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Nov. 26, 2007 (Chicago) -- For the first time, researchers say they have evidence that long-term exposure to secondhand smoke can cause structural damage in the lungs that is indicative of emphysema.
Their study also suggests that the modified magnetic resonance imaging (MRI) technique used to detect the lung damage may be able to spot emphysema long before symptoms occur.
The researchers used global helium-3 diffusion MRI to study the lungs of 13 current or former smokers and 45 people who had never smoked. Of the nonsmokers, 22 had heavy exposure to secondhand smoke, meaning they lived with a smoker or worked in a bar for at least a decade. None had symptoms of lung disease.
The modified MRI detected signs of early lung damage in 67% of smokers and 27% of nonsmokers with heavy exposure to secondhand smoke, says researcher Chengbo Wang, PhD, of the Children's Hospital of Philadelphia.
In contrast, only 4% of nonsmokers who had never smoked and had fewer than 10 years of exposure appeared to have signs of early lung damage, he says.
The research was presented here at the annual meeting of the Radiological Society of North America (RSNA).
Wang tells WebMD that it's long been thought that prolonged exposure to secondhand smoke can cause lung damage and emphysema, but doctors lacked a way to prove it.
"Previous methods of detection weren't sensitive enough," he says.
Helium-3 diffusion MRI offers more detailed images of the lungs than previous techniques, he says.
It works like this: first, helium gas is polarized with a laser; this makes it more visible on MRI.
Then, while lying in a conventional MRI scanner, a person inhales the energized helium. In just six seconds, the scanner collects images showing how the helium gas distributes in the tiny air sacs called alveoli in the lung.
Prolonged exposure to cigarette smoke causes the walls of the air sacs to break down and the air sacs to become bigger and bigger -- early signs of emphysema, Wang says.
As a result, helium travels much further in people with enlarged air sacs than in people with healthy alveoli, he explains.
"Using helium MRI, we were able to detect microscopic changes suggestive of emphysema in smokers and people exposed to secondhand smoke," Wang says.
RSNA spokeswoman Katarzyna Macura, MD, PhD, of Johns Hopkins Medical Institutions in Baltimore, tells WebMD that the modified MRI needs to be studied in larger numbers of people before it's ready for prime time.
"Accessibility and cost are the two big issues that need to be addressed," she says. "Before any recommendations can be made, we need solid data and proof that what we are seeing [on the scan reflects lung changes indicative of emphysema]."