title: Image mapping of untracked free-hand endoscopic views to an ultrasound image-constructed 3D placenta model.
abstract: BACKGROUND
  This study presents a tracker-less image-mapping framework for surgical navigation motivated by the clinical need for intuitive visual guidance during minimally invasive fetoscopic surgery.
  
  
  METHODS
  A navigation framework mapping 2D endoscopic vision to a 3D ultrasound image model is proposed. This maps an endoscopic image onto a 3D placenta model through a one-time ultrasound image-based localization method followed by a series of concurrent image alignments and texture mapping of the untracked endoscopic video stream.
  
  
  RESULTS
  The mean absolute error of our ultrasound image-based localization method was (1.63 mm, 0.93°). The simulation analysis reveals an upper bound mapping performance with a mean error of 1.53 mm. In a phantom experiment, the overall mapping performance is close to this accuracy and achieves a mean absolute error of 2 mm, thereby supporting the feasibility of this method.
  
  
  CONCLUSIONS
  This novel integration of intraoperative visual guidance has potential contributions to innovative fusions of image guidance techniques for effective navigation in minimally invasive fetoscopic surgery.
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Liangjing
authors.identifier: http://orcid.org/0000-0002-3294-0879
authors.initials: L
authors.lastname: Yang
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Junchen
authors.initials: J
authors.lastname: Wang
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Ando
authors.affiliation: Clinical Research Center, National Center for Child Health and Development, Tokyo, Japan.
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Yamashita
authors.affiliation: Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Sakuma
authors.affiliation: Clinical Research Center, National Center for Child Health and Development, Tokyo, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Chiba
mesh_terms: D003198:Computer Simulation; D005260:Female; D005330:Fetofetal Transfusion / Q000000981:diagnostic imaging / Q000601:surgery; D005332:Fetoscopy / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional; D019060:Minimally Invasive Surgical Procedures / Q000379:methods; D008953:Models, Anatomic; D010920:Placenta / Q000000981:diagnostic imaging* / Q000601:surgery*; D011247:Pregnancy; D014463:Ultrasonography
keywords: image mapping; minimally invasive fetal endoscopic surgery; mosaic; surgical navigation; twin-to-twin transfusion syndrome