A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kα ratio

Abstract

Abstract Objective. Lead (Pb) is a well-known toxic element. In vivo bone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure. In vivo human tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom and in vivo measurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate. Approach. In this study, bone and soft tissue (ST) phantoms simulated in vivo bone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g−1 of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g−1 concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1–4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method. Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g−1 for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr K β /K α ratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results. Significance. In vivo bone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.