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Detection of lead in bone phantoms and arsenic in soft tissue phantoms using synchrotron radiation and a portable x-ray fluorescence system
(IOP Publishing, 2017-01-30) Groskopf, Craig; Bennett, Stephen R.; Gherase, Mihai R.; Fleming, David E.B.
The differences and commonalities between x-ray fluorescence results obtained using synchrotron radiation and a portable x-ray fluorescence device were examined using arsenic in soft tissue phantoms and lead in bone phantoms. A monochromatic beam energy of 15.8 keV was used with the synchrotron, while the portable device employed a rhodium anode x-ray tube operated at 40 kV. Bone phantoms, dosed with varying quantities of lead, were made of Plaster of Paris and placed underneath skin phantoms of either 3.1 mm or 3.9 mm thickness. These skin phantoms were constructed from polyester resin, and dosed with varying amounts of arsenic. Using an irradiation time of 120 seconds, arsenic Kα and Kβ, and lead Lα and Lβ characteristic x-ray peaks were analysed. This information was used to calculate calibration line slopes and minimum detection limits for each data set. As expected, minimum detection limits were much lower at the synchrotron for detecting arsenic and lead. Both approaches produced lower detection limits for arsenic in soft tissue than for lead in bone when simultaneous detection was attempted. Although arsenic Kα and lead Lα emissions share similar energies, it was possible to detect both elements in isolation by using the arsenic Kβ and lead Lβ characteristic x-rays. Greater thickness of soft tissue phantom reduced the ability to detect the underlying lead. Experiments with synchrotron radiation could help guide future efforts toward optimizing a portable x-ray fluorescence in vivo measurement device.
Feasibility of measuring zinc in human nails using portable x-ray fluorescence
(Elsevier, 2018-09-24) Fleming, David E.B.; Bennett, Stephen R.; Frederickson, Christopher J.
A variety of adverse health effects have been identified as resulting from zinc deficiency. Zinc supplementation may therefore be indicated for certain individuals or populations. A rapid and straightforward means of assessing zinc status in humans would be of considerable medical benefit. In this study, the feasibility of measuring zinc levels in human fingernails or toenails using a portable x-ray fluorescence technique was assessed. Whole nail models (or phantoms) were constructed from resin, and dosed with various concentrations of zinc. These different concentration “nails” were cut into small slices of 4.4 ± 0.2 mm width. The combination of these various slices into different arrangements allowed the modeling of different time-dependent zinc exposure scenarios. A portable x-ray fluorescence device was tested using an “open beam” configuration having a beam diameter of ~9 mm, and using a “weld mask” configuration with the beam width reduced to 2.9 mm. Minimum detection limits were determined to be 0.15 ± 0.01 ppm for the open beam, and 1.13 ± 0.08 ppm when using the weld mask. By scanning across the length of the model nails, it was demonstrated that differences in zinc levels deposited over time could be detected, and that the weld mask configuration was better suited to resolving spatial changes. The x-ray fluorescence approach was found to be highly sensitive for detecting zinc in nail, and capable of differentiating patterns of zinc uptake over time.
Assessing arsenic and selenium in a single nail clipping using portable X-ray fluorescence
(Elsevier, 2016-12-19) Fleming, David E.B.; Nader, Michel N.; Foran, Kelly A.; Groskopf, Craig; Reno, Michael C.; Ware, Chris S.; Tehrani, Mina; Guimarães, Diana; Parsons, Patrick J.
The feasibility of measuring arsenic and selenium contents in a single nail clipping was investigated using a small-focus portable X-ray fluorescence (XRF) instrument with monochromatic excitation beams. Nail clipping phantoms supplemented with arsenic and selenium to produce materials with 0, 5, 10, 15, and 20 μg/g were used for calibration purposes. In total, 10 different clippings were analyzed at two different measurement positions. Energy spectra were fit with detection peaks for arsenic Kα, selenium Kα, arsenic Kβ, selenium Kβ, and bromine Kα characteristic X-rays. Data analysis was performed under two distinct conditions of fitting constraint. Calibration lines were established from the amplitude of each of the arsenic and selenium peaks as a function of the elemental contents in the clippings. The slopes of the four calibration lines were consistent between the two conditions of analysis. The calculated minimum detection limit (MDL) of the method, when considering the Kα peak only, ranged from 0.210 ± 0.002 μg/g selenium under one condition of analysis to 0.777 ± 0.009 μg/g selenium under another. Compared with previous portable XRF nail clipping studies, MDLs were substantially improved for both arsenic and selenium. The new measurement technique had the additional benefits of being short in duration (~3 minutes) and requiring only a single nail clipping. The mass of the individual clipping used did not appear to play a major role in signal strength, but positioning of the clipping is important.
Assessment of alternative methods for analyzing X-ray fluorescence spectra
(Elsevier, 2019-02-13) Nader, Michel N.; Fleming, David E.B.
When analyzing characteristic peaks in X-ray fluorescence (XRF) spectra, the peak area is the value most often used to quantify peak size. However, some studies have reported the amplitude of the peak instead of the area. When the width of the peak is allowed to vary from trial to trial in order to provide the best possible fit to the data, these two alternative methods can yield slightly different results. In the current study, these two approaches to peak analysis are compared for data obtained from bone reference materials having certified lead concentrations of 1.09 ± 0.03 μg/g, 16.1 ± 0.3 μg/g, 13.2 ± 0.3 μg/g, and 31.5 ± 0.7 μg/g. Measurements were made with an Olympus Innov-X Delta Premium portable XRF system. Using both the area and amplitude methods, lines of best fit were constructed for the lead Lα and lead Lβ signals as a function of lead concentration. Additionally, coefficients of variation were calculated for each reference material and condition of analysis. To assess possible variations over time, the procedure was performed at two points separated by about one year. The amplitude and area methods were found to produce results which were consistent and proportional. Using either method, lead XRF signal plotted as a function of known lead concentration produced adjusted r2 values of ~0.99. The amplitude method provided slightly higher adjusted r2 values overall. Coefficients of variation were generally very similar between the two methods, although more pronounced differences emerged from measurements of the lowest concentration reference material.
Optimization of L-shell X-ray fluorescence detection of lead in bone phantoms using synchrotron radiation
(Wiley, 2017-06-29) Gherase, Mihai R.; Feng, Renfei; Fleming, David E.B.
Closely-related toxicity and retention mechanisms of lead (Pb) in the human body involve the bone tissues where Pb can accumulate and reside on a time scale ranging from years to tens of years. In vivo measurements of bone Pb can, therefore, play an important role in a comprehensive health risk assessment of Pb exposure. In vivo L-shell X-ray fluorescence (LXRF) measurement of bone Pb was first demonstrated over four decades ago. Implementation of the method, however, encountered challenges associated with low sensitivity and calibration procedure. In this study the LXRF measurement was optimized by varying the incident photon energy and the excitation-detection geometry. The Canadian Light Source synchrotron radiation was used to compare two different excitation detection geometries of 90° and 135° using three different X-ray photon energies: 15.8, 16.6, and 17.5 keV. These energies optimized excitation of the L3 subshell of Pb and simulated the most intense K-shell emissions of zirconium, niobium, and molybdenum, respectively. Five rectangular plaster-of-Paris bone phantoms with Pb concentrations of 0, 7, 17, 26, and 34 μg⁄g and one rectangular 3.1 mm-thick resin phantom mimicked the X-ray attenuation properties of human bone and soft tissue, respectively. Optimal LXRF detection was obtained by the 15.8 keV energy and the 90° and 135° geometries for the bare bone and the bone and soft tissue phantoms, respectively.