Radiologists establish connection between lung disease and secondhand smoke

Public policymakers have long sought valid scientific evidence linking lung disease and secondhand smoke. Their wait ended Monday at the 2007 RSNA meeting, when Chengbo Wang, Ph.D., announced clinical trial results using hyperpolarized helium-3 diffusion MRI to make the connection.

Wang and colleagues at the University of Virginia School of Medicine in Charlottesville and The Children's Hospital of Philadelphia used long-time-scale global He-3 diffusion MRI to study the lungs of 43 volunteers. Seven were current and former smokers and 36 had never smoked, but 18 of these volunteers had a high level of exposure to secondhand smoke.

Measurements were translated into apparent diffusion coefficient values for each of the participants. Fifty-seven percent of the smokers and 33% of the nonsmokers with high exposure to secondhand smoke had ADC values greater than 0.024, suggesting that early lung damage was present. In addition, 14% of smokers, 67% of high-exposure nonsmokers, and 39% of low-exposure nonsmokers had ADC values below 0.0185. Relatively low ADC values in adults are a possible indication of a developing respiratory problem such as chronic bronchitis or asthma.

The magnitude of the ADC values correlated directly with the size of lung aveoli. Small aveoli signify healthy lung. Large aveoli suggest pathology, such as obstructive pulmonary disease and emphysema.

From 15% to 20% of active smokers eventually develop chronic obstructive pulmonary disease, said principal investigator Dr. Talissa Altes, an assistant professor of radiology at Children's Hospital of Philadelphia.

"The subjects with high ADC values are people who need to limit their environmental exposure to smoke," Altes said in an interview with Diagnostic Imaging. "They are really vulnerable."

Hyperpolized He-3 diffusion MRI differs from conventional MRI in that the patient inhales a specially prepared helium gas prior to imaging, and the scanner is adjusted to collect images showing this helium gas in tissue. MR measures how far the helium atoms move, or diffuse, inside the lungs during a specific time period - 1.5 seconds in this study.

Using this method, radiologists and physicists can detect changes deep in the small airways and sacs in the lungs that can break down, become enlarged, and develop holes after prolonged exposure to cigarette smoke. He-3 diffusion MRI identifies this damage by measuring the increased distance the helium atoms move.

Hyperpolized He-3 increased the sensitivity of the conventional 1.5T MRI system used in the study by one million-fold, Altes said.

"Researchers have done thousands of spirographs without positive results (linking secondhand smoker with lung damage)," Altes said. "We are very pleased to produce these results with so few patients."

Secondhand smoke has emerged as a public health threat. It has been classified as a carcinogen by the Environmental Protection Agency and linked to heart disease, lung cancer, and a number of respiratory ailments, including asthma and chronic bronchitis. Children are particularly susceptible to the harmful effects of secondhand smoke. According to the American Lung Association, 35% of U.S. children live in homes where regular smoking occurs.

"These findings suggest that breathing secondhand smoke can injure your lungs," Wang said. "Since legislation to limit public exposure to secondhand smoke is still being considered in many states, we hope that our work can be used to add momentum to the drive to pass such legislation."