Performance comparison of two Olympus InnovX handheld x-ray analyzers for feasibility of measuring arsenic in skin in vivo - Alpha and Delta models.

The Figure-Of-Merit (FOM) performance, a combination of detection limit and dose, is compared between two generations of handheld X-Ray Fluorescence (XRF) spectrometers for the feasibility of in vivo XRF measurement of arsenic (As) in skin. The Olympus InnovX Delta model analyzer (40 kVp using either 37 or 17µA) was found to show improvements in Minimum Detection Limit (MDL) using arsenic As-doped skin calibration phantoms with bulk tissue backing, when compared to the first generation InnovX Alpha model (40kVp, 20µA) in 120s measurements. Differences between two different definitions of MDL are discussed. On the Delta system, an MDL of (0.462±0.002) µg/g As was found in phantoms, with a nylon backing behind to mimic bulk tissue behind skin. The equivalent and effective doses were found to be (10±2) mSv and ~7×10-3µSv respectively for the Alpha and (15±4) mSv and ~8×10-3µSv respectively for the Delta system in 120s exposures. Combining MDL and effective dose, a lower (better) FOM was found for the Delta, (1.7±0.4) ppm mSv1/2, compared to (4.4±0.5) ppm mSv1/2 for the Alpha model system. The Delta analyzer demonstrates improved overall system performance for a rapid 2-min measurement in As skin phantoms, such that it can be considered for use in populations exposed to arsenic.

Age and sex influence on bone and blood lead concentrations in a cohort of the general population living in Toronto.

OBJECTIVE: To study the age and sex influence on bone and blood lead concentrations in a cohort of the general population living in Toronto. APPROACH: A 109Cd K x-ray fluorescence (KXRF) measurement system was used from 2009 to 2011 in a study that measured the bone lead (Pb) concentration of 263 environmentally exposed individuals residing in Toronto, Ontario, Canada. Tibia (cortical bone) and calcaneus (trabecular bone) lead contents were measured in 134 males and 129 females between 1 and 82 years of age. Whole blood Pb concentration was measured by TIMS (thermal ionization mass spectrometer). Tibia (Ti) and calcaneus (Cal) Pb were examined versus the age of participants, taking into account uncertainties in bone Pb measurement values. MAIN RESULTS: No significant sex differences were observed in any of the age categories. Participants older than 50 years of age demonstrated the highest concentrations of Pb in their blood, tibia, and calcaneus bones. SIGNIFICANCE: In most of the previous publications, uncertainty was not considered in the regression model of bone Pb and age. However, in this paper, we adjusted the bone Pb values for the uncertainty level. This had a significant influence in regression models of bone Pb and thus we recommend that uncertainty be considered in future studies.

Feasibility of measuring arsenic and selenium in human skin using in vivo x-ray fluorescence (XRF)--a comparison of methods.

In recent years, in vivo measurement systems of arsenic in skin by K-shell x-ray fluorescence (XRF) have been developed, including one which was applied in a pilot study of human subjects. Improved tube-based approaches suggest the method can be further exploited for in vivo studies. Recently, it has been suggested that selenium deficiency is correlated with arsenic toxicity. A non-invasive measurement of both elements could therefore be of potential interest. The main aim of this current study was to evaluate and compare the performance of an upgraded portable XRF system and an advanced version of the benchtop XRF system for both selenium and arsenic. This evaluation was performed in terms of arsenic and selenium Kα detection limits for a 4W gold anode Olympus InnovX Delta portable analyzer (40 kVp) in polyester resin skin-mimicking phantoms. Unlike the polychromatic source earlier reported in the literature, the benchtop tube-based technique involves monochromatic excitation (25 W silver anode, manufactured by x-ray optics, XOS) and a higher throughput detector type. Use of a single exciting energy allows for a lower in vivo dose delivered and superior signal-noise ratio. For the portable XRF method, arsenic and selenium minimum detection limits (MDLs) of 0.59 ± 0.03 ppm and 0.75 ± 0.02 ppm respectively were found for 1 min measurement times. The MDLs for arsenic and selenium using the benchtop system were found to be 0.35 ± 0.01 ppm and 0.670 ± 0.004 ppm respectively for 30 min measurement times. In terms of a figure of merit (FOM), allowing for dose as well as MDL, the benchtop system was found to be superior for arsenic and the two systems were equivalent, within error, for selenium. We shall discuss the performance and possible improvements of each system, their ease of use and potential for field application.

Uncertainty calculations for the measurement of in vivo bone lead by x-ray fluorescence.

In order to quantify the bone lead concentration from an in vivo x-ray fluorescence measurement, typically two estimates of the lead concentration are determined by comparing the normalized x-ray peak amplitudes from the Kalpha(1) and Kbeta(1) features to those of the calibration phantoms. In each case, the normalization consists of taking the ratio of the x-ray peak amplitude to the amplitude of the coherently scattered photon peak in the spectrum. These two Pb concentration estimates are then used to determine the weighted mean lead concentration of that sample. In calculating the uncertainties of these measurements, it is important to include any covariance terms where appropriate. When determining the uncertainty of the lead concentrations from each x-ray peak, the standard approach does not include covariance between the x-ray peaks and the coherently scattered feature. These spectral features originate from two distinct physical processes, and therefore no covariance between these features can exist. Through experimental and simulated data, we confirm that there is no observed covariance between the detected Pb x-ray peaks and the coherently scattered photon signal, as expected. This is in direct contrast to recent work published by Brito (2006 Phys. Med. Biol. 51 6125-39). There is, however, covariance introduced in the calculation of the weighted mean lead concentration due to the common coherent normalization. This must be accounted for in calculating the uncertainty of the weighted mean lead concentration, as is currently the case. We propose here an alternative approach to calculating the weighted mean lead concentration in such a way as to eliminate the covariance introduced by the common coherent normalization. It should be emphasized that this alternative approach will only apply in situations in which the calibration line intercept is not included in the calculation of the Pb concentration from the spectral data: when the source of the intercept is well characterized and known to come from trace contamination by Pb in the plaster of Paris calibration standards. In our approach, the coherent normalization is only applied to one parameter and we no longer take a weighted mean of correlated quantities. Our proposed alternative calculation has essentially no effect on the calculated error of the mean lead concentration, indicating that the existing method of accounting for this covariance is sufficient.