微焦点源X射线相衬成像技术

 相衬成像方法利用硬X射线对低密度弱吸收物质成像，可获得高衬度图像。用菲涅尔衍射理论分析了X射线图像的形成机理。在频域中根据光学传递函数，对物像距离、样品空间频率等对图像相位衬度的影响进行了分析。分辨率和衬度是决定图像可见度的两个依据，分辨率主要依赖于光源的空间相干性，空间相干性又决定于源点尺寸，而时间相干性（单色性）是一个不重要的影响因子。利用多色微焦点源实现了X射线相衬成像技术，获得了有价值的相衬图像，如低原子序数低密度泡沫材料的硬X射线相衬图像，与吸收衬度成像相比，其图像质量得到了很大提高，能观察到泡沫材料的细微结构，分辨率可达μm量级。

Phase-contrast imaging with micro-focus X-ray source

In conventional radiography,X rays which pass through an object along different paths are differentially absorbed,and the intensity pattern of the emerging beam records the distribution of absorbing materials within the sample.A non-conventional X-ray radiography-phase-contrast imaging is described,which records variations of the phase of the emerging radiation,shows dramatic contrast enhancement for low density or weakly absorbing materials with hard X-ray.A general treatment of X-ray image formation by Fresnel diffraction theory is presented.According to the optical transfer function,the distance of object-image and spatial frequency on the imaging phase-contrast is discussed.Resolution and contrast are the criteria used to specify the visibility of an image,resolution in turn depends primarily on the spatial coherence of the source,and the spatial coherence in turn is largely determined by the source size,with chromatic coherence of lesser importance.X-ray phase-contrast imaging with broadband micro-focus source are developed,the phase-contrast images of the low Z or low density samples using hard X-ray are obtained.Compared with the absorption-contrast image of the same sample,the image quality has been greatly improved,the fine-structure of the samples can be observed distinctly in the phase-contrast images,resolution of a few micrometers is achieved.