title: Evaluation of air trapping at CT: comparison of continuous-versus suspended-expiration CT techniques.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiology, Université Pierre-et-Marie-Curie, Hôpital de la Pitié-Salpêtrière, Paris, France. olivier.lucidarme@psl.ap_hop_paris.fr
authors.forename: O
authors.initials: O
authors.lastname: Lucidarme
authors.forename: P A
authors.initials: PA
authors.lastname: Grenier
authors.forename: M
authors.initials: M
authors.lastname: Cadi
authors.forename: I
authors.initials: I
authors.lastname: Mourey-Gerosa
authors.forename: K
authors.initials: K
authors.lastname: Benali
authors.forename: P
authors.initials: P
authors.lastname: Cluzel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000000981:diagnostic imaging*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D012123:Pulmonary Ventilation / Q000502:physiology*; D011856:Radiographic Image Enhancement; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed