title: Reversibility of trapped air on chest computed tomography in cystic fibrosis patients.
abstract: OBJECTIVE
  To investigate changes in trapped air volume and distribution over time and compare computed tomography (CT) with pulmonary function tests for determining trapped air.
  
  
  METHODS
  Thirty children contributed two CTs and pulmonary function tests over 2 years. Localized changes in trapped air on CT were assessed using image analysis software, by deforming the CT at timepoint 2 to match timepoint 1, and measuring the volume of stable (TAstable), disappeared (TAdisappeared) and new (TAnew) trapped air as a proportion of total lung volume. We used the difference between total lung capacity measured by plethysmography and helium dilution, residual volume to total lung capacity ratio, forced expiratory flow at 75% of vital capacity, and maximum mid-expiratory flow as pulmonary function test markers of trapped air. Statistical analysis included Wilcoxon's signed rank test and Spearman correlation coefficients.
  
  
  RESULTS
  Median (range) age at baseline was 11.9 (5-17) years. Median (range) of trapped air was 9.5 (2-33)% at timepoint 1 and 9.0 (0-25)% at timepoint 2 (p=0.49). Median (range) TAstable, TAdisappeared and TAnew were respectively 3.0 (0-12)%, 5.0 (1-22)% and 7.0 (0-20)%. Trapped air on CT correlated statistically significantly with all pulmonary function measures (p<0.01), other than residual volume to total lung capacity ratio (p=0.37).
  
  
  CONCLUSIONS
  Trapped air on CT did not significantly progress over 2 years, may have a substantial stable component, and is significantly correlated with pulmonary function markers.
authors.affiliation: Department of Pediatric Pulmonology & Allergology, Erasmus MC-Sophia Children's Hospital, The Netherlands; Department of Radiology, Erasmus MC, The Netherlands.
authors.forename: Martine
authors.initials: M
authors.lastname: Loeve
authors.affiliation: Department of Pediatric Pulmonology & Allergology, Erasmus MC-Sophia Children's Hospital, The Netherlands; School of Paediatrics and Child Health Research, The University of Western Australia, Australia; Telethon Kids Institute, The University of Western Australia, Australia.
authors.forename: Tim
authors.initials: T
authors.lastname: Rosenow
authors.affiliation: Department of Computer Science, University of Copenhagen, Denmark.
authors.forename: Vladlena
authors.initials: V
authors.lastname: Gorbunova
authors.affiliation: Department of Biostatistics, Erasmus MC, The Netherlands.
authors.forename: Wim C J
authors.initials: WC
authors.lastname: Hop
authors.affiliation: Department of Pediatric Pulmonology & Allergology, Erasmus MC-Sophia Children's Hospital, The Netherlands; Department of Radiology, Erasmus MC, The Netherlands. Electronic address: H.Tiddens@erasmusmc.nl.
authors.forename: Harm A W M
authors.initials: HA
authors.lastname: Tiddens
authors.affiliation: Department of Radiology, Erasmus MC, The Netherlands; Department of Computer Science, University of Copenhagen, Denmark; Department of Medical Informatics, Erasmus MC, The Netherlands.
authors.forename: Marleen
authors.initials: M
authors.lastname: de Bruijne
mesh_terms: D000293:Adolescent; D000328:Adult; D000388:Air; D002648:Child; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008176:Lung Volume Measurements; D008297:Male; D010865:Pilot Projects; D015203:Reproducibility of Results; D012129:Respiratory Function Tests; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014797:Vital Capacity; D055815:Young Adult
keywords: Chest CT; Cystic fibrosis; Quantitative measures; Reversibility; Trapped air