title: Reduced-dose chest CT with 3D automatic exposure control vs. standard chest CT: quantitative assessment of emphysematous changes in smokers' lung parenchyma.
abstract: OBJECTIVE
  To determine the capability of reduced-dose chest CT with three-dimensional (3D) automatic exposure control (AEC) on quantitative assessment of emphysematous change in smoker' lung parenchyma, compared to standard chest CT.
  
  
  METHODS
  Twenty consecutive smoker patients (mean age 62.8 years) underwent CT examinations using a standard protocol (150 mAs) and a protocol with 3D-AEC. In this study, the targeted standard deviations number was set to 160. For quantitative assessment of emphysematous change in lung parenchyma in each subject using the standard protocol, a percentage of voxels less than -950 HU in the lung (%LAA(-950)) was calculated. The 3D-AEC protocol's %LAA was computed from of voxel percentages under selected threshold CT value. The differences of radiation doses between these two protocols were evaluated, and %LAAs(-950) was compared with the 3D-AEC protocol %LAAs.
  
  
  RESULTS
  Mean dose length products were 780.2 ± 145.5 mGy cm (standard protocol), and 192.0 ± 95.9 (3D-AEC protocol). There was significant difference between them (paired Student's t test, p<0.00001). Meanwhile, only setting -960 HU yielded no significant difference (paired Student's t test, p=0.32) between %LAAs(-950) and 3D-AEC protocol %LAAs. In adopting the feasible threshold CT values of the 3D-AEC protocol, the 3D-AEC protocol %LAAs were significantly correlated with %LAAs(-950) (r = 0.98, p<0.001) and limits of agreement from Bland-Altman analysis was 0.52 ± 4.3%.
  
  
  CONCLUSIONS
  Changing threshold CT values demonstrated that reduced-dose chest CT with 3D-AEC can substitute for the standard protocol in assessments of emphysematous change in smoker' lung parenchyma.
authors.affiliation: Department of Radiology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, Hyogo, Japan. hkoyama@med.kobe-u.ac.jp
authors.forename: Hisanobu
authors.initials: H
authors.lastname: Koyama
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Ohno
authors.forename: Youichi
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Keiko
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Onishi
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takenaka
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yoshikawa
authors.forename: Mizuho
authors.initials: M
authors.lastname: Nishio
authors.forename: Sumiaki
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Kenya
authors.initials: K
authors.lastname: Murase
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nishimura
authors.forename: Kazuro
authors.initials: K
authors.lastname: Sugimura
mesh_terms: D004646:Emphysema / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D013902:Radiography, Thoracic; D012907:Smoking / Q000009:adverse effects*; D014057:Tomography, X-Ray Computed / Q000379:methods*