Purpose

Air trapping is a pathophysiologic condition indicating the retention of excess gas in all or part of the lung at any stage of expiration. Expiratory CT has been used to reveal air trapping in patients with airway diseases such as pulmonary emphysema, chronic bronchitis, asthma, and small-airway disease. Air trapping can be classified as extensive and mosaic. Extensive gas trapping is characterized by well-defined low attenuation areas in expiratory scans. Mosaic air trapping is characterized by the appearance of inhomogeneous air emptying on expiratory compared to normal inspiratory chest CT scans. A number of quantitative chest CT methods have been pro- posed to assess extensive gas trapping [1, 2], however those methods fail to detect the diffuse nature of mosaic gas trapping. We have developed an approach to tackle this problem and we have validated the technique in a population of World Trade Center workers with abnormal lung emptying reported by a radiologist.