Yoshiura Takayuki, Masuda Takanori, Matsumoto Yoriaki, Sato Tomoyasu, Kikuhara Yukari, Kobayashi Yukie, Ishibashi Tooru, Oku Takayuki, Funama Yoshinori
Department of Medical Technology, Tsuchiya General Hospital.
Department of Medical Physics, Faculty of Life Sciences, Kumamoto University.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2020;76(8):802-807. doi: 10.6009/jjrt.2020_JSRT_76.8.802.
To compare the radiation dose and image quality using the conventional method for performing the front and side scout view and a new method for performing the side scout view, and then correct the table height at the scan isocenter and perform the front scout view.
We retrospectively analyzed fifty-six children who had underwent computed tomography (CT) examination between June 2014 and August 2018. We divided them into two groups. The conventional method was performed in 3 steps: 1. obtain the front scout view, 2. obtain the side scout view, and 3. main scan. Without table position correction, the new method was performed in 4 steps: 1. obtain the side scout view with table position correction, 2. patient correction at the scan isocenter, 3. obtain the front scout view, and 4. main scan. We used a 64-row CT scanner (LightSpeed VCT; GE Healthcare). Scan parameters were tube voltage 80 kV, automatic tube current modulation, noise index 16, slice thickness 5 mm, rotation time 0.4 s/rot, helical pitch 1.375, and reconstruction kernel standard. We recorded the volume dose index (CTDI) and dose length product (DLP) on the CT console and compared the radiation dose in both groups. To evaluate the image quality in both groups, the mean standard deviation of CT number (SD value) was measured within an approximately 5-10 mm circular region of interest. We measured the scan length of the pediatric patient and accuracy of pediatric positioning at the CT examination. A grid was displayed on the CT axial image, taken to evaluate the error from the scan isocenter during alignment, and the error between the height of half the body thickness and the scan isocenter was recorded.
Scan lengths were median (minimum-maximum) values of 16.2 cm (10.8-21.5 cm) and 16.8 cm (11.5-23.0 cm). There were no significant differences in the scan length between both groups (p=0.47). In the group with table position correction, median (minimum-maximum) values for CTDI, DLP and SD value were 0.40 mGy (0.3-0.7 mGy), 7.6 mGy･cm (4.4-11.5 mGy･cm), and 24.0 HU (18.3-37.5 HU), respectively. In the group without the table position correction, median (minimum-maximum) values for CTDI, DLP and SD value were 0.40 mGy (0.3-0.6 mGy), 7.1 mGy･cm (4.2-13.8 mGy･cm), and 20.3 HU (11.3-28.8 HU), respectively. There were no significant differences in the CTDI and DLP values between both groups (p=0.42 and p=0.44, respectively); however, there were significant differences in the SD value in both groups (p<0.01). The error for the accuracy of pediatric positioning was 0 mm (0 to 0 mm) and 10 mm (-16 to+59 mm) using the conventional and new methods (p<0.01), respectively.
It was suggested that the optimum image could be obtained during CT scan with automatic tube current modulation by using this potential new method (1. obtain the side scout view, 2. patient correction at the scan isocenter, 3. obtain the side scout view, and 4. main scan).
比较使用传统方法进行前后位定位像和侧位定位像以及一种新的侧位定位像方法时的辐射剂量和图像质量，然后在扫描等中心处校正检查床高度并进行前后位定位像。
我们回顾性分析了2014年6月至2018年8月间接受计算机断层扫描（CT）检查的56名儿童。我们将他们分为两组。传统方法分三步进行：1. 获取前后位定位像；2. 获取侧位定位像；3. 进行主扫描。新方法在不校正检查床位置的情况下分四步进行：1. 校正检查床位置后获取侧位定位像；2. 在扫描等中心处对患者进行校正；3. 获取前后位定位像；4. 进行主扫描。我们使用一台64排CT扫描仪（LightSpeed VCT；GE医疗）。扫描参数为管电压80 kV、自动管电流调制、噪声指数16、层厚5 mm、旋转时间0.4 s/rot、螺距1.375以及标准重建核。我们在CT控制台记录容积剂量指数（CTDI）和剂量长度乘积（DLP），并比较两组的辐射剂量。为评估两组的图像质量，在一个约5 - 10 mm的圆形感兴趣区内测量CT值的平均标准差（SD值）。我们测量了儿科患者的扫描长度以及CT检查时儿科定位的准确性。在CT轴位图像上显示一个网格，用于评估对齐过程中与扫描等中心的误差，并记录身体厚度一半高度与扫描等中心之间的误差。
扫描长度的中位数（最小值 - 最大值）分别为16.2 cm（10.8 - 21.5 cm）和16.8 cm（11.5 - 23.0 cm）。两组之间的扫描长度无显著差异（p = 0.47）。在进行检查床位置校正的组中，CTDI、DLP和SD值的中位数（最小值 - 最大值）分别为0.40 mGy（0.3 - 0.7 mGy）、7.6 mGy·cm（4.4 - 11.5 mGy·cm）和24.0 HU（18.3 - 37.5 HU）。在未进行检查床位置校正的组中，CTDI、DLP和SD值的中位数（最小值 - 最大值）分别为0.40 mGy（0.3 - 0.6 mGy）、7.1 mGy·cm（4.
