SonoWand, an ultrasound-based neuronavigation system

OBJECTIVE: We have integrated a neuronavigation system into an ultrasound s canner and developed a single-rack system that enables the surgeon to perfo rm frameless and armless stereotactic neuronavigation using intraoperative three-dimensional ultrasound data as well as preoperative magnetic resonanc e or computed tomographic images. The purpose of this article is to describ e our two-rack prototype and present the results of our work on image quali ty enhancement. DESCRIPTION OF INSTRUMENTATION: The system consists of a high-end ultrasoun d scanner, a modest-cost computer, and an optical positioning/digitizer sys tem. Special technical and clinical efforts have been made to achieve high image quality. A special interface between the ultrasound instrument and th e navigation computer ensures rapid transfer of digital three-dimensional d ata with no loss of image quality. OPERATIVE TECHNIQUE: The positioning system tracks the position and orienta tion of the patient, the ultrasound probe, the pointer, and various surgica l instruments. This makes it possible to update the three-dimensional map d uring surgery and navigate by ultrasound data in a similar manner as with m agnetic resonance data. METHODS: The two-rack prototype has been used for clinical testing since No vember 1997 at the University Hospital in Trondheim. EXPERIENCE AND RESULTS: The image quality improvements have enabled us, in most cases, to extract information from ultrasound with clinical value simi lar to that of preoperative magnetic resonance imaging. The overall clinica l accuracy of the ultrasound-based navigation system is expected to be comp arable to or better than that of a magnetic resonance imaging-based system. CONCLUSION: The SonoWand system enables neuronavigation through direct use of intraoperative three-dimensional ultrasound. Further research will be ne cessary to explore the potential clinical value and the limitations of this technology.