We propose an ultrasound approach which provides, with one single examination and one single device, access to three bone biomarkers: anatomy, tissue quality and blood flow. It unlocks ultrasound imaging inside bone by accounting for ultrasound wave speed heterogeneity and anisotropic wave refraction. This study reports the first in vivo evaluation with a comparison to peripheral Quantitative Computed Tomography (pQCT) and modulations of blood flow. Anatomical multi-layer bone-corrected reconstruction was validated at the tibia of healthy volunteers against pQCT and showed agreement on bone cortex interfaces. Estimation of axial and radial ultrasound wave speeds in cortical bone tissue (i.e. along the tissue symmetry axis and normal to it) demonstrated good reproducibility and positive correlation with bone mineral density measured by pQCT. Pulsatile blood flow was mapped and quantified in cortical and medullary regions. A directional ray selection method was developed to enhance blood signal extraction by reducing strong specular reflections originating from the outer and inner surfaces of the bone cortex. Physiological and non-physiological modulations of blood flow, namely head-up/head-down tilt table maneuvers and arterial occlusions, demonstrated the method sensitivity to blood flow variations. For the first time, reactive hyperemia was observed inside bone cortex. These results demonstrate the feasibility of a portable, non-ionizing, and quantitative ultrasound approach for structural, anatomical, and vascular characterization of bone tissue. This approach may offer new diagnostic capabilities for bone disorders, for instance osteoporosis, delayed fracture healing or osteonecrosis.

BACKGROUND:It has been suggested that ultrasound (US) imaging can be used to assess cortical bone health, which is of particular interest owing to its major role in bone mechanical stability. Intra-cortical US imaging extends B-mode imaging into bone using a dedicated image reconstruction algorithm that corrects for refraction at the bone-soft tissue interfaces. It has shown promising results in a few healthy, predominantly young adults, providing anatomical images of the cortex (periosteal and endosteal surfaces) along with estimations of US wave speed. However, its reliability in older or osteoporotic bones remains uncertain. OBJECTIVE:In this study, we critically assessed the performance of intra-cortical US imaging ex vivo in bones with various microstructural patterns, including bones exhibiting signs of unbalanced intra-cortical remodeling. METHODS:We analyzed factors influencing US image quality, particularly endosteal surface reconstruction, as well as the accuracy of wave speed estimation and its relationship with porosity. We imaged 20 regions of interest from the femoral diaphysis of 5 elderly donors using a 2.5 MHz US transducer. The reconstructed US images were compared to site-matched high-resolution micro-computed tomography images. RESULTS:In samples with moderate porosity, the endosteal surface was accurately identified, and thickness estimates from US and high-resolution micro-computed tomography differed by less than 10%. In highly remodeled bones with increased porosity, pore size and an heterogeneous distribution of pores, the reconstructed endosteal surface appeared less bright and was located above the trabecularized cortex region. We observed a decrease in US wave speed with increasing cortical porosity, aligning well with literature data, suggesting that, based on wave speed value the method could discriminate between bones with low porosity (<5%) and those with moderate to high porosity (>10%). CONCLUSION:This study paves the way for the application of US imaging in diagnosing cortical bone health, particularly for detecting increased cortical porosity and reduced cortical thickness.

Introduction. Transcranial ultrasound imaging is hindered by skull-induced aberrations that degrade focusing and image contrast. Existing correction methods typically rely on external imaging or detailed acoustic models, limiting their applicability in emergency settings. Methods. We propose an adaptive approach based on an effective skull model comprising two interfaces and an effective velocity, estimated directly from Full Matrix Capture data without external information. The estimated parameters are integrated into a Total Focusing Method reconstruction with refraction correction. The method is evaluated experimentally at 3.15 MHz by imaging wire targets located beyond a human skull fragment in four configurations: free-field reference, uncorrected, skull corrected with automatically estimated parameters, and skull corrected with optically scanned surfaces. Results. The effective model reduces the mean Euclidean localization error by 67% (2.16 to 0.71 mm). Comparison with the optical reference isolates interface estimation uncertainty as the dominant residual error source, while confirming that the effective velocity model itself produces comparable performance when provided with accurate interface positions. Discussion. These results demonstrate that a self-estimated model enables reliable localization in transcranial conditions. Improving surface estimation robustness is identified as a key factor for precise target reconstruction.

