Purpose: Tomography using diffracted x-rays produces reconstructions mapping quantities such as crystal lattice parameter(s), crystallite size, and crystallographic texture, information quite different from that obtained with absorption or phase contrast. Diffraction tomography is used to map an entire blue shark centrum with its double cone structure (corpora calcerea) and intermedialia (four wedges).
Approach: Energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation at 6-BM-B, the Advanced Photon Source, were used. Different, properly oriented Bragg planes diffract different x-ray energies; these intensities are measured by one of ten energy-sensitive detectors. A pencil beam defines the irradiated volume, and a collimator before each energy-sensitive detector selects which portion of the irradiated column is sampled at any one time. Translating the specimen along X , Y, and Z axes produces a 3D map.
Results: We report 3D maps of the integrated intensity of several bioapatite reflections from the mineralized cartilage centrum of a blue shark. The c axis reflection’s integrated intensities and those of a reflection with no c axis component reveal that the cone wall’s bioapatite is oriented with its c axes lateral, i.e., perpendicular to the backbone’s axis, and that the wedges’ bioapatite is oriented with its c axes axial. Absorption microcomputed tomography (laboratory and synchrotron) and x-ray excited x-ray fluorescence maps provide higher resolution views.
Conclusion: The bioapatite in the cone walls and wedges is oriented to resist lateral and axial deflections, respectively. Mineralized tissue samples can be mapped in 3D with EDD tomography and subsequently studied by destructive methods.
Contrast in Computed Tomography (CT) most often relies on absorption differences, and reconstructions give absorptivity of each volume element (voxel) but not the material’s identity. This paper describes the first use of in situ position-resolved x-ray diffraction to identify different contents (see below) within an intact mummy. Hawara Portrait Mummy No. 4 (HPM4) was first imaged with a clinical CT scanner, and this 3D “roadmap” guided diffraction mapping at beamline 1-ID of the Advanced Photon Source. Only 24 hrs were available, and the CT data allowed mapping of only the volumes of interest. The long beam path through the mummy was a major complication solved by collecting each diffraction pattern at two detector-mummy separations. Accuracy in diffracting volume positions was 1-2 mm, and precision sufficed for diffraction identification of the materials. Diffraction patterns were collected from the mineralized tissues within the five year old child’s mummy (HPM4), specifically the skull, cervical vertebrae, femora and teeth. Patterns from the femorum lateral and medial sides (and the skull’s left and right sides) could be analyzed separately. Lattice parameters and crystallite sizes of the bones’ mineral phase were comparable with those from modern bone. Within the wrappings, wires were located by diffraction and identified as a modern dual phase steel, probably introduced during earlier conservation. Highly absorbing, millimeter-sized inclusions were identified as calcite. The position of these and other features were found at the positions indicated by the CT scans, and the limitations of the diffraction approach compared to absorption CT are discussed.
Forensic anthropologists are routinely asked to estimate a biological profile (i.e., age, sex, ancestry and
stature) from a set of unidentified remains. In contrast to the abundance of collections and techniques associated with
adult skeletons, there is a paucity of modern, documented subadult skeletal material, which limits the creation and
validation of appropriate forensic standards. Many are forced to use antiquated methods derived from small sample
sizes, which given documented secular changes in the growth and development of children, are not appropriate for
application in the medico-legal setting. Therefore, the aim of this project is to use multi-slice computed tomography
(MSCT) data from a large, diverse sample of modern subadults to develop new methods to estimate subadult age and
sex for practical forensic applications. The research sample will consist of over 1,500 full-body MSCT scans of
modern subadult individuals (aged birth to 20 years) obtained from two U.S. medical examiner’s offices. Statistical
analysis of epiphyseal union scores, long bone osteometrics, and os coxae landmark data will be used to develop
modern subadult age and sex estimation standards. This project will result in a database of information gathered from
the MSCT scans, as well as the creation of modern, statistically rigorous standards for skeletal age and sex estimation
in subadults. Furthermore, the research and methods developed in this project will be applicable to dry bone
specimens, MSCT scans, and radiographic images, thus providing both tools and continued access to data for forensic
practitioners in a variety of settings.
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