Henry Ford Hospital Medical Journal


The physical principles for determining tissue lipid content In vivo by selective radiation attenuation have been studied and are compared to other methods of body composition analysis. Two penetrating photon beams, each monoenergetic but of differing energies, are simultaneously passed through the low Z components of tissue and the relative beam absorption measured. A mathematical function incorporating the unabsorbed and absorbed photon beam intensities is applied to determine experimentally the relative proportion of fat and lean in the tissue. '"Cd is used as the radioactive source of both xrays and gamma radiation. Results of experiments on low 2 phantom material and in vitro animal tissue indicate that the dual photon absorption principle provides accurate two-component quantitation. The fractional lipid content of in vitro mammalian tissue samples has been determined by dual beam photon absorption, with an error of less than 2%. In vivo values are reproducible to better than 2%. Skinfold thickness was measured simultaneously in vivo with adipose tissue content by dual beam absorptiometry. The experimental coefficient of correlation between these two measurements was .98.



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