Submitted to: Journal of Radioanalytical and Nuclear Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/3/2007
Publication Date: 4/1/2008
Citation: Ellis, K.J., Shypailo, R.J. 2008. COHN analysis: Body composition measurements based on the associated particle imaging and prompt-gamma neutron activation analysis techniques. Journal of Radioanalytical and Nuclear Chemistry. 276(1):79-83. Interpretive Summary: Obesity is defined as an excess amount of stored body fat. But there are also changes in the composition of the lean tissues, often with an increased amount of water and a reduced amount of proteins. When a weight loss program of any type is initiated, the focus is to reduce the amount of excess fat without significantly compromising the quality of the lean tissues, especially the amount of protein. To accurately follow changes in the amounts of fat, water, and protein in the body, three separate measurements have had to be performed. In this paper, we describe a new system, based on nuclear principles, that can directly measure the body's content of carbon, oxygen, nitrogen, and hydrogen. Using this information, and knowing the chemical makeup of water, fat, and proteins, it is now possible to accurately measure the relative amounts of each in the living human body, and to monitor changes with weight loss. It will also be possible to monitor changes in body composition when gaining body weight is the objective, such as after a serious illness.
Technical Abstract: The measurement of the body's carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) content can be used to calculate the relative amounts of fat, protein, and water. A system based on prompt-gamma neutron activation analysis (PGNAA), coupled with the associated particle imaging (API) technique, is being developed for this purpose. A compact D,T neutron generator (approx. 10**7 n/sec output) with an internal alpha particle detector is used. The counting system consists of 6 shielded bismuth germanate (BGO) detectors (10.2 cm x 10.2 cm x 10.2 cm) operated with fast-timing electronics to detect only gamma-rays within a 100-ns time window following a trigger pulse generated by the alpha detector. The body can be scanned from the shoulders to the knees within about 30 min, with the equivalent whole-body dose < 0.4 mSv. The cumulative gamma-ray spectra in the 2 MeV to 8 MeV region is collected and analyzed for multiple peaks attributed to body C,O,H, and N. Measurement precision for each element, based on tissue-equivalent phantoms, are in the 2-5% range, which is sufficient for population studies in adults. Further improvements are needed to extend the measurements to pediatric clinical research studies.