title: Soft tissue motion tracking with application to tablet-based incision planning in laser surgery.
abstract: OBJECTIVE
  Recent research has revealed that incision planning in laser surgery deploying stylus and tablet outperforms micromanipulator control. However, vision-based adaption to dynamic surgical scenes has not been addressed so far. In this study, scene motion compensation for tablet-based planning by means of tissue deformation tracking is discussed.
  
  
  METHODS
  A stereo-based method for motion tracking with piecewise affine deformation modeling is presented. Proposed parametrization relies on the epipolar constraint to enforce left-right consistency in the energy minimization problem. Furthermore, the method implements illumination-invariant tracking and appearance-based occlusion detection. Performance is assessed on laparoscopic and laryngeal in vivo data. In particular, tracking accuracy is measured under various conditions such as occlusions and simulated laser cuttings. Experimental validation is extended to a user study conducted on a tablet-based interface that integrates the tracking for image stabilization.
  
  
  RESULTS
  Tracking accuracy measurement reveals a root-mean-square error of 2.45 mm for the laparoscopic and 0.41 mm for the laryngeal dataset. Results successfully demonstrate stereoscopic tracking under changes in illumination, translation, rotation and scale. In particular, proposed occlusion detection scheme can increase robustness against tracking failure. Moreover, assessed user performance indicates significantly increased path tracing accuracy and usability if proposed tracking is deployed to stabilize the view during free-hand path definition.
  
  
  CONCLUSIONS
  The presented algorithm successfully extends piecewise affine deformation tracking to stereo vision taking the epipolar constraint into account. Improved surgical performance as demonstrated for laser incision planning highlights the potential of presented method regarding further applications in computer-assisted surgery.
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167, Hanover, Germany. andreas.schoob@imes.uni-hannover.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schoob
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167, Hanover, Germany.
authors.forename: Max-Heinrich
authors.initials: MH
authors.lastname: Laves
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167, Hanover, Germany.
authors.forename: Lüder Alexander
authors.initials: LA
authors.lastname: Kahrs
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167, Hanover, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Ortmaier
mesh_terms: D000465:Algorithms; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007830:Larynx / Q000601:surgery; D053685:Laser Therapy / Q000379:methods*; D010363:Pattern Recognition, Automated; D025321:Surgery, Computer-Assisted / Q000379:methods
keywords: Epipolar constraint; Soft tissue deformation tracking; Stereo vision; Surgeon interface; User performance