Effect of cerebrospinal fluid modeling on spherically convergent shear waves during blunt head trauma.

The MRI-based computational model, previously validated by tagged MRI and harmonic phase imaging analysis technique on in vivo human brain deformation, is used to study transient wave dynamics during blunt head trauma. Three different constitutive models are used for the cerebrospinal fluid: incompressible solid elastic, viscoelastic, and fluid-like elastic using an equation of state model. Three impact cases are simulated, which indicate that the blunt impacts give rise not only to a fast pressure wave but also to a slow, and potentially much more damaging, shear (distortional) wave that converges spherically towards the brain center. The wave amplification due to spherical geometry is balanced by damping due to tissues' viscoelasticity and the heterogeneous brain structure, suggesting a stochastic competition of these 2 opposite effects. It is observed that this convergent shear wave is dependent on the constitutive property of the cerebrospinal fluid, whereas the peak pressure is not as significantly affected.