XRF and the in vivo evaluation of toxicological metals

X-ray fluorescence (XRF) is rapidly becoming established as a powerful tool in the in vivo study of body composition. One particular area of interest concerns occupational health and the monitoring of heavy metal exposure. An other concerns monitoring of the efficacy of chelation of Fe in those suffe ring from the hereditary blood disorder beta-thalassaemia, Treatment of thi s particular disorder, prevalent amongst peoples of Mediterranean, Middle E astern and south Asian descent, can lead to a build-up of Fe in the body to levels which are potentially toxic. This paper begins by reviewing some im portant developments in biomedical applications of in vivo XRF, Efforts to enhance the ratio of measurement sensitivity to radiation dose are highligh ted. Current interests of this group are focused on the monitoring of skin iron levels in subjects undergoing treatment for beta-thalassaemia, In simu lated skin we are seeking to obtain, for an acceptable dose, a minimum dete ctable level of Fe of 10 mu g (g skin tissue)(-1) using realistic monitorin g periods. The arrangement comprises a high-output tungsten anode x-ray tub e, from which a collimated beam is directed on to a copper foil of thicknes s 0.15 mm, This K-edge filtering gives a peak output energy of approximatel y 8.4 keV and a spread of approximately 1.5 keV at the FWTM, The effective 8.4 keV emission is used to excite Pe in simulated skin. The energy of the filtered source is just above the Fe absorption edge and hence close to the maximum value of the photoelectric cross-section. Preliminary results from this study indicate that for counting periods of the order of 1000 s one c an detect levels of less than 10 mu g (g skin tissue)(-1) using an entrance surface dose-rate of a few mGy min(-1), Copyright (C) 1999 John Wiley & So ns, Ltd.