Preliminary estimates of the calcium/phosphorus ratio at different cortical bone sites using synchrotron microCT.

The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia of female rats (1.5 years of age), using synchrotron radiation microtomography. The use of a monoenergetic x-ray beam, as provided by the synchrotron facility, generates accurate 3D maps of the linear attenuation coefficient within the sample and hence gives the ability to map different chemical components. Data sets were taken at 20 keV for each bone sample and calibration phantoms. From the 3D data sets, multiple 2D slices were reconstructed with a slice thickness of approximately 28 microm and converted to Ca/P ratios using the calibration phantom results. Mean values (M +/- SD) for cortical femoral, front and rear tibias are 2.12 +/- 0.08, 1.75 +/- 0.06 and 1.94 +/- 0.07 respectively. These values were compared with those derived from different animals. Differences between the same bone sites from different animals are not significant (0.1 < p < or = 0.9) while those between different bone sites are highly significant (p < 10(-3)) demonstrating a dependence upon life style and bone use.