title: Improved correlation between CT emphysema quantification and pulmonary function test by density correction of volumetric CT data based on air and aortic density.
abstract: OBJECTIVE
  To determine the improvement of emphysema quantification with density correction and to determine the optimal site to use for air density correction on volumetric computed tomography (CT).
  
  
  METHODS
  Seventy-eight CT scans of COPD patients (GOLD II-IV, smoking history 39.2±25.3 pack-years) were obtained from several single-vendor 16-MDCT scanners. After density measurement of aorta, tracheal- and external air, volumetric CT density correction was conducted (two reference values: air, -1,000 HU/blood, +50 HU). Using in-house software, emphysema index (EI) and mean lung density (MLD) were calculated. Differences in air densities, MLD and EI prior to and after density correction were evaluated (paired t-test). Correlation between those parameters and FEV1 and FEV1/FVC were compared (age- and sex adjusted partial correlation analysis).
  
  
  RESULTS
  Measured densities (HU) of tracheal- and external air differed significantly (-990 ± 14, -1016 ± 9, P<0.001). MLD and EI on original CT data, after density correction using tracheal- and external air also differed significantly (MLD: -874.9 ± 27.6 vs. -882.3 ± 24.9 vs. -860.5 ± 26.6; EI: 16.8 ± 13.4 vs. 21.1 ± 14.5 vs. 9.7 ± 10.5, respectively, P<0.001). The correlation coefficients between CT quantification indices and FEV1, and FEV1/FVC increased after density correction. The tracheal air correction showed better results than the external air correction.
  
  
  CONCLUSIONS
  Density correction of volumetric CT data can improve correlations of emphysema quantification and PFT.
authors.affiliation: Department of Radiology, Chungnam National University Hospital, Chungnam National University School of Medicine, Republic of Korea.
authors.forename: Song Soo
authors.initials: SS
authors.lastname: Kim
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Republic of Korea. Electronic address: seojb@amc.seoul.kr.
authors.forename: Joon Beom
authors.initials: JB
authors.lastname: Seo
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Republic of Korea.
authors.forename: Namkug
authors.initials: N
authors.lastname: Kim
authors.affiliation: Department of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Republic of Korea.
authors.forename: Eun Jin
authors.initials: EJ
authors.lastname: Chae
authors.affiliation: Department of Radiology, Kyung Hee University Hospital at Gangdong, Republic of Korea.
authors.forename: Young Kyung
authors.initials: YK
authors.lastname: Lee
authors.affiliation: Division of Pulmonology, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Republic of Korea.
authors.forename: Yeon Mok
authors.initials: YM
authors.lastname: Oh
authors.affiliation: Division of Pulmonology, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Republic of Korea.
authors.forename: Sang Do
authors.initials: SD
authors.lastname: Lee
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000388:Air / Q000032:analysis*; D000465:Algorithms; D001027:Aortography / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000000981:diagnostic imaging*; D011656:Pulmonary Emphysema / Q000175:diagnosis* / Q000209:etiology; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012129:Respiratory Function Tests / Q000379:methods*; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed / Q000379:methods*