Oregon State University, Department of Nuclear Engineering and Radiation Health Physics, Corvallis, OR 97331, USA.
Health Phys. 2011 May;100(5):502-7. doi: 10.1097/HP.0b013e3181f725af.
Mathematical simulations and benchmark measurements were performed to assess the impact that normal variations in human calcium content have on in vivo K x-ray fluorescence measurements of lead in bone. Four sets of cortical bone tissue simulants were fabricated containing from 20.8% to 23.8% calcium (by weight) for measurement in a surrogate (phantom) of the human leg. The net counts detected in the coherent backscatter peak at 88.034 keV using a Cd source indicate a positive trend, with a variability of up to 17% over the range of assessed calcium content. Mathematical simulations confirm this trend and also demonstrate that the contribution of 87.3 keV Pb Kβ2 counts, which are unresolved in measurements, do not contribute significantly to the coherent peak at low levels of bone-lead content. Both measurements and simulations confirm that calcium is a statistically significant parameter in predicting the K-XRF response and suggest that lead levels may be over-predicted for individuals having low bone density compared to the calibration matrix. Simulations identify a 4.5% negative bias in measured lead values for each 1% increase in calcium weight percent in the bone matrix as compared to the calibration matrix. It is therefore important to accommodate this uncertainty when performing epidemiological studies of populations having a wide range of bone densities.
进行了数学模拟和基准测量，以评估人体钙含量的正常变化对体内骨骼中铅的 KX 射线荧光测量的影响。制备了四组皮质骨组织模拟物，钙含量（按重量计）从 20.8%到 23.8%不等，用于人体腿部的替代（幻影）物测量。使用 Cd 源在 88.034keV 的相干背散射峰处检测到的净计数呈正趋势，在评估的钙含量范围内，其变化幅度高达 17%。数学模拟证实了这一趋势，并还表明，在低骨铅含量下，未在测量中解析的 87.3keV Pb Kβ2 计数的贡献对相干峰没有显著贡献。测量和模拟均证实钙是预测 K-XRF 响应的一个重要统计学参数，并表明与校准矩阵相比，对于骨密度较低的个体，铅水平可能被高估。与校准矩阵相比，模拟表明，对于每增加 1%的骨基质钙重量百分比，测量的铅值会出现 4.5%的负偏差。因此，在对具有广泛骨密度范围的人群进行流行病学研究时，必须考虑到这种不确定性。
