Determination of cortical bone porosity and pore size distribution using a low field pulsed NMR approach

The objective of this study was first to prove the concept of a low field pulsed nuclear magnetic resonance (NMR) process for assessing the cortical porosity and pore size distribution of human bone in vitro, and then to apply the technique to detect age-related changes of bone in these parameters. The Carr-Purcell-Meiboom-Gill NMR spin echo train method is used to determine the porosity, and an inversion NMR spin-spin relaxation (T(2)) spectrum is used to assess the pore size distribution in cortical bone. Using these techniques, cortical porosity and pore size distribution of 19 specimens of human cadaveric bone, ranging from 16 to 89 years of age, were assessed. The NMR results were compared with the histomorphometric data of the same bone samples to verify the efficacy of the NMR approach. Moreover, a coefficient (surface relaxivity) relating the pore size to the T(2) relaxation time was determined empirically for the Haversian canals and the osteocytic lacunae. The results of this study demonstrate that the in vitro NMR approach using T(2) relaxation techniques can directly assess the porosity and pore size distribution (Haversian canals and osteocytic lacunae) in human cortical bone. In addition, this study indicates that the age-related changes in cortical porosity relate predominantly to Haversian canals, whereas the porosity of osteocytic lacunae appears to be independent of age.