Yokomachi Kazushi, Nishimaru Eiji, Fujioka Chikako, Kiguchi Masao, Ishifuro Minoru, Funama Yoshinori, Awai Kazuo
Department of Diagnostic Radiology, Hiroshima University.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2014 Oct;70(10):1166-72. doi: 10.6009/jjrt.2014_jsrt_70.10.1166.
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.
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.
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).
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.
对于急诊或儿科头部CT扫描，如果难以固定头部，可使用由硬海绵制成的简易枕头代替专用头部固定器。然而，如果使用自动曝光控制（AEC）系统，使用简易头部固定器时的辐射剂量可能会因患者检查床的辐射吸收而增加。在本体模研究中，我们比较了使用专用头部固定器和简易头部固定器时的辐射剂量。
我们使用了一个专用型头部固定器和一个由硬海绵制成的枕头型头部固定器（简易头部固定器）。我们将一个由水等效材料制成的直径20 cm的圆柱形体模和一个仿真人头体模放置在头部固定器中，然后用64排CT扫描仪（VCT，GE医疗）对它们进行五次扫描。我们使用AEC进行步进和螺旋扫描；噪声指数设置为2.8。我们使用荧光玻璃剂量计测量人头体模中的辐射剂量，并测量圆柱形体模中五个部位的图像噪声。所有值均取平均值。
在步进扫描中，专用头部固定器和简易头部固定器的平均图像噪声分别为3.30±0.05[标准差]和3.20±0.05。在螺旋扫描中，它们分别为3.00±0.09和2.88±0.03。没有统计学上的显著差异（p = 0.02和0.04，学生t检验）。对于步进扫描，专用头部固定器和简易头部固定器的辐射剂量分别为58.6和70.4 mGy，对于螺旋扫描，分别为41.8和49.0 mGy。因此，对于步进和螺旋扫描，简易头部固定器的剂量均显著更高（p < 0.01和< 0.01）。
我们建议在使用AEC进行头部扫描时使用专用头部固定器，因为其辐射剂量低于简易头部固定器。
