It is designed to measure, in vivo, the total body content of nitrogen in human subjects. This is accomplished by directly measuring the gamma ray emissions from body nitrogen during exposure to a low intensity, collimated neutron beam. Typical scanning time is 450 sec.
Protein is calculated, assuming nitrogen as fixed percentage of total body protein.
This isotope, however, is produced in an excited nuclear state and releases gamma rays when it returns to its groundstate within 10 -14 sec. Body hydrogen also undergoes a similar nuclear reaction producing gamma rays at 2.2 MeV. As the subject is scanned, the spectra are acquired and then analyzed for the 2.2 MeV peak and the 9.5-11.0 energy region for nitrogen. The ratio of these two counts, when compared the similar peaks for a phantom of known nitrogen and hydrogen content, provides the measure of total body nitrogen in the subject. These sources are housed in borated paraffin shields located above and below the scanning bed. Each source is collimated to provide a 23 cm 2 beam at the surface of the shield.