CT radiation dose and image quality
CT radiation dose and image quality
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DOI：
10.1016/j.rcl.2005.07.002
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发表时间：
2005-11-01
影响因子：
1.9
通讯作者：
Payne, JT
中科院分区：
文献类型：
--
作者：
Payne, JT
CT扫描在1973年突然出现在诊断成像领域，快速发展了近十年，然后进入了舒适的中年。但是平静的生活并没有持续多久。技术的进步使CT扫描回到了中心位置。具有更高额定功率的高频发生器和专门设计的具有更高储热能力的CT x射线管使得更快的亚秒级扫描的出现成为可能。随着滑环电能传输的发展，这些进步允许连续的龙门旋转和螺旋或螺旋扫描[1]的诞生。如果这还不够，多行探测器阵列的发展，以增加覆盖面积在一个龙门架旋转。这有助于在一次屏气中对整个器官进行容积CT扫描。软件的改进已经导致了体渲染数据的实时三维显示，如用于虚拟CT结肠镜检查、CT血管造影、CT冠状动脉钙化评分和其他有用的应用[2]。这些技术进步极大地扩展了CT在诊断成像中的作用。美国每年的CT研究数量从1980年的360万例增加到1990年的1330万例，再到1998年增加了一倍多，达到3300万例。到2001年，CT扫描占所有放射学程序的13%以上。不幸的是，CT程序的集体辐射剂量增加的速度甚至快于研究数量的增加。英国国家放射防护委员会指出，1989年，CT研究仅占所有影像学研究的2%，但占患者总剂量的20%。随后的研究分析表明，CT对患者总剂量的贡献已上升至40%。在联合国原子辐射影响科学委员会2000年的一份报告中，所有成像程序中CT检查的频率约为5%，但CT辐射剂量约占总成像剂量的34%，是辐射剂量中最大的单一部门。在美国，某些科室CT对患者总剂量的贡献可能高达67%。CT总辐射剂量的上升主要是由于其使用的增加和每次检查图像数量的增加。在早期，一项CT研究包括20张类似的50张图像。今天，用200 - 1000张或更多的图像进行CT研究并不罕见。最初，CT几乎完全被用来排除恶性疾病或取代更严重危险的手术（有人记得空气造影肺脑图吗？），在大多数情况下，辐射剂量不是问题。今天，随着进行快速多期对比增强研究、筛查研究的能力和使用的增加，CT放射患者的总剂量正在增加。CT成像缺乏良好的辐射剂量管理。自成立以来，CT研究一直采用标准的一刀切技术方案[7]进行。2001年，一系列关于儿童患者患辐射致死性癌症的风险的期刊文章，以及儿童患者使用成人CT成像的事实，引起了媒体的关注，并引起了公众和专业人士的强烈抗议[8 - 11]。这对将注意力集中在更好地使用CT辐射剂量和在CT技术方案中实施尽可能低的合理可达（ALARA）概念具有积极作用。现在推荐选择合适的CT影像学检查标准。提出了CT辐射剂量管理的ALARA概念。问题是：CT手术的适当辐射量是多少？如何优化CT扫描所需的辐射？回答这些问题需要对CT辐射剂量和决定CT扫描辐射量的因素有一个基本的了解。
CT scanning burst on the diagnostic imaging scene in 1973, sprinted for almost a decade, and then settled into comfortable midlife. But the quiet life did not last long. Technologic advances thrust CT scanning back to center stage. High-frequency generators with ever-higher power ratings and specially designed CT x-ray tubes with ever-higher heat storage permitted the advent of faster subsecond scans. These advances along with the development of slip ring electrical energy transfer allowed for continuous gantry rotation and the birth of spiral or helical scanning [1]. If that were not enough, multirow detector arrays were developed to increase the area of coverage during one gantry rotation. This facilitates volume CT scanning of whole organs in a single breath-hold. Improvements in software have led to real-time 3-D displays of volume-rendered data, as used in virtual CT colonoscopy, CT angiography, CT coronary calcium scoring, and other useful applications [2]. These technologic advances have expanded the role of CT in diagnostic imaging greatly. The annual number of CT studies in the United States more than tripled from 3.6 million in 1980 to 13.3 million in 1990 and then more than doubled to 33 million in 1998 [3]. By 2001, CT scanning comprised more than 13% of all radiology procedures. Unfortunately, the collective radiation dose from CT procedures increased even faster than the increase in the number of studies. The National Radiological Protection Board in the United Kingdom indicated that in 1989, CT studies comprised only 2% of all imaging studies but contributed to 20% of the total patient dose. Subsequent study analysis showed that CT contribution to overall patient dose has risen to 40% [4]. In a 2000 report of the United Nations Scientific Committee on the Effects of Atomic Radiation, the frequency of CT examinations for all imaging procedures was approximately 5%, but the CT radiation dose was approximately 34% of the total imaging dose and was the largest single sector of radiation dose [5]. In the United States, CT contribution to overall patient dose in some departments may be as high as 67% [4]. The rising total patient radiation dose from CT primarily is the result of its increased use and increased number of images per examination. In the early days, a CT study consisted of 20 similar to 50 images. Today, it is not unusual to have CT studies with 200 - 1000 images or more. Initially, CT was used almost exclusively to rule out malignant disease or replace procedures of even graver danger (Does anyone remember the air contrast pneumo-encephalogram?) and radiation dose was not an issue in most of these cases. Today, with the capability of performing rapid multiphase contrast enhanced studies, screening studies, and increased use, the collective CT radiation patient dose is adding up. What is lacking is good radiation dose management in CT imaging [6]. Since their inception, CT studies have been performed with standard one-size-fits-all technique protocols [7]. A series of journal articles in 2001 concerning the risk of radiation-induced fatal cancer in pediatric patients, and the fact that pediatric patients were being imaged with adult CT protocols, caught media attention and caused considerable public and professional outcry [8 - 11]. This had the positive effect of focusing attention on better CT radiation dose use and implementation of as-low-as-reasonably-achievable (ALARA) concepts into CT technique protocols. Appropriateness criteria now are recommended in the selection of CT imaging examinations.The ALARA concept i evoked for CT radiation dose management. Questions are being asked: What is an appropriate amount of radiation for CT procedures? How can the radiation needed for CT scanning be optimized? Answering these questions requires a basic understanding of CT radiation dose and the factors that determine the amount of radiation used in CT scanning.