Quantitative assessment of peripheral airway obstruction on paired expiratory/inspiratory thin-section computed tomography in chronic obstructive pulmonary disease with emphysema.

OBJECTIVES: We examined the hypothesis that paired inspiratory/expiratory computed tomography (CT) scans in a limited-lung area that excludes emphysema may provide a more accurate evaluation of peripheral airway obstruction in patients with chronic obstructive pulmonary disease (COPD) with emphysema.
MATERIALS AND METHODS: This study included 32 patients with COPD. The cross-sectional area between -500 and -1024 HU was segmented as whole-lung. The relative areas (RA) less than -950 HU for the whole-lung (RA<-950) were segmented as emphysema, and pixels less than -900 HU for the whole-lung (RA<-900) were segmented to evaluate air trapping. Next, the cross-sectional area between -500 and -950 HU that excludes emphysema was segmented as limited-lung, and pixels between -900 and -950 HU for the limited-lung (RA900-950) were segmented. The changes in RA<-900 (RA<-900-change) and RA900-950 (RA900-950-change) between inspiration and expiration were calculated. Correlations between CT measurements and the results of pulmonary function tests (PFT) were evaluated.
RESULTS: There was no significant difference between the mean inspiratory RA<-950 and expiratory RA<-950 (P = 0.245), but the mean expiratory RA900-950 decreased significantly compared with the mean inspiratory RA900-950 (P < 0.001). The correlation coefficients between PFT parameters and the RA900-900-change in the limited-lung without emphysema were higher than that of the RA<-900-change in the whole-lung.
CONCLUSIONS: The paired inspiratory/expiratory CT measurements in the limited-lung without emphysema correlated more closely with the PFTs. Our observations suggest that paired inspiratory/expiratory CT scans in the limited-lung excluding emphysema are sensitive for the evaluation of airway obstruction in COPD with emphysema.