The true four-compartment model and the design of the C-O-H-N scanner

Authors: Kehayias, Joseph; KEHAYIAS, PAULI - TUFTS UNIVERSITY, MA

Submitted to: International Journal of Body Composition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2008
Publication Date: 7/9/2008
Citation: Kehayias, J.J., Kehayias, P.M. 2008. The true four-compartment model and the design of the C-O-H-N scanner. International Journal of Body Composition Research. 6:2.

Interpretive Summary: The four compartment (4c) model is often used as the gold standard for body composition analysis. It separates the body in water, fat, protein and (solid) bone. By using isotopes, X-rays and neutron activation methods investigators have been able to measure directly all four compartments in vivo in humans. The purpose of this study is to design a whole-body instrument that can measure all four compartments simultaneously, using an inexpensive and safe neutron activation scanner. Experimental data on the assessment of carbon and oxygen by neutron inelastic scattering, hydrogen by prompt neutron capture, and nitrogen and phosphorus by delayed neutron activation are used together with a simulation computer code. All measurements are combined in a single neutron scanner. It is based on a pulsed neutron generator, a scanning bed and uses two photon counting methods: prompt (C,O,H) and delayed (N, P). The simulation code takes into account interferences from structural materials of the device and uses published data on the efficiency of the nuclear reactions used for each element. Fat is calculated from C and O, water from H and O, and protein from N. Bone is measured either from phosphorous (together with N) or by DXA (a separate X-ray based bone density scanner used for osteoporosis screening). Due to current use in Homeland Security applications, fast neutron generators are now available, portable, reliable, and inexpensive. A volunteer can be scanned in 20 min. Predicted precision for 15 mrem of radiation exposure (equivalent to a single chest X-ray) is better than 3% for each element except for phosphorus (5%). The method provides a true 4c approach to modern body composition assessment.

Technical Abstract: Objective: The four compartment (4c) model is often used as the gold standard for body composition analysis. It is not possible, however, to utilize a true 4c model without assessing protein directly. The purpose of this study is to design a fast-neutron based instrument that can measure all four compartments simultaneously using an inexpensive and safe neutron activation scanner. Methods: Experimental data on the assessment of carbon and oxygen by neutron inelastic scattering, hydrogen by prompt neutron capture, and nitrogen and phosphorus by delayed neutron activation are used together with a simulation computer code. All measurements are taken together using a single whole-body neutron scanner. The system is based on a pulsed neutron generator and a scanning bed and uses two counting methods: prompt (C,O,H) and delayed (N, P). The simulation code takes into account interferences from structural materials of the device and uses published nuclear cross sections. Fat is calculated from C and O, water from H and O, and protein from N. Bone is measured either from phosphorous (together with N) or by DXA. Results and conclusions: Due to current use in Homeland Security applications, fast neutron generators are now available, portable, reliable, and inexpensive. A volunteer can be scanned in 20 min. Predicted precision for 15 mrem of radiation exposure is better than 3% for each element except for phosphorus (5%). The method provides a true 4c approach to modern body composition assessment.