MRI Images show damage caused by secondary smoking

January 3, 2008
MRI images show damage caused by secondary smoking
Bright images of minute structural damage in smokers’ lungs were obtained

• Prolonged exposure to cigarette smoke may
cause passageways in the lungs to break down
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• The scanner measured how far the helium atoms
Moved or diffused inside the lungs
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The health impact of second hand smoke has been very controversial (The Hindu, May 23, 2003). Physicians always suspected that second-hand smoke caused microscopic structural damage deep into the lungs. The damage was too tiny to be detected by any medical imaging tool.
Happy ending
Their suspicion had a happy ending, when Dr. Chengbo Wang, a magnetic resonance physicist and his radiologist colleagues in the Department of Radiology at the Children’s Hospital of Philadelphia teamed up with specialists at the University of Virginia School of Medicine to obtain bright medical images of the microscopic structural damage in the lungs of smokers by using a special type of magnetic resonance imaging.
They presented their findings on November 26 this year at the 93rd annual meeting of the Radiological Society of North America (RSNA) at Chicago. They studied 60 adults between ages 41 and 79; Forty five of them never smoked. They divided the non-smokers into groups with low and high exposure to second hand smoke.
The high exposure group smokers had lived with a smoker for at least 10 years, often during childhood (EurekAlert, November 26). The 15 current or former smokers formed the control group.
The research groups inhaled a mixture of nitrogen and He-3, a special type of helium made by polarizing it to make it more visible in the MRI. The researchers adjusted the MRI to take images showing this helium gas in the tissue.
The scanner measured how far the helium atoms moved or diffused inside the lungs during a time period-1.5 seconds-in the present study. The researchers could detect changes deep in the airways and sacs in the lungs.
Prolonged exposure to cigarette smoke may cause the passageways to break down; they may become enlarged; holes may develop. The helium atoms moved greater distance than in the lungs of normal subjects.
One-third of the non-smokers with high exposures to secondhand cigarette smoke had structural changes in their lungs similar to those found in smokers.
Paradoxical results
The researchers interpreted these changes as early signs of damage, representing very mild form of emphysema. Emphysema is a major cause of death in the US and is commonly found in heavy smokers (EurekAlert, Nov 26).
The researchers got some paradoxical results. Among two-thirds of the high exposure group of non-smokers, diffusion measurements were lower than those in the low exposure group.
Dr Wang argued that diffusion is lower in the group as their airways narrowed because of chronic bronchitis. Dr.Katarzyna Macura of John Hopkins School of Medicine, who moderated the RSNA session, noted that the results should be considered preliminary.
Study too small
She wanted animal studies to elucidate and confirm the apparent structural differences (medpage TODAY, Nov 27). She clarified that the study was too small to provide evidence of a cause and effect.
The detection of minute changes in lung is possible now because nearly 30 years ago scientists at Mainz University developed techniques to polarize nuclear spins of isotopes such as helium-3, an isotope which is extremely rare in nature. He-3 became available via the beta decay of tritium (CERN courier, Oct 2, 2001).
Scientists could use a laser beam to polarize helium gas; polarized helium-3 gas is more visible on MRI. Optical pumping of metastable helium-3 atoms can supply relatively large amounts of highly polarized gas.
The magnetic signals from these are a thousand times as large as those normally seen magnetic resonance imaging (CERN Courier, Oct 2, 2001).
Storage and transport of polarized gas from laboratory to hospital is a major challenge. The polarized helium atoms would lose their spin orientation when they collide with the walls of their containers.
Gas storage
Scientists found that they can store the gas at pressures of up to 10 bar for more than 100hours in glass vessels with their inner surfaces coated with a few mono layers of caesium.
Researchers at the Mainz University demonstrated the potential usefulness of He-3 techniques in human lung imaging in 1995. Dr. Wang and his colleagues applied the technique to study microscopic changes in the lungs of smokers.
Dr. Wang hoped that a conclusive study that demonstrates that breathing secondhand smoke can injure the lungs will push legislation prohibiting public exposure.
K.S.PARTHASARATHY
former Secretary, AERB
(ksparth@yahoo.co.uk)