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LEAD Action News Volume 22 Number 4 December 2024 Page 44 of 131

Portable XRF validation and method to quantify

bone lead in vivo

By Dr Aaron Specht, Assistant Professor, School of Health Sciences, Purdue University, USA

Photo from https://www.mpo-mag.com/breaking-news/purdue-researcher-develops-lead-detection-

breakthrough-tech/

Pilot work to validate portable XRF:

Over the last few years, principal investigator Specht’s lab (see biosketch) made substantial

progress in validating a portable XRF machine for quantifying metals in bone in vivo.170-172

As shown in Figure 7a, conventional KXRF and portable XRF measurements of Pb are highly

correlated (R2=0.95) in four goat bones covered by 3 mm of soft tissue. To further validate the

portable XRF against the standard KXRF bone Pb measurement system, 76 human participants

were recruited and their bone Pb content measured. This study confirmed that the average detection

limit (sensitivity) of the portable XRF system (using 5 min measures) is equivalent to that of the

conventional KXRF system (with a 30 min measurement). As shown in Figure 7b, there is a strong

correlation of bone Pb measurements between the portable XRF and KXRF systems (more details

are in a recent paper172).

Conclusion: the portable XRF is sensitive to detect bone Pb, is ideal for the proposed study.

A portable XRF method developed and validated in Dr. Specht’s lab will be used to quantify bone Pb

of participants in vivo. Details of the device and methodology were published previously,171, 172, 214, 215

with the basics summarized here. The portable XRF device is a customized instrument manufactured

by Thermo-Fisher Scientific (Thermo Niton XL3t GOLDD+, Billerica, MA). The x-ray tube has an energy

span up to 50 kV and uses a thermoelectric-cooled silicon drift detector with 25 mm2 area and 1 mm

thickness. The tube was optimized for bone Pb measurement with a voltage of 50 kV, a current of 40

A, and a silver and Fe combination filter. These settings provide the best sensitivity for bone Pb

measurements.214 In response to irradiation, Pb L x-rays are generated, detected, and used to estimate

bone Pb concentration. Before in vivo measurements are performed, Pb-doped bone equivalent

phantoms will be used to calibrate the system. Calibrations and QA/QC procedures will be performed

periodically according to our standard protocols.170 After collecting the spectra, characteristic Pb peaks

will be fitted using a Gaussian function to quantify the net peak and an exponential function to quantify

background. Least-squares algorithms will be used to extract the net counts of the Pb peaks. During

Figure 7a. Portable XRF vs. KXRF

for bone Pb content in goat bones

covered with 3 mm Lucite.

Figure 7b. Correlation of bone Pb

measured by the portable XRF and

KXRF (uncertainty bars shown).

KXRF (ppm)

LXRF (ppm)

515 25 35-5

r2= 0.9531

y = (0.76 ± 0.10)x + (2.50 ± 1.36)

r = 0.78, p <0.001

10 30 50 70-10

-20

Bone Pb-portable XRF

(µg/ g dry bone)

Bone Pb-KXRF (µg/ g bone mineral)

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LEAD Action News Volume 22 Number 4 December 2024 Page 45 of 131

the in vivo measurement, participants will sit comfortably on a chair with his/her right leg placed on

another chair. If it is not possible for the participant to place their leg on another chair, a measurement

with the footrest on the floor can be performed. The pants of the participant will be pulled up, and a 50%

alcohol swipe will be used to clean the skin above the tibia bone. A spot above the center of the tibia

bone or toenail will be marked and a 5-minute measurement will be taken on the spot. The spectrum

will be collected, stored, and analyzed later.

As the device makes use of low energy x-rays, there is a small and safe amount of radiation involved

in the procedure. The whole-body effective dose from a 3-minute bone measurement is ~3.4 µSv.216

We will take a 5-minute bone measurement for participants in this project and the effective dose will be

<10 Sv. This dose is negligible compared to an AP chest x-ray of ~100 Sv and an annual background

dose to the US population of ~3600 Sv.

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