The VIRIM system, which stands for Virtual Reality In Medicine, aims at realising computer aided surgery (CAS) using methods of virtual reality (VR). In contrast to other approaches the visualisation/segmentation system VIRIM implements both real-time volume ray-casting as visualisation method and real-time grey-value segmentation. VIRIM is currently the first realtime volume ray-casting system. In contrast to most other systems no special data preparation like surface extraction is necessary. Different volume ray-casting algorithms can be implemented in VIRIM and arbitrary opacity levels are possible for the structures that are visualised.

The system will be used in operation planning and -control. Preoperatively captured CT (or MRI) data of the patient’s head is used for three-dimensional navigation through the data set. First the path of the endoscope to the lesion to be operated is planned, second during surgery the positions of the endoscopic tools are compared with the preoperatively planned path. The latter method of navigation is necessary since orientation during endoscopic operations is both difficult and critical for successful interventions.

Both for operation planning and -control the surgeon uses a tracking unit that determines the position and the orientation of endoscope and patient. This information is used to visualise the local operation environment relative to the endoscope tip.

The VR environment will be built up 1995 and will first serve for evaluation of the new approach to head surgery in the Clinic for Maxillofacial and Craniofacial Surgery at the University of Heidelberg. After this introductory phase a regular usage is planned