The region near the interface between cortical bone and the medullary cavity-the endosteal surface-is of particular interest for the early detection of osteoporosis. This region is typically the first to exhibit signs of unbalanced remodeling (enlarged pores and increased surface roughness). In this study, we analyze ultrasound reflection at the endosteal surface to introduce a novel potential biomarker of cortical bone health based on specularity. Our hypothesis is that increased pore size and surface roughness enhance ultrasound scattering, thereby reducing specular reflection. We reconstruct maps of specularity by combining a signal processing technique initially designed to enhance specular reflectors in soft tissues with a beamforming technique that accounts for refraction at bone-soft tissue interfaces. Specularity values (between 0 and 1) quantify the similarity between received signals and signals from an ideal specular reflector. Using numerical simulations and ex vivo measurements with a 2.5 MHz phased array we highlight a strong relationship between specularity and bone microstructure, as assessed by high-resolution micro-computed tomography. Among 12 regions of interest (ROI) in the femoral bone of three donors, 8 ROIs without large pores showed high specularity (>0.5) in over 50% of pixels, in contrast to 4 ROIs with signs of extensive remodeling. Both pore volume fraction and pore size were strongly associated with specularity. In simple linear regression analyses, each parameter individually explained 84% of the variability in specularity. These findings suggest that specularity reflects bone microstructure and may potentially serve as a sensitive marker for identifying cortical bone degradation near the endosteal surface.

Marsupials have evolved alongside other mammals on many continents, mainly in the southern hemisphere, developing their own traits and adaptations. Although the relationships between morphology, bite force, and diet have been well studied in many vertebrate groups, this has rarely been the case for marsupials until recently. Present‐day American marsupials' diet and their feeding capacities, considered generalists, remain poorly understood. A better understanding of current American marsupials will lead to more accurate inference models for extinct metatherians. Here, we study and describe for the first time the masticatory apparatus of the Linnaeus' mouse opossum Marmosa murina , along with its performance. Bite forces data were collected for different marsupial species during a field mission in French Guiana in 2017. A 3D bite reconstruction model has been established through dissections and using the lever arm method, based on the static equilibrium of the muscular vectors in the jaw. The optimal gape angle and the contribution of each masticatory muscle to the closing of the mouth were determined. We identify and individualized the different fascicles of the masseter, zygomaticomandibular, temporal, and pterygoid muscles, together with their respective origin and insertion areas. The optimal gape is around 6°, supporting the use of the last molar to get the strongest bite forces. The M. masseter superficialis , the M. temporalis superficialis , and the M. temporalis profundus medialis are the muscles having the greatest impact on the maximum bite force. Our biomechanical model allows a correct approximation of the biting force. However, the muscle stress value has to be increased from 30 N.cm −2 to 44.360 N.cm −2 and 54.209 N.cm −2 to match the in vivo bite forces on the last molar (m4) for Marmosa murina . These high values are rather surprising, suggesting that our model, with the use of standardized constants for all mammals, underestimates true bite forces.

Blood-mimicking fluids (BMFs) play a critical role in ultrasonic imaging and Doppler flow studies by replicating the physical and acoustic properties of blood. This study introduces a novel soybean oil-in-water emulsion as a BMF with particle size akin to red blood cells. Using a millifluidic device, we cross-validated flow profiles through both Doppler velocimetry and optical particle tracking, demonstrating compatibility with theoretical Poiseuille flow models. The millifluidic chip, fabricated via stereolithography, provided an optimized platform for dual optical and ultrasonic assessments. Results showed strong agreement between the two methods across a range of flow rates, affirming the suitability of the emulsion for velocimetry applications. Furthermore, the acoustic properties of soybean oil droplets support their potential as an echogenic and stable alternative to conventional BMFs.

Chondrichthyans possess a tessellated cartilage which is characterized by a layer of mineralized minute plates (i.e., the tesserae) that sheathe soft cartilage. This tissue type composes most of the endoskeleton (including the fins, the branchial arches and the skull). Using the example of the adaptation of Holocephalans to durophagy, here we aim to test the capacity of the tessellated cartilage to strengthen in response to mechanical stress. Relying on an integrative approach (i.e., cranial muscle dissections, finite element models, histological cross sections and embryologic data), we strongly argue that chondrichthyans are capable of calcifying their endoskeleton in response to mechanical stress by mimicking bone microstructures (i.e., cortical thickness and formation of trabeculae). In the absence of bone cells, this mechanism relies on the calcification of Liesegang waves around the chondrocytes that might possess mechanosensing properties. This cartilage ability may have been inherited from the early jawless vertebrates before it played a critical role in the evolution of chondrichthyans who subsequently lost the bony skeleton before thriving through 400 million years and surviving four major extinction crises. Indeed, this ability to mineralize cartilage would have allowed to grow a high diversity of mechanically demanding adaptations within "bone-less" vertebrates.

