title: Extrapolation in the analysis of lung aeration by computed tomography: a validation study.
abstract: BACKGROUND
  Computed tomography (CT) is considered the gold standard for quantification of global or regional lung aeration and lung mass. Quantitative CT, however, involves the exposure to ionizing radiation and requires manual image processing. We recently evaluated an extrapolation method which calculates quantitative CT parameters characterizing the entire lung from only 10 reference CT-slices thereby reducing radiation exposure and analysis time. We hypothesized that this extrapolation method could be further validated using CT-data from pigs and sheep, which have a different thoracic anatomy.
  
  
  METHODS
  We quantified volume and mass of the total lung and differently aerated lung compartments in 168 ovine and 55 porcine whole-lung CTs covering lung conditions from normal to gross deaeration. Extrapolated volume and mass parameters were compared to the respective values obtained by whole-lung analysis. We also tested the accuracy of extrapolation for all possible numbers of CT slices between 15 and 5. Bias and limits of agreement (LOA) were analyzed by the Bland-Altman method.
  
  
  RESULTS
  For extrapolation from 10 reference slices, bias (LOA) for the total lung volume and mass of sheep were 18.4 (-57.2 to 94.0) ml and 4.2 (-21.8 to 30.2) grams, respectively. The corresponding bias (LOA) values for pigs were 5.1 (-55.2 to 65.3) ml and 1.6 (-32.9 to 36.2) grams, respectively. All bias values for differently aerated lung compartments were below 1% of the total lung volume or mass and the LOA never exceeded ± 2.5%. Bias values diverged from zero and the LOA became considerably wider when less than 10 reference slices were used.
  
  
  CONCLUSIONS
  The extrapolation method appears robust against variations in thoracic anatomy, which further supports its accuracy and potential usefulness for clinical and experimental application of quantitative CT.
authors: Department of Anesthesiology and Intensive Care Medicine, University Hospital Leipzig, Liebigstrasse 20, D-04103 Leipzig, Germany. andreas.reske@medizin.uni-leipzig.de
authors: Andreas W
authors: AW
authors: Reske
authors: Anna
authors: A
authors: Rau
authors: Alexander P
authors: AP
authors: Reske
authors: Manja
authors: M
authors: Koziol
authors: Beate
authors: B
authors: Gottwald
authors: Michaele
authors: M
authors: Alef
authors: Jean-Claude
authors: JC
authors: Ionita
authors: Peter M
authors: PM
authors: Spieth
authors: Pierre
authors: P
authors: Hepp
authors: Matthias
authors: M
authors: Seiwerts
authors: Alessandro
authors: A
authors: Beda
authors: Silvia
authors: S
authors: Born
authors: Gerik
authors: G
authors: Scheuermann
authors: Marcelo B P
authors: MB
authors: Amato
authors: Hermann
authors: H
authors: Wrigge
mesh_terms: D000818:Animals; D008168:Lung / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology; D009929:Organ Size; D012756:Sheep; D013552:Swine; D014057:Tomography, X-Ray Computed