利用光学调制传递函数评价原理,在建立了各个成像子系统信号传递关系的基础上,提出了一种近贴式X射线成像光学调制传递特性检测方法。从像增强器约束、射线源约束和噪声约束这3个角度对近贴式X射线成像系统光学调制传递函数进行理论定标。将近贴式X射线成像系统后端的CCD望远系统换成CCD显微系统并对不同空间分辨率的铅栅进行成像与对比度拟合。实验结果表明:时域均衡可以有效提高拟合精度。其拟合结果表明空间分辨率为10线对/mm时其调制传递函数仍有10%,与理论定标结果基本一致。故传统近贴式X射线成像系统的望远光学镜头分辨率才是真正的成像瓶颈。

Using the evaluating principle of modulation transfer function, an optical modulation transfer characteristic detection methodology of proximity focusing X-ray imaging system is brought up on the basis of the signal transfer relationship between each imaging subsystem. From the constraints of image-intensifier tubes, the generation process of ray source and imaging restriction of its spot size constraints, the constraints of noise three perspectives to calibrate theoretical modulation transfer characteristic of proximity X-ray imaging system. Change CCD telescopic system of proximity X-ray imaging system back end to CCD microscopy system, to multi-spatial resolution balls of lead grating imaging and MTF curve fitting, and as the experimental results suggest, the curve fitting precision can be significantly improved by time domain equalization. Fitting results indicate that modulation transfer function still are equal to 10% when spatial resolution reaches 10lp/mm, this is consistent with that of the theoretical calibration. So that the resolution of traditional proximity X-ray imaging system is really the bottleneck.