Cadmium in man measured in vivo by x-ray fluorescence analysis

The sensitivity and detection limit for measurements of the concentration of cadmium in the kidney cortex of man in vivo have been investigated using the technique of X-ray fluorescence. An 11 GB1 241Am source was used to generate the characteristic K alpha X-rays of cadmium. The variation in the sensitivity for the detection of cadmium at various locations in a kidney has been studied. Because of the pronounced variation in sensitivity with depth in tissue, a measurement could be made selectively in the kidney cortex. The minimum detectable Cd concentration varies between 20 and 40 micrograms g-1 for distances between the skin and the kidney surface of 30 to 40 mm; this distance has a measured uncertainty of +/- 3 mm which gives rise to an uncertainty of +/- 30% in the estimated Cd concentration. The mean absorbed dose to the kidney during such a measurement is about 0.6 mGy. The X-ray fluorescence method is more advantageous than the alternative neutron capture gamma ray analysis technique as far as the total irradiation of the patient is concerned. The cadmium concentrations in the kidneys of five exposed persons were found to lie between 30 and 143 micrograms g-1.