Qingwen Ni

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 (T2) 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 T2 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 T2 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.

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

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.

Non-destructive characterization of microdamage in cortical bone using low field pulsed NMR

The microcracking and damage accumulation process in human cortical bone was characterized by performing cyclic loading under four-point bending at ambient temperature. A non-destructive nuclear magnetic resonance (NMR) spin-spin (T(2)) relaxation technique was applied to quantify the apparent changes in bone porosity as a function of cyclic loading and prior damage accumulation, first to unloaded cortical bone to quantify the initial porosity and then to fatigued cortical bone that was subjected to cyclic loading to various levels of modulus degradation and microdamage in the form of microcracks. The NMR T(2) relaxation time and amplitude data of the fatigued bone were compared against the undamaged state. The difference in the T(2) relaxation time data was taken as a measure of the increase in pore size, bone porosity or microcrack density due to microdamage induced by cyclic loading. A procedure was developed to deduce the number and size distributions of microcracks formed in cortical bone. Serial sectioning of the fatigued bone showed the formation of microcracks along the cement lines or within the interstitial tissue. The results on the evolution of microdamage derived from NMR measurements were verified by independent experimental measurements of microcrack density using histological characterization techniques. The size distribution and population of the microcracks were then utilized in conjunction with an analytical model to predict the degradation of the elastic modulus of cortical bone as a function of damage accumulation.

The characterization of human cortical bone microdamage by nuclear magnetic resonance

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.

Characterization of synthesized NANO-encapsulated drug for bone loss on hind limb suspension rat model by NMR and micro-CT

A formulation of nano-encapsulated enantiomer of (+) promethazine with desired release rate has been synthesized for establish a localized drug delivery system. It was tested on a hind limb suspension (HLS) disuse rat model, and by using a non-destructive Nuclear Magnetic Resonance (NMR) relaxation technique, and micro computed tomography (Micro-CT) analysis technique to qualitatively evaluate the effectiveness of the new bone formations as well as to compare the current commercial anti-bone loss drug Alendeonate. Our studies suggest that nano-encapsulated (+) promethazine in controlled release formulations conjugating bone-targeting functional groups are effective in promoting bone growth in a disuse rat model.

Assessment of structural changes of human teeth by low-field nuclear magnetic resonance (NMR)

A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spin relaxation is described for assessment of age-related structural changes (dentin and pulp) of human teeth in vitro. The technique involves spin-spin relaxation measurement and inversion spin-spin spectral analysis methods. The spin-spin relaxation decay curve is converted into a T(2) distribution spectrum by a sum of single exponential decays. The NMR spectra from the extracted dentin-portion-only and dental pulp-cells-only were compared with the whole extracted teeth spectra, for the dentin and pulp peak assignments. While dentin and pulp are highly significant parameters in determining tooth quality, variations in these parameters with age can be used as an effective tool for estimating tooth quality. Here we propose an NMR calibration method-the ratio of the amount of dentin to the amount of pulp obtained from NMR T(2) distribution spectra can be used for measuring the age-related structural changes in teeth while eliminating any variations in size of teeth. Eight teeth (third molars) extracted from humans, aged among 17-67 years old, were tested in this study. It is found that the intensity ratio of dentin to pulp sensitively changes from 0.48 to 3.2 approaching a linear growth with age. This indicates that age-related structural changes in human teeth can be detected using the low-field NMR technique.

The characterization and comparison of human cortical bone and teeth structural changes by low field NMR

It is known that NMR proton spin-spin (T2) or spin-lattice (T1) relaxation time measurements and analytical processing techniques have been used to determine microstructural characteristics of various types of fluid filled porous materials with characteristic pore sizes ranging from sub-micron to sub-millimeter. Currently this method has been developed and applied to quantify the porosity, pore size distribution and microdamage in human cortical bone [1–3]. The observed proton NMR relaxation signals are a convolution of the relaxation of fluid in the pores throughout the observed system with the longer relaxation time corresponding to larger pore sizes. Thus, regions within the bone matrix in which fluid may accumulate can effectively be treated as a “pore” and will be manifest as a change in the relaxation signal. Deconvolution of the relaxation signal can provide quantitative information about the relaxation distributions of fluid inside bone, i.e., the distribution of water within bone tissue. Since teeth are comprised of fluid-filled porous materials, and dentin is like bone, we also applied this rapid, non-destructive and non-invasive technique to detect and quantify age-related teeth structural changes particularly for both dentin and pulp based on broadline pulsed NMR.Copyright

The Assessment of Loosely and Tightly Bound Water in Water Distribution Changes of Human Cortical Bone by NMR

Bone quality in terms of water distribution, porosity, and pore size distributions in cortical bone and relate these measures can be used to correlate bone mechanical properties. The objective of this paper is to demonstrate that non-destructive low-field NMR technique can be used to determine the mobile and the bound water distribution, and further determine the loosely and the tightly bound water in cortical bone in vitro.© 2008 ASME

The characterization of age-related human cortical bone porosity, water distribution changes by nuclear magnetic resonance

Previous studies have shown that bone fracture toughness is also significantly correlated to changes in porosity, microarchitecture, osteonal morphology, collagen integrity, microdamage, and the interactions of water with collagen and mineral phases, all of which are measures of bone quality. Currently, the influence of water removal on the strength and toughness of cortical bone has studied by Nyman et al [1]. The results have shown that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness. However, in that paper the loss of water was used the dehydration method for such mechanism studies. Here, we hypothesize that the NMR relaxation technique can non-destructively and non-invasively assess the porosity, bound water (water bound to collage and mineral phases) and mobile water (water within the pores).Copyright

Creating a distributed physics department

To preserve their undergraduate physics programs, a group of state universities in Texas has jointly offered upper level undergraduate physics courses through the Texas Electronic Coalition for Physics for the past nine years. At the start of the 2002 academic year they formalized their relationship to successfully create a fully functioning distributed physics department. We report on the status of this innovative project, the inter-institutional organizational structures that have evolved to support this initiative, the successes achieved by the distributed department during its first year, and the problems encountered and possible solutions.