Single‐sided NMR to estimate morphological parameters of the trabecular bone structure

Abstract

Single-sided 1 H-NMR is proposed for the estimation of morphological parameters of trabecular bone, and potentially the detection of pathophysiological alterations of bone structure. In this study, a new methodology was used to estimate such parameters without using an external reference signal, and to study intratrabecular and intertrabecular porosities, with a view to eventually scanning patients. Methods: Animal trabecular bone samples were analyzed by a single-sided device. The Carr-Purcell-Meiboom-Gill sequence of 1 H nuclei of fluids, including marrow, confined inside the bone, was analyzed by quasi-continuous T 2 distributions and separated into two 1 H pools: short and long T 2 components. The NMR parameters were estimated using models of trabecular bone structure, and compared with the corresponding micro-CT. Results: Without any further assumptions, the internal reference parameter (short T 2 signal intensity fraction) enabled prediction of the micro-CT parameters BV/TV (volume of the trabeculae/total sample volume) and BS/TV (external surface of the trabeculae/ total sample volume) with linear correlation coefficient >0.80. The assignment of the two pools to intratrabecular and intertrabecular components yielded an estimate of average intratrabecular porosity (33 ± 5)%. Using the proposed models, the NMR-estimated BV/TV and BS/TV were found to be linearly related to the corresponding micro-CT values with high correlation (>0.90 for BV/TV; >0.80 for BS/TV) and agreement coefficients. Conclusion: Low-field, low-cost portable devices that rely on intrinsic magnetic field gradients and do not use ionizing radiation are viable tools for in vitro preclinical studies of pathophysiological structural alterations of trabecular bone. K E Y W O R D S bone quality, intratrabecular porosity, morphological parameters, single-sided portable NMR, trabecular bone 3354 | BARBIERI Et Al. 1 | INTRODUCTION High-field whole-body MRI is an essential tool for medical diagnosis. It is noninvasive and does not use ionizing radiation. However, low-field single-sided NMR 1,2 may also provide an appealing approach for the assessment of biological tissue properties. Single-sided devices have demonstrated their potential in human and animal models like human skin, 3,4 silicone breast implants, 5 breast tissue, 6,7 intestine, 8,9 tendon, 10 articular cartilage, 11 bone, 12,13 fluid components of trabecular bone, 13 and human mummies. 14 Single-sided devices allow the detection of signal from a sensitive volume (a slab), suitably selected inside an object, regardless of its extension, and placed on the magnet surface. They have the additional advantages of low acquisition, running and maintenance costs, as they consist of small permanent magnets, and are portable. Recently, 12,13 we proposed a method for applying singlesided NMR devices to animal trabecular samples, for the evaluation of a parameter commonly used to assess trabecular bone structure, the ratio (BV/TV) of the volume occupied by the trabeculae (BV) in a sample to the tot...

Characterization of Structural Bone Properties through Portable Single-Sided NMR Devices: State of the Art and Future Perspectives

“…The second component was attributed to fluids within the inter-trabecular spaces. Figure 2 presents a schematic representation of trabecular bone along with a T 2 distribution obtained from a trabecular bone sample cored from a pig shoulder [50] to highlight the connection between the T 2 components and the trabecular bone constituents. It is important to notice that MRI has been incorporating the concepts of NMR relaxometry in quantitative MRI (qMRI) methodologies such as T 1 and T 2 mapping.…”

“…The latter parameter was first introduced in [15] and is defined as the volume within the trabeculae occupied by the fluids divided by the total volume of the trabeculae. The reader is invited to read reference [50] for a detailed derivation of the models. [63].…”

“…The second component was attributed to fluids within the inter-trabecular spaces. Figure 2 presents a schematic representation of trabecular bone along with a distribution obtained from a trabecular bone sample cored from a pig shoulder [ 50 ] to highlight the connection between the components and the trabecular bone constituents.…”

“…Moreover, the need for an external reference could be a drawback in a possible future in vivo application. The procedure was then further developed in [ 50 ], reducing at least in part the need for a reference sample and extending the study to the estimation of the structural parameter BS/TV (% of the total external surface of the trabeculae with respect to the total volume of the analyzed tissue). These goals were achieved by optimizing the experimental set-up to maximize the Signal-to-Noise ratio, giving a physical interpretation to the quasi-continuous distributions, and by applying simple theoretical models to obtain NMR estimates of BV/TV and BS/TV.…”

“…Portable NMR also has the added advantages of low purchasing, running, and maintenance costs, largely due to the absence of superconducting magnets (permanent magnets are employed instead). Portable NMR devices [ 28 , 29 , 30 , 31 , 32 , 33 , 34 ] have been applied in various fields such as agriculture [ 35 ], cultural heritage [ 36 , 37 , 38 ], porous media [ 39 ], and biomedicine including testing of silicone breast implants [ 40 ] and ex vivo studies of various biological tissues: tendon [ 41 ], articular cartilage [ 42 , 43 ], skin [ 44 ], breast [ 45 ], and bone tissue [ 46 , 47 , 48 , 49 , 50 ]. In vivo studies on humans have also been conducted on skin [ 51 ] and tendons [ 52 ].…”