Scientists use excited helium to detect early lung disorders

Those who think that inhaling helium gas is reserved for clichéd and uninspired comedy routines may want to reconsider.

Researchers at the Medical Center have used hyperpolarized, or excited, helium gas to complement current MRI scans and detect subtle changes in rats' lungs. The researchers published their findings in the Oct. 10 issue of the proceedings of the National Academy of Sciences of the USA and noted that their technique would be especially useful in spotting early-stage pulmonary diseases like emphysema.

"We believe the concept of hyperpolarized gas [diffusion] measurement will contribute greatly to the scope of pulmonary studies of airway diseases in both the research and clinical arenas," the team wrote in the PNAS article.

One of the problems of taking a traditional MRI scan of the lungs is that the technique relies on measuring protons in water. While water comprises approximately 75 percent of the human body and is found in sufficient amounts in most tissues, the lungs are mostly filled with air. This presents a problem for researchers because the air does not register on an MRI scan, making it difficult to spot changes in the lung structure.

However, hyperpolarized helium gas overcomes this obstacle because it enables MRI scans to pick up the signal generated by the inhaled gas. A complete picture of the lungs can then be assembled with computer modeling. In other words, the image obtained by using excited helium illuminates the areas where the conventional proton MRI yields no signal.

"We can look at the rate of diffusion of the gas and using the diffusion coefficient see the changes in the microscopic structure [of the lungs]," said Allan Johnson, professor of radiology and lead author of the study. "[This information] can tell us what's wrong by allowing us to see places where the [the gas] doesn't flow effectively."

Johnson also pointed out that using hyperpolarized helium gas allows researchers to obtain information from a live specimen that could previously be obtained only through microscopic analysis of dead tissue.

Enphysema is characterized by the destruction of the porous spaces in the lungs, called alveoli, and an enlargement of gas exchange spaces-a condition that can be reversed if detected early enough. In the study, the researchers simulated the effects of emphysema by treating rats' lungs with elastase, an enzyme that enlarges the alveoli in a fashion similar to the modeled disease. They then compared the treated rats with normal rats to demonstrate the effectiveness of MRIs using hyperpolarized gas. The idea to use excited helium along with MRIs originated at Princeton University, where it was first proposed by Drs. William Happer and Gordon Cates. Johnson's interest in the area arose after he met with Happer during one of his visits to Duke, and in 1995 translated into the joint creation of the first images of hyperpolarized helium in a rat.