Assessment of water distribution changes in human cortical bone by nuclear magnetic resonance

Abstract

A NMR spin–spin (T2) relaxation technique has been described for determining water distribution changes in human cortical bone tissue. The advantages of using NMR T2 relaxation techniques for bone water distribution are illustrated. The CPMG T2 relaxation data can be inverted to T2 relaxation distribution and this distribution then can be transformed to a pore size distribution with the longer relaxation times corresponding to larger pores. The FID T2 relaxation data can be inverted to T2 relaxation distribution and this distribution then can be transformed to bound- and mobile-water distribution with the longest relaxation time corresponding to mobile water and the middle relaxation time corresponding to bound water. The technique is applied to quantify apparent changes in porosity, bound and mobile water in cortical bone. Overall bone porosity is determined using the calibrated NMR fluid volume from the proton relaxation data divided by overall bone volume. The NMR bound and mobile water changes were determined from cortical bone specimens obtained from male and female donors of different ages. Differences in water distribution were found between specimens from male and female donors. Furthermore, the distribution of water within a single specimen was found to be non-homogeneous. Our results show that the ratio of the average bound to mobile water in bone from male donors is higher than in bone from female donors when the bone porosities are similar between male and female groups. We also show that the average bone porosity multiplied by the ratio of bound to mobile water is constant for both male and female bone groups. This parameter may be used as a measure of bone quality describing both porosity and water content, both of which may be important determinants of bone strength and fracture resistance.

Volumetric Cortical Bone Porosity Assessment with MR Imaging: Validation and Clinical Feasibility

“…Ultrashort echo time (TE) (UTE) magnetic resonance (MR) imaging allows for the assessment of cortical bone by using detection of proton signal from mobile water in pore spaces (ie, pore water) and water bound to collagen matrix by hydrogen bonds (ie, bound water) (23)(24)(25)(26)(27). Furthermore, proton nuclear MR spectroscopic imaging of cadaveric human cortical bone suggests that the bound water fraction with short T2 (~300 to 400 msec) and pore water fraction with longer T2 values (~1 msec to 1 second) are positively and negatively associated with bone strength, respectively (28).…”

Measurements of mobile and bound water by nuclear magnetic resonance correlate with mechanical properties of bone

“…1A) of each specimen. As previously described [17], this NMR technique quantifies the proton solid, bound and mobile components in bone when a broadline NMR system is set at a proton frequency of 27 MHz. Specifically, we used a 0.5 MHz to 40 MHz system built at Southwest Research Institute (San Antonio, TX) that has an electromagnet 19 inches in diameter with a 4 inch gap between the poles of the magnetic field.…”

“…Recently, we developed a technique using NMR to non-destructively estimate the distribution of water in bone tissue [17]. When hydrogen nuclei absorb energy from a radio frequency (RF) pulse, their relaxation rate within a magnetic field depends on the surrounding diffusion characteristics and the energy of their chemical bonds with other elements.…”

“…These specimens were analyzed first by a NMR relaxation technique (Fig.1) [17] and then by three point bending so that correlations between NMR and mechanical properties could be tested for significance. Lastly, we measured selected compositional measures of bone as well as porosity to provide insight into the aging effects on mobile and bound water.…”

Assessment of simulated and functional disuse on cortical bone by nuclear magnetic resonance

“…The proton intensities within the different phases can be used to estimate the water in the different components; particularly it can be used to determine the bound and mobile water distributions. Using the FID decay signal with the computational inversion technique, the distribution of T 2-Fid determines the protons in solid, bound and mobile water phases (Ni et al, 2007).…”