title: 3D position estimation of flexible instruments: marker-less and marker-based methods.
abstract: OBJECTIVE
  Endoscopic images can be used to allow accurate flexible endoscopic instrument control. This can be implemented using a pose estimation algorithm, which estimates the actual instrument pose from the endoscopic images.
  
  
  METHODS
  In this paper, two pose estimation algorithms are compared: a marker-less and a marker-based method. The marker-based method uses the positions of three markers in the endoscopic image to update the state of a kinematic model of the endoscopic instrument. The marker-less method works similarly, but uses the positions of three feature points instead of the positions of markers. The algorithms are evaluated inside a colon model. The endoscopic instrument is manually operated, while an X-ray imager is used to obtain a ground-truth reference position.
  
  
  RESULTS
  The marker-less method achieves an RMS error of 1.5, 1.6, and 1.8 mm in the horizontal, vertical, and away-from-camera directions, respectively. The marker-based method achieves an RMS error of 1.1, 1.7, and 1.5 mm in the horizontal, vertical, and away-from-camera directions, respectively. The differences between the two methods are not found to be statistically significant.
  
  
  CONCLUSIONS
  The proposed algorithms are suitable to realize accurate robotic control of flexible endoscopic instruments, enabling the physician to perform advanced procedures in an intuitive way.
authors.affiliation: MIRA-Institute for Biomedical Technology and Technical Medicine, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands. r.reilink@utwente.nl
authors.forename: Rob
authors.initials: R
authors.lastname: Reilink
authors.forename: Stefano
authors.initials: S
authors.lastname: Stramigioli
authors.forename: Sarthak
authors.initials: S
authors.lastname: Misra
mesh_terms: D000465:Algorithms; D003106:Colon / Q000000981:diagnostic imaging / Q000601:surgery; D004724:Endoscopy / Q000295:instrumentation*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008954:Models, Biological; D011859:Radiography; D015203:Reproducibility of Results; D012371:Robotics / Q000295:instrumentation*; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*