CT低剂量研究中扫描参数的前瞻性设计

Explore of Design of Parameters for Clinical Research Trials of Low-dose CT

目的综合一些影响CT低剂量扫描的因素，前瞻性设计CT低剂量临床研究中试验扫描参数。方法①以kV为120kV，层厚10nun，每转曝光时间10s，20—300mA．以10mA为间隔进行头部体模测试扫描，分析噪声水平以及图像质量，获得符合诊断要求的低荆量参数作为参照曝光条件。②参照X线对数法原理，将头部体模测试作参照曝光条件换算成点值系数，③根据人体各部厚度差异、骨组织量差异、靶器官组织密度对比差异适当修正曝光点数；④不同个体以体型划分修正曝光点数：小儿以不同年龄段适当修正曝光点数。⑤技术参数适当修正＇层厚为薄层扫描进行曝光点数补偿。结果1、分析噪声水平与体模图像质量，100mAs可以满足颅脑的诊断要求．但噪声增大；2、部分部位点值系数与扫描条件：成人颅脑42个点，120KV，100mAs，或140KV，70mAs；婴儿头颅395个点，120KV，60mAs：标准成人肺部38个点，120KV，40mAs；标准成人肝脏42个点，120KV，100mAs；标准体型泌尿系统结石病人40个点，120KV，60mAs。结论以点值系数形式综合各影响图像质量因素．根据不同实验目的．缩小CT低剂量扫描临床研究参数设置区间有一定价值。

Objective Integrated low-dose CT scan of the impact factors, Forward-looking design with low-dose CT scanning parameters of clinical research trials. Methods@Setting parameters of scanning of head phantom test were as followed： kV： 120kV; Slice thickness： 10ram; Exposure time per turn： 1.0s; 20-300mA （as 10mA the test interval for scanning）. Noise levels and image quality were analyzed to obtain the low-dose parameters met the diagnostic requirements as the reference exposure condition; ②The exposure conditions were converted into the forms of point and figure, and converted between the mAs and KV by the principle of X- ray logarithmic method;③With the head phantom test as the reference exposure condition, the nmnber of exposure point was corrected appropriately according to the thickness of different parts of human body, differences on the amount of bone tissue, differences on tissue density of target organs; ④The number of exposure point was corrected by the classification of body form to different individuals; And corrected appropriately according to different age group for the children; ⑤Technical parameters were corrected appropriately. The number of exposure point was compensated for thin layer scanning. Results ①In the analysis of noise levels and phantom image quality, 100mA met the diagnostic requirement of brain, but the noise increased; @Some parts of the point value of the coefficient and scanning conditions： The exposure value of adult brain was 42 points （120KV, 100mAs or 140KV, 70mAs）. The exposure value of baby skull was 39.5 points （120KV, 60mAs）. The exposure value of adult lung was 38 points （120KV, 40mAs）. The exposure value of adult liver was 42 poims （120KV, 100mAs）. The exposure value of patients with standard size and urinary stones was 40 points （120KV, 60mAs）. Conclusions Consolidate the factors affecting image quality in the form of points, Depending on the experimental purpose, low-dose CT scans to reduce the parameter range of clinical research have a certain value.