New Magnetic Resonance Imaging Technique Allows Researchers to Visualize Early-Stage Emphysema
Since 90 percent of the lungs' volume is air, using the latest non-invasive techniques to detect subtle pulmonary damage presents formidable challenges to doctors. Duke University Medical Center researchers believe that they have developed a new method that may ultimately lead to the detection of such lung disorders as emphysema long before symptoms are apparent.
In studies with rats, the researchers employed a "souped up" form of helium gas in conjunction with the latest in magnetic resonance imaging (MRI) technologies to create detailed images that allowed them to distinguish normal tissue from the early stages of emphysema in rat lungs.
"We believe that this technique will play an important role in conducting research into the mechanisms of many lung diseases,as well as eventually becoming an important imaging tool for clinicians," said G. Allan Johnson, director of Duke's Center for In Vivo Microscopy.
The results of the Duke team's research were published in the Oct. 10 issue of the Proceedings of the National Academy of Science. The research was funded by a grant from the National Center for Research Resources and a grant from the National Heart Lung and Blood Institute, both part of the National Institutes of Health.
Conventional MRI scanners work by measuring protons in water, which is found almost everywhere in the body. The challenge posed by lungs is that only about 10 percent of the organ's volume is actual tissue - the rest is air, which does not register on atypical MRI scan.
To overcome this obstacle, the researchers used high power laser beams to "hyperpolarize," or excite, helium gas to make it an effective signal source when introduced into the lungs. This hyper polarized gas is inert and poses no hazard to humans or animals. The gas remains polarized in the lung for up to 30 seconds, where it provides an exceptionally strong signal for the MRI system.
The techniques for polarizing gas were originally developed by Drs. William Happer and Gordon Cates at Princeton University. The Duke researchers, working with the Princeton group, produced the first images with hyperpolarized helium in a rat in
1995. Less than a year later, the technique was extended to human studies by the Princeton/Duke team with the first human images using hyperpolarized helium.
"Earlier studies have been successful detecting defects in animals and patients with advanced lung disease, where large areas of tissue destruction have obstructed airflow," Johnson said. "However, newer techniques are needed to find the earlier, and more subtle, changes in smaller air spaces."
In their study, the researchers compared normal rats and those who were models for early-stage emphysema. Each rat breathed in the hyperpolarized helium gas, while being imaged on one of the Duke Center's special MR "microscope" systems with spatial resolution more than 100 times that of clinical MRI scanners.
The researchers measured the microscopic structure in the lung by measuring the diffusion of the gas in the porous spaces (alveoli). In injured areas where the gas could move more freely, the apparent diffusion was higher. This enabled the researchers to detect very subtle changes in the tissue microstructure caused by the injury.
Johnson said this method will become an important tool for better understanding a wide range of diseases and disorders effecting the lungs, ranging from effects of airborne pollutants and particulate matter to asthma and chronic obstructive pulmonary disease (COPD).
Since the technique measures changes in the lungs and airways in real time, researchers could also observe the effects of different drugs or treatments as they are introduced.
Members of the Duke team include X. Josette Chen, now at the Sunnybrook & Women's College Health Sciences Center in Toronto; Laurence Hedlund and Mark Chawla at Duke; Harald Moller, now at the Institut for Physikalische Chemie, Westfalische Wilhelms-Universitat, Munster, Germany; and Robert Maronpot, now at National Institute of Environmental Health Sciences, Division of Chemical Pathology and Toxicology, Research Triangle Park.