CT扫描中的散射线分析

Analysis to the scattered radiation in CT scan

目的 :探讨CT扫描中散射线剂量与管电流、管电压的关系,以及散射线降到机房本底水平所需的时间。方法 :首先记录扫描机房本底剂量水平,然后在CT检查床上放置体部水膜,按照A组140 k V、250 m A,B组120 k V、250 m A,C组140 k V、100 m A,D组120 k V、100 m A 4组条件进行扫描,曝光时间均为5.1 s。于距离扫描架2.5 m处利用辐射剂量仪连续记录不同时间散射线剂量,同时采用高频摄像机记录剂量仪的数字变化,每种扫描条件重复扫描10次,记录曝光开始后30 s散射线辐射剂量,以辐射剂量仪显示的第7秒的数字作为曝光结束后的散射线剂量。结果:曝光结束后5 s内散射线剂量最大,随时间延长逐渐减低。扫描时管电流、管电压值越大,散射线剂量越大,曝光结束后最初5 s散射线剂量各组比较差异有统计学意义。不同扫描条件曝光结束后散射线剂量达到机房本底水平的时间为曝光后20~23 s。结论:散射线剂量与扫描时管电流、管电压有关。采用低剂量CT扫描可降低散射线强度。曝光结束后5 s内机房散射线剂量最大,CT操作技师应做好散射线防护。

Objective：To study the relationship between the scattered radiation dose and the scan tube voltage and current in CT scan,and to study the time required of the scattered radiation dose down to the background levels of the CT room. Meth-ods：The background dose level of CT scan room was recorded first. Then the water model was placed on the CT examination bed. Four conditions A：140 kV,250 mA;B：120 kV,250 mA;C：140 kV,100 mA;D：120 kV,100 mA were used in CT scan and the exposure times of every scanning conditions was 5.1 seconds. The scattered radiation dose was continuous recorded using the radiation dosimeter in 2.5 meter distance to the gantry,while the digital changes of the radiation dosimeter was recorded using high-frequency camera. Every scanning conditions was scanned 10 times repeated and the scattered radiation dose was recorded for 30 seconds from the exposure starting. The digital of the radiation dosimeter displayed in the seventh seconds was as the scattered radiation dose after the end of exposure. Results：The scattered radiation dose was attained the maximum within 5 seconds after the end of exposure and decreased gradually with time. When scanning the tube voltage and current larger the greater the scattered radiation dose. There were significant differences of the scattered radiation dose in each group after the end of exposure in the first 5 seconds. The time that the scattered radiation dose after the end of exposure reduced to the background level in different scanning conditions was 20-23 seconds. Conclusion：The scattered radiation dose is related with tube voltage and tube current. Low-dose CT scans can reduce the intensity of the scattered radiation dose. The dose of scat-tered radiation is maximum within 5 seconds after the end of exposure. CT technicians should be prepared scattered radiation protection.