Figure 4From: Evaluation of a Validation Method for MR Imaging-Based Motion Tracking Using Image Simulation(a) A marker sphere showing OCV. (b) An OCV showing the tetrahedron in which the appearance of markers varies uniquely. The most symmetric appearances are 1 mid voxel, 2 mid face, 3 mid edge, and 4 voxel corner. Appearance 5 is in the middle of the tetrahedron and shows the resulting asymmetric appearance.Back to article page