Investigation of the accuracy of a portable 109Cd XRF system for the measurement of iron in skin

We have previously reported the design of a portable 109Cd x-ray fluorescence (XRF) skin iron measurement system with a low detection limit of 1.35 μg Fe per g of tissue, which delivers a skin surface dose of 1.1 mSv in iron overload and iron deficiency disease. The system has been found to be precise but must also provide accurate measurements of iron levels in the skin. This article describes testing of the system's accuracy. Ten pigskin samples were measured using both the portable XRF system and ICP-MS analysis. The two techniques reported a non-significant mean difference of 2.5 ± 4.6 μg Fe per g. However, the ICP-MS measurements reported a wider range of values than determined by XRF, with two individual samples having ICP-MS results that were significantly elevated (p > 0.05) compared to XRF. Synchrotron µXRF maps of iron in pigskin, obtained at the BioXAS beam line of the Canadian Light Source, indicated small areas of high iron levels in the skin, mainly in the dermis, attributed to small blood vessels. Monte Carlo models (using the EGS 5 code) determined that if these iron 'hot spots' were towards the back of the skin, they would be measured by the ICP-MS analysis but not by the XRF system, potentially explaining the discrepancies between ICP-MS and XRF results in the two samples. The synchrotron µXRF maps also showed higher iron concentration at the skin surface than in deeper skin layers. Monte Carlo models verified that the XRF system was most sensitive to these skin layers. The results suggest that with highly elevated skin surface iron levels, the XRF system would not provide an accurate estimate of average skin iron levels, but could, with correction factors, provide an accurate estimate of the iron levels in the surface layers of skin.&#xD.