title: Assessment of video tracking usability for training simulators.
abstract: OBJECTIVE
  A simulator was developed to mimic commercial CAS systems in implementing most tasks required to carry out a surgical operation. As tracking systems are generally expensive components, an alternative solution based on low-cost video-based tracking was used. Video tracking accuracy was assessed to determine whether or not this kind of approach was suitable for use in the training domain. Ultimately, video-based tracking should enable sufficiently accurate registration between a bony model and its virtual 3D representation.
  
  
  METHODS
  Video tracking was assessed using two types of camera. For each one, common accuracy tests were realized as a series of 10 trials at ranges of 0.5-1.0 m from the camera lens. The pointer used as a digitizer was equipped with tracked video markers. Three sizes of marker were evaluated to estimate the impact of marker size on accuracy.
  
  
  RESULTS
  For the better of the two cameras tested, results were encouraging. Results are presented as rounded whole-number values in millimeters. The noise test gave accuracies of 2 mm for the 80-mm marker, 3 mm for the 60-mm marker and 5 mm for the 40-mm marker. Relative accuracies, as evaluated on a grid of equally spaced dots, were 4 mm with the 80-mm marker, 7 mm with the 60-mm marker and 12 mm with the 40-mm marker. A pivoting test around the pointer tip gave 3 mm of accuracy for the 80-mm marker, 5 mm for the 60-mm marker and 11 mm for the 40-mm marker. An additional pivoting test was completed on increasing the distance of the marker from the pointer tip, giving accuracies of 5 mm for the 80-mm marker, 6 mm for the 60-mm marker and 13 mm for the 40-mm marker. The registration test gave accuracies of 8 mm for the 80-mm marker, 9 mm for the 60-mm marker and 11 mm for the 40-mm marker.
  
  
  CONCLUSIONS
  The video-based approach offers sufficient accuracy to achieve registration in the domain of CAS training.
authors.affiliation: Maurice E. Müller Research Center for Orthopaedic Surgery, Institute for Surgical Technology and Biomechanics University of Bern Switzerland.
authors.forename: Julien
authors.initials: J
authors.lastname: de Siebenthal
authors.forename: Paul-Alfred
authors.initials: PA
authors.lastname: Grützner
authors.forename: Andreas
authors.initials: A
authors.lastname: Zimolong
authors.forename: Urs
authors.initials: U
authors.lastname: Rohrer
authors.forename: Frank
authors.initials: F
authors.lastname: Langlotz
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000193:education*; D003198:Computer Simulation; D006801:Humans; D008954:Models, Biological; D017145:Models, Educational; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000193:education*; D014741:Video Recording