Super-resolved shear shock focusing in the human head

TL;DR

This paper reports the first observation of super-resolved shear shock wave focusing in the human head, revealing potential mechanisms for brain injury at small scales due to nonlinear shear waves.

Contribution

It demonstrates super-resolution of shear shock waves in the human head, combining imaging and simulations to explore nonlinear shear wave behavior relevant to brain injury.

Findings

Super-resolution of shear shock waves observed in a human head phantom.

Shear shocks can cause localized injuries as small as a grain of rice.

Nonlinear shear waves may be a primary injury mechanism in brain trauma.

Abstract

Shear shocks, which exist in a completely different regime from compressional shocks, were recently observed in the brain. These low phase speed ($\approx$ 2 m/s) high Mach number ($\approx$ 1) waves could be the primary mechanism behind diffuse axonal injury due to a very high local acceleration at the shock front. The extreme nonlinearity of these waves results in unique behaviors that are different from more commonly studied nonlinear compressional waves. Here we show the first observation of super-resolved shear shock wave focusing. Shear shock wave imaging and numerical simulations in a human head phantom over a range of frequencies/amplitudes shows the super-resolution of shock waves in the low strain and high strain-rate regime. These results suggest that even for mild accelerations injuries as small as a grain of rice on the scale of mm$^2$ can be easily created deep inside the brain.