Small-angle X-ray scattering (SAXS) probes nanoscale features in reciprocal space. Apart from statistical information of size and shape in the probed volume, the orientation of anisotropic nanostructures can be directly obtained from the anisotropy of the scattering patterns. By using a focused X-ray beam and raster-scanning a sample through the beam, images can be created with a real-space resolution defined by beam- and stepsize while each pixel contains information from the nanostructure in reciprocal space. For an extension of the technique to computed tomography, new reconstruction algorithms as well as experimental schemes probing additional tilt angles of the tomography axis have been developed in order to retrieve 3D reciprocal space maps in each voxel, extending the method to 6 dimensions. The technique is in particular powerful for hierarchical systems where relevant length scales are spanning over many orders of magnitudes. For the example of bone, the arrangement of mineralized collagen fibrils in the nanoscale can be probed over extended macroscopic samples millimeters or even centimeters in size.
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