Optimization of L-shell X-ray fluorescence detection of lead in bone phantoms using synchrotron radiation

Abstract

Closely-related toxicity and retention mechanisms of lead (Pb) in the human body involve the bone tissues where Pb can accumulate and reside on a time scale ranging from years to tens of years. In vivo measurements of bone Pb can, therefore, play an important role in a comprehensive health risk assessment of Pb exposure. In vivo L-shell X-ray fluorescence (LXRF) measurement of bone Pb was first demonstrated over four decades ago. Implementation of the method, however, encountered challenges associated with low sensitivity and calibration procedure. In this study the LXRF measurement was optimized by varying the incident photon energy and the excitation-detection geometry. The Canadian Light Source synchrotron radiation was used to compare two different excitation detection geometries of 90° and 135° using three different X-ray photon energies: 15.8, 16.6, and 17.5 keV. These energies optimized excitation of the L3 subshell of Pb and simulated the most intense K-shell emissions of zirconium, niobium, and molybdenum, respectively. Five rectangular plaster-of-Paris bone phantoms with Pb concentrations of 0, 7, 17, 26, and 34 μg⁄g and one rectangular 3.1 mm-thick resin phantom mimicked the X-ray attenuation properties of human bone and soft tissue, respectively. Optimal LXRF detection was obtained by the 15.8 keV energy and the 90° and 135° geometries for the bare bone and the bone and soft tissue phantoms, respectively.