Development and validation of a three dimensional ultrasound based navigation system for tumor resection.

BACKGROUND Intraoperative navigation is a rapidly emerging procedure in orthopaedic surgery and neurosurgery. For abdominal tumors (e.g. liver metastasis) and soft tissue tumors there is only limited experience with navigation techniques due to problems of organ shift and tissue deformation. We have developed a navigation system for tumor resection in soft tissue based on 3D ultrasound imaging and optical tracking. METHODS Two different modes of navigation were evaluated and compared with conventional surgery in an experimental soft tissue model. Both techniques were based on 3D ultrasound and an optical tracking system for intraoperative real time registration of surgical instruments. These two techniques were used: a) Indirect navigation with ultrasound guided insertion of a tracked hook needle into the tumor; and b) Direct navigation using a 3D image which was obtained with an optically tracked 3D ultrasound probe. It was the aim of both techniques to achieve a circumferential resection margin of 2cm around the tumor. RESULTS A total of 23 resections were performed consisting of indirect (n=7) and direct (n=10) navigation and conventional surgery (n=6) as gold standard. For indirect navigation a median deviation from the ideal resection margin (accuracy) of 0.32cm was measured. Direct navigation showed an accuracy of 0.16cm compared to 0.42cm with conventional surgery. Navigated surgery showed for both techniques a significant increase of resection accuracy compared to conventional resection (p<0.05). CONCLUSION 3D ultrasound based indirect and direct optoelectronic navigation for resection of soft tissue tumors is feasible and may improve intraoperative orientation with increased surgical precision.