基于微焦斑源X射线传播的相衬成像模拟

从标量衍射及部分相干光衍射理论出发,结合硬X射线特点,建立基于微焦斑X射线源的衍射成像模型.该模型将Fresnel积分运算转换到空间频域,利用快速傅里叶变换计算衍射光场.根据部分相干光理论分析,有限大小光源的物体衍射光场为光源光强分布与点源所形成的物体衍射光场的卷积,将卷积运算转换到空间频域并利用快速傅里叶变换算法提高运算速度.模拟衍射结果表明,物体到X射线源的距离、X射线光子能量以及X射线源焦斑尺寸均影响自由空间传播相衬成像系统的图像衬度.研究结果有助于X射线相衬成像系统的设计和性能优化.

The simulation of X-ray phase-contrast imaging with partially coherence source

An X-ray diffraction imaging model based on microfocus X-ray tube was presented . The model used the scalar diffraction and partial coherent X-ray diffraction theories, taking the hard X-ray features in consideration. In this model, the Fresnel integral was performed in the spatial frequency domain, and the X-ray diffraction field was calculated by means of the fast Fourier transform (FFT). According to the partial coherent theory, the X-ray intensity in the image plane was the convolution of the intensity of object irradiated by the X-ray beam from an ideal point source with the intensity distribution of the expanded source. Thus the intensity distribution in the image plane can be obtained by transforming the convolution in the real space to the multiplication in the spatial frequency domain, and its calculation efficiency can be improved by using the FFT. The simulation results show that the image contrast is determined by the distance from the source to object plane, by the energy of X-ray photon, and by the size of X-ray focal spot. The simulation is helpful for the design of X-ray phase contrast imaging system based on the free space propagation.