High Precision In-Vivo Neutron Activation Analysis: A New Era for Compartmental Analysis in Body Composition

Abstract

Since the high-water mark days of the 1960s when the combination of newly available isotope dilution spaces and the mathematics of compartmental analysis seemed on the verge of revolutionizing physiologic research (Bassingthwaighte, 1970), there has been a general decline in the applications of body composition methods to clinical medicine. In retrospect, concept outstripped competence, as the spaces that could be measured accurately, such as blood volume, turned out to be easier to cure (by transfusion) than to measure, and the mathematical expression of complex solutions for ferrokinetics and iodine kinetics through multiple compartments could rarely be turned to clinical benefit. The reasons were several, but important among them, a “respectable” standard error of measurement of ±5% was combined with a clinical uncertainty, at least as large, as to how “normal” could be defined. The terrain has now changed, in part because some new body compartments can be measured, in part because we have developed age-, sex-, and race- specific definitions of “normal”, but, in largest measure, because new precisions of measurement have been achieved, especially in the techniques of in-vivo neutron activation analysis. We shall consider some specific examples of their application. The benefits we envisage from high-precision in-vivo neutron activation (IVNA) derive largely iron understanding the interdependence of the body compartments, and, therefore, from the development of a series of models which interrelate the compartments.