A novel approach to lead concentration measurements in bone using the L-shell x-ray fluorescence and strontium Kβ/Kα ratio.*

Lead (Pb) is a well-known toxic element which accumulates in the bone after years or decades of exposure. Long-term Pb exposure is, therefore, assessed by in vivo bone Pb concentration measurements. In vivo bone Pb x-ray fluorescence (XRF) measurements are typically done in tibia bone to minimize the soft tissue (ST) x-ray attenuation. Bone Pb L-shell XRF (LXRF) can use compact XRF systems – a useful feature for potential bone Pb surveys. An optimal grazing-incidence position (OGIP) method was developed in our lab to enhance Pb detection by mitigating the x-ray scatter. The obstacle to in vivo applications is the unknown ST x-ray attenuation. The average ST x-ray linear attenuation coefficient and ultrasound-measured thickness past approach gave inaccurate results. In our method, the measured Kβ/Kα ratio of strontium (an essential trace element in the bone) was used to estimate the ST attenuation of the Pb x-rays. Plaster-of-Paris (poP) bone phantoms made with known Pb and Sr concentrations and polyoxymethylene (POM) ST phantoms of varying thickness were measured. The concordance correlation coefficients between the computed and the known Pb concentrations were in the -0.444 to 0.998 range.