AN IMPROVED INSTRUMENT FOR THE IN-VIVO DETECTION OF LEAD IN BONE

An improved instrument for the fluorescence excitation measurement of concentrations of lead in bone has been developed. This is based on a large area high purity germanium detector and a point source of Cd-109 . The source is positioned in a tungsten shield at the centre of the d etector face such that 88keV photons cannot enter the detector directl y. In vivo measurements are calibrated with plaster of Paris phantoms. Occupationally non-exposed men show a minimum detectable concentratio n of about 6 mug/g bone mineral. Measurements of tibia lead concentrat ions in 30 non-occupationally exposed men between the ages of 23 and 7 3 showed an annual increment of 0.46 mug/g bone mineral/year. The mean deviation from the regression of tibia lead upon age was 3.5 mug/g bo ne mineral. Tibia lead concentration in one subject with a history of exposure to lead was 69.6 (SD 3.5) mug/g bone mineral. The improved pr ecision of the point source large detector system means that greater c onfidence can be placed on the results of in vivo measurements of lead concentration. This will allow studies of the natural history of non- occupational lead accumulation in normal subjects and should permit in vestigations of the efficacy of therapeutic interventions in subjects poisoned with lead.