title: Optimal threshold in CT quantification of emphysema.
abstract: OBJECTIVE
  To determine the optimal threshold by quantitatively assessing the extent of emphysema at the level of the entire lung and at the level of individual lobes using a large, diverse dataset of computed tomography (CT) examinations.
  
  
  METHODS
  This study comprises 573 chest CT examinations acquired from subjects with different levels of airway obstruction (222 none, 83 mild, 141 moderate, 63 severe and 64 very severe). The extent of emphysema was quantified using the percentage of the low attenuation area (LAA%) divided by the total lung or lobe volume(s). The correlations between the extent of emphysema, and pulmonary functions and the five-category classification were assessed using Pearson and Spearman's correlation coefficients, respectively. When quantifying emphysema using a density mask, a wide range of thresholds from -850 to -1,000 HU were used.
  
  
  RESULTS
  The highest correlations of LAA% with the five-category classification and PFT measures ranged from -925 to -965 HU for each individual lobe and the entire lung. However, the differences between the highest correlations and those obtained at -950 HU are relatively small.
  
  
  CONCLUSIONS
  Although there are variations in the optimal cut-off thresholds for individual lobes, the single threshold of -950 HU is still an acceptable threshold for density-based emphysema quantification.
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Wang
authors.forename: Suicheng
authors.initials: S
authors.lastname: Gu
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Leader
authors.forename: Shinjini
authors.initials: S
authors.lastname: Kundu
authors.forename: John R
authors.initials: JR
authors.lastname: Tedrow
authors.forename: Frank C
authors.initials: FC
authors.lastname: Sciurba
authors.forename: David
authors.initials: D
authors.lastname: Gur
authors.forename: Jill M
authors.initials: JM
authors.lastname: Siegfried
authors.forename: Jiantao
authors.initials: J
authors.lastname: Pu
mesh_terms: D015984:Causality; D015897:Comorbidity; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010414:Pennsylvania / Q000453:epidemiology; D015995:Prevalence; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*