Yoshiura K, Welander U, McDavid W D, Li G, Shi X-Q, Kawazu T, Tatsumi M, Matsuo T, Kanda S
Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, Maidashi 3-1-1, Fukuoka, Japan.
Dentomaxillofac Radiol. 2003 May;32(3):191-7. doi: 10.1259/dmfr/25806978.
To construct perceptibility curves (PCs) for given calibration settings in order to define psychophysical properties of the Digora storage phosphor system and to evaluate the effects of automatic exposure correction (AEC) on the PCs.
The Digora system was calibrated at two exposures, 80 microC kg(-1) (high calibration) and 40 microC kg(-1) (low calibration). Since the grey levels displayed in the radiographs are adjusted by AEC, dose-response functions at high calibration were obtained using AEC on and off modes. The dose-response function at low calibration was obtained with AEC off. The PC at each experimental setting was calculated using known physical parameters of the system and the performance of the average observer used in a previous study. In addition, PCs were also constructed using transmitted radiation flux behind the test object calculated from the attenuation coefficient in order to study observer and system performance. PCs obtained under these conditions were compared.
The PC using calculated transmitted radiation flux behind the test object showed a wide plateau at the peak owing to AEC, while the PC obtained by a modified approach showed a higher but narrower peak. There were no differences between the two PCs using AEC on and off modes when the PCs were constructed using a modified approach. There were no differences between the two PCs obtained at high and low calibration settings or between the three PCs obtained with AEC on except for the position along the exposure axis.
Psychophysical properties of the Digora system may be determined if we employ registered exposures from a dose-response function with AEC off under a given calibration setting. Under these circumstances the shape and height of the PCs will be unchanged irrespective of the AEC mode.
为给定的校准设置构建可感知性曲线（PCs），以定义Digora存储磷光体系统的心理物理学特性，并评估自动曝光校正（AEC）对PCs的影响。
Digora系统在两种曝光量下进行校准，80微库仑/千克（高校准）和40微库仑/千克（低校准）。由于X线片中显示的灰度级由AEC调整，因此在高校准下使用AEC开启和关闭模式获得剂量响应函数。低校准下的剂量响应函数在AEC关闭时获得。每个实验设置下的PC使用系统的已知物理参数和先前研究中使用的平均观察者的性能进行计算。此外，还使用根据衰减系数计算的测试对象后方的透射辐射通量构建PCs，以研究观察者和系统性能。比较在这些条件下获得的PCs。
使用测试对象后方计算的透射辐射通量得到的PC在峰值处由于AEC显示出较宽的平台期，而通过改进方法获得的PC显示出更高但更窄的峰值。当使用改进方法构建PC时，使用AEC开启和关闭模式的两种PC之间没有差异。在高校准和低校准设置下获得的两种PC之间，以及在AEC开启时获得的三种PC之间，除了沿曝光轴的位置外没有差异。
如果我们在给定的校准设置下使用AEC关闭时剂量响应函数的记录曝光量，则可以确定Digora系统的心理物理学特性。在这些情况下，无论AEC模式如何，PCs的形状和高度都将保持不变。
