A phantom study of x-ray fluorescence measurements of iron and zinc concentrations in superficial cutaneous blood

Monitoring essential trace elements in the human body is an important part of a clinical metabolic health assessment. Rapid, non-invasive, non-destructive, and low-dose monitoring of iron (Fe) and zinc (Zn) in the cutaneous blood was investigated by x-ray fluorescence (XRF) measurements. The method is as an alternative to clinical blood measurements using inductively coupled plasma mass spectrometry (ICP-MS). Six water solutions containing Fe in 0, 100, 200, 300, 400, and 500 mg/L and Zn in 0, 10, 20, 30, 40, and 50 mg/L concentrations were placed in polyoxymethylene cylinders (0.9 mm thick and 2.5 mm inner diameter) mimicking skin and its microvasculature. Spatially selective excitation of the elements in the solution was performed by employing a small x-ray beam (1.5-mm lateral size) from an integrated x-ray tube and polycapillary x-ray lens system. A silicon-based x-ray detector, a positioning stage, and a grazing-incidence method developed in our lab were used to acquire three 300-s x-ray spectra for each concentration. Spectral Kα peak area measurements yielded Fe and Zn calibration lines. Detection limits of (80±7) mg/L for Fe and (6.6±0.7) mg/L for Zn were computed by dividing the threefold peak area uncertainty with calibration line slope. Since blood levels are in the range of 310 to 610 mg/L for Fe and 4 to 17 mg/L for Zn, in vivo Fe and Zn measurements are feasible. Future work will assess radiation dose and the effects of varying skin x-ray attenuation on detection and concentration measurement.