Over the last decade, Interactive Image Guided Surgery of medical procedures. In optimal control theory, observability (IIGS) has become one of the most important applications of comput-is a necessary criterion for controlling desired parts of a sysers in medicine. Through the interactive use of computer generated tem [25]. The improved controllability of IIGS systems has images from medical imaging and the estimated position of subcuta-been made possible in the last decade with increased ability neous surgical instruments, the surgeon is able to perform surgery in to process computer graphics and images in real-time. IIGS conditions of obscuration or minimally invasive surgery without the systems use 3-D computer models obtained from segmentaconstant use of medical imaging machinery (x-ray, MRI) in the op-tion and volume rendering of preoperative imaging in the operating room. These systems can also be used for the preoperative erating room [29]. The intraoperative use of 3-D medical implanning of surgical procedures and have been used to assist in the improvement ofprostheses. IIGS has many benefits such as reduced ages coupled with real-time optical tracking of medical instrurecovery time for the patient and reduced stress on the surgeon as ments has improved the surgeon's ability to place and control the surgical plan can be practiced ahead of time, recorded, and pre-the end effectors [6]. IIGS systems differ from other medical sented in the operating room. In the current literature, such systems software because they provide added visibility and guidance to were only analyzed and evaluated from limited perspectives. We re-the surgeon to improve operative decisions and surgical outview the state of the art in the analysis of IIGS systems and discuss come. IIGS systems involve several processes such as comthe limitations of the models and methods that were used. We present plex image transformations, registration and real-time tracking a novel approach to model IIGS systems. We have developed our no-during surgery. The question that remains to be answered is: tation, modeling techniques and analysis methods so that they can be "Although IIGS systems have the potential to improve surgical applied to domains other than surgical interactive systems. outcome, are they safe?"