Parameters for Identifying Brain Response Properties in Vivo

Abstract

Under normal conditions brain tissue exhibits viscoelastic response which can be characterized by viscoelastic parameters including the instantaneous (short-time) and equilibrium (long-time) elastic response, relaxation behavior, and creep behavior. To measure the material coefficients associated with these types of response it is necessary to perform experiments which, for brain tissue, must be done in-vitro. Nevertheless, certain experiments can be performed on brain tissue in-vivo in which case (i) the measured parameters, e.g. pressure, displacement, can be used in the solution to the mechanics problem, which best simulates the experimental configuration, to calculate the actual material coefficients (cf. 1,3), or (ii) the measured parameters can be considered as pseudo response coefficients and used directly to monitor and identify controlled changes in the system (cf. 1,2). Here we consider the latter point of view and describe several pseudo response parameters which are directly measurable in-vivo and which are analogous to material response coefficients used to characterize nonlinear viscoelastic materials.