Imaging Technique With Potential For Medical Diagnostics

A unique new imaging method, called polarized nuclear imaging, combines powerful aspects of both magnetic resonance imaging and gamma-ray imaging. Developed by two physicists in the University of Virginia's departments of physics and radiology, it has potential for new types of high-resolution medical diagnostics as well as industrial and physics research applications.

"This method makes possible a truly new, absolutely different class of medical diagnostics," said Wilson Miller, who, along with his colleague Gordon Cates, directed the research. "We're combining the advantages of using highly detectable nuclear tracers with the spectral sensitivity and diagnostic power of MRI techniques."

"We have demonstrated the feasibility of the new technique by producing a proof-of-principle image in a manner never before accomplished," Cates said. "In our technique, rather than imaging protons in water, as in MRI, we image a radioactive isotope of xenon that has been polarized using laser techniques."

Cates and his colleagues believe that the technique, once refined, could provide a new, relatively inexpensive way to visualize the gas space of the lungs by having patients inhale a gas containing the isotopes and using PNI to produce an image. The method likewise might work to image targeted areas of the body by injecting isotopes into the bloodstream. Because the technique would use such small quantities of tracer material, when it comes to medical use, the radioactivity would pose little to no danger to people.

Since magnetic resonance imaging has never been used in combination with radioactive tracers, there is a potential for obtaining new types of diagnostic information that have not been available previously.

MRI, which is widely used for detecting cancer and other abnormalities in the body, is effective because it uses a variety of contrast mechanisms to sort out specific characteristics in an image. And highly sensitive gamma-ray detectors can resolve miniscule amounts of radioactive tracer material, key to homing in on points of particular interest. The new UVA technique uses magnetic resonance to obtain the spatial information and then collects image information by detecting gamma rays produced by the tracer material -- an isotope of xenon Xe-131m, which is a byproduct of Iodine 131 (used for treatment of thyroid problems).

"Unlike MRI, which detects faint radio waves, we detect gamma rays that are emitted from the xenon isotope," Cates said. "Since it is possible to detect a gamma ray from even a single atom, we gain an enormous increase in imaging sensitivity, and dramatically reduce the amount of material needed for performing magnetic-resonance techniques."