title: Optimizing radiation exposure for CT localizer radiographs.
abstract: BACKGROUND
  The trend towards submillisievert CT scans leads to a higher dose fraction of localizer radiographs in CT examinations. The already existing technical capabilities make dose optimization of localizer radiographs worthwhile. Modern CT scanners apply automatic exposure control (AEC) based on attenuation data in such a localizer. Therefore not only this aspect but also the detectability of anatomical landmarks in the localizer for the desired CT scan range adjustment needs to be considered.
  
  
  METHODS
  The effective dose of a head, chest, and abdomen-pelvis localizer radiograph with standard factory settings and user-optimized settings was determined using Monte Carlo simulations. CT examinations of an anthropomorphic phantom were performed using multiple sets of acquisition parameters for the localizer radiograph and the AEC for the subsequent helical CT scan. Anatomical landmarks were defined to assess the image quality of the localizer. CTDIvoland effective mAs per slice of the helical CT scan were recorded to examine the impact of localizer settings on a helical CT scan.
  
  
  RESULTS
  The dose of the localizer radiograph could be decreased by more than 90% while the image quality remained sufficient when selecting the lowest available settings (80kVp, 20mA, pa tube position). The tube position during localizer acquisition had a greater impact on the AEC than the reduction of tube voltage and tube current. Except for the use of a pa tube position, all changes of acquisition parameters for the localizer resulted in a decreased total radiation exposure.
  
  
  CONCLUSIONS
  A dose reduction of CT localizer radiograph is necessary and possible. In the examined CT system there was no negative impact on the modulated helical CT scan when the lowest tube voltage and tube current were used for the localizer.
authors.affiliation: Institute of Medical Physics and Radiation Protection-IMPS, University of Applied Sciences, Gießen, Germany. Electronic address: evi.bohrer@web.de.
authors.forename: Evelyn
authors.initials: E
authors.lastname: Bohrer
authors.affiliation: Department of Radiology, Justus-Liebig University, University Hospital Gießen, Gießen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schäfer
authors.affiliation: Institute of Medical Physics and Radiation Protection-IMPS, University of Applied Sciences, Gießen, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Mäder
authors.affiliation: Department of Diagnostic and Interventional Radiology, Technische Universität München, Germany.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Noël
authors.affiliation: Department of Radiology, Justus-Liebig University, University Hospital Gießen, Gießen, Germany.
authors.forename: Gabriele A
authors.initials: GA
authors.lastname: Krombach
authors.affiliation: Institute of Medical Physics and Radiation Protection-IMPS, University of Applied Sciences, Gießen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Fiebich
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D010388:Pelvis / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000592:standards*; D013909:Thorax / Q000000981:diagnostic imaging; D015898:Tomography Scanners, X-Ray Computed / Q000706:statistics & numerical data*; D014057:Tomography, X-Ray Computed / Q000592:standards*
keywords: Automatic exposure control; Belichtungsautomatik; Computed tomography; Computertomographie; Dose reduction; Dosisreduzierung; Localizer radiograph; Monte Carlo simulation; Monte-Carlo-Simulation; Röhrenstrommodulation; Tube current modulation; Übersichtsaufnahme