Measurement of total-body calcium, sodium, chlorine, nitrogen, and phosphorus in man by in vivo neutron activation analysis.

Abstract

Summary In vivo activation with 14-MeV fast neutrons moderated with polyethylene has been shown capable of inducing the following activities in human subjects: 49Ca, 24Na, 38Cl, 28Al(P), 13N, and 56Mn. The Ca, Na, and Cl activities produced by thermal neutrons with a uniform flux density throughout a phantom can be converted to absolute grams with an accuracy of ±4%. It is, of course, possible that measurements might be less accurate in patients that differ grossly in shape or size from the phantom. However, the precision (that is, reproducibility) of the measurements in the same patient is better than ±4%. Because of the nonuniformity of the fast-neutron fluence with depth, the levels of N and P produced by the fast neutrons cannot be determined with the same accuracy as Na, Cl, and Ca. Nevertheless, total body levels of N have been determined with high precision (average of ±1.6%) in successive measurements on the same patient. The levels of 56Mn produced are measurable, but because of its low level and the interference of 27Mg, the statistical accuracy is not sufficiently satisfactory at present. Representative value for Ca, Na, Cl, P, and N for a number of patients with various disease states are presented in application of the above techniques. When these values are normalized to lean-body mass, i.e., expressed in terms of measured 40K, the variation between the different disease states and the sexes is greatly diminished. It is clear that in vivo activation of Ca and P is an invaluable technique in kinetic studies of calcium metabolism in aging and in any condition involving changes in the total-body levels of Ca and P, such as immobilization and weightlessness. Disorders of calcium metabolism associated with chronic renal dialysis can be studied by this technique. The measurement of body Na and Cl are useful in electrolyte imbalance disease states. Nitrogen reflects protein metabolism, and it is of considerable usefulness in the evaluation of a number of disease states. Thus it is obvious that in vivo neutron activation analysis has considerable potential for use in medical research and diagnosis in living man.