Liang Baohui, Fu Yajun, Cao Mingna
School of Medical Imaging, Bengbu Medical College, Bengbu Medical College, Bengbu 233030, China.
Department of Radiology, First Affiliated Hospital, Bengbu Medical College, Bengbu 233030, China.
Nan Fang Yi Ke Da Xue Xue Bao. 2020 Jun 30;40(6):799-805. doi: 10.12122/j.issn.1673-4254.2020.06.05.
To explore a method for calculating water equivalent diameter () based on localizer CT images for calculation of the size specific dose estimates (SSDE).GE Revolution CT and LightSpeed VCT were used to scan CT dose index phantoms 16 cm and 32 cm in diameter at the tube voltages of 80, 100 and 120 kV to obtain the axial image and anteroposterior localizer radiograph. According to the definition of CT Hounsfield unit, the axial images were used to calculate the conversion factors that convert the phantom thickness to water equivalent thickness. The gray value of the localizer radiograph and the water equivalent thickness were calibrated with a linear equation, and the parameters of the calibration were used to calculate the water equivalent thickness. The method was verified using 2 CT dose index phantoms and in 22 patients undergoing chest and abdominal CT examination.Comparison of the water equivalent diameter () based on the localizer radiograph and axial image of the 2 phantoms showed that the percentage difference between from the axial images and from the localizer radiograph was below 3%. The trend of variations with location in the two methods was sonsistent. The difference in in intermediate region of interest between the axial image and the localizer radiograph from the 22 patients was below 6.6%. With the mean in the ROI, the maximum percentage difference was 7.5%.Calibration of the gray value of the localizer radiograph and the water equivalent thickness using the axial image and localizer radiograph of CT dose index phantoms allows quick calculation of the SSDE based on the parameters of calibration.
探索一种基于定位器CT图像计算水等效直径（）的方法，用于计算大小特定剂量估计值（SSDE）。使用GE Revolution CT和LightSpeed VCT在80、100和120 kV的管电压下扫描直径为16 cm和32 cm的CT剂量指数体模，以获取轴向图像和前后定位器射线照片。根据CT亨氏单位的定义，利用轴向图像计算将体模厚度转换为水等效厚度的转换因子。用线性方程对定位器射线照片的灰度值和水等效厚度进行校准，并使用校准参数计算水等效厚度。使用2个CT剂量指数体模和22例接受胸部和腹部CT检查的患者对该方法进行验证。比较基于2个体模的定位器射线照片和轴向图像的水等效直径（），结果显示轴向图像的与定位器射线照片的之间的百分比差异低于3%。两种方法中随位置变化的趋势一致。22例患者轴向图像和定位器射线照片在感兴趣中间区域的差异低于6.6%。在感兴趣区域的平均值下，最大百分比差异为7.5%。利用CT剂量指数体模的轴向图像和定位器射线照片对定位器射线照片的灰度值和水等效厚度进行校准，可基于校准参数快速计算SSDE。