Ultrasound imaging of the cortex of long bones may enable the measurement of the cortical thickness and the ultrasound wave speed in cortical bone tissue. However, with bone loss, the cortical porosity and the size of the pores increase, resulting in strong ultrasound diffuse scattering whose magnitude can exceed that of the specular reflection from the bone-marrow (endosteal) interface. In this study we adapt to bone a specular beamforming technique proposed to better image a needle in soft tissue. Our approach takes into account both wave refraction and specular reflection physics to enhance the contrast of bone surfaces and reduce speckle from intracortical pores. In vivo ultrasound data were acquired at the center of the human tibia in a plane normal to the bone axis of 11 young healthy volunteeers. Ex vivo ultrasound data were acquired from 16 regions of interest from the femoral diaphysis of three elderly donors (donors 66-98 y.o.) using a 2.5 MHz US transducer. A single-element trans mission synthetic aperture imaging sequence was implemented on a research ultrasound system with a 2.5MHz phased array transducer. Image reconstruction was performed: (A) a delay-and-sum (DAS) algorithm with optimized f-number, correction of refraction at the soft tissue-bone interface and subject-specific ultrasound wave speed and (B) an adaptive algorithm using Snells law of reflection. The improvement of image quality was evaluated with contrast ratios of the average intensities: CEI between the endosteal surface and the center of the cortex. In vivo, specular beamforming improved the visibility of the endosteum (CEI ) by 1 to 13 dB while maintaining the relative contrast between the outer and inner surfaces of the cortex. These results suggest that the visualization of the intra-osseous anatomy can be enhanced if Snells law and wave refraction are taken into account during image reconstruction.

Decreased thickness of the bone cortex due to bone loss in the course of ageing and osteoporosis is associated with reduced bone strength. Cortical thickness measurement from ultrasound images was recently demonstrated in young adults. This requires the identification of both the outer (periosteum) and inner (endosteum) surfaces of the bone cortex. However, with bone loss, the cortical porosity and the size of the vascular pores increase resulting in enhanced ultrasound scattering which may prevent the detection of the endosteum. The aim of this work was to study the influence of cortical bone microstructure variables, such as porosity and pore size, on the contrast of the endosteum in ultrasound images. We wanted to estimate the range of these variables for which ultrasound imaging of the endosteum is feasible. We generated synthetic data using a two-dimensional time-domain code to simulate the propagation of elastodynamic waves. A synthetic aperture imaging sequence with an array transducer operating at a center frequency of 2.5 MHz was used. The numerical simulations were conducted for 105 cortical microstructures obtained from high resolution X-ray computed tomography images of ex vivo bone samples with a porosity ranging from 2% to 24 %. Images were reconstructed using a delay-and-sum (DAS) algorithm with optimized f-number, correction of refraction at the periosteum, and sample-specific wave-speed. We observed a range variation of 18 dB of endosteum contrast in our data set depending on the bone microstructure. We found that as porosity increases, speckle intensity inside the bone cortex increases whereas the intensity of the signal from the endosteum decreases. Also, a microstructure with large pores (diameter >250 μm) was associated with poor endosteum visibility, compared with a microstructure with equal porosity but a more narrow distribution of pore sizes. These findings suggest that ultrasound imaging of the bone cortex with a probe operating at a central frequency of 2.5 MHz using refraction-corrected DAS is capable of detecting the endosteum of a cortex with moderate porosity (less than about 10%) if the largest pores remain smaller than about 200 μm.

