New simulation technology to help relieve brain swelling

A new simulation technology is expected to help surgeons plan a life-saving procedure known as decompressive craniectomy for victims of brain trauma to relieve swelling before they cut a hole in the skull.

The technology, developed by a team of researchers led by engineers at Stanford University, takes information from magnetic resonance images and then create mathematical models to predict how certain injuries affect specific parts of the brain, showing extreme damage in red, mild damage in green, and safe areas in blue.

If without the simulation, it requires a fair amount of guesswork on how best to proceed.

"In other parts of the body we can take a small sample of the affected tissue, but you can't cut out a slice of the brain," said Ellen Kuhl, a professor of mechanical engineering and member of Stanford Bio-X, who worked with Johannes Weickenmeier, a postdoctoral scholar at Stanford, and Alain Goriely, a professor of mathematics at the University of Oxford in England, on the project. "What we've begun to develop are simulations to show how the brain reacts to trauma."

The group has published a trio of scholarly papers, the latest of which appeared in Physical Review Letters.

Surgeons have performed decompressive craniectomies for more than a century. But, as Kuhl explained, the shape of the brain is essential to its function. It consists of billions of fragile filaments, called axons, bundled together in purposeful patterns. When parts of this amalgam bulge out, axons stretch and shear. Surgeons currently rely on experience to limit the collateral damage that might occur when dire circumstances force them to perform a decompressive craniectomy.

The simulations are based on a technique called finite element analysis, a computational tool to divide a complex object into smaller pieces, the finite elements, and predict how each piece will react to pressure, heat, vibration or other mechanical forces. Kuhl first applied the technique to the human heart, giving surgeons new ways to understand different treatment strategies before opening a patient's chest. In 2014 her work became part of the Living Heart Project, a consortium of academic, industrial and regulatory scientists working to establish biophysical simulations as a platform for planning surgical interventions.

"This is a new tool to help surgeons decide where and how big to make the hole, by giving them a way to visualize the effects of the procedure on the brain tissue," Kuhl was quoted as saying by a news release from Stanford.

She and her collaborators reviewed prior brain research and did their own experiments to establish how much stretching axons could tolerate before they are damaged. "When you get to the point where axons stretch near or above 30 percent, you see serious damage," she said.

As computer models must know the amount of brain swelling before surgeons cut open the skull, the group inferred these swelling volumes by studying medical scans of brains that had undergone concussions or other traumatic injuries. Goriely developed mathematical estimates to predict the effects of swelling on axonal stretch, and Weickenmeier divided the brain into 1.2 million finite elements. Each of these elements experiences its own forces and responds by its own deformation. To visualize the net result of all these elements, the group created red-green-blue maps to highlight extreme, moderate and negligible axonal stretch.

Then they play what-if scenarios to illustrate how skull openings of different sizes in different regions affect the axons inside the brain. "We were surprised to see that even very small swelling volumes can cause axonal stretches beyond the damage threshold of 30 percent," Kuhl said, adding that she hopes brain surgeons and other researchers will join the effort to improve these models and find new ways to apply simulations to peer beneath the skull.

"We are just at the beginning of a long-term effort to give neurosurgeons new tools to look inside the brain and make more informed decisions." Endit