title: Air trapping: comparison of standard-dose and simulated low-dose thin-section CT techniques.
abstract: OBJECTIVE
  To prospectively investigate the effect of radiation dose reduction on the visual quantification of air trapping at expiratory thin-section computed tomography (CT).
  
  
  METHODS
  In this ethical committee-approved study, 27 lung transplant recipients (12 women, 15 men; mean age, 54 years +/- 2 [standard error of the mean]) underwent expiratory thin-section CT at 140 kVp and 80 mAs (effective). All patients gave written informed consent. Dose reduction corresponding to 60, 40, and 20 mAs (effective) was simulated. The extent of air trapping in both original and dose-reduced studies was scored by three independent readers. The effects of tube current-time product, reader, reading session, and body mass index on average air trapping scores were assessed with analysis of variance. Agreements between and within observers were assessed with a weighted kappa statistic. Subjective scores for diagnostic confidence were attributed (3 = high, 2 = medium, 1 = low), and their means were calculated for each tube current-time product value.
  
  
  RESULTS
  No significant effect on average air trapping scores as a result of tube current-time product (P = .222), reader (P = .217), reading session (P = .705), or body mass index (P = .505) could be detected. At 80 mAs, agreement between readers was excellent; agreement decreased to good or moderate at lower tube current settings. Agreement within readers decreased with a decrease in dose but remained good even at 20 mAs. Confidence also decreased, with mean scores decreasing from 2.33 +/- 0.73 (standard deviation) to 1.04 +/- 0.19 when dose decreased.
  
  
  CONCLUSIONS
  At 140 kVp, the tube current-time product can be reduced from 80 to 20 mAs without impairing the visual quantification of air trapping at expiratory thin-section CT and with acceptable decreases in agreement between and within readers and in reader confidence.
authors.affiliation: Department of Radiology, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. alexander.bankier@meduniwien.ac.at
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Bankier
authors.forename: Cornelia
authors.initials: C
authors.lastname: Schaefer-Prokop
authors.forename: Viviane
authors.initials: V
authors.lastname: De Maertelaer
authors.forename: Denis
authors.initials: D
authors.lastname: Tack
authors.forename: Peter
authors.initials: P
authors.lastname: Jaksch
authors.forename: Walter
authors.initials: W
authors.lastname: Klepetko
authors.forename: Pierre Alain
authors.initials: PA
authors.lastname: Gevenois
mesh_terms: D000328:Adult; D000368:Aged; D001988:Bronchiolitis / Q000000981:diagnostic imaging* / Q000209:etiology*; D005260:Female; D006801:Humans; D016040:Lung Transplantation / Q000009:adverse effects* / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed