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Source output stability is important for accurate measurement in prompt gamma neutron activation. This is especially true when measuring low-concentration elements such as in vivo nitrogen (~2.5 % of body weight). We evaluated the stability of the compact DT neutron generator within an in vivo nitrogen measurement system. Review of gamma event/time patterns and data from an auxiliary detector showed significant variations among repeated phantom runs. Neutron generator instability had a significant effect on measurement precision. The neutron generator used in our system must be monitored for output consistency. Adjustments must be made to measurement results to correct for generator instability.

Many body composition measurement systems are calibrated against a single-sized reference phantom. Prompt-gamma neutron activation (PGNA) provides the only direct measure of total body nitrogen (TBN), an index of the body’s lean tissue mass. In PGNA systems, body size influences neutron flux attenuation, induced gamma signal distribution, and counting efficiency. Thus, calibration based on a single-sized phantom could result in inaccurate TBN values. We used Monte Carlo simulations (MCNP-5; Los Alamos National Laboratory) in order to map a system’s response to the range of body weights (65–160 kg) and body fat distributions (25–60%) in obese humans. Calibration curves were constructed to derive body-size correction factors relative to a standard reference phantom, providing customized adjustments to account for differences in body habitus of obese adults. The use of MCNP-generated calibration curves should allow for a better estimate of the true changes in lean tissue mass that many occur during intervention programs focused only on weight loss.

The prompt- and delayed-gamma neutron activation techniques have been used for the non-invasive measurement of human body composition. In recent years, neutron irradiators have used only transuranic isotopic sources (238PuBe, 241AmBe, 252Cf). However, in today’s security-minded environment, the use of alternate neutron sources may provide some advantages. We have examined several designs for an irradiator that would use a high-output, miniature D-T neutron generator (MF Physics). The use of this type of neutron source will lessen the storage, security, and transport issues associated with continuous-output isotopic neutron sources. To determine the scientific impact of this decision, we have performed Monte Carlo simulations (MCNP-4B2; Los Alamos National Laboratory) to aid in the design of the irradiator system, evaluating shielding materials, collimation, and source-to-subject distance, for the measurement of total body nitrogen (TBN). Based on internal flux distributions within the simulated body region of a subject, several design options were identified. The final design will be selected based on the optimization of precision, dose, and exposure time.

Total body chlorine (TBC1) provides an estimate of extracellular water. We have examined the feasibility of measuring TBC1 using the 5.6, 6.1, and 8.6 MeV C1 peaks produced during in vivo prompt-gamma neutron activation (dose

The feasibility of measuring total body carbon (TBC) based on prompt-gamma activation analysis (PGAA) of the human body was examined. Preliminary analyzes for 33 healthy pre-menopausal women indicated a range of TBC values (7.1±4.4 kg) which translated to 17.1±6.5 kg body fat (27.9%±7.9% of body weight). An advantage of the PGAA measurement is that fat mass can be obtained simultaneous with that of total body protein mass, both indices serving as useful body composition markers of the nutritional status.

Total body neutron activation analysis (NAA) was used to examine the elemental composition of 22 piglets in the weight range 0.7 kg to 3.4 kg. The accuracy of the NAA technique, compared to direct chemical carcass analysis, established it as an equivalent chemical criterion (reference) method. The body composition of 14 human infant cadavers was also examined by NAA and by dual-energy x-ray absorptiometry (DXA). The DXA-derived lean, fat, and bone compartments were compared with an NAA chemical model of composition. Each of the three compartments was significantly correlated (r=0.85–0.95,p

Total body nitrogen (TBN) can be used to estimate total body protein, an important body composition component at the molecular level. A system using the associated particle technique in conjunction with prompt gamma neutron activation analysis has been developed for the measurement of TBN in vivo. The system uses a compact D, T neutron generator (~107 n/s) coupled to an internal alpha-particle detector, and a counting system with six bismuth germinate detectors. 14 Subjects were scanned from shoulders to hips (20 min scan time

Few data exist on the elemental composition of the human body during infancy. The scarcity of the data is due, in part, to the destructive nature of total body analyses normally required for the classical chemical approach. To help determine such data for infants, we have developed a neutron activation facility for nondestructive postmortem analyses. The system consists of a multisource241AmBe irradiator and a multidetector NaI(T1) whole body counter. The total body contents of K, Ca, P, Na and Cl are determined. Postmortem examinations have been performed in twelve infant cadavers. These results are compared with those of the reference fetus.

Neutron activation analysis provides an accurate elemental assessment of body compositional compartments; the analytical technique identifies skeletal, muscle, protein, and fat masses. Our irradiator system uses 56241AmBe sources (4.4·107 n/s each) which can be arranged in four basic geometries to examine body sizes from a preterm infant (500 g, 30 cm) to a very large adult (120 kg, 2m). Both in vivo and human cadaver studies have been performed. Precisions of 1 to 2% for total body Ca, P, Na, and Cl have been obtained.

We have examined several whole body counting geometries for exclusive use in total body potassium (TBK) measurements in preterm infants. This paper describes two counters, one for very-low-birth-weight (VLBW) infants with body weights under 2000 g, and a second counter for larger preterm infants. Both systems use large-volume NaI(Tl) detectors (10.2 cm × 10.2 cm × 45.7 cm) and are operated in a low background room. The standard error for a TBK measurement decreases from 5% at 1 kg body weight to 2% at 4.5 kg weight.

Characteristic gamma-rays are emitted promptly by elements during exposure to neutrons. These emissions enable a radioanalytical analysis of the body's composition of protein (nitrogen), water (hydrogen), and fat (carbon). We have used this method in vivo to determine the body composition of obese and lean pigs (10 to 20 kg body wt) fed an altered cholesterol diet.

Energy Requirements during First Two Years of Life Based on Measurements of Energy Expenditure and Growth