Scanning X-ray imaging with small-angle scattering contrast

An X-ray scanning imaging technique using the integrated intensity of the small-angle X-ray scattering (SAXS) signal is presented. The technique is based on two-dimensional scanning of a thin sample section with an X-ray microbeam, collecting SAXS patterns at every scanning step using a two-dimensional detector. The integrated intensity within pre-defined regions of interest of the SAXS patterns is used to image bulk nanostructural features in the specimen with micrometre resolution which are usually not accessible by other methods such as light microscopy or scanning electron microscopy. The possibilities and limitations of the method are discussed with particular emphasis on the sources of contrast in the SAXS region for three biological specimens: cortical bone, eggshell and hair. Two main sources of image contrast are identified in the form of orientation effects for strongly anisotropic systems like cortical bone and differences in the local volume fraction of the scattering entities in eggshell. Moreover, other parameters than the integrated intensity can be quantitatively deduced from the SAXS patterns, for instance, the mean thickness of mineral platelets in bone or the strain distributions in a hair deformed plastically by microindentation.