Key Point

Research suggests that tracing hyperpolarized helium through the lungs with MRI may diagnose early emphysema before symptoms or deficits in lung function are apparent.

MADISON, WISCONSIN—Hyperpolarized gases have been used with MRI to identify changes in the lungs of emphysema patients. New research suggests that tracing hyperpolarized helium 3 (3He) with MRI is capable of diagnosing emphysematous changes in smokers’ lungs before they show any clinical signs of the disease. Additionally, the method—which uses an apparent diffusion coefficient (ADC) map—correlated with pulmonary function test results, such as Dlco, plus pack-years of smoking and age.¹

Sean B. Fain, PhD, and colleagues evaluated eight healthy nonsmokers (people who had smoked less than 100 cigarettes in their lifetime) and 11 healthy smokers. Smoking histories ranged from five to more than 30 pack-years. Participants had a mean age of 46.5. All participants had an FEV1 above 75% of predicted and normal chest findings. Pulmonary function tests were conducted, including FEV1, FEV1/FVC ratio, Dlco, and the alveolar partial pressure of CO (Paco). All participants inhaled polarized 3He prior to MRI, and ADCs were measured for both smokers and nonsmokers. Additionally, thin-section CT was performed. According to Dr. Fain, Assistant Professor of Medical Physics and Radiology at the University of Wisconsin, Madison, "Helium MRI, particularly diffusion-weighted imaging, seems to provide regional information about lung structure and function that is not available from other techniques." He added, "Emphysema-like structural changes in the lungs were detected in smokers before any other symptoms were apparent."

SUPERIOR RESULTS

Ventilation-weighted 3He MRI showed no defects in 53% of participants. Small peripheral defects were apparent in 32% of participants, and only 16% of participants had severe defects. Mean ADC values increased significantly with decreasing FEV1/FVC ratio but did not correlate with FEV1. This suggests that "elevated values of 3He gas diffusion into the alveolar space correlate with degraded pulmonary function in asymptomatic individuals," the authors asserted. ADC values correlated with Dlco, especially in smokers. The technique also correlated with pack-years of smoking, regardless of age, suggesting that it is highly sensitive in the early detection of emphysema. In contrast, pack-years of smoking was associated with Dlco, but not with FEV1/FVC ratio or FEV1. CT had a near-significant correlation with Dlco, but not with pack-years of smoking. MRI with hyperpolarized 3He allowed researchers to measure lung structure with 2.5 times more precision than with CT and 10 times more precision than with MRI alone. "The helium MRI method allows us to measure length scales that are on the order of 100 to 300 µm. This is superior to the spatial resolutions depicted on CT and conventional MRI," Dr. Fain explained.

Dr. Fain believes that a more accessible and less expensive method than helium MRI is needed for screening asymptomatic smokers. "The main benefit of the new imaging technique," he asserts, "is as a tool for regional evaluation of lung structure in circumstances where more specific information is needed." He cited evaluating a patient’s response to therapy or monitoring disease progression as two such instances.

n an editorial, Eduard E. de Lange, MD, states that "the results are encouraging that regional emphysematous changes can be identified at an early stage when there are no clinical symptoms."² He believes that hyperpolarized gas diffusion-weighted MRI might enable the effects of new treatments aimed at modifying disease to be monitored, and most importantly, the technique "could be used to detect early emphysema and, thereby, help smokers to stop their smoking habit, particularly when they are shown the visible changes in the lung." Dr. Fain acknowledges that future research should compare helium MRI with multidetector CT densitometry in a large population. He believes that the technique may also be useful for monitoring idiopathic pulmonary fibrosis, asthma, and bronchiolitis obliterans.

—Tamara Gibb

Reference
1. Fain SB, Panth SR, Evans MD, et al. Early emphysematous changes in asymptomatic smokers: detection with 3He MR imaging. Radiology. 2006;239:875-883.
2. de Lange EE. Science to practice: what is new about detecting emphysema? Radiology. 2006;239:619-620.

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