Micro-stereometry: a frameless computerized navigating system for open microsurgery

We are introducing a new type of ultrasonic-based three dimensional (3D) ranging system for the localization of small hand-held surgical tools to be used during operation in open and stereotactic brain surgery. The new device has been extensively tested in the laboratory and showed a linear localization accuracy of +/- .4 mm. The calibration of the system is automatically done by an active calibration frame as well as by pointing to fiducial markers. The position of the tool is sent to a visualization unit and overlaid in realtime on preoperatively scanned computed tomography (CT) and magnetic resonance imaging (MRI) pictures. First clinical tests showed the improved accuracy, handling, and versatility of the new stereometric navigation system, which will soon become the backbone of a computer-aided surgery (CAS) system with a variety of locatable tools.