title: Relationship between CT air trapping criteria and lung function in small airway impairment quantification.
abstract: BACKGROUND
  Small airways are regarded as the elective anatomic site of obstruction in most chronic airway diseases. Expiratory computed tomography (CT) is increasingly used to assess obstruction at this level but there is no consensus regarding the best quantification method. We aimed to evaluate software-assisted CT quantification of air trapping for assessing small airway obstruction and determine which CT criteria better predict small airway obstruction on single breath nitrogen test (SBNT).
  
  
  METHODS
  Eighty-nine healthy volunteers age from 60 to 90 years old, underwent spirometrically-gated inspiratory (I) and expiratory (E) CT and pulmonary function tests (PFTs) using SBNT, performed on the same day. Air trapping was estimated using dedicated software measuring on inspiratory and expiratory CT low attenuation area (LAA) lung proportion and mean lung density (MLD). CT indexes were compared to SBNT results using the Spearman correlation coefficient and hierarchical dendrogram analysis. In addition, receiver operating characteristic (ROC) curve analysis was performed to determine the optimal CT air-trapping criterion.
  
  
  RESULTS
  43 of 89 subjects (48,3%) had dN2 value above the threshold defining small airway obstruction (i.e. 2.5% N2/l). Expiratory to inspiratory MLD ratio (r = 0.40) and LAA for the range -850 -1024 HU (r = 0.29) and for the range -850 -910 HU (r = 0.37) were positively correlated with SBNT results. E/I MLD was the most suitable criterion for its expression. Expiratory to inspiratory MLD ratio (E/I MLD) showed the highest AUC value (0.733) for small airway obstruction assessment.
  
  
  CONCLUSIONS
  Among all CT criteria, all correlating with small airway obstruction on SBNT, E/I MLD was the most suitable criterion for its expression in asymptomatic subjects with mild small airway obstruction
  
  
  BACKGROUND
  Registered at Clinicaltrials.gov, identifier: NCT01230879.
authors.affiliation: Radiology Department, CHU Montpellier, 371 avenue Doyen Gaston Giraud 34295, Montpellier cedex 05, France. s-bommart@chu-montpellier.fr.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Bommart
authors.forename: Grégory
authors.initials: G
authors.lastname: Marin
authors.forename: Arnaud
authors.initials: A
authors.lastname: Bourdin
authors.forename: Nicolas
authors.initials: N
authors.lastname: Molinari
authors.forename: François
authors.initials: F
authors.lastname: Klein
authors.forename: Maurice
authors.initials: M
authors.lastname: Hayot
authors.forename: Isabelle
authors.initials: I
authors.lastname: Vachier
authors.forename: Pascal
authors.initials: P
authors.lastname: Chanez
authors.forename: Jacques
authors.initials: J
authors.lastname: Mercier
authors.forename: Hélène
authors.initials: H
authors.lastname: Vernhet-Kovacsik
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology*; D001944:Breath Tests; D003430:Cross-Sectional Studies; D045853:Exhalation; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012129:Respiratory Function Tests / Q000379:methods; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*