Incorrect vector after calibration of surgical instruments for image guidance. The problem and the solution: Technical note

Recently, the use of intra-operative image guidance has gained an increasin g role in neurosurgery for both spinal and cerebral interventions. Some mod ern neuronavigation systems are able to register any surgical instrument an d create a virtual pointer. A virtual elongation of the digitized instrumen t is frequently used for neuroendoscopic procedures and spinal instrumentat ion. The instrument is equipped with a universal instrument adapter clamp a nd digitized by touching the tip of the instrument into a calibration cone. An algorithm calculates the vector of the instrument using two points: the tip of the instrument, and the geometrical center of the instrument adapte r geometry. If a virtual elongation of the calibrated instrument is perform ed, the neuronavigation software may calculate an incorrect virtual target point. We developed an instrument calibration matrix (ICM) that automatical ly calibrates the correct vector, tip, and diameter of the instrument used for image-guided surgery. The ICM is easy to handle and does not cause a ti me delay during surgery. Virtual, elongation of the surgical instruments sh ows correct anatomic data, which are fundamental for planning ventricular t apping and spinal screw placement in particular. The instrument calibration matrix is essential if surgical instruments are digitized and used for neu ronavigation. It helps to avoid misplanning of surgical vectors and mis-pla cement of the used instruments.