Calibration of tracking systems in a surgical environment

Abstract

The purpose of this paper was to assess to what extent an optical tracking system (OTS) used for position determination in computer-aided surgery (CAS) can be enhanced by combining it with a direct current (dc) driven electromagnetic tracking system (EMTS). The main advantage of the EMTS is the fact that it is not dependent on a free line-of-sight. Unfortunately, the accuracy of the EMTS is highly affected by nearby ferromagnetic materials. We have explored to what extent the influence of the metallic equipment in the operating room (OR) can be compensated by collecting precise information on the nonlinear local error in the EMTS by using the OTS for setting up a calibration look-up table. After calibration of the EMTS and registration of the sensor systems in the OR we have found the average euclidean deviation in position readings between the dc tracker and the OTS reduced from 2.9+/-1.0 mm to 2.1+/-0.8 mm within a half-sphere of 530-mm radius around the magnetic field emitter. Furthermore we have found the calibration to be stable after re-registration of the sensors under varying conditions such as different heights of the OR table and varying positions of the OR equipment over a longer time interval. These results encourage the further development of a hybrid magnetooptical tracker for computer-aided surgery where the electromagnetic tracker acts as an auxiliary source of position information for the optical system. Strategies for enhancing the reliability of the proposed hybrid magnetooptic tracker by detecting artifacts induced by mobile ferromagnetic objects such as surgical tools are discussed.

Electromagnetic Tracking in Medicine—A Review of Technology, Validation, and Applications

“…The error compensation can be performed online during the use of the tracking system, based on another independent [31,32] Combination of EM and optical tracking systems Birkfellner et al [17] Using discrete LUT Meskers et al [107] Measurements averaged over time at reference points Perie et al [136] LUT based on plexi phantom Day et al [26] Employing a calibration phantom Interpolation Raab et al [148] First polynomial fit Thormann et al [177] Online correction by Hardy's multiquadric method Himberg et al [57] Multi-sensor data collection with LEGO Ikits et al [62] 4 th order polynomial fit Bryson et al [21] 4 th order polynomial fit Hagedorn et al [50] Delaunay tetrahedralization for rotations Kindratenko et al [71] 3-5 th order polynomial fit Nakamoto et al [124] 0-4 th order polynomial fit Traub et al [181] Interpolation on the top of LUT Fischer [35] Thin-Plate Spline Interpolation, Bernstein-polynoms Kelemen [67] Delaunay tetrahedralization and polynomial fit Extrapolation Kelemen [67] Extrapolation based on global polynomial fit…”

Safety of Interactive Image-Guided Surgery

“…This procedure is the gold standard for registration because it minimizes errors in transformation. This procedure is, however more invasive than other methods Birkfellner et al (1998);Starreveld et al (2001).…”

Improved Tracking Using a Hybrid Optcial-Haptic Three-Dimensional Tracking System

“…Birkfellner et al [7] developed a hybrid tracking system that combines an electromagnetic tracking system and optical tracker in order to avoid obstructions of the line-of-sight necessary for the operation of the OTS while maintaining an interrupted tracking and the accuracy needed in computer aided-surgery. More recently Harders et al [8] introduced a hybrid tracking method that combines the IR optical tracker with a vision based tracking approach III.…”