Doyle P, Martin C J
Health Physics, Department of Clinical Physics and Bio-Engineering, Gartnavel Royal Hospital, Glasgow G12 OXH, UK.
Phys Med Biol. 2006 Nov 7;51(21):5475-85. doi: 10.1088/0031-9155/51/21/006. Epub 2006 Oct 6.
The energy responses of digital radiography detectors differ from those of screen-film systems. To provide a consistent level of image quality at different tube potentials automatic exposure control (AEC) devices must be calibrated to suit the energy response of the image receptor with which they are intended for use. AEC calibration for digital radiography systems requires an alternative parameter to optical density, ideally one related to the quality of a digital image. Energy responses of computed radiography (CR) and indirect digital radiography (IDR) image receptors have been calculated, and compared with those for screen-film systems. Practical assessments of the relative sensitivities of a CR detector made using the detector dose indicator (DDI), pixel value and signal-to-noise ratio showed similar variations with tube potential. The DDI has been used to determine the correct kV compensation curve required to calibrate the AECs for the loss in detector sensitivity with tube potential. AECs are set up relative to a predetermined air kerma incident on the detector at 80 kV for CR and IDR systems using this curve and the method used is described. Factors influencing the calibration of AECs for digital radiography including techniques, types of phantom and contributions from scatter are reviewed, and practical methods recommended for use.
数字射线摄影探测器的能量响应与屏-片系统不同。为了在不同管电压下提供一致的图像质量水平，自动曝光控制（AEC）设备必须进行校准，以适应其预期使用的图像接收器的能量响应。数字射线摄影系统的AEC校准需要一个替代光学密度的参数，理想情况下是一个与数字图像质量相关的参数。已经计算了计算机射线摄影（CR）和间接数字射线摄影（IDR）图像接收器的能量响应，并与屏-片系统的能量响应进行了比较。使用探测器剂量指示器（DDI）、像素值和信噪比进行的CR探测器相对灵敏度的实际评估显示，其随管电压的变化类似。DDI已被用于确定校准AEC所需的正确千伏补偿曲线，以补偿探测器灵敏度随管电压的损失。使用此曲线为CR和IDR系统设置相对于在80 kV下入射到探测器上的预定空气比释动能的AEC，并描述了所使用的方法。综述了影响数字射线摄影AEC校准的因素，包括技术、体模类型和散射的影响，并推荐了实际使用的方法。
