Using a supercomputer simulation to reproduce traumatic brain injury at a higher level of detail and under more conditions than ever before, a team of researchers has identified key factors in causing strain to brain tissues.
The study, conducted by researchers in the U.S. Office of Naval Research-funded PANTHER program, promises a better understanding of the type of head motions that are the most injurious for the brain. Their findings could lead to better solutions for protecting members of the military, athletes and the public from traumatic brain injuries.
PANTHER is a large transdisciplinary research effort that brings together scientists from academia, industry and federal agencies to study different aspects of traumatic brain injury, ranging from in-vitro studies of nerve cells to helmet design to computational modeling.
Its director, Christian Franck, the Grainger Institute for Engineering associate professor of mechanical engineering at UW-Madison, is among the authors of the paper, which was published in the journal Brain Multiphysics in March 2021. Rika Carlsen, an associate professor of mechanical and biomedical engineering at Robert Morris University, led the study.
Every year in the United States, there are an estimated 1.7 million new cases of traumatic brain injury assessed in emergency rooms, and the incidence of sports-related concussions may approach 3.8 million annually. Scientific evidence now supports the idea that what doctors might once have dismissed as a “minor concussion”—or even shocks to the head causing no obvious injury—can cause silent damage to the brain. After time, especially if it happens more than once, this silent damage can build. The end result can be a number of symptoms including loss of coordination, memory problems, seizures and even death.
However, there’s much researchers still don’t know about how concussions and other traumatic brain injuries actually develop in the brain. Existing methods for estimating damage to the brain just aren’t detailed or comprehensive enough. That’s why the PANTHER researchers performed one of the most detailed and thorough series of computational simulations of brain injury to date to identify the type of head motions that are the most injurious. To run the massive, repeated simulations needed to tease out important factors for brain injury, they turned to the National Science Foundation-funded Bridges platform at the Pittsburgh Supercomputing Center.
In his UW-Madison lab, Franck is researching the critical threshold of how much mechanical stress and strain it takes to injure brain cells. Carlsen plans to use Franck’s cellular injury data in her computational model in order to provide better injury prediction in real-world events than currently possible.
“Essentially, Carlsen’s simulations are connecting my experimental data on actual cellular-level injury to possible head motions,” Franck says.
Carlsen used finite element analysis to simulate the brain under stress from a number of movements. This method splits the brain into pieces, so that the computer can do the math on individual pieces and then assemble those pieces into the whole brain. Finite element analysis is a way of approximating the entire brain and, while it’s not an exact solution, the method reduces the size of the computation so it’s possible with modern supercomputers.
While previous finite element analysis simulations of brain injuries were in three dimensions, computing limitations forced them to split the brain into a small number of relatively large pieces. By splitting the brain into two-dimensional slices with 10,000 pieces, Carlsen was able to incorporate a high level of anatomical detail into her models without a significant increase in the computational cost. The researchers used this 2D simulation to look at how abrupt angular motions of the head—sagittal, as if nodding “yes”; axial, or shaking the head “no”; or coronal, swaying the head from shoulder to shoulder—affected the strain on nerve fibers. This allowed a finer resolution. They also repeated these simulations about 600 times, changing a number of factors to see how the virtual brain’s tissues were stressed in each “injury.”
The simulations identified both angular velocity (how fast the head is moving at an angle) and angular acceleration (the rate at which that velocity is increasing) as being important for predicting strain on brain tissues. The PANTHER team mapped its predictions to clinical measurements in papers by other researchers and found that concussive sports injuries generally have higher predicted strain and strain rate in the brain than sports impacts that didn’t cause concussion. This was an important real-life verification that the team’s simulations are on the right track.
Franck says more work needs to be done to predict the extent of brain injury accurately. There may be other important factors or combinations of factors the researchers didn’t include in their simulations, which will be the focus of future work.
Franck says these initial findings are encouraging as the PANTHER team moves forward with the goal of developing computational head models that are capable of rapidly predicting brain injury.
“This paper is a first step toward a comprehensive, anatomically realistic 3D human head model actually capable of predicting brain injury based on state-of-the art finite element models, machine learning approaches, and resolution of the biomechanics at the cell level,” Franck says. “This kind of interdisciplinary collaboration is unique to PANTHER and unique in the world. We’re excited of the possibilities this will bring, and the kind of new head and brain protection strategies, and consumer products, this will yield.”
Additional authors on the paper include Alice Fawzi, Yang Wan and Haneesh Kesari of Brown University.
This work was supported by funding from the Office of Naval Research.