Harrison R M, Day M J
Phys Med Biol. 1983 Nov;28(11):1319-31. doi: 10.1088/0031-9155/28/11/011.
Experimental measurements of threshold contrast (CT) as a function of air kerma rate at the input plane of the image intensifier have been made for several diagnostic fluoroscopy units in clinical use. Threshold contrasts are determined by viewing a test object containing holes of fixed diameter and various depths under defined irradiation conditions. Kerma rate variations are effected by introducing aluminum sheets into the x-ray beam at fixed values of tube potential and current. At low kerma rates where quantum noise dominates, low tube potentials (60 kVp) usually yield lower values of CT than do higher potentials (100 kVp). At higher kerma rates the opposite is often true. A simple theoretical model for noise propagation in fluoroscopic imaging systems using models of diagnostic x-ray spectra lends qualitative support to the experimental findings. The often-quoted suggested upper limit of 100 mu R s-1 (0.87 mu Gy s-1) at the input phosphor would seem to be justified under the test conditions since little improvement in CT is usually observed at higher kerma rates. However, application to clinical practice would ideally require the use of more realistic phantom studies.
针对临床上使用的多个诊断性荧光透视设备，已对影像增强器输入平面处的阈值对比度（CT）随空气比释动能率的变化进行了实验测量。阈值对比度是通过在规定的照射条件下观察一个包含固定直径和不同深度孔洞的测试物体来确定的。通过在管电压和管电流固定值的情况下向X射线束中引入铝板来实现比释动能率的变化。在量子噪声占主导的低比释动能率下，低管电压（60 kVp）通常比高管电压（100 kVp）产生更低的CT值。在较高比释动能率下情况往往相反。使用诊断性X射线光谱模型的荧光透视成像系统中噪声传播的简单理论模型，为实验结果提供了定性支持。在测试条件下，输入荧光屏处常被引用的建议上限100 μR s⁻¹（0.87 μGy s⁻¹）似乎是合理的，因为在较高比释动能率下通常观察到CT几乎没有改善。然而，应用于临床实践理想情况下需要使用更符合实际的体模研究。
