| dc.description.abstract | In this dissertation, a non-invasive intracranial pressure (ICP) monitoring technique is introduced by developing a head dynamic model. The technique is based on modal frequency testing and vibration responses analysis of the skull. To examine and verify this methodology, we conducted vibration tests on a hemispherical shell to stand as a surrogate for human cranium to measure the effect of cerebrospinal fluid (CSF) pressure on human skull dynamic response; we utilized a hammer-impact modal testing methodology on the simulated hemispherical shell to extract its dynamic response characteristics. To be able to examine the CSF-skull dynamics interactions, we measured the skull impulse responses using mechanical tensile tests at different strain rates. The modal analysis by finite elements eigenvalue analysis of the upper cranium skull model was conducted to find the material properties of the skull. Linear elastic, as well as, nonlinear hyperelastic material models were assumed for the skull to find its material parameters. In the simulation of the human head, the cranium was modeled as a closed clamped hemispherical aluminum shell under internal fluid pressure. The interactions of CSF with the simulated cranium were studied and the frequency responses were obtained at different interior pressures. A numerical procedure for dynamic analysis of the systems was developed to measure the modal frequencies of the setup. We examined the changes to the peaks of frequency response under different fluid pressure. The results of modal analyses demonstrate changes in the frequency of bending-wave vibration modes, while longitudinal-wave modes are nominally altered under variable pressure conditions. A single-degree of freedom vibrational model was also developed to fit to the data for the sensitive modes. Linear regression analysis of the results reveals that the dynamic model’s equivalent damping and stiffness parameters are sensitive to fluid pressure variations while the equivalent mass parameter is relatively unaffected. As a result of this study we conclude that variance in CSF pressure has a measurable effect on the dynamic characteristics of the cranium and vice-versa. A calibrating system to connect the dynamic changes of the head can stand as a non-invasive system for ICP changes. | en_US |
