title: Comparison of standard- and low-radiation-dose CT for quantification of emphysema.
abstract: OBJECTIVE
  This study was performed to compare standard- and low-radiation-dose techniques in the CT quantification of emphysema.
  
  
  METHODS
  The study population consisted of 36 men and 20 women who were current or former heavy smokers and underwent standard-dose (effective tube current, 100-250 mAs) chest CT at our institution within 6 months of having undergone low-dose (effective tube current, 30-60 mAs) chest CT. All CT scans were reconstructed at 5-mm slice thickness with a smooth filter. CT-measured lung volume, mean and median lung attenuation, and percentage of lung volume with attenuation lower than multiple thresholds (emphysema index values) were compared by Pearson correlation, two-tailed and paired Student's t tests, and regression analysis.
  
  
  RESULTS
  There were no significant differences in mean attenuation (-848 vs -846 H, p > 0.35) for the low dose and the standard dose or in median lung attenuation (-879 vs -878 H, p > 0.66). Low- and standard-dose emphysema indexes were correlated at all attenuation thresholds (r = 0.86-0.97). Mean emphysema indexes were higher on the low-dose scans, but the mean difference at all thresholds was less than 3%. The differences were significant (p < 0.05) only at the lower index thresholds, correlated with differences in lung volume (r < or = 0.86), and increased with greater differences in dose.
  
  
  CONCLUSIONS
  Low-dose technique has minimal effect on CT quantification of emphysema.
authors.affiliation: Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd., St. Louis, MO 63110, USA. gieradad@wustl.edu
authors.forename: David S
authors.initials: DS
authors.lastname: Gierada
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Pilgram
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Whiting
authors.forename: Cheng
authors.initials: C
authors.lastname: Hong
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bierhals
authors.forename: Jin Hwan
authors.initials: JH
authors.lastname: Kim
authors.forename: Kyongtae T
authors.initials: KT
authors.lastname: Bae
mesh_terms: D000368:Aged; D004307:Dose-Response Relationship, Radiation; D004646:Emphysema / Q000000981:diagnostic imaging*; D006801:Humans; D008875:Middle Aged; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D011874:Radiometry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*