In vivo methods of analysis in the study of elemental composition of the body

• Main Author: Nicolaou, G. E.
• Published: University of Surrey 1983
• Subjects: 612; Physiology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.344401

Knowledge of elemental composition of biological systems has become particularly important as an index of health status. In this work techniques are developed, which allow body composition studies, based upon neutron activation analysis and X-ray transmission tomography. The neutron irradiation facility comprises a 5Ci Am/Be neutron source and is designed to allow prompt, delay and cyclic activation analysis to be performed during the same experiment, thus extracting maximum information about body elemental composition for the same radiation dose. The measurement of the liver concentration of selenium is performed, using cyclic neutron activation, via the isomer 77Se(17.6s). A detection limit of 0.6 ppm is obtained. The combination of cyclic and prompt activation allows the measurement of both cadmium and selenium in liver, during the same experiment. A detection limit for cadmium of 10 ppm is obtained. The dose delivered to a 'patient' during the whole experiment is 0.5 X 10-2Sv. A Monte Carlo code which allows the determination of the solid angle subtended by a collimated detector and a distributed photon source is developed. This information is essential in the quantification of activity. The code is modified to predict the best positioning of the detector, with respect to the neutron source, for minimum photon, interference in prompt activation when the detector and the source are proximal. Qualitative and quantitative analysis of the cortical and trabecular bone regions of a long bone is performed using X-ray transmission tomography. The cross-sectional area of the cortical bone is found to increase away from the proximal and distal ends whereas the reverse occurs for trabecular bone. The specific gravity of the two bone regions increases from the knee to the ankle end. A similar result is observed for the Ca/P ratio. A comparison of the anterior and posterior cortex reveals a higher specific gravity in the latter. These results are consistent with the distribution of weight on the human tibia.