MADISON, Wis. - Asymptomatic emphysema can be revealed by a new magnetic resonance imaging technique that is more sensitive to lung changes than computed tomography, investigators here reported.
MADISON, Wis., May 30 ? Asymptomatic emphysema can be revealed by a new magnetic resonance imaging technique that is more sensitive to lung changes than computed tomography, investigators here reported.
The technique, which involves two MRI scans of the lungs of patients who have inhaled hyperpolarized helium 3, surpasses computed tomography for the early diagnosis of emphysema, reported Sean B. Fain, Ph.D., and colleagues in the June issue of Radiology.
"With this technology, we have shown that it is possible to measure the severity of emphysema and its progression through time without the radiation exposure of lung CT tests," said Dr. Fain, an assistant professor of medical physics and radiology at the University of Wisconsin.
In a study comparing the technique with CT in asymptomatic smokers and healthy non-smokers, the investigators found that the MRI results correlated significantly with pulmonary function measurements for diagnosing emphysema, and revealed significantly abnormalities in the lungs of long-time smokers.
The investigators compared the imaging technique in 11 smokers (six men and five women, mean age 47) with no symptoms of emphysema and eight age-matched controls (four men and four women, mean age 46). The volunteers inhaled hyperpolarized He3, and then underwent a ventilation scan to reveal areas of obstruction in the lung.
The investigators then conducted a second MRI scan to construct an apparent diffusion coefficient map for revealing relative differences in air sac size. They compared mean apparent diffusion coefficient (ADC) values for smokers and nonsmoker with spirometry results, measures of diffusing capacity of the lung for carbon monoxide (DLCO) and cigarette pack-years smoked, using Spearman rank correlation coefficient (rs) and multiple linear regression analysis.
"The ADC maps are very sensitive to changes in the lung structure," Dr. Fain said. "With this tool, it was shown that even smokers that appear healthy have enlarged lung airspaces that suggest emphysema is already developing."
The researchers also compared mean ADC value with thin-section CT emphysema index of relative area less than -950 Hounsfield Units (inspiratory RA950, a quantitative measure that correlates with histologic findings of emphysema) on a regional basis using linear mixed-effect models.
They found that the mean ADC values and number of pack-years smoked were significantly correlated (rs = 0.60; 95% confidence interval, 0.21 - 1.00, P = 0.007). The relationship between smoking duration and ADC values remained significant after adjustment for age (P = 0.003)
DLCO was also strongly correlated with smoking duration (rs = -0.63; 95% CI, -0.97 to -0.29; P = 0.004), and there were statistically significant negative correlations between mean ADC values and percentage of predicted DLCO (rs = -0.79; 95% CI, -0.93 to -0.64; P