Design of an XRF system for in vivo measurement of lead in bone

The toxicological effects of lead in humans have been long known. The long-term exposure is best measured by the lead in bone, which is known to contain over 90% of the body´s lead burden. We are in the process of developing a faster, more accurate measurement system based on the latest techniques pioneered in astrophysics and synchrotron light source research. We report here on the first phase of the program, which is aimed at determining the parameters for obtaining the maximum sensitivity with L X-ray fluorescence; a further phase will be concerned with K XRF. The studies are being carried out at the National Synchrotron Light Source at Brookhaven National Laboratory (BNL NSLS) using a monochromatic, polarized X-ray beam, tunable over the energy range from 8 keV (well below the L_III binding energy of 13.035 keV) to 30 keV (well above the L_I binding energy of 15.86 keV). We used cylindrical bone phantoms made from plaster of paris, doped with 17 ppm and 115 ppm of lead, and covered with 5 mm of Lucite to simulate the overlaying skin tissue. At an excitation energy of 16.5 keV, and with an available planar Ge detector in an XRF geometry that made effective use of the polarized beam, we were immediately able to measure 17 ppm of lead in bone phantom in a few minutes