The University Record, April 12, 1999
By Sally Pobojewski
News and Information Services
U-M scientists have put a new spin on an old technology by using xenon to generate the first high-resolution magnetic resonance images of the heart and lung tissue in a living laboratory rat. The key to their success is a customized laser system-designed and built by U-M physicists-that aligns or "polarizes" molecules of xenon gas and delivers it to the rat in controlled single-breath doses.
The U-M is one of several institutions developing next-generation magnetic resonance imaging (MRI) technology. Current MRI scanners use a powerful magnetic field to polarize protons in water molecules in the patient's body, much as a bar magnet aligns iron filings. These polarized protons are detected by radio waves and processed in a computer to produce detailed images of internal soft tissue.
Instead of water molecules, the U-M's prototype MRI system detects signals from molecules of xenon that have been polarized by a laser optical pumping system before being inhaled by the animal.
"Xenon has many advantages for use in MRI technology," says Scott Swanson, co-director of the study and an assistant research scientist in radiology in the Medical School. "The gas dissolves in the bloodstream where it is carried throughout the body to provide a direct, quantitative measurement of blood flow through an organ. It is non-reactive, safe in measured doses, and can be polarized in higher concentrations than water molecules. Plus we can differentiate relative concentrations of xenon in tissue, blood and gas, which is not possible with current technology."
Swanson presented the latest U-M research results and MRI images during an invited presentation at the American Physical Society Centennial Meeting last month.
The U-M system's ability to detect polarized xenon in tissue, blood and gas within the lungs is significant, according to Swanson. It allows simultaneous measurement of lung ventilation and perfusion, which is not possible with conventional MRI. "The ability to compare the gas or ventilation image with the blood or perfusion image could help physicians locate a pulmonary embolism or diagnose chronic obstructive pulmonary disease," Swanson says.
"These images demonstrate for the first time that magnetic resonance imaging with noble gases shows great promise as a diagnostic tool," says Timothy E. Chupp, professor of physics and co-director of the research project. "While many technical obstacles remain before the technology is ready for human use, our results indicate it could be used to monitor perfusion through the heart, lungs and kidneys. In a previous study, we demonstrated the feasibility of laser-polarized xenon to track regional cerebral blood flow through the brain."
According to Chupp, future U-M research will focus on finding ways to increase xenon polarization from current levels of about 5 percent to 35 percent, which will provide the resolution required for clinical applications.
Funding for the research project is provided by the National Institutes of Health and the National Science Foundation. Initial funding was provided by the Office of the Vice President for Research. The U-M holds a patent on the laser optical pumping method and an additional patent is pending on the laser polarization and noble gas delivery system.
Collaborators on the project include Matthew Rosen, graduate student, and Kevin Coulter and Robert Welsh, research scientists.