title: Follow-up of CT-derived airway wall thickness: Correcting for changes in inspiration level improves reliability.
abstract: OBJECTIVE
  Airway wall thickness (AWT) is affected by changes in lung volume. This study evaluated whether correcting AWT on computed tomography (CT) for differences in inspiration level improves measurement agreement, reliability, and power to detect changes over time.
  
  
  METHODS
  Participants of the Dutch-Belgian lung cancer screening trial who underwent 3-month repeat CT for an indeterminate pulmonary nodule were included. AWT on CT was calculated by the square root of the wall area at a theoretical airway with an internal perimeter of 10mm (Pi10). The scan with the highest lung volume was labelled as the reference scan and the scan with the lowest lung volume was labelled as the comparison scan. Pi10 derived from the comparison scan was corrected by multiplying it with the ratio of CT lung volume of the comparison scan to CT lung volume on the reference scan. Agreement of uncorrected and corrected Pi10 was studied with the Bland-Altman method, reliability with intra-class correlation coefficients (ICC), and power to detect changes over time was calculated.
  
  
  RESULTS
  315 male participants were included. Limit of agreement and reliability for Pi10 was -0.61 to 0.57mm (ICC=0.87), which improved to -0.38 to 0.37mm (ICC=0.94) after correction for inspiration level. To detect a 15% change over 3 months, 71 subjects are needed for Pi10 and 26 subjects for Pi10 adjusted for inspiration level.
  
  
  CONCLUSIONS
  Correcting Pi10 for differences in inspiration level improves reliability, agreement, and power to detect changes over time.
authors: Department of Respiratory Medicine, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: e.pompe@umcutrecht.nl.
authors: Esther
authors: E
authors: Pompe
authors: Department of Radiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors: Eva M
authors: EM
authors: van Rikxoort
authors: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Onno M
authors: OM
authors: Mets
authors: Department of Radiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors: Jean-Paul
authors: JP
authors: Charbonnier
authors: Institute for Medical Image Computing, Fraunhofer MEVIS, Bremen, Germany.
authors: Jan-Martin
authors: JM
authors: Kuhnigk
authors: Department of Public Health, Erasmus Medical Center, Rotterdam, The Netherlands.
authors: Harry J
authors: HJ
authors: de Koning
authors: University of Groningen, University Medical Center Groningen, Groningen, Department of Radiology, The Netherlands.
authors: Matthijs
authors: M
authors: Oudkerk
authors: University of Groningen, University Medical Center Groningen, Groningen, Department of Radiology, The Netherlands; University of Groningen, University Medical Center Groningen, Center for Medical Imaging-North East Netherlands, Groningen, The Netherlands.
authors: Rozemarijn
authors: R
authors: Vliegenthart
authors: Department of Respiratory Medicine, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Pieter
authors: P
authors: Zanen
authors: Department of Respiratory Medicine, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Jan-Willem J
authors: JJ
authors: Lammers
authors: Department of Radiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors: Bram
authors: B
authors: van Ginneken
authors: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Pim A
authors: PA
authors: de Jong
authors: Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors: Firdaus A A
authors: FAA
authors: Mohamed Hoesein
mesh_terms: D001530:Belgium; D002986:Clinical Trials as Topic; D005500:Follow-Up Studies; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000503:physiopathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D015203:Reproducibility of Results; D012907:Smoking / Q000009:adverse effects; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014109:Total Lung Capacity
keywords: Airway wall thickness; Computed tomography; Follow-up; Lung volume; Reliability