Application of the associated particle technique for the whole-body measurement of protein, fat and water by 14 MeV neutron activation analysis--a feasibility study.

A small and compact sealed tube neutron generator with an integral alpha particle detector has been used for applying the associated particle technique for prompt-gamma 14 MeV neutron activation analysis of total body carbon (TBC), total body nitrogen (TBN) and total body oxygen (TBO). Ground sheep meat samples in the weight range 20-40 kg and of varying composition have been scanned using two 12.5 cm diameter x 10 cm Nal(Tl) crystals for gamma-ray detection. The content of protein, fat and water was calculated from their fractional content of C, N and O using a four-compartment model of body composition, which included minerals. The precision for measuring TBC, TBN and TBO has been obtained from the mean count rates of ten repeat irradiations of the same sample. The accuracy has been confirmed by comparison against chemical analysis. The reproducibilities for measuring TBN have been found to be comparable to those obtained when the same samples were analysed using prompt-gamma thermal-neutron activation analysis in an existing body composition facility. Based on the results obtained, we conclude that an instrument comprising the neutron generator and four 15 cm x 15 cm x 45 cm NaI(Tl) gamma ray detectors can be assembled to determine, in vivo, protein, fat and water in an approximately 41 kg sample with precisions of 4.4%, 5.0% and 2.1% (CV) respectively within a 15 min scan. The radiation dose equivalent delivered due to neutrons would be approximately 0.03 mSv.