Modeling and measurement of the vibrational response of the ovine head as it relates to intracranial pressure

Abstract

A combined experimental and analytical approach was taken to understand the vibrational characteristics of the ovine head, as a framework to use vibrational measurements to monitor changes in intracranial pressure. Modal analysis was performed on excised ovine heads to establish the spatial and spectral behavior of the head as a function of the presence of the soft extracranial and intracranial tissues and boundary conditions. Measurements of ovine cranial bone thickness, density, moisture content, and modulus of elasticity provided material property values for incorporation into analytical models of the ovine skull. Simplified spherical models were used in a parametric analysis to determine the sensitivity of the skull to changes in material properties and geometry. A detailed finite element model of the ovine skull was obtained by digitizing the cranial cavity of an ovine skull in 3D. Isotropic, homogeneous material properties which were measured for ovine cranial bone were incorporated into the detailed geometric model. The calculated modal shapes from the finite element model were validated by high correlations to experimental modal shapes as calculated by the Modal Assurance Criterion. While the finite element model described the vibrational behavior of the head adequately, it was relatively insensitive to increases in internal pressure of 50 cm H2O