title: Reliability of absolute and relative measurement of total body nitrogen by the 14N(n, 2n)13N reaction.
abstract: Measurements of total body nitrogen by in vivo neutron activation analysis using the 14N(n, 2n)13N reaction, may conveniently be calibrated using phantoms in which nitrogen is uniformly distributed. However, the response of the method varies considerably in the thickest body sections and in order to validate the calibration, it is necessary also to consider the spatial distributions both of nitrogen and of the major interfering element, oxygen. The effects of these spatial distributions have been calculated for the experimental conditions obtained at the East Kilbride facility for total body in vivo neutron activation analysis. The response for total body nitrogen was found to depend strongly on body weight (in the rang e 40 to 100 kg) but only weakly on total body content of adipose tissue (0 to 65% of body weight). It differed little from the response calculated for the nitrogen distributed uniformly within the body. The calculation was tested successfully against measured changes in the net response for nitrogen resulting from 'homogenisation' of inhomogeneous phantoms.
mesh_terms: D001823:Body Composition; D006801:Humans; D008961:Models, Structural; D009501:Neutron Activation Analysis / Q000379:methods; D009584:Nitrogen / Q000032:analysis*
chemical_list: D009584:Nitrogen