Optimum photon energies for the measurement of bone mineral and fat fractions.
Relative error functions have been calculated for the various single and double photon energy techniques used for the measurement of linear bone mineral and fat mass in vivo. By considering only those errors arising from statistical fluctuations in photon counting useful information for guidance in the most efficient operation of the method is obtained. The results indicate that statistically the single energy method is always significantly better than the double energy method for measurement of both bone and fat fractions in soft tissue at total thicknesses up to 15 g/cm-2. In those circumstances where it may be necessary to use the double-photon energy technique there is an optimum sample thickness of 5 g/cm-2 for minimum error. Values of photon energy which permit measurement with the maximum precision in the minimum count time are deduced for a wide range of practical conditions and are presented along with a table of potentially suitable radioisotopes.