In vivo measurements of aluminum and strontium in human bone

Abstract

<p>This thesis investigated a means of improving bone aluminum measurement using neutron activation analysis which has been previously demonstrated for measuring trace and minor elements in human tissues. Currently, a KN Van de Graaff-accelerator was used with irradiation parameters of 2 MeV proton energy and 100 μA current, to activate aluminum via the 27 Al(n, γ) 28 Al reaction. A minimum detectable limit of 1.14 mg of aluminum in hand was achieved, accompanied with a hand dose of 48 mSv delivered to the subject. Further improvements in the sensitivity of aluminum assessment has been investigated by Monte Carlo modeling, and a new irradiation cavity has been proposed. The cavity design focused on increasing the thermal neutron flux to the hand, while providing additional shielding to the subject, and therefore, it should allow ethics approval for in vivo testing and application. A source-based x-ray fluorescence (XRF) technique of bone strontium was also developed. The designed XRF system was tested in vivo on ten subjects, successfully detecting the strontium quantities in the finger bone. Furthermore, three normalization techniques were investigated such as: coherent normalization, the strontium Kα/Kβ x-ray ratio and the Sr/Ca ratio in bone. The feasibility of normalizations show that none of the normalization can be reliably applied to healthy subjects. Therefore, an ultrasound measurement was an integral part of strontium XRF, as a means to measure overlying tissue thickness at the measurement site that was necessary for the estimation of bone strontium concentration during the course of this work.</p>