title: Effect of localizer radiograph on radiation dose associated with automatic exposure control: human cadaver and patient study.
abstract: OBJECTIVE
  To evaluate the effect of localizing radiograph on computed tomography (CT) radiation dose associated with automatic exposure control with a human cadaver and patient study.
  
  
  METHODS
  Institutional review board approved the study with a waiver of informed consent. Two chest CT image series with fixed tube current and combined longitudinal-angular automatic exposure control (AEC) were acquired in a human cadaver (64-year-old man) after each of the 8 combinations of localizer radiographs (anteroposterior [AP], AP lateral, AP-posteroanterior [PA], lateral AP, lateral PA, PA, PA-AP, and PA lateral). Applied effective milliampere second, volume CT dose index (CTDIvol) and image noise were recorded for all 24-image series. Volume CT dose indexes were also recorded in 20 patients undergoing chest and abdominal CT after PA and PA-lateral radiographs with the use of AEC. Data were analyzed using analysis of variance and linear correlation tests.
  
  
  RESULTS
  With AEC, the CTDIvol fluctuates with the number and projection of localizer radiographs (P < 0.0001). Lowest CTDIvol values are seen when 2 orthogonal localizer radiographs are acquired, whereas highest values are seen when single PA or AP-PA projection localizer radiographs are acquired for planning (P < 0.0001). In 20 patients, CT scanning with AEC after acquisition of 2 orthogonal projection localizer radiographs was associated with significant reduction in radiation dose compared to PA projection radiographs alone (P < 0.0001).
  
  
  CONCLUSIONS
  When scanning with AEC, acquisition of 2 orthogonal localizer radiographs is associated with lower CTDIvol compared to a single localizer radiograph.
authors.affiliation: From the *Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA; and †Department of Radiology, Ljubljana University Medical Center, Ljubljana, Slovenia.
authors.forename: Sarabjeet
authors.initials: S
authors.lastname: Singh
authors.forename: Dean
authors.initials: D
authors.lastname: Petrovic
authors.forename: Ethen
authors.initials: E
authors.lastname: Jamnik
authors.forename: Shima
authors.initials: S
authors.lastname: Aran
authors.forename: Sarvenaz
authors.initials: S
authors.lastname: Pourjabbar
authors.forename: Maggie L
authors.initials: ML
authors.lastname: Kave
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Bradley
authors.forename: Garry
authors.initials: G
authors.lastname: Choy
authors.forename: Mannudeep K
authors.initials: MK
authors.lastname: Kalra
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*