Lors de la planification d’une PTH, il n’existe pas de méthode permettant d’évaluer quantitativement la qualité osseuse et les facteurs garantissant une ostéo-intégration des implants. Le scanner préopératoire réalisé pour la planification d’une PTH permet d’évaluer la DMO. Le but de notre étude était de valider la mesure de la DMO comme un marqueur de la qualité osseuse sur ce scanner préopératoire. La DMO est un reflet de la qualité mécanique osseuse dans la planification préopératoire des PTH. Les patients opérés d’une arthroplastie totale de hanche primaire pour une coxarthrose ou une dysplasie congénitale de hanche avec des implants non cimentés et une planification 3D (P3D) ont été inclus. La densité minérale osseuse corticale a été calculée sur les macro-TDM de planification. Lors de l’intervention, la tête et le col fémoral ont été collectés. Ces échantillons osseux ont été scannés avec un micro-scanner calibré. À partir du micro-scanner, les valeurs de DMO ont été extraites et une analyse en éléments finis a été conduite pour déterminer les propriétés mécaniques osseuses. Les relations entre la DMO, les coefficients apparents d’élasticité et la porosité ont été analysées en calculant leurs coefficients de corrélation. Les valeurs de DMO de la corticale médiale mesurées sur le micro- et le macro-scanner étaient significativement corrélées (cc = 0,52). La DMO corticale angulaire moyenne mesurée sur le micro-scanner était de 1472,33 mg/cm 3 (SD : 357,53 mg/cm 3 , 980,64–2830,6 mg/cm 3 ). Il n’existait pas de corrélation significative entre la mesure de la DMO corticale et les modules apparents d’élasticité sauf pour 2 modules d’élasticité apparents E yy et G zy . La DMO corticale et la porosité étaient inversement corrélées avec un coefficient de Spearman de −0,41 (IC 95 : [−0,71 ; −0,02], p = 0,03). Il existait également une corrélation inverse entre tous les modules apparents d’élasticité qu’elle que soit leur orientation et la porosité ( p < 0,01). La DMO fournit des informations sur la porosité qui cependant reste le facteur majeur dans l’évaluation de la qualité osseuse mécanique. IV.

Objective: Ultrasound backscattered signals encompass information on the microstructure of heterogeneous media such as cortical bone, in which pores act as scatterers and result in the scattering and multiple scattering of ultra-sound waves. The objective of this study was to investigate whether Shannon entropy can be exploited to charac-terize cortical porosity.Methods: In the study described here, to demonstrate proof of concept, Shannon entropy was used as a quantita-tive ultrasound parameter to experimentally evaluate microstructural changes in samples with controlled scat-terer concentrations made of a highly absorbing polydimethylsiloxane matrix (PDMS). Similar assessment was then performed using numerical simulations on cortical bone structures with varying average pore diameter (Ct. Po.Dm.), density (Ct.Po.Dn.) and porosity (Ct.Po.).Results: The results suggest that an increase in pore diameter and porosity lead to an increase in entropy, indicat-ing increased levels of randomness in the signals as a result of increased scattering. The entropy-versus-scatterer volume fraction in PDMS samples indicates an initial increasing trend that slows down as the scatterer concentra-tion increases. High levels of attenuation cause the signal amplitudes and corresponding entropy values to decrease drastically. The same trend is observed when porosity of the bone samples is increased above 15%.Conclusion: Sensitivity of entropy to microstructural changes in highly scattering and absorbing media can poten-tially be exploited to diagnose and monitor osteoporosis.

In this work we infer the underlying distribution on pore radius in human cortical bone samples using ultrasonic attenuation data. We first discuss how to formulate polydisperse attenuation models using a probabilistic approach and the Waterman Truell model for scattering attenuation. We then compare the Independent Scattering Approximation and the higher-order Waterman Truell models' forward predictions for total attenuation in polydisperse samples. Following this, we formulate an inverse problem under the Prohorov Metric Framework coupled with variational regularization to stabilize this inverse problem. We then use experimental attenuation data taken from human cadaver samples and solve inverse problems resulting in nonparametric estimates of the probability density function on pore radius. We compare these estimates to the "true" microstructure of the bone samples determined via microCT imaging. We find that our methodology allows us to reliably estimate the underlying microstructure of the bone from attenuation data.

