High resolution Ca/P maps of bone architecture

The Ca/P ratio was measured in cortical bone samples from the femoral neck, front and rear tibia of female rats (1.5 yr of age), using synchrotron radiation microtomography. 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. MicroCT data sets were collected at 20 and 28 keV for each bone sample and two calibration phantoms. From the 3D data sets, multiple 2D slices were reconstructed with a slice thickness of ∼14 μm. Regions of interest were defined around suitable sites and were converted to Ca/P ratios using the data collected from the test phantoms. 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. Differences between the same bone sites from different animals are not significant (0.3-3). Differences between estimates made at 20 and 28 keV are not significant (p>0.5).