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

To determine the utility of expiratory scans for diagnosis of inhomogeneous attenuation on thin-section computed tomographic (CT) scans.

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.

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 expiratory 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).

Expiratory scans significantly improved diagnostic accuracy in patients with inhomogeneous attenuation on inspiratory scans, and they helped in the diagnosis of diffuse lung disease.