Carla Garavaglia

Two 1H-nuclear magnetic resonance methods to measure internal porosity of bone trabeculae: By solid-liquid signal separation and by longitudinal relaxation

Parameters related to pore-space structure of the trabeculae in cancellous bone are difficult to determine quantitatively, but they can be important to characterize changes induced in bone by diseases such as osteoporosis. We present two nuclear magnetic resonance (NMR) methods to measure the internal porosity φtrab of the trabeculae, based on two different measurements of the fraction of intratrabecular and intertrabecular pore-space in animal femur samples. These procedures have been developed within the more general framework of the NMR studies for fluids in porous media. In the first method we use the ratio between the amount of collagen (solid-like) 1H and that of the fluids in the samples. In the second, which can be applied only on defatted and water saturated samples, we use the distributions of longitudinal relaxation times. The φtrab values obtained are constant for porosity φ of the samples over the range 40%–70%, with each method giving φtrab=(29±4)%, which is consistent with the only data ava...

Solid-liquid nuclear magnetic resonance relaxation and signal amplitude relationships with ranking of seasoned softwoods and hardwoods

In H1 NMR (nuclear magnetic resonance) relaxation measurements for a set of eight hardwood and softwood samples, each free induction decay (FID) is fitted by the sum of a “solid” signal of the form Aexp[−c(t∕TS)2][1−g(t∕TS)2+h(t∕TS)4] plus a “liquid” signal Bexp(−t∕T2-FID). Distributions of longitudinal (T1) relaxation times were computed separately for the solid and liquid components, giving also the solid/liquid H1 ratio α. From measurements on the samples dried, seasoned, and hydrated, the moisture content (liquid/solid weight ratio) was found to be approximately 0.50∕α. For each of the “seasoned” samples (10%–13% moisture content) a single T1 peak was found for the solid and two for the liquid, with the longer liquid T1 close to that of the solid, but with some differences exceeding perceived experimental uncertainties. None of the solid or liquid-long T1’s is much less than 20ms, even though liquid-short times go as low as 0.35ms, appearing to negate simple solid-to-liquid exchange on a millisecond t...

From porous media to trabecular bone relaxation analysis: spatial variation of marrow 1H relaxation time distributions detected in vitro by quasi-continuous distribution analysis ☆

Quasi-continuous distributions of T(1) and T(2) of 1H nuclei were analyzed in vitro at 20MHz on some twenty fresh bone samples of pig femur. Large numbers of data points allowed a detailed investigation. Relaxation data were inverted by UPEN (Uniform PENalty inversion). In all samples the widths of the distributions, covering more than two decades, are not even close to being compatible with single exponential components. Moreover, the T(1) and T(2) distributions show enough character to distinguish the samples. We observe a spatial variation of these characteristics and in particular a second peak centered at 500-600 ms appearing in some proximal femur samples. The quasi-continuous distribution allows one to correlate the water content of the sample with parts of the distributions in specific time ranges. The signal fraction with T(1) values longer than a cutoff time of about 170 ms is in very good agreement with the water content of the samples and is significantly larger in the group of samples cored from proximal femur. Also T(2) distributions differentiate the samples, and the signal fraction with T(2) shorter than about 30 ms is significantly larger in the group of distal femur samples.

Continuous distribution analysis of marrow 1H magnetic resonance relaxation in bone

Longitudinal and transverse NMR relaxation of 1H nuclei were studied in vitro on fresh animal femur samples. A large number of data points were taken, starting at 100 micros for T(1) by inversion-recovery, at 200 micros for T(2) by single-echo sequences, and at 600 micros for T(2) by CPMG echo-trains. Quasi-continuous distributions of relaxation times were computed, giving wide distributions for all samples. Bulk marrow removed from the medullary cavity showed T(2) distributions from about 20 ms to 600 ms and T(1) distributions from about 40 ms to 2 s. The 1H nuclei in trabecular bone samples, where marrow is confined, may show long tails for T(2) at relaxation times down to 250 micros, the origin of which is still not known. These tails are absent in bulk marrow from the medullary cavity. The differences observed in T(1) distributions among trabecular bone samples are in accordance with the different marrow compositions. Discrete exponential fits were computed also, and in most cases four discrete exponential components were required to fit the experimental data adequately. However, the discrete components do not seem to correspond to any physically distinguishable separate compartments.