Our lab has been working on the development of a portable L- shell x-ray fluorescence (LXRF) device to quantify lead in bone in human in vivo. The purpose of this project is to determine the accuracy of the portable LXRF machine in measuring the lead content of condor bones in vivo. While the K-shell x-ray fluorescence (KXRF) machine is the most accurate machine to measure lead content in vivo because it has sufficient energy to overcome soft tissue attenuation, it is not very practical for use in a research lab with animals or for researchers covering a large migratory territory of condors (from California to Arizona). The portable LXRF machine is lightweight; does not require continuous maintenance, a radioisotope source, or nitrogen cooling; and provides immediate spectra for analysis in a couple of minutes.

I calibrated the system with Pb-doped bone-equivalent phantoms that were covered with 0.54 mm, 1 mm, and 1.5 mm Lucite to mimic the effects of soft tissue attenuation. Seventeen condor cadaver bones were measured twice (for reproducibility) and the spectra were analyzed with our in- house spectral fitting program written with Mat-Lab. Significant correlation was observed between the bone Pb concentrations measured by the portable XRF and ICP-MS (R2 = 0.68, 0.63, and 0.74 for 0.54, 1, and 1.54 mm tissue thicknesses, respectively) and the linear regression of the KXRF results versus the 0.54 mm, 1 mm, and 1.54 mm Lucite thickness measurements was R2 = 0.89, 0.81, and 0.84. Two measurements of the same set of bones (Lucite thickness at 0.54 mm, 1 mm, and 1.54 mm) gave rise to the strong correlation with an R2 of 0.95, 0.76, and 0.81 respectively, which shows a great reproducibility of results.

In conclusion, the portable LXRF device has sufficiently proven to provide accurate measurements.