MicroCT analysis of calcium/phosphorus ratio maps at different bone sites

The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia of rats, rabbits and lambs using synchrotron microCT. Use of a monoenergetic X-ray beam, as provided by the synchrotron facility, generates accurate 3-D maps of the linear attenuation coefficient within the sample and hence gives the ability to map different chemical components. Data were taken at 20 keV for each bone sample and calibration phantoms. From the 3-D data sets, multiple 2-D slices were reconstructed with a slice thickness of ∼28 μm and converted to Ca/P ratios using the calibration phantom results. Average values for each animal and bone site were estimated. Differences between the same bone sites from different animals are not significant (0.3< p < 0.5 ) while those between different bone sites and different animals are highly significant ( p < 1 0 - 3 ) demonstrating a dependence upon lifestyle and bone use. The spatial distribution of Ca/P was found to be non-uniform for some bones and some animals possibly indicating the structural mechanism for obtaining bone strength.