A DYNAMIC MATERIAL PARAMETER-ESTIMATION PROCEDURE FOR SOFT-TISSUE USING A POROELASTIC FINITE-ELEMENT MODEL

A three-dimensional finite element model for a poroelastic medium has been coupled with a least squares parameter estimation method for the purpose of assessing material properties based on intradiscal displace ment and reactive forces. Parameter optimization may be based on eithe r load or displacement control experiments. In this paper we present t he basis of the finite element model and the parameter estimation proc ess. The method is then applied to a rest problem and the computationa l behavior is discussed. Sequential optimization on different paramete r groups was found to have superior convergence properties. Some guide lines for choosing the starting parameter values for optimization were deduced by considering the form of the objective function. For load c ontrol experiments, in which displacement data is used for the optimiz ation, the starting values for the elastic modulus should be lower in magnitude than an ''anticipated'' modulus. The permeability starting v alues should be higher than an anticipated permeability. For displacem ent control experiments, the reverse is true. The optimization scheme was also tested on data with random variations.