Update - Research - Get the Picture?

Get the Picture?
2/28/2007

Researchers from the Viterbi School of Engineering, the College of Letters, Arts and Sciences, the Los Angeles Natural History Museum and the School of Dentistry collaborate to improve imaging and 3-D modeling techniques.
By Ben Creighton

Ask any red-blooded eight-year-old for their top-five most fearsome creatures on the face of the earth and no doubt you would get the usual litany of sharp-toothed, ferocious man-eating beasts. Tigers, lions, perhaps a disgruntled bear or rabid pit bull might crack this list. But the mammal that packs the most powerful bite probably eludes all but the truly dedicated Mutual of Omaha's Wild Kingdom enthusiast—the spotted hyena.


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3-D model of spotted hyena skull courtesy of the National History Museum of Los Angeles County

Hyenas, spotted and otherwise, are the primary focus of Jack Tseng— a PhD candidate in the College's integrative and evolutionary biology program working at the Los Angeles Natural History Museum. Their images adorn his office walls, their bones fill his cabinets and their somewhat ambiguous evolutionary history occupies much of his time and attention.

His research focuses on the craniofacial and tooth morphology of modern hyenas as compared to their ancient forebears. Both ancient and modern hyenas were unique in their ability to crush and digest bone—an extremely advantageous adaptation that also leads to distinct jaw and tooth shape and function.

Tseng hopes to clarify the evolutionary lineage of the hyena family by studying the skull and tooth shape of both ancient and modern hyena and comparing them to animals with similar morphology such as ancient dogs.

But how do you compare animals that lived 18,000,000 years apart? The answer to that question brought Tseng to the School of Dentistry and imaging experts Reyes Enciso and James Mah.

"If I want to understand the evolution and the special adaptations hyenas have made, first I have to understand the biomechanics of their jaws and I am doing that virtually," says Tseng.

Using a hospital scanner, Tseng took nearly 1,000 images of two hyena skulls—one ancient giant hyena and its contemporary relative. To assemble those images into a 3-D model necessary for the type of analysis Tseng hoped to do required special expertise and software. As it turns out, the dental school's Craniofacial Virtual Reality Lab fit the bill.

With Enciso’s help, Tseng compiled the CT images into a 3-D, interactive rendering in Amira—3-D imaging software used in the lab. He then digitally removed rock matrix that had attached itself to the fossil over millions of years.

The next step for Tseng will be to convert his 3-D rendering into a format that can be read by finite element analysis software. More commonly used by engineers, the software allows users to define the mechanical properties for a given object and to generate computer models of how that object will respond to external forces and pressures.

By plotting thousands of points on the skull, Tseng will use finite element analysis to understand the masticatory forces of the hyena jaw. Coupled with other data, such as geometric analysis of tooth structure, he hopes to determine if modern hyenas are directly descended from their larger, ancient relatives or are actually sister lineages that diverged from one another millions of years ago.

"That's where the comparison gets really interesting. It may be that they didn't come from a common ancestor but evolved independently. If you compare them to ancient dogs which also have similar teeth then you have this iterative evolution of the same morphology in animals that are not necessarily related," says Tseng.

This project is the centerpiece of a collaboration between the School of Engineering, the Natural History Museum of Los Angeles County and the School of Dentistry. Led by Henryk Flashner, professor of aerospace and mechanical engineering at the Virterbi School of Engineering, the group recently secured a USC Zumberge grant that will cover the costly finite element software.

Reyes will use the same techniques as Tseng to create functional 3-D models of the airways of sleep apnea patients. Through these models, she hopes to understand how the shape of the airway affects muscular collapsing—which prevents breathing— while the patient sleeps.

Armed with Reyes' data, clinicians will be able to accurately treat these patients. Currently, surgeons may have to perform multiple surgeries to relieve the symptoms of obstructive sleep apnea.

"Hopefully it can guide treatment. Our goal is to tell exactly how much of the soft palate needs to be cut or how far the mandible needs to be advanced to help the patient," says Enciso.

While there is little common ground between their research objectives, both Enciso and Tseng consider the collaboration to be mutually beneficial and hope to continue to learn from one another as their respective projects progress.

"I have never worked with finite elements, so I am looking forward to learning from Jack and his mentor Dr. Flashner as he develops his models. That is the wonderful thing about working at a major university like USC, there is a wealth of bright, intelligent people to work with and learn from," says Enciso.