A novel L-shell x-ray fluorescence bone lead quantification method based on direct x-ray soft tissue attenuation measurement using a microbeam and a bone and soft tissue phantom assembly*

Lead (Pb) is a well-known toxic element residing in the human bone for many years. Therefore, in vivo measurement of bone Pb concentration is a metric of long-term human exposure. The L-shell x-ray fluorescence (LXRF) large population bone Pb surveys can be designed with portable x-ray tubes and detectors. In the past studies the x-ray attenuation of the soft tissue (XAST) overlying the bone was accounted for using ultrasound and average elemental compositions to calculate its linear attenuation coefficient (μ). The procedure proved inaccurate. A cylindrical plaster-of-Paris (bone) and a 3-mm thick cylindrical-shell polyoxymethylene (POM) (soft tissue) were used in a scanning microbeam XAST measurement. The μ_POM measurements were in excellent agreement (<5%) with the μ_POM calculations using the POM chemical formula (CH₂O)_n and the NIST XCOM database. A relationship between the XAST and the Pb calibration line slopes for 0, 1, and 3 mm POM thickness values was recently demonstrated by our group which can lead to a more accurate in vivo Pb LXRF measurement method.