Citation

Giammarinaro B, Coulouvrat F, Pinton G. J. Biomech. Eng. 2016; 138(4): 041003.

Copyright

(Copyright © 2016, American Society of Mechanical Engineers)

DOI

10.1115/1.4032643

PMID

26833489

Abstract

Shear waves that propagate in soft solids, such as the brain, are strongly nonlinear and can develop into shock waves in less than one wavelength. We hypothesize that these shear shock waves could be responsible for certain types of traumatic brain injuries and that the spherical geometry of the skull bone could focus shear waves deep in the brain, generating diffuse axonal injuries. Theoretical models and numerical methods that describe nonlinear polarized shear waves in soft solids such as the brain are presented. They include the cubic nonlinearities that are characteristic of soft solids and the specific types of non-classical attenuation and dispersion observed in soft tissues. The numerical methods are validated with analytical solutions, where possible, and with self-similar scaling laws where no known solutions exist. Initial conditions based on a human head CT were used to simulate focused shear shock waves in the brain. Three regimes are investigated with shock wave formation distances of $2.54m$, $0.018m$ and $0.0064m$. We demonstrate that under realistic loading scenarios and when the shock wave propagation distance and focal distance coincide nonlinear propagation can easily overcome attenuation to generate shear shocks deep inside the brain. Due to these effects the accelerations in the focal are larger by a factor of 15 compared to acceleration at the skull surface. These results suggest that shock wave focusing could be responsible for diffuse axonal injuries.

Language: en