The goal of the Phase II program is to develop an accelerator-based irradiation facility for resonant-gamma absorption (RGA) measurements of body nitrogen and calcium.Two major applications are nutritional assessment of critically ill (e.g., AIDS) patients and osteoporosis screening.In vivo neutron- activation analysis (IVNA) is currently the most accurate technique for quantifying body composition. RGA will achieve comparable or better accuracy in a shorter time period and with radiation doses that are 3-4 orders of magnitude lower than required by IVNA. Unlike elaborate, expensive IVNA facilities, a clinical RGA instrument will be compact and simple enough to be installed in a hospital and operated by their staff. During Phase I SRL determined that issues such as target cooling, radiation shielding, nonresonant gamma absorption and gamma-ray detection efficiency were easily solved with existing technology. In addition, the RGA concept was demonstrated experimentally by measuring the nitrogen content of a dewar containing liquid nitrogen. In Phase II, the RGA technique will be applied to both N and Ca. RGA will be demonstrated on anthropomorphic phantoms with sizes and shapes comparable with the extremes of human subjects. Phase II will demonstrate the low-dose potential of RGA to measure nitrogen and calcium body content with an accuracy of several percent.
