降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。

Optimizing scan parameters to reduce the radiation dose on 16 slices CT examination of children

Objective To demonstrate the relationship of scan parameters (mAs,kVp) with radiation dose and image noise, then to help to adjust the scanning parameters in reasonable image noise level for imaging children, to formulate appropriate multislice CT scan protocols for pediatric patients on limited radiation dose. Methods The CTDI(computed tomography dose index) was obtained at both 1.0 cm below surface and the center with 16 cm and 32 cm diameter CT dose index phantoms and a standard 100 mm CT pencil ion chamber in the different acquisition parameters (mAs and kVp). The image|noise values in 20 cm water phantom with 2 mm×5 mm thickness were obtained as a standard of image quality. On the basis of noise equivalent CT image, we implemented a pediatric protocol table for daily children CT imaging in order to reduce the radiation dose for pediatric patients. Results The CTDI values were directly proportional to the mAs in same kVp. Higher kVp had higher CTDI. If other technical factors were kept constant, CTDI values on 16 cm phantom was 58% higher than that on 32 cm phantom. The displayed dose in CT scanner was higher than the dose that was actually measured. At constant kVp, the mAs reduced the image noise nonlinearly. Conclusion An acceptable image quality can be achieved for pediatric patients by reducing the scanning technique parameters to 10%|85% to those used for adults.