Patella lead x-ray fluorescence measurements are independent of sample orientation

In vivo x-ray fluorescence bone lead measurements assess long-term lead exp osure. Tibia, calcaneus, and patella are the most commonly sampled bones. P atella measurements also include lead signals from the distal femur, proxim al tibia, and synovium. It is therefore important to know whether the orien tation of the patella relative to the measurement system substantially affe cts the measured patella lead concentrations and their measurement uncertai nties. This study examined whether these parameters exhibited a dependence on the orientation of the patella with respect to the measurement system, a dependence that could arise from varying nonpatella contributions. There w as no effect of orientation on measured patella lead concentration, but the re was a highly significant effect of orientation on the measurement uncert ainty. These data do not conclusively show that there are no nonpatella con tributions to a patella lead measurement; rather, that any such contributio ns are not a function of measurement orientation over the range of orientat ions considered. Further study is required if the contribution of nonpatell a tissues to a patella lead XRF-measured concentration is to be fully addre ssed. This study also filled a gap in the literature by quantifying the wit hin-patella (29%) and between-patella (71%) variability of measured patella lead concentrations from replicate measures of nine patellae. (C) 2001 Ame rican Association of Physicists in Medicine.