Normalisation with coherent scatter signal: improvements in the calibration procedure of the Co-57-based in vivo XRF bone-Pb measurement

The feasibility of a normalised calibration variable to account for interpa tient variability for in vivo Co-57 XRF (X-ray fluorescence) finger bone-le ad measurements was assessed. Normalising the lead X-ray intensities to the coherent scatter signal was investigated by experiment and Monte Carlo sim ulation. The X-ray to coherent ratios for a fixed lead concentration were w ithin 5-10% of the mean; within uncertainty, over a physiologically relevan t range of finger bone sizes and overlying tissue thicknesses. This is an a cceptable level of variation to introduce, as it is less than the uncertain ty of a typical in vivo measurement. Normalisation has several advantages c ompared with the current method of correcting for interpatient variation, a s it eliminates the need for transporting extensive equipment to on-site me asurements, reduces the subject dose by a factor of two, and increases the objectivity of the bone-Pb assessment. (C) 2001 Elsevier Science Ltd. All r ights reserved.