Improved clinical facility for in vivo nitrogen measurement

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Abstract
The design and construction of a hospital clinical facility for in vivo prompt gamma neutron activation analysis for total body nitrogen (TBN) measurement is described. The use of 252Cf neutron sources gives a better signal-to-background ratio compared with 238Pu-Be sources of equal strength, thus yielding better reproducibility of measurements. By measuring the hydrogen and nitrogen signals separately using appropriate gating circuits, signal-to-background ratio is further improved. Measurements using a urea phantom (5.63 kg nitrogen as urea in 34.53 kg of water) show that 2*6 mu g 252Cf sources gives a nitrogen signal-to-background ratio of 5.6. Approximately 30 minutes of patient's time is required for each TBN measurement with an estimated reproducibility of +or-3.8% (CV). The radiation dose to the patient is about 0.2 mSv (effective dose equivalent; QF=10) per 20 min measurement.