不同机型PET-CT中CT采集条件与受检者有效剂量关系的研究

摘要

Objective:To study on the relationship between collecting conditions of CT and effective dose for subject in different models of PET-CT in order to provide a reference for the determination of the optimal collecting scheme that could suit different models of PET-CT.Methods: Two models of PET-CT which included GE Discovery ST-16 PET-CT and GE Discovery Elite were adopted as experiment equipment, and the agent dosage of CT part obtained from simulation experiment of anthropomorphic phantom(Model RS-550). Collecting conditions of CT included: (1)auto-tube current was 30-250 mA, noise index(NI) was 8-30,the interval was 2, and the other conditions used actually clinical collecting conditions: tube voltage was 120kV, and pitches respectively were1.75 for ST-16 and 0.984 for Elite, and rotation speeds respectively were 0.8s for ST-16 and 0.5s for Elite. (2)both of low limits of auto tube current of the two models of PET-CT were 30mA, and range of high limit was from 210 to 350mA, and the interval was 20mA, and NI was 14, and the other conditions were the same with above those in (1). (3)Pitch: ST-16 respectively chose 1.75, 1.375 and 0.938, and Elite respectively chose 1.375 and 0.984, and tube voltage was 120kV, and auto tube current was 30-250mA, and NI was 14, and rotation speed of ST-16 and Elite were respectively were 0.8s and 0.5s. (4)rotation speed of two models of PET-CT respectively chose 0.5s, 0.8s and 1.0s, and tube voltage chose 120kV, and auto tube current chose 30-250mA, and NI was 14, and pitches of ST-16 and Elite respectively were 1.75 and 0.984. The above conditions were respectively was applied to scan anthropomorphic phantom(Model RS-550) through simulated step-scan method of clinical PET-CT, and then the dose-length product(DLP) under different conditions were recorded and the effective dose(EDCT)was calculated.Result: 1)When the automatic tube current, Pitch and rotation speed were unchanged, the effective doses caused by CT part of the both of two models of PET-CTs were decreased with the increasing of NI, and the decreasing amplitude of ST-16 was larger than that of Elite. 2)When the NI, Pitch and rotation speed were unchanged, the EDct of the two models of PET-CTs was increased with the increasing of automatic tube current, and the increasing amplitude of ST-16was larger than that of Elite. 3)When the automatic tube current, NI and rotation speed were unchanged, the EDct of the two models of PET-CTs was decreased with the increasing of Pitch. 4)When the automatic tube current, NI and Pitch were unchanged, the effective dose was increased with the increasing of rotation speed. 5)Under different scanning condition, the totally effective dose of the two models of PET-CTs was in the range of 4.93mSv and 24.00mSv. 6)Under the clinical scanning condition, the effective dose of all of the patients who received Elite were lower than that of ST-16.Conclusion: Different model of PET-CT commonly chooses different scanning condition in clinical application, therefore, the radiation dose of scanning in different condition exists obviously difference. In clinical application, the scanning condition should choose the optimal collecting scheme of different model by combining with the clinical requirement.%目的:研究不同机型PET-CT中CT采集条件与受检者有效剂量的关系,为确定适合不同机型的临床最优化采集方案提供参考依据.方法:实验使用GE Discovery ST-16和Discovery Elite两种机型的PET-CT,CT部分所致剂量使用仿真人体模型(Model RS-550)实验获得.CT采集条件:①自动管电流30~250 mA,噪声指数(NI)值8~30,间隔2,其他采用中国医学科学院肿瘤医院临床实际采集条件,即管电压120kV,螺距(Pitch):Discovery ST-16型为1.75,Discovery Elite型为0.984,转速:Discovery ST-16型为0.8s,Discovery Elite型为0.5s;②自动管电流低限均为30 mA,高限为210~350 mA,间隔为20 mA,NI值为14,其他临床实际采集条件同上;③Pitch:Discovery ST-16型分别为1.75、1.375和0.938,Discovery Elite分别为1.375和0.984,管电压120kV,自动管电流为30~250mA,NI值为14,转速:Discovery ST-16型为0.8s,Discovery Elite型为0.5s;④两机型转速均分别为0.5s、0.8s和1.0s,管电压120 kV,自动管电流为30~250mA,NI值14,Pitch:Discovery ST-16型为1.75,Discovery Elite型为0.984.模拟临床PET-CT分段扫描方式使用上述条件分别对仿真人体模型RS-550进行扫描,记录各种条件下剂量长度乘积(DLP),并计算有效剂量(EDCT).结果:①对固定的自动管电流、Pitch及转速,两机型CT部分所致有效剂量随NI值增加而降低,且Discovery ST-16型降低幅度大于Discovery Elite型;②对固定的NI值、Pitch及转速,两机型的EDCT随自动管电流的增加线性增加,Discovery ST-16型增加幅度大于Discovery Elite型;③对固定的自动管电流、NI值及转速,EDCT随Pitch的增加而降低;④对固定的管电流、NI值及Pitch,有效剂量随转速的增加而增加;⑤不同扫描条件下,两机型总有效剂量在4.93~24.00 mSv范围内;⑥在临床扫描条件下,Discovery Elite型受检者EDCT均低于Discovery ST-16型.结论:不同型号的PET-CT,在临床使用中多采用不同CT扫描条件,而扫描所致辐射剂量也因此有较大变化.在临床应用中,应结合临床需求选择适用于不同机型的最佳采集方案.