Many diseases are accompanied by wasting with a consequent loss of
protein. The establishment of nutritional status in such patient
groups would enable the efficacy of management regimens to be
evaluated. The nutritional model adopted will be a compromise
between its useful complexity and the practicality of measuring each
compartment. The advantages of the four compartment model (protein,
water, minerals and fat) adopted for this thesis, over simpler two
compartment (fat and fat free mass) models are discussed.Protein is related to nitrogen by the universally accepted
multiplicative factor of 6.25. Prompt neutron activation analysis
(NAA) (1AN(n,fc)15"N} has been shown to be superior to delayed NAA
{1AN(n,2n)l3N} for the measurement of protein. These advantages are
in respect of : specificity of reaction product; number of
interfering reactions; uniformity of combined activation/detection
sensitivity; radiation dose for a given precision and cost of
apparatus. Furthermore, only the prompt technique is feasible for
studies involving the critically ill. Additionally, radio-isotopic
neutron sources can be used and the advantages of Californium-252
(252Cf) over alternative sources are discussed. The disadvantage of
the prompt technique is the high count rate at the detectors, caused
by the simultaneous irradiation and detection of the subject.A consequence of the high count rate during the protein measurement
is pulse pile-up, which leads to spectrum distortion and has been
identified as the principal contributor to the nitrogen background.
Consideration has been given to the characteristics of the pulse
processing system to minimise this pile-up. The combination of
source and detector shielding materials has been determined
empirically by minimising the nitrogen background. Comparison has
been made of alternative unilateral and bilateral
irradiation/detection geometries for prompt NAA and the latter
chosen for construction of clinical apparatus. The apparatus enables
the in-vivo measurement of total body protein by prompt NAA using
2S2Cf with a precision of ±3%, from a 40 minute scan for a whole
body dose equivalent of 0.18mSv.Techniques for predicting the nitrogen background from a subject
spectrum are presented. Calibration of the apparatus to convert a
nitrogen:hydrogen counts ratio to a mass ratio and the continued
requirement for recalibration as the 252Cf decays is discussed. The
prompt technique requires total body nitrogen to be calculated from
the nitrogen:hydrogen mass ratio by the independent estimate of
total body hydrogen. A circularity in the relationships used
enables this estimate to be made by measuring total body water by an
isotope dilution technique. Finally, data-from a study on normal
subjects is presented and prediction equations generated for total
body nitrogen based on anthropometrics. The results are compared
with findings from other centres
