Recently, the capabilities of real-time PC-based video image processing and computer graphic systems converged to make possible the display of a virtual graphical image correctly registered with a view of the 3D environment of the user’s object of interest. The generation of an Augment Reality scene can now be done with a PC computer graphics system. An Augmented Reality (AR) system generates a composite view for the user. It is a combination of the real scene viewed by the user and a virtual scene generated by the computer (a 3D model) that augments the scene with additional information. Fig. 1 displays one possible AR scene where a phantom is overlaid with graphics models of tumors. One of the most important issues to consider for a very accurate AR application is the method for tracking the various elements of the environment such as the video camera.