Longitudinal follow-up study of smoking-induced lung density changes by high-resolution computed tomography

To evaluate the ability of high-resolution computed tomography (HRCT) to de tect longitudinal changes in structural abnormalities caused by smoking, HR CT and pulmonary function tests were used to examine nonsmokers, current sm okers, and past smokers annually for 5 yr. Inspiratory HRCT was taken for t he upper, middle, and lower lung fields, while expiratory images were obtai ned for the upper and lower lung fields only. We estimated the three quanti tative CT parameters including MLD (mean CT value), HIST (CT value with the most frequent appearance), and %LAA (relative area of low attenuation with CT values less than -912 HU). Most of the pulmonary function tests, except ing FEV1, did not change annually, whereas many of the inspiratory HRCT par ameters did. In nonsmokers, only %LAA in the middle or lower lung fields ex hibited an annual increase. In current smokers, %LAA in the upper lung fiel d was augmented, while inspiratory MLD or HIST in the middle or lower lung field became more positive. In past smokers, %LAA in any lung field examine d increased. The annual change in %LAA in the upper lung field was larger f or past smokers than nonsmokers, with little difference between past and cu rrent smokers. Expiratory CT parameters showed few annual changes in all gr oups. In conclusion, (1) aging increases airspace abnormalities, mainly in the lower lung field; (2) although continuous smoking worsens airspace abno rmalities mainly in the upper portion of the lung, this trend does not seem to slow down even after smoking cessation; and (3) inspiratory HRCT images are superior to expiratory images for longitudinal estimation of structura l abnormalities caused by aging and smoking.