Prevalence of Emphysema in Individuals Who Underwent Screening CT for Lung Cancer in Nagano Prefecture of Japan

BACKGROUND: Screening for lung cancer with low-dose spiral computed tomography (CT) was carried out in Nagano prefecture in Japan. OBJECTIVE: To study the prevalence of emphysema in 7,847 individuals based on the Nagano spiral CT screening and to correlate the prevalence and severity of emphysema with various factors. METHODS: Spiral CT images with scan parameters of 120 kV, 50 mA, 10-mm collimation and a pitch of 2 obtained at full inspiration were retrospectively evaluated in 7,847 individuals. Emphysema was defined as the presence of low-attenuation areas in the lung parenchyma. Extent of emphysema was graded on a four-level scale and correlated with gender, age and smoking habits. RESULTS: There were 4,288 males and 3,559 females. Mean age of the subjects was 61 years; 45.8% of the participants were smokers. Overall prevalence of emphysema was 2.9%; the prevalence was significantly higher in males (5.0%) than in females (0.5%); it was also significantly higher in smokers, and increased with age. Emphysema was positively correlated with age, but there was no correlation with smoking indices. Emphysema was mostly mild and localized in the upper lung. The logistic model revealed that gender, age and smoking indices were significant factors for developing emphysema. CONCLUSIONS: Overall prevalence of emphysema was 2.9%. The prevalence was higher in males and in older people. Smoking was also related to a higher prevalence of emphysema but not to its severity.