In vivo measurement of total body carbon using 238Pu/Be neutron sources.

Total body carbon has been measured by in vivo neutron activation analysis (IVNAA) in 278 surgical gastroenterological patients and 29 normal volunteers. This is based on the inelastic scattering reaction [12C (n,n') 12C*] for neutrons with energy above 4.8 MeV, producing 4.43 MeV gamma rays. Since only part of the body is scanned, total body carbon is estimated as the ratio of the gamma ray emission from carbon to the emission from hydrogen, using hydrogen as the internal standard. The precision of the estimate is +/- 1.6 kg for a whole body dose of 0.3 mSv. There is a significant difference between the estimates of total body water from IVNAA measurements of carbon and nitrogen and measurements of body water in these subjects by tritium dilution (t = 3.1, p less than 0.005).