Paired inspiratory-expiratory thin-section CT findings in patients with small airway disease.

The objective of this study was to evaluate minimal small airway disease (SAD) as reflected on paired inspiratory-expiratory CT findings. Seventy-two subjects, 34 with SAD, 11 with normal lung function, and 27 with chronic obstructive pulmonary diseases (COPD), underwent thin-section CT during deep inspiration and expiration at upper, middle, and lower lung levels. Evaluation of CT measurement was performed between inspiratory and expiratory CT attenuation of lung parenchyma, in non-dependent and dependent lung at each of the three levels. Visual assessment of mosaic patterns and attenuation differences was also performed using the inspiratory and expiratory images. Patients with SAD were differentiated from those with COPD, by visual assessment and from the CT measurements. Visual assessment failed to differentiate between the SAD and normal groups. However, one measurement, an inspiratory-expiratory attenuation difference in the dependent lower lung, was different between SAD and normal group. Early small airway disease may be indicated by an inspiratory-expiratory attenuation difference in the dependent lower lung using the simple method of a paired inspiratory-expiratory CT.