I can see clearly now

Cates.
Photo by Jack Mellott.

It seems commonplace now. Tear a ligament, rupture a spinal disc or, worse, suffer a heart attack, and your doctor will likely recommend magnetic resonance imaging -- or MRI -- as an important first step on the road to recovery. Developed in the late 1970s, MRI has revolutionized medicine, radically improving doctors’ ability to diagnose everything from minor sports injuries to life-threatening diseases. MRI uses a magnetic field and pulses of radio wave energy to provide pictures of organs and other bodily structures that cannot be obtained from an X-ray, ultrasound or CT scan. Despite its benefits, though, MRI falls short in providing clear images of the lungs, colon and other internal cavities.

Yet now, thanks to the research of U.Va. physics professor Gordon D. Cates, medical imaging is poised for another dramatic leap forward. In 1994, while he was still on the faculty at Princeton University, Cates and fellow physicist William Happer published an article in Nature in which they unveiled a breakthrough technique that uses specially treated gases and provides better images than a standard MRI offers.

Our bodies are composed mostly of water, which -- as we learn in basic chemistry class -- contains two hydrogen atoms for every one of oxygen. The protons nestled in these hydrogen nuclei spin constantly, governed by the same magnetic forces that cause the Earth to spin on its axis. The conventional MRI machine is a huge magnetic field that briefly lines up, or polarizes, these spinning protons like tiny compass needles and, in so doing, creates a picture. The more polarized the protons, the clearer the image. But since our lungs have tiny air sacs and small amounts of water, there is less for the machine to “read,” and clear imaging proves more difficult. “The problem,” Cates says, “is the spinning protons [in the lungs’ hydrogen nuclei] don’t line up very well. The imaging isn’t as precise as you want it to be.”

To provide sharper images of lungs, Cates and Happer explored the idea of using laser-polarized helium 3 and xenon 129, two of the so-called “noble” gases. A patient inhales the gas and holds his or her breath for 10 seconds or so while a machine scans the lungs. Less dense than water, the gas can get into spaces where water cannot and provide roughly 100,000 times higher polarization. Cates says, “Gases are exciting because they can get a polarization closer to one, meaning the protons are pretty well lined up. With gases, you have a great way of imaging spaces in lungs.” 

Encouraged by the results of his early research, Cates left Princeton in 2000 for U.Va., where he now serves as the director of the U.Va. Institute of Nuclear and Particle Physics. U.Va.’s allure, he says, was its “strong nuclear physics program and medical research,” which have allowed him “to push the technology in new directions.”

For decades, researchers have successfully polarized helium 3 with lasers, producing remarkable results with imaging. But there are drawbacks. Helium 3 does not come from the natural environment. Its main supply is nuclear power plants and nuclear weapons manufacturing, Cates explains. “If hyperpolarized gas imaging were to be a commonly used medical technique, it would strain this supply, [and] we would need to go to xenon.”

Unlike helium 3, xenon 129 is found in nature and therefore is more abundant. Xenon also absorbs more easily into the bloodstream and tissues. Currently, Cates is focused on “developing a new, second-generation polarizer” that can “do a better job bringing xenon 129 to the same footing as helium 3.”

Hyperpolarized gas imaging, or what Cates refers to as “breathable magnet” technology, must undergo more clinical testing before it can achieve the status of standard MRI as a widely used diagnostic tool. In the coming years, it may well be the first line of defense against vascular and brain disease, colon cancer and other serious conditions. In the meantime, Cates remains committed to finding a way to take the perfect image.