Diagnostics & Imaging Week
CHICAGO – Secondhand cigarette smoke kills.
At least that's what health researchers and officials have been telling the public for years. And now a study presented at the Radiological Society of North America (RSNA; Oak Brook, Illinois) meeting this week gives this statement real ammunition, providing evidence that secondhand cigarette smoke produces structural damage to the lungs and increases susceptibility to chronic obstructive pulmonary disease (COPD).
Researchers at the University of Virginia School of Medicine (Charlottesville) and The Children's Hospital of Philadelphia used helium-3 (3He) diffusion MRi to study the lungs of 60 volunteers.
Chengbo Wang, PhD, MR physicist in the Department of Radiology at The Children's Hospital presented results at a Monday morning RSNA press conference, noting that the team developed the technique to determine which non-smoking patients either had, or showed, a tendency to develop COPD. Wang noted that 15% to 30% of smokers develop COPD.
Wang said he believes the team's early results confirm that secondhand smoke is a public health threat. Secondhand smoke is classified as a carcinogen by the U.S. Environmental Protection Agency and has been linked to heart disease, lung cancer and a number of respiratory illnesses including asthma and bronchitis.
Children are particularly susceptible to the harmful affects of secondhand smoke. According to the American Lung Association (Chicago), 35% of American children live in homes where regular smoking occurs.
Wang described the challenge of developing a methodology sensitive enough to pick up subtle changes in the lung tissue never before detectable.
"For lung cancer and cardiovascular disease, there is some link with secondhand smoke," he said. "For COPD, there has been no research that could confirm this." He said that it had been "hypothesized" that exposure to secondhand smoke could damage the lungs "but previous methods of analyzing lung changes were not sensitive enough to detect it."
In the study, 45 people had never smoked and of these 22 of them had a high level of exposure to secondhand smoke; another 15 adults were current or former smokers
To utilize the long-time-scale, global 3He diffusion MRI employed by the researchers, patients inhaled a specially prepared helium gas before imaging. The MRI scanner, a modified 1.5 Tesla system from Siemens Medical Solutions (Malvern, Pennsylvania), then collected images showing the gas in the lung tissue. MRI measured how far the helium atoms diffused inside the lungs during a 1.5 second breathhold.
Using these measurements, researchers detected changes deep in the small airways and alveolar sacs — areas that can be destroyed, develop holes or become enlarged after prolonged exposure to cigarette smoke.
The group identified lung damage consistent with emphysema by measuring the increased distance the helium atoms moved. Those measurements were translated into apparent diffusion coefficient (ADC) values, with the increased ADC values indicating that the helium atoms were able to travel farther during the measurement period.
Talissa Altes, MD, a pediatric radiologist at Children's Hospital of Philadelphia and co-author of the study, told Diagnostics & Imaging Week that the device "has been modified to do broadband imaging – that is, to image things other than hydrogen which is what we typically image."
She said that with the hyperpolarized helium gas "we get almost a factor of a million increase in signal, which translates into whatever you want, speed, resolution, signal-to-noise ratio, however you want to distribute it. We translated it into signal-to-noise ratio and speed."
In the study, 67% of the smokers and 27% of the non-smokers who had high exposure to secondhand cigarette smoke had ADC values greater than 0.024, suggesting early lung damage was present, said Wang.
"We know the lung is a complex structure," he said. "We also know that lung function tests are not sensitive enough to pick up early damage.
"Currently the best method to detect COPD is CT. We noted that for some smokers, their lung function tests are just normal and healthy. In our pictures, the global ADC didn't change a lot, but we could definitely see small, localized changes. The sensitivity is clearly improved and is very helpful in catching early disease."
For the 27% of nonsmokers who had high ADC values, their early lung damage looked familiar to researchers, said Wang.
"For some smokers, there is so much lung damage, we use CT, and you can see the changes due to emphysema,"
He added: "We observed that around 30% of the study group showed similar changes, and we hypothesized this kind of change is mild emphysema. We need more study to confirm this."
The results of the trial were eye-opening for some study subjects as well, with Wang relating the experience of one woman who participated.
"When she looked at her pictures she was very surprised," he said. "She went home and asked her husband to quit smoking as soon as possible. Before, she thought the smoking only hurt him. Now it looks like the smoking also hurts her."
Wang said he hopes this study, though small, will help to inform future policy concerning smoking.
"Even with secondhand smoke, it is clear there's damage to human health," he said. "I really think public policy needs to reflect this and restrict smoking in public spaces. If people want research to prove there's harm in secondhand smoke, I feel we have it."