title: Locally rigid, vessel-based registration for laparoscopic liver surgery.
abstract: OBJECTIVE
  Laparoscopic liver resection has significant advantages over open surgery due to less patient trauma and faster recovery times, yet is difficult for most lesions due to the restricted field of view and lack of haptic feedback. Image guidance provides a potential solution but is challenging in a soft deforming organ such as the liver. In this paper, we therefore propose a laparoscopic ultrasound (LUS) image guidance system and study the feasibility of a locally rigid registration for laparoscopic liver surgery.
  
  
  METHODS
  We developed a real-time segmentation method to extract vessel centre points from calibrated, freehand, electromagnetically tracked, 2D LUS images. Using landmark-based initial registration and an optional iterative closest point (ICP) point-to-line registration, a vessel centre-line model extracted from preoperative computed tomography (CT) is registered to the ultrasound data during surgery.
  
  
  RESULTS
  Using the locally rigid ICP method, the RMS residual error when registering to a phantom was 0.7 mm, and the mean target registration error (TRE) for two in vivo porcine studies was 3.58 and 2.99 mm, respectively. Using the locally rigid landmark-based registration method gave a mean TRE of 4.23 mm using vessel centre lines derived from CT scans taken with pneumoperitoneum and 6.57 mm without pneumoperitoneum.
  
  
  CONCLUSIONS
  In this paper we propose a practical image-guided surgery system based on locally rigid registration of a CT-derived model to vascular structures located with LUS. In a physical phantom and during porcine laparoscopic liver resection, we demonstrate accuracy of target location commensurate with surgical requirements. We conclude that locally rigid registration could be sufficient for practically useful image guidance in the near future.
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK. yi.song@ucl.ac.uk.
authors.forename: Yi
authors.initials: Y
authors.lastname: Song
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: Johannes
authors.initials: J
authors.lastname: Totz
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Thompson
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: Stian
authors.initials: S
authors.lastname: Johnsen
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: Dean
authors.initials: D
authors.lastname: Barratt
authors.affiliation: Royal Free Campus, 9th Floor, Royal Free Hospital, UCL Medical School, Rowland Hill Street, London, UK.
authors.forename: Crispin
authors.initials: C
authors.lastname: Schneider
authors.affiliation: Royal Free Campus, 9th Floor, Royal Free Hospital, UCL Medical School, Rowland Hill Street, London, UK.
authors.forename: Kurinchi
authors.initials: K
authors.lastname: Gurusamy
authors.affiliation: Royal Free Campus, 9th Floor, Royal Free Hospital, UCL Medical School, Rowland Hill Street, London, UK.
authors.forename: Brian
authors.initials: B
authors.lastname: Davidson
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Ourselin
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK.
authors.forename: David
authors.initials: D
authors.lastname: Hawkes
authors.affiliation: Centre For Medical Image Computing, Engineering Front Building, University College London, Malet Place, London, UK. m.clarkson@ucl.ac.uk.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Clarkson
mesh_terms: D000818:Animals; D002138:Calibration; D004195:Disease Models, Animal; D010535:Laparoscopy / Q000379:methods*; D016014:Linear Models; D008099:Liver / Q000098:blood supply* / Q000000981:diagnostic imaging; D008113:Liver Neoplasms / Q000601:surgery*; D019047:Phantoms, Imaging; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography
keywords: Laparoscopic; Liver surgery; Registration; Ultrasound