title: Accurate measurement of small airways on low-dose thoracic CT scans in smokers.
abstract: BACKGROUND
  Partial volume averaging and tilt relative to the scan plane on transverse images limit the accuracy of airway wall thickness measurements on CT scan, confounding assessment of the relationship between airway remodeling and clinical status in COPD. The purpose of this study was to assess the effect of partial volume averaging and tilt corrections on airway wall thickness measurement accuracy and on relationships between airway wall thickening and clinical status in COPD.
  
  
  METHODS
  Airway wall thickness measurements in 80 heavy smokers were obtained on transverse images from low-dose CT scan using the open-source program Airway Inspector. Measurements were corrected for partial volume averaging and tilt effects using an attenuation- and geometry-based algorithm and compared with functional status.
  
  
  RESULTS
  The algorithm reduced wall thickness measurements of smaller airways to a greater degree than larger airways, increasing the overall range. When restricted to analyses of airways with an inner diameter < 3.0 mm, for a theoretical airway of 2.0 mm inner diameter, the wall thickness decreased from 1.07 ± 0.07 to 0.29 ± 0.10 mm, and the square root of the wall area decreased from 3.34 ± 0.15 to 1.58 ± 0.29 mm, comparable to histologic measurement studies. Corrected measurements had higher correlation with FEV₁, differed more between BMI, airflow obstruction, dyspnea, and exercise capacity (BODE) index scores, and explained a greater proportion of FEV1 variability in multivariate models.
  
  
  CONCLUSIONS
  Correcting for partial volume averaging improves accuracy of airway wall thickness estimation, allowing direct measurement of the small airways to better define their role in COPD.
authors.affiliation: Division of Medical Education, Washington University School of Medicine, St Louis, MO. Electronic address: blutey@dom.wustl.edu.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Lutey
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO.
authors.forename: Susan H
authors.initials: SH
authors.lastname: Conradi
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St Louis, MO.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Atkinson
authors.affiliation: Division of Biostatistics, Washington University School of Medicine, St Louis, MO.
authors.forename: Jie
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Division of Biostatistics, Washington University School of Medicine, St Louis, MO.
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Schechtman
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Washington University School of Medicine, St Louis, MO.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Senior
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO.
authors.forename: David S
authors.initials: DS
authors.lastname: Gierada
mesh_terms: D000368:Aged; D056151:Airway Remodeling / Q000502:physiology; D000465:Algorithms; D055745:Bronchioles / Q000473:pathology* / Q000503:physiopathology; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D012129:Respiratory Function Tests; D012720:Severity of Illness Index; D012907:Smoking / Q000473:pathology* / Q000503:physiopathology; D014057:Tomography, X-Ray Computed