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Evaluation of Air Trapping at CT: Comparison of Continuous- versus Suspended-Expiration CT Techniques¹

¹ From the Department of Radiology, Université Pierre-et-Marie-Curie, Hôpital de la Pitié-Salpêtrière, 47 boulevard de l’Hôpital, 75651 Paris cedex 13, France (O.L., P.A.G., M.C., I.M.G., P.C.); Institut National de la Santé et de la Recherche Médicale, Paris, France (P.A.G.); and Cyclotron Biomedical de Caen, Caen, France (K.B.). From the 1997 RSNA scientific assembly. Received March 29, 1999; revision requested May 10; final revision received January 7, 2000; accepted January 12. Address correspondence to O.L. (e-mail: olivier.lucidarme@psl.ap_hop_paris.fr).

PURPOSE: To compare thin-section computed tomographic (CT) scans obtained during suspended end expiration with helical CT scans obtained during continuous expiration for the assessment of air trapping.

MATERIALS AND METHODS: Forty-nine patients with an airway disease were examined with suspended-end-expiration CT after a 6–8-second expiratory maneuver, which was followed with continuous-expiration CT during a 10-second expiratory maneuver. The extent of expiratory air-trapping areas was calculated by two observers by using a semiquantitative grid score. The relative decrease in attenuation in the areas of air trapping was evaluated with a visual continuous-scale score.

RESULTS: Air trapping was noted in 36 and 35 patients with continuous-expiration CT and with suspended-end-inspiration CT, respectively. The extents of and relative attenuation decreases in air-trapping areas in patients with air-trapping areas on at least one expiratory CT scan increased significantly in scans obtained with continuous-expiration CT compared with those obtained with suspended-end-expiration CT, respectively, with mean extent scores of 0.24 ± 0.20 (SD) and 0.18 ± 0.20 (paired t test, P = .001) respectively, and with mean relative contrast decrease scores of 0.35 ± 0.23 and 0.27 ± 0.23 (paired t test, P = .007), respectively.

CONCLUSION: When suspended-end-expiration CT images are ambiguous, complementary continuous-expiration CT can be used to improve the conspicuity and apparent extent of air trapping.

Index terms: Lung, abnormalities, 60.26, 60.751, 60.754, 60.755 • Lung, CT, 60.12111, 60.12115, 60.12118 • Lung, function • Lung, ventilation

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