PET/CT中CT自动管电流调制模式下受检者有效剂量的研究

目的 研究PET/CT中CT自动管电流模式下受检者有效剂量与管电流阈值及噪声指数的关系，为确定最优化采集条件提供理论基础。方法 选用GE Discovery ST-16型和Discovery Elite型PET/CT，使用RS-550型仿真人体模型获得PET/CT中CT所致受检者有效剂量。两机型采用相同采集条件，即管电压120 kV，螺距为1.375，转速0.8 s/转，噪声指数（NI）8-30，间隔为2，自动管电流低限均为30 mA，高限为200~350mA，间隔为50 mA。模拟临床PET/CT的头颈部和体部分段扫描方式对仿真人体模型进行扫描。记录各种采集条件下剂量长度乘积（DLP），计算有效剂量（ED_CT）。结果 采用相同采集条件，CT扫描所致有效剂量随噪声指数增大而降低，且曲线随自动管电流高限的增加而陡峭；Discovery Elite型扫描CT所致受检者全身有效剂量低于Discovery ST-16型。结论 对确定的受检者，PET/CT中CT所致有效剂量随扫描条件不同有较大差异。可以根据不同临床需求，选择最优化采集方案，从而尽可能降低受检者的有效剂量。

Study on the effective dose of CT in PET/CT on automatic tube current modulation

Objective To investigate the relationship between effective dose and tube current threshold, as well as noise index of CT in PET/CT, and to provide theoretical basis for optimal acquisitions through the mode of automatic tube current modulation (ATCM).Methods Two sets of PET/CT (Discovery ST-16 and Discovery Elite) and an anthropomorphic phantom (RS-550) were used to acquire the effective dose caused by CT in PET/CT.CT acquisition conditions were as follows in both ST-16 and Elite PET/CT:tube voltage 120 kVp, pitch 1.375,rotation speed 0.8 s,noise index ranged from 8 to 30 with an interval of 2,the low limit of current was 30mA,and the high limit ranged from 200 mAto 350 mA with an interval of 50 mA. Simulating the clinical head-neck and body conditions, the phantom was scanned, and the dose-length product(DLP) was recorded to estimate the effective dose (ED_CT) of CT.Results With the same acquisition conditions, the effective dose decreased along with the increasing noise index, and the curve became steeper with increasing high limit of tube current. The whole body effective dose caused by CT was lower in Elite PET/CT than that in ST-16 with the same acquisition conditions.Conclusion The effective dose caused by CT in PET/CT differs from variable scan conditions. It shows that the radiation dose can be effectively reduced by choosing appropriate acquisition conditions according to different clinical needs.