POTTERS and metalworkers have known for thousands of years that a perfect object will ring when tapped, while a damaged one will go 鈥渃lunk鈥�. Now an American engineer has translated this knowledge into a tool to diagnose the fragile bones caused by osteoporosis, which leads to millions of broken bones every year. Andrew Dimarogonas, professor of mechanical engineering at Washington University in St Louis, says that his patented device should be safer and more accurate than X-rays.
鈥淚n osteoporosis, which primarily affects older people, bone mass is reduced, the bone is porous and contains tiny fractures,鈥� Dimarogonas explains. 鈥淪uch bones dampen sounds when they are tapped, they sound 鈥榙ead鈥�, just like a cracked teacup or bell goes 鈥榗lunk鈥�; rather than ringing.鈥�
His device looks like an electric drill and projects a series of sound waves into the body in the audible range, from 100 to 1000 megahertz, over a period of between 2 and 3 seconds. A microphone listens for their echoes. The reflected waves are sent to a PC, which takes about 30 seconds to analyse them and produce a reading indicating the bones鈥� ability to dampen the sound. 鈥淭he better the bone is at damping sound, the worse its mechanical strength,鈥� says Dimarogonas. The entire test can be carried out in five minutes, so if the technique proves itself and is approved by the Food and Drug Administration, it could become a part of every routine physical.
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鈥淯nlike X-ray machines, which cost between $100 000 and $300 000, we expect this device could be sold for $20 000 or less,鈥� says Dimarogonas.
Previous researchers have used both X-rays and ultrasound to test for osteoporosis. But both methods have limitations, says Dimarogonas. 鈥淴-rays are now used to examine people suspected of being osteoporotic, but the tests cost about $300 apiece and expose patients to radiation. In addition, X-rays measure bone density, which does not necessarily correlate with the bone鈥檚 mechanical strength, which is the important factor.鈥�
Doctors have also tried ultrasonic probes similar to those used in antenatal scanning. But the results have never been good enough for them to come into widespread use. 鈥淯ltrasonic probes produce waves in the megahertz frequency range, and these are scattered by soft tissue. In addition, ultrasound measures the elasticity of what it encounters, not damping,鈥� he says, adding that damping is the crucial measure which is crucial to bone strength,鈥� he says.
Over the past two years he has tested the new device on animals. 鈥淲e are now testing the technique with human cadavers, so that we can test their bones鈥� strength afterwards, and check how well it correlates with our results. I have also loaned two of my devices to doctors, and we hope that by the end of 1996 they will have tested over a thousand patients.鈥�
