title: Surface registration for use in interactive, image-guided liver surgery.
abstract: OBJECTIVE
  Liver surgery is difficult because of limited external landmarks, significant vascularity, and inexact definition of intra-hepatic anatomy. Intra-operative ultrasound (IOUS) has been widely used in an attempt to overcome these difficulties, but is limited by its two-dimensional nature, inter-user variability, and image obliteration with ablative or resectional techniques. Because the anatomy of the liver and intra-operative removal of hepatic ligaments make intrinsic or extrinsic point-based registration impractical, we have implemented a surface registration technique to map physical space into CT image space, and have tested the accuracy of this method on an anatomical liver phantom with embedded tumor targets.
  
  
  METHODS
  Liver phantoms were created from anatomically correct molds with "tumors" embedded within the substance of the liver. Helical CT scans were performed with 3-mm slices. Using an optically active position sensor, the surface of the liver was digitized according to anatomical segments. A surface registration was performed and RMS errors of the locations of internal tumors are presented as verification. An initial point-based marker registration was performed and considered the "gold standard" for error measurement.
  
  
  RESULTS
  Errors for surface registration were 2.9 mm for the entire surface and 2.8 mm for embedded targets.
  
  
  CONCLUSIONS
  This is an initial study considering the use of surface registration for the purpose of physical-to-image registration in the area of liver surgery.
authors.affiliation: Division of Hepatobiliary Surgery and Liver Transplantation, Vanderbilt University, Nashville, Tennessee 37235, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Herline
authors.forename: J L
authors.initials: JL
authors.lastname: Herring
authors.forename: J D
authors.initials: JD
authors.lastname: Stefansic
authors.forename: W C
authors.initials: WC
authors.lastname: Chapman
authors.forename: R L
authors.initials: RL
authors.lastname: Galloway
authors.forename: B M
authors.initials: BM
authors.lastname: Dawant
mesh_terms: D003198:Computer Simulation; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000601:surgery*; D019047:Phantoms, Imaging; D013813:Therapy, Computer-Assisted; D014057:Tomography, X-Ray Computed; D014584:User-Computer Interface