The field of interactive image-guided surgery is in the formative stages. Experience with rigid stereotactic localizing devices and standard 2D images has shown that conventional surgery can be performed through less invasive approaches with greater precision and shorter operating room times. The goal of this project is to take advantage of the increasing availability of high performance computers and recent advances in image processing science to develop the next generation of virtual stereotactic surgical tools: interactive, 3D computer models registered to physical space for the purposes of surgical planning and intraoperative guidance. Recent research efforts in the laboratory have yielded a robust automated segmentation algorithm which has proven reliable in preliminary studies. The proposed project intends to exploit the unique material and human resources of the laboratory to develop software to integrate these algorithms into interactive, intraoperative surgical planning and guidance tools that are robust and transparent to untrained users. Computer scientists and image processing specialists in the laboratory, working closely with surgeons and radiologists, will develop software on two dedicated supercomputers and a SUN workstation network. The segmentation algorithms will be enhanced and expanded, 3D rendering speed increased and novel methods of registration explored. The results will be implemented and evaluated in the operating room and interventional MR suite. Protocols will be developed to assess reliability, accuracy, and precision based on currently accepted standard comparative measures. This proposal represents a first step toward developing the software resources for enhanced-reality techniques in surgery. The ultimate outcome of this work should be increased precision in surgery, a reduction in the length of procedures, and increased utilization of minimally invasive techniques. If successful, these consequences will translate into a significant improvement in patient care, decreased OR and hospitalization time, and a measurable cost reduction for the healthcare system.