A microbeam grazing-incidence approach to L-shell x-ray fluorescence measurements of lead concentration in bone and soft tissue phantoms

Abstract

ObjectiveL-shell x-ray fluorescence (LXRF) is a non-invasive approach to lead (Pb) concentration measurements in the human bone. The first studies were published in the early 1980s. In the same period the K-shell x-ray fluorescence (KXRF) method using a Cd-109 radionuclide source was developed and later improved and refined. Lower sensitivity and calibration difficulties associated with the LXRF method led the KXRF to be the most adopted method for in vivo human bone Pb studies. In the present study a microbeam-based grazing-incidence approach to Pb LXRF measurements was investigated.ApproachThe microbeam produced by an integrated x-ray tube and polycapillary x-ray lens (PXL) unit was used to excite cylindrical plaster-of-Paris (poP) bone phantoms doped with Pb in seven concentrations: 0, 8, 16, 29, 44, 59, and 74 µg g−1. Two 1 mm- and 3 mm-thick cylindrical shell soft tissue phantoms were made out of polyoxymethylene (POM) plastic. Three bone-soft tissue phantom sets corresponding to the 0, 1, and 3 mm POM thickness values resulted. Each phantom was placed between the microbeam and the detector; its position was controlled using a positioning stage. Small steps (0.1–0.5 mm) and short 30 s x-ray spectra acquisitions were used to find the optimal phantom position according to the maximum observed Sr Kα peak height. At the optimal geometry, five 180 s x-ray spectra were acquired for each phantom set. Calibration lines were obtained using the fitted peak heights of the two observed Pb Lα and Pb Lβ peaks.Main resultsThe lowest detection limit (DL) values were (2.9 ± 0.2), (4.9 ± 0.3), and (23 ± 3) µg g−1, respectively. The order of magnitude of the absorbed radiation dose in the POM plastic for the 180 s irradiation was estimated to be <1 mGy.SignificanceThe results are superior to a relatively recently published LXRF phantom study and show promise for future designs of in vivo LXRF measurements.

Improvements and reproducibility of an optimal grazing-incidence position method to L-shell x-ray fluorescence measurements of lead in bone and soft tissue phantoms

“…The OGIP methodology employed in this study significantly reduced the total x-ray exposure and data acquisition times reported in our previous study [25]. In the previous approach, the precision of finding the OGIP was strongly dependent on the step size in the phantom positioning sequence.…”

“…In a commercial poP product, Pejović-Milić et al [33] measured a concentration of 4 mg Sr/g Ca. Hence, short-time (10 s) acquisition spectra were sufficient to determine the optimal bone phantom positions as in our previous study [25]. Sr K-edge and Pb L 3 -edge energies are relatively close at 13.0 and 16.1 keV, as provided in the first two columns of table 2.…”

“…Gherase and Al-Hamdani investigated in a recent publication an optimal grazing-incidence position (OGIP) approach to the bone Pb LXRF measurements using the sub-millimeter x-ray beam produced by an integrated x-ray tube and x-ray lens table-top system [25]. Measurements of the Pb concentration in a small volume (~1 mm 3 ) within the superficial 1–2 mm depth of the outer cortical bone tissue is clinically relevant.…”

“…The experimental conditions of Gherase and Al-Hamdani study [25] did not meet the requirements of traditional grazing-incidence XRF experiments whereas the angle between the incident beam and sample surface is very small approaching the critical angle of total reflection of only a few milliradians. However, the experimental results demonstrated that the OGIP effectively mitigated the negative effect of the scattered photons on the Pb detectability [25]. Using five 180 s trials, a Pb detection limit of ~5 μg⁄g was found corresponding to a 2 mm layer of polyoxymethylene (POM) overlying the poP Pb-doped bone phantoms.…”

“…Second, significant deviations from linearity were observed in the Pb calibration data for the bare bone phantoms. While bone phantom density variation was invoked as a potential origin, the authors later considered that reproducibility issues with the OGIP procedure could have affected the outcomes [25].…”