Occupational nuclear medicine: Trace element analysis of living human subjects

Several trace elements are toxic when present in excessive amounts. Such overloads occur most commonly in the occupational setting, although some environmental exposures are also of concern. The relationship between chronic exposure and health effects is best explored with the aid of knowledge of the quantity of element in question stored in the body. In vivo elemental analysis can provide this knowledge non-invasively for a number of elements of toxicological importance. In vivo analysis presents specific challenges, particularly the fact that the body is an extended medium, giving rise to extensive scattering and absorption. Also of primary importance, the radiation dose must be kept as low as reasonably possible and must in every case be within the range of other diagnostic procedures. Both the incident radiation and the detected signal must have an adequate mean free path in human tissue. This means that neutron activation analysis (NAA) and X-ray fluorescence (XRF) are the two most studied techniques. For some elements, analytical methods are established while others are under active development. For still others, no promising technique is currently available. The most fully developed techniques are for lead and cadmium. For lead three different XRF approaches have been put forward, although one, 109Cd excited K XRF is most widely used. For cadmium, both prompt gamma NAA and XRF have been developed to the extent of full human studies. Amongst elements for which application to human studies has begun or is likely to begin shortly are aluminum and manganese, both using NAA.