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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.