Measurement of phosphorus content in normal and osteomalacic rabbit bone by solid-state 3D radial imaging

In osteomalacia decreased mineralization reduces the stiffness and static strength of bone. We hypothesized that hypomineralization in osteomalacic bone could be quantified by solid-state (31)P magnetic resonance imaging (SS-MRI). Hypomineralization was measured with a 3D radial imaging technique at 162 MHz (9.4T) in rabbit cortical bone of hypophosphatemic (HY) and normophosphatemic (NO) animals. The results were compared with those obtained by quantitative micro-CT (micro-CT) and (31)P solution NMR. 3D images of 277 microm isotropic voxel size were obtained in 1.7 hr with SNR approximately 9. Mineral content was lower in the HY relative to the NO group (SS-MRI: 9.48 +/- 0.4 vs. 11.15 +/- 0.31 phosphorus wet wt %, P < 0.0001; micro-CT: 1114.6 +/- 28.3 vs. 1175.7 +/- 23.5 mg mineral/cm(3); P = 0.003). T(1) was shorter in the HY group (47.2 +/- 3.5 vs. 54.1 +/- 2.7 s, P = 0.004), which suggests that relaxation occurs via a dipole-dipole (DD) mechanism involving exchangeable water protons, which are more prevalent in bone from osteomalacic animals.