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1、Technologies of Radiation Dose Reduction in CT Scanning,Contents,Contents,The use of CT has increased rapidly Since CT was introduced into clinical practice in 1973, this important and clinically effective imaging technology has undergone an explosive increase in the number of CT scanners and the fr
2、equency of CT examinations. CT的使用量迅速增加 自从1973年进入临床实践以来，CT作为一种重要的、有效的成像技术，其扫描仪数量及检查频率都有了爆炸式增长。,Cancer Risk of Radiation Dose in CT,Estimated Number of CT Scans Performed Annually in the United States 估计美国每年所做的CT扫描量,Cancer Risk of Radiation Dose in CT,The radiation exposure of CT has increased rapidly
3、 Medical radiation exposure to the public has been reported to have increased over the past 10 15 years and now accounts for nearly 50% of the total collective dose to the U.S. population, where nearly half of all medical radiation to patients comes from CT. CT电离辐射迅速增加 在过去的10-15年里，医源性辐射有所增加，目前已近占美国人
4、口总集体剂量50，其中近50%的辐射来自于CT检查,Cancer Risk of Radiation Dose in CT,Cancer risk of CT radiation for adult according to different articles About 1 in 150 women (20 years old) who undergo CT coronary angiography (CTCA) will develop cancer (the risk is about half of that for women 40 years old and up to one
5、third for women 60 years old). Smith-Bindman R. Arch Intern Med 2009;169(22):207886. Estimated cancer risks for adult patients undergoing ECG-gated CTCA were were 0.065% (about 1 in 1500) and 0.17% (about 1 in 600) for men and women respectively, with three quarters of the risk being lung cancer. Hu
6、da W. AJR Am J Roentgenol 2011;196(2):15965.,Cancer Risk of Radiation Dose in CT,Cancer risk of CT radiation for children according to different articles For a single slice CT scan of a 1-year old child, the paediatric fatal cancer risk was 0.11% and 0.055% (approximately 1 in 900 and 1 in 1800) for
7、 abdomen and head CT respectively. Brenner D. AJR Am J Roentgenol 2001;176(2):28996. For paediatric coronary CT angiography, the paediatric fatal cancer risk was great (1 in 300715 for boys and 1 in 120230 for girls). Feng ST. Eur J Radiol 2010;76(2)e19-23 epub Children have increased risks of radia
8、tion-related cancer, especially for thyroid, breasts and brain, non-melanoma skin cancer, and leukemia. Kleinerman RA. Pediatr Radiol 2006;36(Suppl. 2):1215,Cancer Risk of Radiation Dose in CT,Cancer Risk It has been estimated that about 1.5-2.0% of all cancers in the United States may be attributab
9、le to the radiation from CT studies 据估计1.5-2.0%的癌症与CT辐射剂量有关,Cancer Risk of Radiation Dose in CT,Cancer Risk of Radiation Dose in CT,In the face of uncertainty about the biologic effects of radiation exposure at low doses, the prudent course of action with regard to medical imaging is to keep doses t
10、o patients as low as reasonably achievable (the ALARA principle) while ensuring that information is sufficient for accurate diagnoses and the guidance of interventional procedures. 面对暴露在低剂量辐射的生物学效应的不确定性，医疗成像谨慎的做法是在辐射剂量尽可能低的条件下（ALARA原则上）获得足够的准确的诊断和指导介入程序的图像。,Contents,Technologies of Radiation Dose Re
11、duction,Lowing milliampere second Lowing tube voltage Increasing pitch Prospective ECG-triggering Appropriate shortening of scan range of Z-axis,降低管电流 降低管电压 增大螺距 前瞻性心电门控 适当缩短Z轴横断面扫描范围,Technologies of Radiation Dose Reduction,Lowing milliampere second（mAs） Radiation exposure is linearly proportional
12、to milliamperes Lowing current mainly affect density resolution of low-contrast tissues, such as the brain and liver. Image quality of low-contrast tissues was significantly degraded when the milliampere was decreased substantially. Automated tube current modulation (ATCM) 降低管电流 辐射剂量与管电流呈线性比例关系 降低管电
13、流主要影响低对比组织的密度分辨率，如颅脑及肝组织 大幅度降低管电流会使低对比组织的图像质量明显降低 自动管电流调节技术（ATCM）,Lowing milliampere second（mAs） Radiation exposure is linearly proportional to milliamperes 降低管电流 辐射剂量与管电流呈线性比例关系,Technologies of Radiation Dose Reduction,Technologies of Radiation Dose Reduction,Lowing tube voltage Radiation exposure
14、is exponential to kilovoltage However, lowering of tube voltage increases the image noise, which would damage image quality The reduction of image noise can be achieved by increasing current appropriatly or using iterative reconstruction Automatic tube voltage selection (ATVS) 降低管电压 辐射剂量与管电压的平方呈正比关系
15、 但是，降低管电压会增加图像噪声，影响图像质量 可以通过适当提高管电流或使用迭代重建算法减少图像噪声 自动管电流调节技术（ATVS）,Lowing tube voltage Radiation exposure is exponential to kilovoltage 降低管电压 辐射剂量与管电压的平方呈正比关系,Technologies of Radiation Dose Reduction,Technologies of Radiation Dose Reduction,Increasing pitch Radition dose is inversely proportional to
16、 pitch Increasing pitch will decrease the number of overlapping sections for the total acquisition volume and shorter image acquisition times and threrfore decrease the radiation dose Increasing pitch will decrease the spatial resolution of the Z-axis, which would make small nodular lesions easily missed Cardiac function cannot be assessed in CTCA scanning with high pitch 增大螺距 辐射剂量与螺距呈反比 扫描时，增大螺距会减少总采集容积的重叠，缩短扫描时间，降低辐射剂量 增大螺距会使Z轴空间分辨率降低，使小结节病变的容易漏诊 大螺距心脏扫描后不能进行心