Recent advances in resonant ultrasound spectroscopy (RUS) leverage accurate measurements of the anisotropic stiffness of hard tissues at millimeter scale. RUS is the only available technique to date to assess the entire stiffness tensor of bone from a unique rectangular parallelepiped specimen. Accurately measured stiffness constants are required for bone mechanics models and may provide information on some fundamental aspects of hard tissues biology such as regulation of bone mass, remodeling and healing. In this chapter, we review the anisotropic stiffness data of human hard tissues measured with RUS, mostly during the last decade. Hard tissues covered here include human enamel and dentin, cortical bone from the femur and tibia of human adults, and child cortical bone tissue, accounting for 288 specimens in total. Data was collected in the literature and from previous works of our group. We performed a comparative study to depict the differences in the elastic properties of these hard tissues. Our objectives were to: (1) document the range of anisotropic stiffness constants in human hard tissues (orthotropic or transverse isotropic symmetry); and (2) provide empirical laws between mass density and anisotropic stiffness of cortical bone at different skeletal sites. Finally, we discuss the challenges and perspectives to use RUS for large collections of specimens.

Ultrasonic bone imaging is a complex task, primarily because of the low energy contained in the signals reflected from the internal bone structures. In this study, the reconstruction of a bone-mimicking phantom echographic image using time-domain topological energy (TDTE) is proposed. A TDTE image results from a combination of forward and adjoint fields. The first is a solution of a numerical model that reproduces the setup of the experimental data acquisition to the best extent possible. The second has similar characteristics, but the source term is the time-reversed residue between the forward field and signals obtained from the experiment. The acquisition-reconstruction system used a linear phased-array transducer with a 5 MHz center frequency to acquire the signals and was coupled with a k-wave toolbox to implement the numerical models and perform the image reconstruction. The results showed good agreement between the geometry of the real phantom and the ultrasonic images. However, thickness evaluation errors were observed, which may be due to incorrect assumptions about the velocity models throughout the medium, a priori assumed to be known. Thus, this method has shown promising results and should be applied to the real femoral neck as a long-term objective.

Introduction: No method exists to quantify the bone quality and factors that will ensure osteointegration of total hip arthroplasty (THA) implants. A preoperative CT scan can be used to evaluate the bone mineral density (BMD) when planning a THA procedure. The aim of this study was to validate BMD measurement as a marker of bone quality based on a preoperative CT scan. Hypothesis: BMD reflects the bone's mechanical properties for the purposes of preoperative THA plan-ning.Methods: Patients who underwent primary THA for hip osteoarthritis or dysplasia with cementless implants and 3D preoperative plan were enrolled prospectively. The cortical BMD was calculated on CT scans used in the preoperative planning process. During the surgical procedure, the femoral head and neck were collected. These bone samples were subsequently scanned with a calibrated micro-CT scanner. The BMD was derived from the micro-CT scan and used as input for a finite element model to determine the bone's mechanical properties. Correlations between BMD, apparent moduli of elasticity and porosity were calculated.Results: The values of cortical BMD measured on the micro-CT and CT scan were significantly correlated (cc = 0.52). The mean angular cortical BMD measured with the micro-CT scan was 1472.33 mg/cm3 (SD: 357.53 mg/cm3, 980.64-2830.6 mg/cm3). There was no significant correlation between cortical BMD and the various apparent moduli of elasticity, except for Eyy and Gzy. Cortical BMD and porosity were inversely correlated with a Spearman coefficient of -0.41 (CI95: [-0.71; -0.02], p = 0.03). There was also an inverse correlation between the apparent moduli of elasticity (independent of their orientation) and porosity (p < 0.01).Discussion: BMD provides information about porosity, which is a major factor when evaluating the bone's mechanical properties before THA. Level of evidence: IV. (c) 2022 Published by Elsevier Masson SAS.

Resonant ultrasound spectroscopy (RUS) allows to accurately characterize the complete set of elastic constants of an anisotropic material from a set of measured mechanical resonant frequencies of a specimen. This method does not suffer from the drawbacks and limitations of the conventional sound velocity approach, but has been reported to fail to measure bone because of its strong viscoelastic damping. In this study, we take advantage of recent developments of RUS to overcome this limitation. The frequency response of a human cortical bone specimen (about 5×7×7 mm3) was measured between 100 and 280 kHz. Despite an important overlapping of the resonant peaks 20 resonant frequencies could be retrieved by using a dedicated signal processing method. The experimental frequencies were progressively matched to the frequencies predicted by a model of the sample whose elastic constants were adjusted. The determined diagonal elastic constants were in good agreement with concurrent sound velocity measurements performed in the principal directions of the specimen. This study demonstrates that RUS is suitable for an accurate measurement of cortical bone anisotropic elasticity. In particular, precision of measured Young and shear moduli is about 0.5%.