Synopsis: Brain Tissue Amplifies Waves

Ultrasound images reveal an amplification effect for shear waves traveling through the brain that may contribute to head injuries.

Few experiments have been able to visualize the brain’s response to a blow to the head. A new imaging study analyzes wave-like disturbances in the brain that might be generated from a head impact. The researchers find that so-called shear waves, which push on a medium perpendicular to their direction of travel, amplify the acceleration experienced by neurons as the waves move through the brain. The finding suggests the waves may play an important role in head-trauma injuries.

Brain tissue is a nonlinear material, meaning that waves traveling through it are likely to become distorted. But whether these effects matter in head trauma has been difficult to assess. That’s because most imaging techniques lack the necessary combination of spatial resolution and penetration depth.

To acquire their images, Gianmarco Pinton and colleagues at the University of North Carolina, Chapel Hill, developed an ultrasound technique for monitoring tissue distortions in response to shear waves at high speed and with high resolution. The researchers immerse a pig brain in gelatin, in which they jiggle a plate up and down to produce shear waves that penetrate the brain. The team captured the wave profiles at about 6000 frames per second and with a resolution of 1 $𝜇$m, or a tenth the width of a blood cell. This is enough spatial and time resolution to see that, after entering the brain, the initially smooth waves quickly develop a shock front that provides 9 times more acceleration to the surrounding tissue. It is, however, an open question whether these findings apply to real head traumas, in which the waves would have to pass from the skull through the meninges and cerebrospinal fluid.

This research is published in Physical Review Applied.

–Jessica Thomas

Jessica Thomas is the Editor of Physics.

More Features »

Announcements

More Announcements »

Magnetism

Read More »

Next Synopsis

Particles and Fields

Read More »

Related Articles

Biological Physics

Synopsis: Soft Biological Tissues Can Be Piezoelectric

Artery walls, tendons, and heart valves can generate an electric voltage when squeezed—an effect that could be harnessed to diagnose important diseases. Read More »

Biological Physics

Synopsis: Collective Dynamics from Individual Random Walks

The jerky, random motion of bacteria has now been reproduced using artificial microswimmers, yielding collective behaviors similar to those of real-world bacterial swarms.      Read More »

Mechanics

Synopsis: Simulations Unravel Fibers’ Twisted Topology

How an elastic filament deforms under stress has been quantified in simulations, with implications for the design of artificial muscles. Read More »