Scattered x-radiation can be used for computed tomographic reconstruction of the distribution of crystallographic phases within the interior of specimens, and diffraction patterns can be measured for each volume element (voxel) within a reconstructed slice. This modality has been applied to systems as diverse as mineralized tissues and inorganic composites. Use of high energy x-rays (E < 40 keV) offers advantages including the ability to study volumes deep with specimens and to sample large ranges of reciprocal space, i.e., many reflections. The bases of diffraction tomography are reviewed, and the power of the technique is illustrated by the results obtained for specimens containing: a) different materials (SiC/Al composite), b) different polytypes (calcite/aragonite in a bivalve attachment system); c) mixtures of nanocrystalline and amorphous phases; d) a single phase, but volumes with different lattice parameters (hydroxyapatite, hAp, the mineral in bone and tooth); e) a single phase containing a spatial distribution of crystallographic texture (bone); a single phase with a spatial distribution of strains produced by in situ loading (bone). Finally, challenges and future directions are discussed.
Biological materials are complex and their investigation demands advanced characterization tools capable of elucidating
their structure in three dimensions without the need for complicated sample preparation. Herein, we discuss our
implementation of diffraction/scattering computed tomography (DSCT). DSCT is based on the use of diffraction
information for tomographic reconstructions rather than linear attenuation as in regular μ-CT. This provides much
additional information on the material under investigation. We illustrate the use of DSCT by discussion of data on a
biomineralized attachment organ from a marine mussel. DSCT allowed mapping the spatial distribution of calcium
carbonate polymorphs aragonite and calcite even though they were indistinguishable in absorption tomography. Detailed
analysis of reconstructed diffraction patterns may provide additional insights as exemplified in the present case by
mapping of the degree of chemical substitution in calcite.