title: Development and validation of a viscoelastic and nonlinear liver model for needle insertion.
abstract: OBJECTIVE
  The objective of our work is to develop and validate a viscoelastic and nonlinear physical liver model for organ model-based needle insertion, in which the deformation of an organ is estimated and predicted, and the needle path is determined with organ deformation taken into consideration.
  
  
  METHODS
  First, an overview is given of the development of the physical liver model. The material properties of the liver considering viscoelasticity and nonlinearity are modeled based on the measured data collected from a pig's liver. The method to develop the liver model using FEM is also shown. Second, the experimental method to validate the model is explained. Both in vitro and in vivo experiments that made use of a pig's liver were conducted for comparison with the simulation using the model.
  
  
  RESULTS
  Results of the in vitro experiment showed that the model reproduces nonlinear and viscoelastic response of displacement at an internally located point with high accuracy. For a force up to 0.45 N, the maximum error is below 1 mm. Results of the in vivo experiment showed that the model reproduces the nonlinear increase of load upon the needle during insertion.
  
  
  CONCLUSIONS
  Based on these results, the liver model developed and validated in this work reproduces the physical response of a liver in both in vitro and in vivo situations.
authors.affiliation: Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, Okubo 3-4-1, Shinjuku, Tokyo 169-8555, Japan. you-k@aoni.waseda.jp
authors.forename: Yo
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Akinori
authors.initials: A
authors.lastname: Onishi
authors.forename: Takeharu
authors.initials: T
authors.lastname: Hoshi
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kawamura
authors.forename: Makoto
authors.initials: M
authors.lastname: Hashizume
authors.forename: Masakatsu G
authors.initials: MG
authors.lastname: Fujie
mesh_terms: D000465:Algorithms; D000818:Animals; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D008099:Liver / Q000502:physiology* / Q000601:surgery*; D008954:Models, Biological; D009339:Needles; D017711:Nonlinear Dynamics; D015203:Reproducibility of Results; D033081:Shear Strength; D013552:Swine; D014783:Viscosity