Ph.D. Dissertation Defense: Harsha T. Garimella " An embedded element based human head model to investigate axonal injury "

Traumatic brain injury is a significant public health problem in the world. Axonal injury is a common type of mechanism of traumatic brain injury primarily characterized by damage to the axons.  Enhanced understanding of the axonal deformation during a mechanical impact may facilitate a better understanding of the short and long-term sequela. The objective of this dissertation is to develop, validate and employ a multiscale model of the axonal fiber tracts that simulates the white matter of the brain and can be used to investigate the evolution of axonal damage under injurious loading conditions. An axonal fiber tract consists of hundreds or thousands of axons aligned together, which can experience mechanical deformation under a non-physiological loading such as impact loading in sports or vehicular accidents, blast loading in terrorist bombings or warfare.
To model axonal injury, we developed a new embedded element based head model using an explicit description of the diffusion tensor magnetic resonance tractography. This approach enables us to resolve the complex mechanical response of the axonal fibers during injurious loading conditions. The most promising aspect of this modeling approach is the capability of modeling the fiber tracts explicitly in a conventional finite element head model. This model was extensively validated against experimental results followed by an in-depth finite element analysis. Upon subjecting to impact and blast loading conditions, the model revealed some new insights into the evolution of the axonal injury. The model was subsequently improved in terms of anatomical resolution and material complexity -- making it more biofidelic in nature. We have also made theoretical improvements to the embedded element technique and developed an open source finite element library in this direction. Finally, we examined the potential extension of this embedded element technique into a multiphysics domain such as electro-physics.


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