title: Tissue surface information for intraoperative incision planning and focus adjustment in laser surgery.
abstract: OBJECTIVE
  Introducing computational methods to laser surgery are an emerging field. Focusing on endoscopic laser interventions, a novel approach is presented to enhance intraoperative incision planning and laser focusing by means of tissue surface information obtained by stereoscopic vision.
  
  
  METHODS
  Tissue surface is estimated with stereo-based methods using nonparametric image transforms. Subsequently, laser-to-camera registration is obtained by ablating a pattern on tissue substitutes and performing a principle component analysis for precise laser axis estimation. Furthermore, a virtual laser view is computed utilizing trifocal transfer. Depth-based laser focus adaptation is integrated into a custom experimental laser setup in order to achieve optimal ablation morphology. Experimental validation is conducted on tissue substitutes and ex vivo animal tissue.
  
  
  RESULTS
  Laser-to-camera registration gives an error between planning and ablation of less than 0.2 mm. As a result, the laser workspace can accurately be highlighted within the live views and incision planning can directly be performed. Experiments related to laser focus adaptation demonstrate that ablation geometry can be kept almost uniform within a depth range of 7.9 mm, whereas cutting quality significantly decreases when the laser is defocused.
  
  
  CONCLUSIONS
  An automatic laser focus adjustment on tissue surfaces based on stereoscopic scene information is feasible and has the potential to become an effective methodology for optimal ablation. Laser-to-camera registration facilitates advanced surgical planning for prospective user interfaces and augmented reality extensions.
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.forename: Dennis
authors.initials: D
authors.lastname: Kundrat
authors.forename: Lukas
authors.initials: L
authors.lastname: Kleingrothe
authors.forename: Lüder A
authors.initials: LA
authors.lastname: Kahrs
authors.forename: Nicolas
authors.initials: N
authors.lastname: Andreff
authors.forename: Tobias
authors.initials: T
authors.lastname: Ortmaier
mesh_terms: D003867:Depth Perception; D004724:Endoscopy / Q000379:methods*; D006801:Humans; D053685:Laser Therapy / Q000379:methods*; D007834:Lasers; D025321:Surgery, Computer-Assisted / Q000379:methods*