Nov. 30, 2000 A leader in semiconductor physics for some 20 years, Arnold Honig, professor of physics in Syracuse University's College of Arts and Sciences, has devoted his career to discovering how minute particles of matter behave in temperatures that are as close to absolute zero as technology allows. Honig's most recent work on highly polarized nuclear spin systems, including the development of a method that has received a U.S. patent, may help revolutionize the field of medical magnetic resonance imaging (MRI).
MRI is a non-invasive diagnostic tool that creates computerized images of internal body tissues. While the system can create high-quality images of the more dense body tissues, it does not work well on organs such as the lungs, which contain more gas than tissue. However, researchers discovered that high-quality lung images could be obtained by having patients inhale a small amount of a highly polarized gaseous contrast agent. One such agent is a rare gas called Xenon 129. The current optical method for polarizing Xenon 129 is expensive and does not yield large enough quantities to be useful on a wide scale.
The possibility of finding a better way to polarize the gas presented an intriguing physics challenge for Honig, who created the first spin-polarized hydrogen-deuteride (HD) targets that are critical in a large nuclear physics experiment under way at Brookhaven National Laboratory on Long Island. Researchers at the new Thomas Jefferson National Accelerator Facility in Newport News, Va., and at major laboratories in France and Japan are duplicating Honig's technique to create targets for other experiments in nuclear physics.
Honig is a pioneer in the spin-polarization field, having published his first paper on HD frozen spin systems some 30 years ago, before the technology to conduct the experiments was fully available. He began experimenting with highly polarized HD targets about six years ago; four years ago, he started looking at the Xenon puzzle.
"No one had been able to polarize Xenon at extremely low temperatures," Honig says. "We wanted to see if we could do it. There is some very interesting physics involved in the process. In addition to the physics, we had an idea that the experiment, if successful, could have broader applications."
The challenge was to find an agent that would rapidly polarize Xenon at the low temperatures and that could subsequently be removed in a way that would allow the gas to retain its high polarization at the high temperatures within which it would be used.
"The agent needs to be switched on at low temperatures and effectively switched off at room temperatures," Honig says. "And it must be done in a way that does not appreciably reduce the high polarization."
Honig and his research group developed what they dubbed the "Relaxation Switch Method" of spin polarization, for which they recently received a U.S. Patent. Honig says his process--used with a custom-designed refrigerator and modest ancillary equipment--could potentially produce about 150 liters of highly polarized Xenon gas a day, which translates into a cost of about $100 per dose. The older method results in about 20 liters of gas a day per machine at a cost of about $500 per dose.
Honig is continuing to refine the process using the prototype equipment he built in his laboratory, and he is working with Oxford Instruments in England to further develop the prototype. He says applying hyperpolarized contrast agents to current MRI techniques has the potential to greatly enhance the sensitivity and resolution of MRI images, and by doing so, open up new diagnostic applications for MRI.
Honig, who is excited about the potential application of his experiment, never doubted he could resolve the underlying physics questions. "Of course the experiments worked," he says with a grin, "I always knew that we would push until they did."
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