Combined cortical thickness and bone density determination by photon absorptiometry

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Abstract
Bone cortical thickness and density were measured in rat femurs in vitro by a photon absorptiometry technique. A scan perpendicular to the long bone axis using photons from highly collimated 109Cd or 125I sources yielded the bone wall thickness and attenuation at mid-shaft. A 2nd scan after the bone was rotated axially 90.degree., measured the wall or shaft thickness identically responsible for the mid-shaft attenuation of the 1st scan. The mid-shaft attenuation of the 2nd scan was due to the bone thickness derived from the 1st scan. Two complementary measurements are derived by this technique. The bone density is then directly calculated with an estimated accuracy of 10% (coefficient of variation) using empirically determined mass attenuation coefficients. Measurements of mass attenuation coefficients of ashed and dried samples were compared with calculated coefficients for estimated bone composition. The mass attenuation coefficient for bone in vivo estimates that bone density can be accurately derived from this technique.