Effects of Differences in Head Holder on Image Quality and Radiation Dose in Head CT

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  • Yokomachi Kazushi
    Department of Diagnostic Radiology, Hiroshima University Department of Diagnostic Radiology, Institute and Graduate School of Biomedical Sciences, Hiroshima University
  • Nishimaru Eiji
    Department of Diagnostic Radiology, Hiroshima University
  • Fujioka Chikako
    Department of Diagnostic Radiology, Hiroshima University
  • Kiguchi Masao
    Department of Diagnostic Radiology, Hiroshima University
  • Ishifuro Minoru
    Department of Diagnostic Radiology, Hiroshima University
  • Funama Yoshinori
    Department of Medical Physics, Faculty of Life Sciences, Kumamoto University
  • Awai Kazuo
    Department of Diagnostic Radiology, Institute and Graduate School of Biomedical Sciences, Hiroshima University

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Other Title
  • 頭部CT撮影における頭部固定具が画質と線量に及ぼす影響
  • 臨床技術 頭部CT撮影における頭部固定具が画質と線量に及ぼす影響
  • リンショウ ギジュツ トウブ CT サツエイ ニ オケル トウブ コテイグ ガ ガシツ ト センリョウ ニ オヨボス エイキョウ

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Purpose: 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. Materials and 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). Conclusion: 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.

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