The characterization of human cortical bone microdamage by nuclear magnetic resonance

Abstract

A nuclear magnetic resonance (NMR) spin–spin (T2) relaxation technique has been described for detecting post-damage microstructural changes in human cortical bone tissue. The technique is applied to quantify apparent changes in bone porosity resulting from cyclic loading induced microdamage in cortical bone. Overall bone porosity is determined using the calibrated NMR fluid volume from the proton relaxation data divided by the overall bone volume. The NMR porosities obtained from cortical bone specimens pre- and post-damage are compared with the currently available but destructive histomorphometrically determined porosity. The advantages of using NMR T2 relaxation techniques for bone microdamage are illustrated. The T2 relaxation data can be inverted to T2 relaxation distribution. The inversion T2 relaxation distribution can then be transformed to a pore-size distribution with the longer relaxation times corresponding to larger pores if the surface relaxivity constant is known. It is shown that by using NMR 2 MHz or 27 MHz proton resonance, similar surface relaxivity constants are obtained. It is also demonstrated that the NMR T2 relaxation data are sensitive to changes resulting from the creation of microdamage in cortical bone, which can be interpreted as an effective increase in bone porosity. These results indicate that the detection of cortical bone microdamage is possible by this technique.