Determination of bone density by coherent-Compton scattering.

Bone density previously has been determined by counting the number of Compton and coherently scattered photons using incident radiation from 241Am (60 keV). We have improved this technique by using more nearly optimal scattering angles and a higher incident beam energy. Three factors make this method clinically attractive; (a) sensitivity to changes in both bone density and elemental composition, (b) elimination of attenuation corrections for overlaying structures, and (c) the ability to measure the axial skeleton. An intrinsic Ge detector with high resolution (500 eV at 100 keV) allowed measurement of forward scatter at angles as low as 30 degrees (from the incident beam), thereby maximizing the fluence of the coherent photons which are highly forward directed. Preliminary results showed high correlations (r = 0.97-0.99) between the coherent-Compton ratio and density of bone phantoms using both 241Am and 153Gd sources. The skin dose for a measurement using 153Gd was calculated to be 1.5 cGy at 3% counting precision.