In Vivo Neutron Activation at the Brookhaven National Laboratory

Abstract

Eight of the body elements are the most active in biological chemistry: H, C, N, Na, P, Cl, K, and Ca. They can be measured with great precision and accuracy in the in vivo neutron activation (IVNA) facilities at Brookhaven National Laboratory (BNL). IVNA includes the delayed-gamma, prompt-gamma, and inelastic neutron scattering systems. The major body compartments, in conjunction with total body water (TBW) measured by tritiated-water dilution, are defined by the contents of these elements, and measured with high precision. To be specific, body fat mass is derived from total body carbon, combined with total body calcium and nitrogen; protein mass from total body nitrogen; extracellular fluid from total body sodium and chlorine; body cell mass from total body potassium; and skeletal mass from total body calcium. These measurements are vital to research in growth and development (Fomon 1982), the aging process (Cohn 1976), malnutrition (Barac-Niet 1979), and diseases such as osteoporosis (Aloia 1994), and the acquired immunodeficiency syndrome (AIDS) (Kotler 1989). The current widespread interest in the study of body composition indicates the importance of having a rapid, reliable, and relatively inexpensive way of determining it. These methods are relatively invasive (radiation in the 500 millirem range), time consuming, and require large capitalization, making them available only at specialized sites. The precisions available from current techniques, from 0.8 to 3%, render these methods optimal for calibrating simpler instruments that may be routinely used in clinical studies of body composition by methods described elsewhere in this book. The IVNA facilities at BNL have been used to advance body composition research for more than 20 years (Cohn 1972, Vartsky 1979a,b, Kehayias 1987, Dilmanian 1990, Ma 1992). This experience in designing and studying phantoms, in Monte Carlo simulation, and in modeling body configurations, is well suited to the calibration of other instruments.