Hyperpolarized MR demonstrates value in emphysema

A study evaluating MR's contribution to diagnosis of emphysema may breathe new life into the use of hyperpolarized gases, contrast agents that provide the means for MR to image the lungs. It's not certain whether the positive findings, published in the June issue of Radiology, will lead to an economically viable commercial path for the technology. But at the very least they have proven that hyperpolarized MR can do what no other modality can. They have also provided encouragement for GE Healthcare, which owns the technology, to commercialize it.

The research, conducted at the University of Wisconsin in Madison, indicates that hyperpolarized MR imaging can identify early signs of emphysema in smokers who show none of its symptoms.

"This is the first time structural changes have been shown in the lungs of asymptomatic smokers," said lead author Sean B. Fain, Ph.D., an assistant professor of medical physics and radiology at UW. "With this technology, it is possible to measure the severity of emphysema and its progression through time."

Clinical proof of diagnostic efficacy could help the cause of hyperpolarized MR, which has foundered for much of the last decade. In the late 1990s, helium and xenon promised to take MR where it could not go on its own - into the lungs. The future looked bright given the dozen or so drugs under development for chronic obstructive pulmonary disease. But then the momentum faltered.

Practical and economic challenges, regulatory changes, and difficulties encountered in the development of COPD drugs combined to sink hyperpolarized MR. The research from UW might turn this around, according to Jonathan Allis, Ph.D., global head of imaging for medical diagnostics at GE Healthcare.

"These type of data linked to potential disease-modifying therapeutics will potentially generate large scale commercial interest," he said. "It is of direct clinical relevance and of direct importance to pulmonologists."

The research is part of a growing body of evidence, some of it derived from GE's own clinical studies, that hyperpolarized MR is of genuine clinical utility, he said. Whether helium is the contrast medium of commercial choice, however, remains to be determined.

"Although we have shown helium to be a reproducible technique for the evaluation of lung function, our focus now is on commercializing xenon imaging," Allis said. "The UW study is particularly encouraging, as it illustrates that apparent diffusion coefficient changes have already occurred in asymptomatic smokers."

In the study, 19 volunteers inhaled hyperpolarized helium just prior to undergoing two MR lung scans. Eleven were smokers with no symptoms of emphysema. Eight were nonsmokers. The initial scan showed obstructed areas of the lungs. The second rendered ADC maps indicating the size of the air spaces in the lungs.

In emphysema, the alveoli, tiny sacs in the lungs that ferry oxygen to blood, gradually break down. The researchers hypothesized that helium molecules would have more space to move around in lungs with fewer functioning alveoli. Because emphysema increases air space, the ADC maps showed the location and severity of the disease.

"These maps are very sensitive to changes in the lung structure," Fain said. "Even smokers who appear healthy have enlarged lung airspaces that suggest emphysema is developing."

The ADC maps demonstrated a progressive breakdown of lung structure associated with a history of increased smoking. All smokers with a history of smoking more than one pack of cigarettes per day for 18 years showed significant abnormalities compared with nonsmokers.

CT failed to show the same defects found with helium-enhanced MR. MR was more than twice as precise in measuring lung structure, according to the researchers.

"This approach allows us to look at lung microstructures that are on the scale of less than a millimeter," Fain said.

In addition to early disease detection, hyperpolarized MR can be used to plan surgery and to monitor patient response to drug therapies, Fain said. It might also be used to better understand the mechanisms of other lung conditions, such as asthma and COPD.