title: Variability in densitometric assessment of pulmonary emphysema with computed tomography.
abstract: OBJECTIVE
  The objectives of this study were to investigate whether computed tomography (CT) densitometry can be applied consistently in different centers; and to evaluate the reproducibility of densitometric quantification of emphysema by assessment of different sources of variation, ie, intersite, interscan and inter- and intraobserver variability, in comparison with intersubject variability.
  
  
  METHODS
  In 5 different hospitals, 119 patients with emphysema were scanned using standardized protocols. In each site, an observer performed a quantitative densitometric analysis (including blood recalibration) on the corresponding patient group (n=23-25) and one observer analyzed the entire group of 119 patients. After several months, the latter observer analyzed all data for a second time. Subsequently, different sources of variation were assessed by variance component analysis with and without volume correction of the data.
  
  
  RESULTS
  Inter- and intraobserver variability marginally contributes to the total variability (<0.001%). The interscan variability was 0.02% of the total variation after application of volume correction. The intersite variability was 48% as a result of one deviating CT scanner. Air recalibration normalized deviating air densities in CT scanners. Within sites, the intersubject variability ranged between 93% and 99% based on the analysis of 2 subsequent CT scans of the patients.
  
  
  CONCLUSIONS
  Almost all variability in the density measurement of emphysema originates from differences between scanners and from differences in severity of emphysema between patients. Lung densitometry with multislice CT scanners is a highly reproducible measurement, especially if corrected for lung volume, because this reduces interscan variability.
authors.affiliation: Division of Image Processing, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands, and the Department of Respiratory Medicine, Gentofte Hospital, Hellerup, Denmark. m.e.bakker@lumc.nl
authors.forename: M Els
authors.initials: ME
authors.lastname: Bakker
authors.forename: Jan
authors.initials: J
authors.lastname: Stolk
authors.forename: Hein
authors.initials: H
authors.lastname: Putter
authors.forename: Saher B
authors.initials: SB
authors.lastname: Shaker
authors.forename: David G
authors.initials: DG
authors.lastname: Parr
authors.forename: Eeva
authors.initials: E
authors.lastname: Piitulainen
authors.forename: Erich W
authors.initials: EW
authors.lastname: Russi
authors.forename: Asger
authors.initials: A
authors.lastname: Dirksen
authors.forename: Robert A
authors.initials: RA
authors.lastname: Stockley
authors.forename: Johan H C
authors.initials: JH
authors.lastname: Reiber
authors.forename: Berend C
authors.initials: BC
authors.lastname: Stoel
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods / Q000706:statistics & numerical data*; D000328:Adult; D000368:Aged; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000706:statistics & numerical data*