title: Calibration of the motor-assisted robotic stereotaxy system: MARS.
abstract: BACKGROUND
  The motor-assisted robotic stereotaxy system presents a compact and light-weight robotic system for stereotactic neurosurgery. Our system is designed to position probes in the human brain for various applications, for example, deep brain stimulation. It features five fully automated axes. High positioning accuracy is of utmost importance in robotic neurosurgery.
  
  
  METHODS
  First, the key parameters of the robot's kinematics are determined using an optical tracking system. Next, the positioning errors at the center of the arc--which is equivalent to the target position in stereotactic interventions--are investigated using a set of perpendicular cameras. A modeless robot calibration method is introduced and evaluated. To conclude, the application accuracy of the robot is studied in a phantom trial.
  
  
  RESULTS
  We identified the bending of the arc under load as the robot's main error source. A calibration algorithm was implemented to compensate for the deflection of the robot's arc. The mean error after the calibration was 0.26 mm, the 68.27th percentile was 0.32 mm, and the 95.45th was 0.50 mm.
  
  
  CONCLUSIONS
  The kinematic properties of the robot were measured, and based on the results an appropriate calibration method was derived. With mean errors smaller than currently used mechanical systems, our results show that the robot's accuracy is appropriate for stereotactic interventions.
authors.affiliation: Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany. heinig@rob.uni-luebeck.de
authors.forename: Maximilian
authors.initials: M
authors.lastname: Heinig
authors.forename: Ulrich G
authors.initials: UG
authors.lastname: Hofmann
authors.forename: Alexander
authors.initials: A
authors.lastname: Schlaefer
mesh_terms: D000465:Algorithms; D001921:Brain / Q000601:surgery*; D002138:Calibration; D046690:Deep Brain Stimulation / Q000379:methods; D004867:Equipment Design; D006801:Humans; D012371:Robotics / Q000295:instrumentation*; D013238:Stereotaxic Techniques / Q000295:instrumentation*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*; D013523:Surgical Equipment