医用X射线CT辐射剂量影响因素研究
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| 时间：2009-01-16 20:54:22 来源： 作者： |
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An evaluation on influence factors of radiation dose for the medical X-ray computed tomography
LU He-qing，ZHU Guo-ying，ZHUO Wei-hai，GUO Chang-yi，GAO Lin-feng，LIU Hai-kuan．
Institute of Radiation Medicine，Fudan University，Shanghai 200032，China；Shanghai Municipal Center for Disease Control and Prevention，Shanghai 200336，China
【Ａｂｓｔｒａｃｔ】 Objective To evaluate those factors which affect on to the radiation dose of multi-slice CT, such as voltage and current of tube, diameter of phantom, depth of inside phantom, pitch, collimation, field of view, algorithm and tube current modulation technology and so on. Methods A pencil-like ion chamber, head and body dose phantom, and Chinese anthropomorphic phantom were used to measure the characteristic quantum of CT dosimetry when different voltage and current of tube, diameter of phantom, depth of inside phantom, pitch, collimation, field of view, algorithm and tube current modulation technology were adopted. Results When all other parameters kept unchanged, the tube voltage was direct proportional to CTDI(CT dose index), the tube current was positive linear correlation to CTDI, the diameter of phantom was inverse proportional to CTDI, radiation dose of CT was decreasing while measuring depth increased of inside phantom, pitch was inverse proportional to accumulated dose, overexposure from spiral scanning out of topogram range led to the increasing of radiation dose, collimation was inverse proportional to CTDI, CTDI was not affected by field of view and algorithm, and radiation dose of CT was decreased by using tube current modulation technology. Conclusion Radiation dose of CT can be decreased by reducing voltage and current of tube, increasing pitch，limiting the block number of helical scanning during a single CT examination，increasing width of collimation, decreasing scan parameters of slim patients rationally and adopting tube current modulation technology.
【Ｋｅｙ ｗｏｒｄｓ】 Multi-slice CT(MSCT)； CT dose index； Pitch； Collimation
众多受检者、患者所受的医疗照射已经成为全民所受各种电离辐射照射中最大的又是不断增加的人工电离辐射照射来源[1]。近年来，CT在放射诊断中应用越来越广泛，在设备数量和接受CT检查人数上均逐年增加。在过去20年间，全世界CT检查频率增长超过8倍[2],由此而来的受检者接受的辐射剂量也相应增加。据报道，在英国，CT检查人次占所有放射检查的4％，但辐射剂量却占到受检者总辐射剂量的40％[3]。另外单次CT检查给予受检者的辐射剂量高于常规X射线检查。我国CT设备发展非常迅速，CT绝对数已居世界第三位[4]，轴扫CT和单层螺旋CT正逐步被双层和多层螺旋CT代替，多层CT应用日益普及，多层CT具有扫描速度快，重建图像质量好，可进行大范围容积扫描和三维图像重建，提高了诊断准确率和单位时间检查效率。与单层CT比较，多层CT由于采用更薄的层厚，在较短的时间内覆盖较大的范围，可能会产生更大的X射线辐射[5]。CT检查引起的照射可能会增加致癌的风险，特别是对辐射敏感的儿童[6]。因此，CT医疗照射有可能成为各类医疗照射所致集体剂量的最大来源，CT医疗照射防护已成为涉及广大公众的重要公共卫生问题，在国内外已成为辐射防护领域的重点和热点问题。CT医疗照射防护不仅仅是放射防护人员的职责，也是临床医生与放射医师应共同承担的责任[7]。为做好CT检查的放射防护和X射线CT医疗照射防护最优化工作，优化CT扫描条件，使其符合正当化和最优化原则[8,9]，尽量减少受检者接受的辐射剂量，需要研究影响多层CT剂量的主要因素。本文在不同扫描条件下，根据剂量实测结果，总结出不同影响因素所致CT剂量变化的规律。管电流调制技术是一个自动曝光控制系统，系统的功能包括可以根据受检者身材和脏器的解剖形态自动调整球管电流，以及对于每一次球管旋转的在线可控式球管电流调制。这样就在较低的射线剂量水平上提供稳定的图像质量。本文采用管电流调制与管电流恒定两种方法，分别对胸部进行扫描，评价管电流调制技术对胸部扫描剂量的影响程度。
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