Soft tissue navigation: Transferring pre-operative planning data into the operation room

Purpose: Computer-assisted surgery has been established in orthopedic and neurosurgery, and is now becoming available as support for soft tissue surgery. Such technology should bridge the gap between pre-operative imaging and the intra-operative scenario by providing tool guidance and enhanced visualization during the surgery. The work to be presented addresses the integration of a clinically applicable navigation system for enhancing spatial orientation during complex hepatic resections. One challenging aspect is the detection of organ motion and its compensation during surgery. Methods and Materials: The system being developed consists of an interface to preoperative planning (MeVis Distant Services) and contains an integrated ultrasound transducer (Terason 8IOA) and an optical tracking system (NDI Vicra or Atracsys InfiniTrack) for spatial referencing of transducers and surgical instruments. The navigated ultrasound is used for acquiring 3D-information on organ motion during surgery. The combination of image processing and mechanical modeling of soft tissues allows the calculation of the organ deformation, used for updating the planning data. The actualized planning datasets are then visualized together with navigated surgical tools. This enables tool guidance and provision of information on the location of critical structures. Results: An integrated hardware/software framework has been developed. It combines navigation, interactive display and ultrasound imaging on a transportable platform. Several methods for the detection of soft tissue motion are currently being evaluated for liver surgery. The soft tissue navigation system is ready to be applied in preclinical trials. The authors work on the transfer of the technology into clinical reality.