辐射成像系统中，射线沿闪烁体厚度方向产生的光经过镜头形成一个弥散的像。这通常是此类系统空间分辨的主要限制因素。建立了几何光学成像模型，描述了近心光路中此图像的空变特性。用点扩散函数均方根半径表征系统空间分辨性能，给出了图像点扩散函数均方根半径的表达式，其与闪烁体厚度、折射率、镜头相对孔径、成像倍率、射线入射点相对位置直接相关。将硅酸镥晶体3维发光强度分布与镜头进行耦合，分析了闪烁体发光强度分布对耦合的影响。采用点扩散函数均方根半径为最小的原则，建立了一个推导闪烁体相对于物镜放置在最佳位置的方法。

In a radiographic imaging system, the created light along the thickness direction of the scintillator is focused by a lens to form a blurred image, which is a limiting factor for the spatial resolution of the imaging system. Geometric optics models have been developed to describe the imaging process. To parameterize the spatial resolution, the standard deviation of the blurred image has been expressed by the parameters of the imaging system. A method is found to optimize the position of a thick scintillator with respect to the object focal plane of the lens, in which the deviation of the blurred image will be minimized.