ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

A COMPUTATIONAL METHOD TO ESTIMATE THE ELASTIC
PARAMETERS OF BIOMECHANICAL MODELS FOR THE IN-VIVO
HUMAN LIVER
F. Martínez-Martínez 1 , M.A. Lago 1 , M.J. Rupérez 1 , C. Monserrat 1 , E. Pareja 2 , M.
Cortés 2 , R. López 2 and S. Brugger 2
1. ABSTRACT
In this work, a computational method to estimate the elastic parameters of models for
the in-vivo human liver is presented. A function based on similarity coefficients from
Medical Image, the Geometric Similarity Function (GSF), is formulated in order to
compare the similarity between two voxelized meshes, one from a simulated
deformation and the other from the real deformation caused for example, by the
breathing of the patient obtained from CT images. An iterative searching algorithm
(ISA) is implemented, where the model parameters change in each iterate depending on
the results of GSF, in order to find the optimum parameter. The method shows that the
ISA finds the parameters of two synthetic cases: The Young’s modulus of a linear
elastic model for a cube and the parameters of a Mooney-Rivlin’s model for an ex-vivo
human liver.
2. INTRODUCTION
Computer-Aided Surgery (CAS) is a useful technique that allows guiding the surgeons
to perform more reliable surgical interventions. In particular, CAS helps the surgeons
ensure the proper positioning of a needle in a biopsy or replace accurately a joint
implant. When the interventions are focused on organs, biomechanical models of them
can be useful to model the deformable behavior of soft tissue. In some interventions
where really accurate results are needed, a good biomechanical model is essential. This
is the case of the liver, which is subjected to the deformation due to the patient
breathing during radiotherapy or during some kind of biopsies [1-3]. In these cases it is
fundamental to know where the tumor is located to radiate the dose or to place the
biopsy needle. To achieve accurate results in biomechanical modeling, two critical
aspects must be solved: to select a model that better represents the behavior of the liver
tissue and to obtain the parameters that characterize its constitutive equations.
Many researchers have estimated the parameters of biomechanical models
experimentally. They measured the mechanical response of ex-vivo or in-vitro liver
tissue samples by means of indentation tests [4-6] or a combination of compression and
elongation tests [7-8]. However, these models are not able to reproduce faithfully the
liver behavior due to the mechanical differences between in-vivo and ex-vivo tissue
1
Instituto Interuniversitario de Investigación en Bioingenieria y Tecnología Orientada al Ser Humano
(UPV) Universiat Politècnica de València, Spain.
2
Unidad de Cirugía y Trasplante Hepático, Hospital Universitari i Politècnic La Fe, Valencia, Spain.