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New device to detect osteoporosis stems from basic research at MIT

Professor George Pratt (left) demonstrates the sonometer, a device he invented to measure bone density, with Kevin Wilson (Ph.D '85), who works for Hologics, the company manufacturing the device.
Professor George Pratt (left) demonstrates the sonometer, a device he invented to measure bone density, with Kevin Wilson (Ph.D '85), who works for Hologics, the company manufacturing the device.
Photo / Donna Coveney

A new device for detecting osteoporosis is a result of basic research originally aimed at horses that began at MIT about 20 years ago.

The device, which was approved by the US Food and Drug Administration on March 13, is based on work by Professor George W. Pratt of the Department of Electrical Engineering and Computer Science and colleagues. It uses ultrasound to estimate bone density of the heel. Osteoporosis, a disease that occurs in half of all women past menopause, is characterized by decreased bone density that can lead to fractures.

The Sahara Clinical Bone Sonometer, produced by Hologic, Inc., can identify women at risk of developing osteoporosis. "Once alerted to the possible onset of the disease, physicians and patients can take measures to prevent further bone loss," according to the company, which developed the device based on four patents it licensed from MIT.

Professor Pratt noted that one of the authors of the patents, Paul Duchnowski, was an MIT sophomore when the work was conducted. Dr. Duchnowski is currently a research associate at the Research Laboratory of Electronics.

Currently the most common method for detecting osteoporosis uses X-rays. Bone-density testing is primarily done at city hospitals that have the space and can afford the X-ray equipment. Because the Sahara is small and easy to operate, doctors could use it in their offices. As a result, access to testing could increase, especially in rural areas.

The device could also have another application. NASA recently purchased one and is evaluating it for a space flight to monitor the bone density of astronauts.

How does it work? "The velocity of sound through a material depends on the density of the material," Professor Pratt said. So by measuring how quickly a pulse of ultrasound travels from one side of the heel to the other, the device can determine the density of the bone therein.


The research that led to the device was originally focused on horses. In earlier work Professor Pratt had developed gait-analysis technology to help predict whether a given horse would be a good racer. That got him interested in another question. "I wanted to find out if there was anything you could do to determine if a horse was at risk of breaking a leg," said Professor Pratt, who at one time was an adjunct professor of veterinary medicine.

The ultrasound technology he and colleagues invented determines not only the density of bone but also its mechanical strength. Specifically, it can determine the extent of microfractures. The accumulation of such fractures, in turn, can lead to a break.

Key to the development of the technology was Professor Pratt's own racehorse, Rocky. "I used Rocky to optimize the signal, the frequencies -- the whole thing. He was very patient."

Later, he and his team applied the technology to human runners, including a year-long study of women on the Harvard track team. "We knew that over a year, runners develop shin splints, stress fractures and other conditions, and we wanted to see if we could correlate these with ultrasonic measurements. We found that we could," Professor Pratt said.

His team ran a similar study on 200 runners in the 1987 Boston Marathon, taking ultrasound measurements before and after the race. "We found changes in the velocity of sound through the kneecap and tibia, and we could correlate these changes to the runners' finishing times," Professor Pratt said. The elite runners, who have very strong bones, had very small changes in the velocity. "They had fewer microfrac-tures," Professor Pratt explained.

The studies on human runners, in turn, led to the researchers' application of the technology to osteoporosis. Referring to the original focus on horses, Professor Pratt concluded, "Lots of significant developments come from sources that are unexpected."

He also emphasized the importance of very good students and support from his department for a project that was not tightly related to his field. "That's the kind of fertile soil you need for these kinds of strange plants to grow. I mean, what's a guy in electrical engineering doing thinking about racehorses?"

The original research that led to the new osteoporosis device was sponsored by the National Institutes of Health. Professor Pratt's collaborators on the work included researchers from the Tufts University School of Veterinary Medicine. Jeffrey Seeder of Craftex Mills was critical to moving the technology into the marketplace.

A version of this article appeared in MIT Tech Talk on April 1, 1998.

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