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Determination of whole body magnesium by in vivo neutron activation.

Abstract In vivo studies utilizing 28 Mg provide an incomplete description of the effects of endocrine and metabolic factors on Mg homeostasis and conservation since the majority of body Mg does not exchange with the injected radioisotope. Neutron activation analysis has been shown to be a feasible technique for in vivo determinations of total body calcium, sodium, chlorine, iodine, nitrogen and phosphorus in man and animals. The 11 per ent of body Mg which exists as 26 Mg is capable of being transmuted by thermal neutron irradiation to 27 Mg [ 26 Mg( n , γ) 27 Mg], a radionuclide which emits gamma rays at 0·84 and 1·01 MeV with a half-life of 9·5 min. Studies of the thermal neutron beam from the Brookhaven Medical Research Reactor indicate a variation in depth flux density of ±4·0 per cent across a rat phantom when it is irradiated rotationally in a specially designed holder apparatus. The induced gamma ray activity from 27 Mg is linearly related to the total Mg content of the rat phantom over the range 50–500 mg. The gamma ray activity is measured with a 25 cm 3 Ge(Li) semiconductor detector and both the 0·84 and the 1·01 MeV emissions are measured. The technique is non-destructive and multiple determinations of whole body Mg in the same rat are possible. Absolute values for body Mg content may be attainable by the use of appropriate phantoms.