title: [Effects of differences in head holder on image quality and radiation dose in head CT].
abstract: OBJECTIVE
  For emergency or pediatric head CT scans, a simplified pillow made of hard sponge instead of a dedicated head holder may be used if it is difficult to immobilize the head. However, the radiation dose when using a simplified head holder may be increased due to radiation absorption by the patient couch if the automatic exposure control (AEC) system is used. In this phantom study, we compared the radiation dose delivered when using a dedicated and a simplified head holder.
  
  
  METHODS
  We used a dedicated-type and a pillow-type head holder made of hard sponge (simplified head holder). We placed a 20 cm-diameter cylindrical phantom made of water-equivalent material and an anthropomorphic head phantom in the head holders and then scanned them five times with a 64-detector CT scanner (VCT, GE Healthcare). We performed step-and-shoot and helical scanning with AEC; the noise index was set to 2.8. We measured the radiation dose using fluorescent glass dosimeters in the head phantom and the image noise at five sites in the cylindrical phantom. All values were averaged.
  
  
  RESULTS
  With step-and-shoot scans, the mean image noise with the dedicated and the simplified head holder was 3.30 ± 0.05 [SD] and 3.20 ± 0.05, respectively. With helical scans they were 3.00 ± 0.09 and 2.88 ± 0.03, respectively. There was no statistically significant difference (p = 0.02 and 0.04, Student's t-test). The radiation doses with the dedicated and the simplified head holder were 58.6 and 70.4 mGy, respectively, for step-and-shoot scanning and 41.8 and 49.0 mGy, respectively, for helical scanning. The doses were thus significantly higher with the simplified head holder for both step-and-shoot and helical scanning (p < 0.01 and < 0.01).
  
  
  CONCLUSIONS
  We recommend the use of a dedicated head holder for head scanning with AEC since the radiation dose was lower than with the simplified head holder.
authors.affiliation: Department of Diagnostic Radiology, Hiroshima University.
authors.forename: Kazushi
authors.initials: K
authors.lastname: Yokomachi
authors.forename: Eiji
authors.initials: E
authors.lastname: Nishimaru
authors.forename: Chikako
authors.initials: C
authors.lastname: Fujioka
authors.forename: Masao
authors.initials: M
authors.lastname: Kiguchi
authors.forename: Minoru
authors.initials: M
authors.lastname: Ishifuro
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Funama
authors.forename: Kazuo
authors.initials: K
authors.lastname: Awai
mesh_terms: D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D011829:Radiation Dosage; D011877:Radionuclide Imaging; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*