3D tomography of shark vertebrae via energy dispersive diffraction

Tomography using diffracted x-rays produces reconstructions mapping quantities including crystal lattice parameter(s), crystallite size and crystallographic texture; this information is quite different from that obtained with absorption contrast or phase contrast. Diffraction tomography can be performed using energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation. In EDD, different, properly-oriented Bragg planes diffract different x-ray energies; these intensities are measured by an energy sensitive detector. A pencil beam defines the irradiated volume, and a collimator before the energy sensitive detector selects which portion of the irradiated column is sampled at any one time. A 3D map is assembled by translating the specimen along X, Y and Z axes. This paper reports results of 3D mapping of the integrated intensity of several reflections from the bioapatite in the mineralized cartilage centrum of a blue shark. The multiple detector EDD system at 6-BM-B, the Advanced Photon Source was used to map an entire blue shark centrum. The shark centrum consists of a double cone structure (corpora calcerea) supported by the intermedialia consisting of four wedges. The integrated intensities of the c-axis reflection and of a reflection with no c-axis component reveals the bioapatite within the cone wall is oriented with its c-axes lateral, i.e., perpendicular to the axis of the backbone, whereas the bioapatite within the wedges is oriented with its c-axes axial. Results of absorption microCT (laboratory and synchrotron) and x-ray excited x-ray fluorescence mapping are included to provide higher resolution data of the structures underlying the EDD maps. Application of EDD tomography to 3D mapping of large specimens promises to add to the understanding of other mineralized tissue samples which cannot be sectioned.