Researchers at Sandia National Laboratories and the University of New Mexico are comparing supercomputer simulations of blast waves on the brain with clinical studies of veterans suffering from mild traumatic brain injuries (TBIs) to help improve helmet designs.
Paul Taylor and John Ludwigsen of Sandia's Terminal Ballistics Technology Department and Corey Ford, a neurologist at UNM's Health Sciences Center, are in the final year of a four-year study of mild TBI funded by the Office of Naval Research.
The team hopes to identify threshold levels of stress and energy on which better military and sports helmet designs could be based. They could be used to program sensors placed on helmets to show whether a blast is strong enough to cause TBI.
Many TBI sufferers experience no or subtle immediate symptoms that may keep them from seeking medical attention. The sensors could alert them to a potential problem.
"Our ultimate goal is to help our military and eventually our civilian population by providing guidance to helmet designers so they can do a better job of protecting against some of these events we are seeing clinically and from a physics perspective," said Taylor, Sandia's principal investigator on the project. "To do that we've got to know what are the threshold conditions that correlate with various levels of TBI."
The study is the only TBI research that combines computer modeling and simulation of the physical effects of a blast with analyses of clinical magnetic resonance images (MRIs) of patients who suffer such injuries, Taylor said.
Immediately following blast waves, soldiers can suffer brief losses of consciousness, but more damage evolves weeks later, Ford said. The symptoms - headaches, memory loss, mood disorders, depression and cognitive problems - can prevent sufferers from working, he said.
Taylor is applying shock wave physics to understand how sensitive brain tissue is affected by waves from roadside bombs or blunt impacts within the first 5-10 milliseconds. That's before a victim's head moves any significant distance in response to the blast.
"This stuff is over before you have any chance to react and probably before you even knew it happened to you," Taylor said. Humans' fastest reaction times as teenagers are 75-100 milliseconds.
Ford says levels of energy transmitted into the brain by a blast wave "could be part of the injury mechanism associated with TBI and the mechanism by which it happens may not be mitigated by traditional methods of protecting the head with a helmet."
At Sandia, researchers created a computer model of a man's head and neck. The model includes the jaw - another first in TBI research - because a lot of blasts come from improvised explosive devices (IEDs) at ground level, sending waves traveling at the speed of sound through the jaw and facial structure before they reach the brain, Taylor said.
Sandia's team used the National Library of Medicine's Visible Human Project, which was established in 1989 to build a digital image library of volumetric data representing complete, normal adult male and female anatomy.
Using images of the male, whose age was close to that of most military personnel, Taylor, with Ford as a medical consultant, created geometric models of the seven tissue types in the human head - scalp, bone, white and gray brain matter, membranes, cerebral spinal fluid, and air spaces. Over a year, they catalogued each of the tissue types seen in about 300 "slices" of the cadaver's head, dividing what they saw into one-millimeter cubes and assigning each a tissue type for the computer simulation.
Taylor also imported digitally processed, computed tomography (CT) scans of various helmet designs into the simulations to assess the protective merits of each against blast loading.
In a typical blast simulation, 96 processors on Sandia's Red Sky supercomputer take about a day to process a millisecond of simulated time and at least 5 milliseconds are required to capture a single blast event, Taylor said.
The 3-D simulations are visualized using two-dimensional multi-colored images of a man's head that record an enormous amount of data. Taylor and Ford have focused on three types of energy entering the brain that may cause TBI: compressive isotropic energy associated with crushing; tensile isotropic energy that tends to expand parts of the brain and could lead to cavitation; and shear energy that causes distortion and tearing of soft tissue. The pressure and stress within the brain show up as colors moving in slow motion through and around the brain cavity on videos created from the simulations.