Determination of correct AEC function with computed radiography cassettes.
Determination of correct AEC function with computed radiography cassettes.
复制标题
使用计算机放射摄影盒确定正确的 AEC 功能。
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
Heggie Jc
中科院分区：
文献类型：
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作者：
Wilkinson Le;Heggie Jc
自动曝光控制（AEC）功能的评估一直被认为是评估任何通用X射线照相设备的重要标准。在AEC上通常进行的测试中，只有光束质量依赖性与最终射线照片上产生的光密度密切相关。在该测试中，根据射线照片上的光密度是否控制在明确定义的限值内，确定AEC功能是否令人满意。对于计算机X射线摄影（CR），其中传统的屏-膜组合被存储荧光屏取代，数字图像在胶片上呈现的过程将所得的光密度限制在非常小的范围内，与入射到CR荧光板上的空气比释动能无关。这意味着光密度的测量不能用作AEC功能的直接测量，并且不能以传统方式执行诸如光束质量依赖性的测试。为了克服这一点，入射空气比释动能和CR系统提供的计算机生成的指数之间的关系进行了研究，两个市售系统，一个由富士医疗系统和柯达提供的其他。折射率和入射空气比释动能之间的关系可以用来代替光密度来监测AEC性能与光束质量的关系。已经确定，富士CR系统的入射空气比释动能与灵敏度数之间存在反线性关系，柯达CR系统的曝光指数与入射空气比释动能之间存在对数关系。为了进一步量化这些关系，灵敏度数和曝光指数对光束质量和入射kVp的依赖关系进行了研究。使用上述研究的结果，可以建立灵敏度数值和曝光指数的可接受限值，以测试与光束质量相关的正确AEC功能。
It has long been recognized that the assessment of Automatic Exposure Control (AEC) function is an important criterion in the assessment of any general radiographic x-ray installation. Of the tests commonly performed on an AEC, only Beam Quality Dependence relates intimately with the optical density produced on the resultant radiograph. In this test the AEC function is ascertained as being satisfactory or otherwise, on the basis of whether the optical density on the radiograph is controlled within well defined limits. With computed radiography (CR), where the conventional screen-film combination is replaced by a storage phosphor screen, the process by which the digital image is presented on film restricts the resultant optical densities to an extremely tight range, independent of the air kerma incident upon the CR phosphor plate. The implication of this is that the measurement of optical density can not be used as a direct measure of AEC function, and a test such as Beam Quality Dependence cannot be performed in the conventional manner. To overcome this, the relationship between incident air kerma and a computer generated index supplied with the CR system was investigated for two commercially available systems, one supplied by Fuji Medical Systems and the other by Kodak. The relationship between the index and incident air kerma could then be used as a substitute for optical density in monitoring AEC performance with respect to beam quality. It has been determined that an inverse linear relationship exists between the incident air kerma and the Sensitivity Number for the Fuji CR system and that a logarithmic relationship exists between the Exposure Index and incident air kerma for the Kodak CR system. In order to quantify these relationships further, the dependence of Sensitivity Number and Exposure Index on beam quality and incident kVp have been investigated. Using the results from the above investigations, acceptable limits for both Sensitivity Number and Exposure Index, can be established to test for correct AEC function, with respect to Beam Quality Dependence.