Seibert J A, Shelton D K, Moore E H
Department of Radiology, University of California Davis Medical Center, Sacramento 95817, USA.
Acad Radiol. 1996 Apr;3(4):313-8. doi: 10.1016/s1076-6332(96)80247-9.
Computed radiography provides correct optical density on film, independent of the incident radiation exposure, but it can result in under- or overexposure of the imaging plate. In the current study, we evaluated the radiation exposure trends of computed radiography over a 2-year period for portable chest examinations to determine and compare the radiographic techniques of the computed radiography system relative to conventional screen-film detectors.
A Fuji computed radiography system was interfaced to a digital workstation to track system usage and examination demographics, including examination type and sensitivity number. Hard-copy films were used for diagnosis. The sensitivity number, a value inversely related to incident exposure on the imaging plate, was used to determine whether the proper techniques were used by the technologists.
The initial use of the computed radiography system revealed a broad distribution of exposures being used; complaints regarding noisy films (e.g., underexposure) resulted in subsequent overexposure for a significant number of films. A quality-control audit indicating excessive exposure resulted in educational feedback and a tighter distribution of exposures within the optimal range as determined by our radiologists. The average technique was approximately equivalent to a 200-speed system.
Computed radiography provides excellent dynamic range and rescaling capabilities for proper film optical density, and thus fewer repeat examinations. However, underexposure results in suboptimal image quality that is related to excessive quantum mottle. Overexposure requires film audits to limit unnecessary radiation exposure. In general, the optimal exposures are achieved with approximately 1.5-2 times the incident detector exposure of a 400-speed rare-earth system. The ability of computed radiography to reduce radiation exposure is unlikely when compared with a typical rare-earth screen-film combination (400 speed) in terms of adequate image quality for the diagnosis of subtle, low-contrast findings. For certain diagnostic procedures (e.g., nasogastric tube placement verification), lower exposures can be tolerated.
计算机X线摄影可在胶片上提供正确的光学密度，与入射辐射曝光量无关，但可能导致成像板曝光不足或过度曝光。在本研究中，我们评估了计算机X线摄影在2年期间用于便携式胸部检查的辐射曝光趋势，以确定并比较计算机X线摄影系统相对于传统屏-片探测器的射线照相技术。
将富士计算机X线摄影系统连接到数字工作站，以跟踪系统使用情况和检查人口统计学信息，包括检查类型和敏感度数值。使用硬拷贝胶片进行诊断。敏感度数值与成像板上的入射曝光量呈反比，用于确定技术人员是否使用了正确的技术。
计算机X线摄影系统最初使用时，曝光量分布较广；关于胶片噪声（如曝光不足）的投诉导致大量胶片随后过度曝光。一项表明曝光过度的质量控制审核导致了教育反馈，并使曝光量在我们放射科医生确定的最佳范围内分布更紧密。平均技术水平约相当于200速系统。
计算机X线摄影为获得合适的胶片光学密度提供了出色的动态范围和重新定标能力，从而减少了重复检查。然而，曝光不足会导致图像质量欠佳，这与过量的量子斑点有关。过度曝光需要进行胶片审核以限制不必要的辐射暴露。一般来说，最佳曝光量约为400速稀土系统入射探测器曝光量的1.5至2倍。就诊断细微的低对比度病变的足够图像质量而言，与典型的稀土屏-片组合（400速）相比，计算机X线摄影降低辐射暴露的能力不太可能实现。对于某些诊断程序（如鼻胃管放置验证），较低的曝光量是可以接受的。
