Assessment of human long-term lead exposure using a confocal L-shell x-ray fluorescence method for bone lead measurements

铅是一种众所周知的有毒元素。它在人体内的存在会对人体产生严重的负面影响 即使在微量浓度下也会影响人类的健康和发展。儿童的发育健康问题 暴露在铅中，如认知能力下降，听力受损，多动症和青春期延迟 尤其令人担忧的是。根据环境保护署(EPA)的数据，2010年估计 535,000名儿童的血液水平为5μg/dL，美国约有2,400万户家庭仍有 严重的含铅油漆危害。据报道，1-5岁儿童的血铅水平也较高。 来自低收入家庭和某些种族和民族群体的10岁以下儿童。铅主要积累在 在长时间暴露后的骨组织中。因此，活体X射线荧光(XRF)测量 骨铅含量是评价人体铅负荷的重要指标。这些测量结果是 目前使用基于探测铅的K壳层XRF光子(KXRF)的分析方法执行 在胫骨中使用109Cd放射源。由于相对较高的成本和辐射安全问题 在放射源周围，KXRF方法的使用仅限于世界各地的几个实验室。这个 开发一种新的、廉价、便携和易于使用的骨铅测量方法具有 有可能大规模评估儿童的铅暴露情况。过去研究过的另一种选择是 利用低光子能量的L壳层X射线荧光检测骨中铅(LXRF)。不幸的是，LXRF研究 报告的灵敏度和准确度值不符合活体人铅骨的要求 测量。通过使用共焦x射线，可以对过去的lxrf方法进行重大改进。 荧光(C-XRF)技术。C-XRF是传统XRF的一种新方法，除了 X射线源和探测器，使用两个多毛细管X射线透镜(PXL)：一个将激发光束聚焦在 样品(~1nL)内的小体积元(SVE)，而另一个引导出射XRF光子 把同样的SVE放到X射线探测器上。C-XRF技术的优势是： 1.由于与PXL相关的X射线散射减少，铅的最低检测下限(MDL)更高 准直入射和出射的X射线束， 2.定义良好的入射-出射X射线束几何结构支持综合光谱校准 手术不需要单独的软组织测量， 3.改进了辐射剂量和铅MDL之间的权衡，这是可能的，因为显著减少 C-XRF技术照射的人体组织体积。 人体胫骨上覆软组织模型中铅C-XRF测量的系统研究 建议。这一结果可以指导设计一种便携式、易于使用的C-XRF设备，该设备可以显著地 提升体内骨铅测量作为研究、诊断和筛查工具的作用。

Lead is a well-known toxic element. Its presence in the human body has serious negative consequences on the human health and development even in trace concentrations. Developmental health problems in children exposed to lead such as reduced cognitive abilities, impaired hearing, hyperactivity and delayed puberty are particularly concerning. According to the Environmental Protection Agency (EPA) in 2010 an estimated 535,000 children had a blood level of 5 μg/dL and about 24 million homes in the United States still had significant lead-based paint hazards. Blood lead levels were also reported to be higher for children ages 1-5 years old from lower-income families and for certain racial and ethnic groups. Lead accumulates predominantly in the bone tissue following prolonged exposure. Therefore, in vivo x-ray fluorescence (XRF) measurements of lead concentration in bone is an important assessment tool for human lead burden. These measurements are currently performed using an analytical method based on the detection of K-shell XRF photons of lead (KXRF) in the tibia bone using a 109Cd radioactive source. Due to the relatively high costs and radiation safety concerns surrounding radioactive sources, the KXRF method usage was limited to several laboratories worldwide. The development of a novel, inexpensive, portable, and easy-to-use method for bone lead measurements has the potential to assess on a large scale the lead exposure of children. An alternative investigated in the past was to use the lower photon energy L-shell XRF detection of lead in bone (LXRF). Unfortunately, the LXRF studies reported sensitivity and accuracy values which did not meet the requirements of in vivo human lead bone measurements. Significant improvements to the past LXRF method can be made by using a confocal x-ray fluorescence (C-XRF) technique. The C-XRF is a novel approach to the traditional XRF that, in addition to the x-ray source and detector, uses two polycapillary x-ray lenses (PXLs): one focuses the excitation beam on a small volume element (SVE) within the sample (~1 nL) while the other guides the emergent XRF photons from the same SVE onto the x-ray detector. The advantages of the C-XRF technique are: 1. Better minimum detection limit (MDL) of lead due to x-ray scatter reduction associated with the PXLs collimation of the incident and emergent x-ray beams, 2. Well-defined incident-emergent x-ray beam geometry supports an integrated spectrometric calibration procedure eliminating the need of separate soft tissue measurements, 3. Improved tradeoff between the radiation dose and lead MDL which is possible by the significantly reduced human tissue volume irradiated in the C-XRF technique. A systematic study of lead C-XRF measurements in human tibia bone phantoms with overlying soft tissue is proposed. The results can lead to the design of a portable easy-to-use C-XRF device which can significantly elevate the role of in vivo bone lead measurement as a research, diagnostic, and screening tool.