3D imaging and AI shed new light on muscle anatomy
Anatomical researchers at the University of Missouri say they are using artificial intelligence (AI) to see inside an animal or a person — down to a single muscle fiber. In their work, the researchers are using contrast imaging data and machine learning approaches to model the 3D architecture of anatomical structures such as jaw musculature.
AI can teach computer programs to identify a muscle fiber in an image, such as a CAT scan. Then, say the researchers, they can use that data to develop detailed 3D computer models of muscles to better understand how they work together in the body for motor control.
The researchers used that approach recently when they began to study the bite force of a crocodile.
“The unique thing about crocodile heads is that they are flat, and most animals that have evolved to bite really hard, like hyenas, lions, T. rexes and even humans have really tall skulls, because all those jaw muscles are oriented vertically,” says Casey Holliday, an associate professor of pathology and anatomical sciences. “They’re designed that way so they put a big vertical bite force into whatever they’re eating. But a crocodile’s muscles are oriented more horizontally.”
The 3D models of muscle architecture could help the researchers determine how muscles are oriented in crocodile heads to help increase their bite force.
“Jaw muscles have long been studied in mammals with the assumption that relatively simple descriptors of muscle anatomy can tell you a great deal about skull function,” says Kaleb Sellers, a former student of Holliday’s who is now a postdoctoral researcher at the University of Chicago. “This study shows how complex jaw muscle anatomy is in a reptile group.”
Historically, say the researchers, anatomical research involved dissecting animals with a scalpel or scissors. Holliday was first introduced to the benefits of using digital imaging to study anatomy when he joined the “Sue the T. rex” project in the late 1990s. To date, it remains one of the largest and most well-preserved Tyrannosaurus rex specimens ever discovered.
The T. rex’s giant skull was transported to Boeing’s Santa Susana Field Laboratory in California to be imaged in one of the aerospace company’s massive CAT scanners normally used to scan jet engines on commercial airplanes.
“At the time,” says Holliday, “it was the only CAT scanner in the world big enough to fit a T. rex skull, and also had the power needed to push X-rays through rocks. Coming out of college I had looked at becoming a radiology technician, but with the Sue project I was learning all about how they CAT scanned this thing, and that really caught my fancy.”
“The digitization process is not only useful to our lab and research,” says Emily Lessner, a recent MU alumna who developed her passion for “long-dead animals” by working in Holliday’s lab. “It makes our work shareable with other researchers to help hasten scientific advancement, and we can also share them with the public as educational and conservation tools. Specifically, my work looking at the soft tissues and bony correlates in these animals has not only created hundreds of future questions to answer, but also revealed many unknowns.”
The researchers say plans are also in the works to take their 3D anatomical models a step further by studying how human hands have evolved from their evolutionary ancestors. While about 90% of the research done in the MU lab involves studying things that exist in the modern world, says Holliday, the data they collect can also inform the fossil record, like additional knowledge about how the T. rex moved and functioned.
“With better knowledge of actual muscle anatomy, we can really figure out how the T. rex could really do fine motor controls, and more nuanced behaviors, such as bite force and feeding behavior,” says Holliday.
For more, see “New frontiers in imaging, anatomy, and mechanics of crocodylian jaw muscles.”
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