The intracranial system consists of three main basic components - the brain, the blood and the cerebrospinal fluid. The physiological processes of each of these individual components are complex and they are closely related to each other. Understanding them is important to explain the mechanisms behind neurostructural disorders such as hydrocephalus. This research project consists of three interrelated studies, which examine the mechanical properties of the brain at the macroscopic level, the mechanics of the brain during hydrocephalus and the study of fluid hydrodynamics in both the normal and hydrocephalic ventricles. The first of these characterizes the porous properties of the brain tissues. Results from this study show that the elastic modulus of the white matter is approximately 350Pa. The permeability of the tissue is similar to what has been previously reported in the literature and is of the order of 10-12m4/Ns. Information presented here is useful for the computational modeling of hydrocephalus using finite element analysis. The second study consists of a three dimensional finite element brain model. The mechanical properties of the brain found from the previous studies were used in the construction of this model. Results from this study have implications for mechanics behind the neurological dysfunction as observed in the hydrocephalic patient. Stress fields in the tissues predicted by the model presented in this study closely match the distribution of histological damage, focused in the white matter. The last study models the cerebrospinal fluid hydrodynamics in both the normal and abnormal ventricular system. The models created in this study were used to understand the pressure in the ventricular compartments. In this study, the hydrodynamic changes that occur in the cerebral ventricular system due to restrictions of the fluid flow at different locations of the cerebral aqueduct were determined. Information presented in this study may be important in the design of more effective shunts. The pressure that is associated with the fluid flow in the ventricles is only of the order of a few Pascals. This suggests that large transmantle pressure gradient may not be present in hydrocephalus.

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Germanovich, Leonid; Committee Co-Chair: Skrinjar, Oskar; Committee Member: Mayne, Paul; Committee Member: Puzrin, Alexander; Committee Member: Rix, Glenn.

We propose a new approach for defining mechanical properties of the brain tissue in-vivo by taking MRI or CT images of a brain response to ventriculostomy operation, i.e., the relief of the elevated pressure in the ventricular cavities. Then, based on 3-D image analysis, the displacement fields are recovered from these images. Constitutive parameters of the brain tissue are determined using inverse analysis and a numerical method allowing for computations of large strain deformations. We tested this approach in controlled laboratory experiments with silicone brain models mimicking brain geometry, mechanical properties, and boundary conditions. The ventriculostomy was simulated by inflating and deflating internal cavities that model cerebral ventricles. Subsequently, the silicone brain model was described by a hyperelastic (neo-Hookean) material. The obtained mechanical properties have been verified with direct laboratory tests. Properties of real brain tissue are more complicated, but the proposed approach requires only conventional medical images collected before and after ventriculostomy. Breast cancer is the second most prevalent cancer in women, and an operative mastectomy is frequently a part of the treatment. Women often choose to follow a mastectomy with a reconstruction surgery using a breast implant. Furthermore, there is a growing demand for breast augmentation for the sake of aesthetic improvement. In this dissertation, we also developed a quantitative large-strain 3-D mechanical model of female breast deformation. The results show that the stiffness of skin and the constitutive parameters of the breast tissue are important factors affecting breast shape. Our results also suggest that the published Mooney-Rivlin parameters of breast tissue are underestimated by at least one or two orders of magnitude. Scale analysis, representing female breast as a cantilever beam, confirms these conclusions. Subdural hematoma (tearing and bleeding between scull and brain) is one of the major complications of the ventriculostomy operations. Understanding the mechanism of subdural hematoma is critically important for development of more effective medical treatments. In this work, we developed a simple, spherically-symmetrical poroelastic model of the ventriculostomy operation and studied brain response to the pressure change in the ventricles. The observed effect of the material properties on the occurrence of subdural hematoma may be useful for making clinical decisions.