Coursey Courtney, Frush Donald P, Yoshizumi Terry, Toncheva Greta, Nguyen Giao, Greenberg S Bruce
Division of Pediatric Radiology, Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC 27710, USA.
AJR Am J Roentgenol. 2008 Jan;190(1):W54-61. doi: 10.2214/AJR.07.2017.
The purpose of our study was to assess the effect on radiation dose and image noise during pediatric chest 16-MDCT using automatic tube current modulation and bismuth breast shields.
Age-based chest 16-MDCT was performed on an anthropomorphic phantom representing a 5-year-old child. Two scans were obtained in each of four sequences: first, without a shield; second, with a 2-ply bismuth shield; third, using automatic tube current modulation with a scout image obtained after placement of the shield; and fourth, using automatic tube current modulation with a scout image obtained before placement of the shield. Metal oxide semiconductor field effect transistor technology was used to measure the radiation dose in 20 organ locations. Effective dose was estimated using the console dose-length product. Noise was measured by recording the SD of Hounsfield units in identical regions of interest.
The bismuth breast shield reduced the dose to the breast by 26%. Shielding and automatic tube current modulation reduced the breast dose by 52%. Multiple organ doses were lowest when the shield was placed after the scout radiograph had been obtained. When the shield was placed after the scout image was obtained, the mean noise in the range of shielding increased from 11.4 to 13.1 H (superior mediastinum) and from 10.0 to 12.8 H (heart) (p < 0.01). Increased noise, however, was near the target noise index (measured in SD of Hounsfield units) of 12.0 H (SD). Using automatic tube current modulation, the effective dose was reduced by 35% when the shield was placed after the scout and by 20% when the shield was present in the scout.
The greatest dose reduction is achieved by placing the shield after obtaining the scout image to avoid Auto mA compensation due to density of shield. With this technique, image noise increased but remained close to the target noise index.
本研究旨在评估使用自动管电流调制和铋制乳房防护板对儿童胸部16层螺旋CT辐射剂量和图像噪声的影响。
在一个模拟5岁儿童的人体模型上进行基于年龄的胸部16层螺旋CT扫描。四个序列中的每个序列均进行两次扫描：第一次，不使用防护板；第二次，使用双层铋制防护板；第三次，在放置防护板后获取定位像并使用自动管电流调制；第四次，在放置防护板前获取定位像并使用自动管电流调制。采用金属氧化物半导体场效应晶体管技术测量20个器官部位的辐射剂量。使用控制台剂量长度乘积估算有效剂量。通过记录感兴趣的相同区域内亨氏单位的标准差来测量噪声。
铋制乳房防护板使乳房剂量降低了26%。防护板和自动管电流调制使乳房剂量降低了52%。当在获取定位射线照片后放置防护板时，多个器官的剂量最低。当在获取定位像后放置防护板时，防护范围内的平均噪声从11.4 H（上纵隔）增加到13.1 H，从10.0 H（心脏）增加到12.8 H（p < 0.01）。然而，增加的噪声接近目标噪声指数（以亨氏单位标准差测量）12.0 H（标准差）。使用自动管电流调制时，在获取定位像后放置防护板时有效剂量降低了35%，在定位像中存在防护板时有效剂量降低了20%。
在获取定位像后放置防护板可实现最大程度的剂量降低，以避免因防护板密度导致的自动毫安补偿。采用该技术时，图像噪声增加但仍接近目标噪声指数。
