L-shell x-ray fluorescence measurements of lead in bone: theoretical considerations.

This paper reviews several theoretical considerations pertinent to the use of lead L-shell x-rays for the in vivo measurement of lead in bone: the method of correcting for attenuation, the contributions to the measurement uncertainty, interferences, the depth of bone sampled and the signal strength. Both the predicted bone lead concentration and the measurement uncertainty therein are influenced by the choice of linear attenuation coefficient with which to correct for overlying tissue. Measurement uncertainty is also influenced by inter-individual variability in body composition, methodological uncertainty in the ultrasound measurement of overlying tissue thickness and discrepancy between the site of LXRF and the site of ultrasound measurement. Interference with the Pb Lalpha x-rays by As Kalpha has been overstated and is probably negligible, interference from lead in non-bone tissues may not be. The depth of bone from which the signal is obtained and a crude estimate of signal strength are calculated for different bone compositions for both K and L x-ray fluorescence.