded voxel. If nearest neighbour interpolation were used to construct the voxel array, the intensity of this voxel would be set according to the nearby pixel on B-scan n. Again assuming nearest neighbour interpolation, the same intensity would be attached to the reslice pixel which lies entirely inside this voxel. With direct visualization, however, the intensity of the reslice pixel would be inherited from the nearby pixel on B-scan n+1. Thus, the intermediate voxel representation causes visualization artefacts, which are avoided by direct rendering.