Feasibility of chromium measurement in skin using a portable hand-held XRF system

Chromium (III) is a trace mineral that plays an important role in glucose and lipid metabolism in the body, in addition to being used in clinical formulations for the treatment of hypoglycemia. Chromium (Cr) deficiency in humans is known to cause insulin resistance and diabetes, however, effects of over exposure are not well studied or understood. This study aims to determine the feasibility of measuring Cr in skin using a portable InnovX XRF system at 40 kVp and 100 A with a mean beam energy of 20 keV. Calibration lines were developed for K-alpha and K-beta X-ray peaks using fiberglass resin phantoms with 1000 mg/L Cr(III) atomic standard solution, assuming a homogeneous distribution of Cr in skin. This assumption was validated through previously acquired XRF data from tissue cross-sections. Analysis of these data not only showed the presence of Cr in tissue samples, but also that Cr was distributed evenly across the tissue cross-section. Phantom concentrations were validated using delayed neutron activation analysis of fragments of each phantom via the neutron capture reaction Cr-50 (n,gamma)Cr-51. Minimum detection limit (MDL) of the XRF system was determined using these calibration lines to be 5 +/- 1 mu g/g. This system was used to acquire data from the skin surface of five different parts of the body on four cadavers through a 300 s acquisition at each location. Cr was measurable at the 95% confidence level in 90% of the cadaver skin sites. The effective dose was determined to be 0.013 mu Sy which is small compared to a dental X-ray. However, the beam was very narrow so the skin dose delivered at the central axis of the beam was 201 mSv. Although the Cr levels did not vary significantly between the cadavers, the different parts of the body showed statistically significant differences in Cr levels. The XRF system used for this study shows promise as an effective monitoring tool for quantifying Cr levels in skin, although adjustments to produce a less collimated beam, and interrogate a larger area of skin, will be preferable so that the central dose is not as intense.