Author
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KEHAYIAS, JOSEPH - TUFTS-HNRCA |
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Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/15/2003 Publication Date: 5/1/2004 Citation: Kehayias, J.J. 2004. Use of d-t produced fast neutrons for in vivo body composition analysis: a reference method for nutritional assessment in the elderly. Analytical and Bioanalytical Chemistry 2004;379:188-191. Interpretive Summary: Monitoring changes in body composition serves as the measure of success for many nutritional interventions. Managing malnutrition, obesity, aging, AIDS etc. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Irradiation of the body with neutrons provide information on the fat and muscle content by measuring elements of the body such as carbon, oxygen, nitrogen and phosphorus. This is performed in our laboratory using a miniature neutron generator at safe, low levels of radiation. We use carbon and oxygen to study changes in fat and lean tissue. Phosphorus and nitrogen are used for muscle and protein. This combination of measurements makes possible the assessment of the 'quality' of fat free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue loss with aging and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. Technical Abstract: Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the 31P(n, alpha) 28Al reaction, and nitrogen for protein via the (n, 2n) fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D-T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma ray spectra are collected using large BGO detectors and analysed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI (Tl) detectors. A combination of measurements makes possible the assessment of the 'quality' of fat free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment. |
