The feasibility of measuring total body carbon by counting neutron inelastic scatter gamma rays

Abstract

A technique is examined for measuring the mass of C of both ambulatory and non-ambulatory subjects. The method is based upon the detection of the 4.43 MeV .gamma.-rays emitted from C nuclei when the body is irradiated with fast neutrons. The supine subject is irradiated laterally by a horizontal collimated beam of 14 MeV neutrons and the emitted .gamma.-rays are counted by a shielded NaI(TI) detector placed underneath the subject. The method was calibrated for all sizes of subjects from 30-90 kg and there appears to be no significant interference from the other bulk elements of the body. Body C was measured in 6 normal volunteers; body N was also determined by measuring the 13N induced in each subject in a second irradiation. Body fat was estimated from the measured C and N, and the values compared with those derived from skinfold thicknesses. The technique is proposed as a method of estimating long-term energy expenditure.