Inhomogeneous lung attenuation at thin-section CT: Diagnostic value of expiratory scans

PURPOSE: To determine the utility of expiratory scans for diagnosis of inhomogeneous attenuation on thin-section computed tomographic (CT) scans. MATERIALS AND METHODS: On the basis of clinical information and pulmonary function test results disease in 53 patients with inhomogeneous attenuation on inspiratory scans was classified into four groups-infiltrative, airway, vascular, or mixed. Without knowledge of the diagnosis, inhomogeneous attenuation was classified as (a) ground-glass opacity due to infiltrative disease, (b) mosaic perfusion due to airway disease, or (c) mosaic perfusion due to vascular-disease, and the degree of confidence was indicated. Each case was reclassified if necessary on the basis of expiratory scan findings. RESULTS: A correct diagnosis was made more often on the basis of both inspiratory and expiratory scans than on the basis of inspiratory scans alone (92% [49 of 53 patients] vs 79% [42 of 53], respectively [P <.05]). Accuracy increased from 81% (21 of 26) to 89% (23 of 26) in cases of infiltrative disease and from 84% (16 of 19) to 100% (19 of 19) in cases of airway disease. A correct interpretation with high confidence level was reached more often with scans than on the basis of inspiratory scans alone (92% [49 of 53] vs 45% [24 of 53], respectively [P< .0001]). The extent of air trapping correlated significantly with pulmonary function test results. With expiratory Scans, the classification of inhomogeneous attenuation was changed in 15% (eight of 53) of cases and the confidence level was improved in 51% (27 of 53) (P< .0001). CONCLUSION: Expiratory scans significantly improved diagnostic accuracy in patients with inhomogeneous attenuation On inspiratory scans, and-they helped in the diagnosis of diffuse lung disease.