In vivo imaging of rat cortical bone porosity by synchrotron phase contrast micro computed tomography.

Cortical bone is a dynamic tissue which undergoes adaptive and pathological changes throughout life. Direct longitudinal tracking of this remodeling process holds great promise for improving our understanding of bone development, maintenance and senescence. The application of in vivo micro-computed tomography (micro-CT) has enabled longitudinal tracking of trabecular bone microarchitecture with commercially available scanners generally operating in the 10-20 µm voxel range with absorbed doses reported between 0.5 and 1 Gy. Imaging of cortical bone microarchitecture (porosity) requires higher resolution and thus in vivo imaging of these structures has not been achieved due to excessive radiation dose. In this study we tested the hypothesis that synchrotron propagation phase contrast micro-CT can enable in vivo imaging of cortical porosity in rats at doses comparable to those currently employed for trabecular bone imaging. Synchrotron imaging experiments were conducted at the Canadian Light Source using the bending magnet beamline of the BioMedical Imaging and Therapy (BMIT) facility. Protocol optimization (propagation distance, projection number) was conducted ex vivo on rat (Sprague-Dawley) forelimbs with dose determined by ion chamber and lithium fluoride crystal thermoluminescent dosimeters. Comparative ex vivo imaging was performed using laboratory in vivo scanning systems, identifying a range of doses between 1.2-3.6 Gy for common protocols. A final in vivo synchrotron protocol involving a 2.5 Gy dose was implemented with live rats. The resulting images demonstrated improved delineation of cortical porosity through the improved edge enhancement effect of phase contrast, opening the door to novel experimental studies involving the longitudinal tracking of remodeling.

Point taken: An unusual case of incisor agenesis and mandibular trauma in Early Bronze Age Siberia.

This paper focuses on the mandible of an adult male individual (radiocarbon dated to 4420-3995cal BP) from the Early Bronze Age Cis-Baikal cemetery of Ust'-Ida I (Siberia, Russian Federation). The mandible contains two features of interest: (1) bilaterally missing central incisors, and (2) the tip of a lithic projectile point embedded in the symphyseal region. Despite the absent teeth, the mandible presents a dental arcade without diastemata, appearing normal and complete on first glance. Three different levels of CT (computed tomography) imaging-ranging from clinical to synchrotron-based-were employed in order to establish the aetiology behind the missing dentition, whether subsequent to the projectile trauma or entirely unrelated to it. Results indicate that the mandible exhibits two highly unusual but unrelated features: probable bilateral agenesis of the central incisors and perimortem trauma to the mental symphysis. In addition, the embedded tip was successfully matched via digital imaging to photographs of a broken projectile point, an artefact recovered from the facial region of the skeleton.