The feasibility of measuring bone uranium concentrations in vivo using source excited K x-ray fluorescence

X-ray fluorescence (XRF) has been demonstrated to be an extremely useful technique for measuring trace quantities of heavy metals in various tissues within the body. This study investigates the applicability of XRF to the measurement of bone uranium concentration. The factors affecting the accuracy and minimal detectable concentration of bone uranium in vivo are discussed. The system chosen employs a 57Co source to excite the uranium K x-rays, with the source and detector in an approximate 180 degrees backscatter geometry relative to the sample position. It is demonstrated, with experiment and Monte Carlo simulation, that the x-ray to coherent peak ratio is linearly related to concentration and is independent of variations in source-sample geometry, thickness of overlying tissue and tibia size. Preliminary in vivo measurements indicate that this system has a minimum detectable concentration of approximately 20 micrograms U/g bone mineral which may not be sufficiently precise for a monitoring system for occupational workers. Future work will involve attempts to enhance this precision through the use of alternative sources for the excitation of uranium x-rays as well as possible modifications to the detector and electronics.