Ultrasound Characterization of Cortical Bone Using Shannon Entropy.

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 ultrasound waves. The objective of this study was to investigate whether Shannon entropy can be exploited to characterize cortical porosity.

Methods: In the study described here, to demonstrate proof of concept, Shannon entropy was used as a quantitative ultrasound parameter to experimentally evaluate microstructural changes in samples with controlled scatterer concentrations made of a highly absorbing polydimethylsiloxane matrix (PDMS).

The influence of intra-cortical microstructure on the contrast in ultrasound images of the cortex of long bones: A 2D simulation study.

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.

Using ultrasonic attenuation in cortical bone to infer distributions on pore size.

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.

Femoral neck phantom imaging using time-domain topological energy method.

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.

Does the bone mineral density measured on a preoperative CT scan before total hip arthroplasty reflect the bone's mechanical properties?

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.

Documenting the Anisotropic Stiffness of Hard Tissues with Resonant Ultrasound Spectroscopy.

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.

Measurement of Cortical Bone Elasticity Tensor with Resonant Ultrasound Spectroscopy.

Resonant Ultrasound Spectroscopy estimates the stiffness coefficients of a material from the free resonant frequencies of a single specimen. It is particularly suitable for complete stiffness characterization of anisotropic materials available only as small samples (typically a few mm), and it does not suffer from some limitations associated to quasi-static mechanical test and ultrasound wave velocity measurements. RUS has been used for decades on geological samples and single crystals, but was until recently not applied to mineralized tissues such as bone.

Introduction.

Diagnostic ultrasound imaging has gained wide acceptance for a broad range of clinical uses. In many cases, ultrasonography is the first-line imaging modality selected for its ease of access and absence of ionizing radiation. Over the last decades, ultrasonography has considerably evolved and is currently contributing to important improvements in patient diagnosis and treatment.

Maximum effect of the heterogeneity of tissue mineralization on the effective cortical bone elastic properties.

The mineralization level is heterogeneous in cortical bone extracellular matrix as a consequence of remodeling. Models of the effective elastic properties at the millimeter scale have been developed based on idealizations of the vascular pore network and matrix properties. Some popular models do not take into account the heterogeneity of the matrix.

Cortical bone viscoelastic damping assessed with resonant ultrasound spectroscopy reflects porosity and mineral content.

Viscoelasticity is an essential property of bone related to fragility, which is altered in aging and bone disease. Bone viscoelastic behavior is attributed to several mechanisms involving collagen and mineral properties, porosities, and bone hierarchical tissue organization. We aimed to assess the relationships between cortical bone viscoelastic damping measured with Resonant Ultrasound Spectroscopy (RUS), microstructural and compositional characteristics.

Bulk Wave Velocities in Cortical Bone Reflect Porosity and Compression Strength.

The goal of this study was to evaluate whether ultrasonic velocities in cortical bone can be considered as a proxy for mechanical quality of cortical bone tissue reflected by porosity and compression strength. Micro-computed tomography, compression mechanical testing and resonant ultrasound spectroscopy were used to assess, respectively, porosity, strength and velocity of bulk waves of both shear and longitudinal polarisations propagating along and perpendicular to osteons, in 92 cortical bone specimens from tibia and femur of elderly human donors. All velocities were significantly associated with strength (r = 0.

Pre-operative bone mineral density is a predictive factor for excellent early patient-reported outcome measures in cementless total hip arthroplasty using a proximally fixed anatomic stem. A prospective study at two year minimum follow-up.

Purpose: The goal of the study was to analyze the impact of the pre-operative bone mineral density on the patients' reported outcomes at two year minimum follow-up of cementless THA using a proximally fixed anatomic stem.

Methods: A prospective study included all patients who underwent a cementless THA using a specific proximally fixed anatomic stem and a 3D preoperative CT scan-based planning. The bone mineral density (BMD) of the metaphyseal cancellous bone was computed in a volume (of 1 mm thick and of 1 cm surface) at the level of the calcar 10 mm above the top of the lesser trochanter.

Modification of regional bone mineral density due to femoral rasping in cementless proximally fixed total hip arthroplasty.

Background: Three-dimensional planning (3DP) in total hip arthroplasty using computed tomography (CT) to analyze bone mineral density (BMD) at the stem-femur interface has a high reported accuracy and excellent mid-term results in the literature. However, 3DP does not take into account the effect of femoral rasping on BMD distribution within the rasped cavity. Characterizing the impact of femoral rasping on BMD may help avoid mechanical failures, but this data is not accurately investigated.

Artificial neural network to estimate micro-architectural properties of cortical bone using ultrasonic attenuation: A 2-D numerical study.

The goal of this study is to estimate micro-architectural parameters of cortical porosity such as pore diameter (φ), pore density (ρ) and porosity (ν) of cortical bone from ultrasound frequency dependent attenuation using an artificial neural network (ANN). First, heterogeneous structures with controlled pore diameters and pore densities (mono-disperse) were generated, to mimic simplified structure of cortical bone. Then, more realistic structures were obtained from high resolution CT scans of human cortical bone.

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients.

Trabecular architecture in the humeral metaphyses of non-avian reptiles (Crocodylia, Squamata and Testudines): Lifestyle, allometry and phylogeny.

The lifestyle of extinct tetrapods is often difficult to assess when clear morphological adaptations such as swimming paddles are absent. According to the hypothesis of bone functional adaptation, the architecture of trabecular bone adapts sensitively to physiological loadings. Previous studies have already shown a clear relation between trabecular architecture and locomotor behavior, mainly in mammals and birds.

Homogenization of cortical bone reveals that the organization and shape of pores marginally affect elasticity.

With ageing and various diseases, the vascular pore volume fraction (porosity) in cortical bone increases, and the morphology of the pore network is altered. Cortical bone elasticity is known to decrease with increasing porosity, but the effect of the microstructure is largely unknown, while it has been thoroughly studied for trabecular bone. Also, popular micromechanical models have disregarded several micro-architectural features, idealizing pores as cylinders aligned with the axis of the diaphysis.

Ex vivo cortical porosity and thickness predictions at the tibia using full-spectrum ultrasonic guided-wave analysis.

Unlabelled: The estimation of cortical thickness (Ct.Th) and porosity (Ct.Po) at the tibia using axial transmission ultrasound was successfully validated ex vivo against site-matched micro-computed tomography.

Bone-conducted sound in a dolphin's mandible: Experimental investigation of elastic waves mediating information on sound source position.

Mammals use binaural or monaural (spectral) cues to localize acoustic sources. While the sensitivity of terrestrial mammals to changes in source elevation is relatively poor, the accuracy achieved by the odontocete cetaceans' biosonar is high, independently of where the source is. Binaural/spectral cues are unlikely to account for this remarkable skill.

Quantification of stiffness measurement errors in resonant ultrasound spectroscopy of human cortical bone.

Resonant ultrasound spectroscopy (RUS) is the state-of-the-art method used to investigate the elastic properties of anisotropic solids. Recently, RUS was applied to measure human cortical bone, an anisotropic material with low Q-factor (20), which is challenging due to the difficulty in retrieving resonant frequencies. Determining the precision of the estimated stiffness constants is not straightforward because RUS is an indirect method involving minimizing the distance between measured and calculated resonant frequencies using a model.

Modal analysis for the assessment of cementless hip stem primary stability in preoperative THA planning.

This numerical vibration finite element (FE) study introduces resonance three-dimensional planning (RP3D) to assess preoperatively the primary stability of a cementless stem for total hip arthroplasty. Based on a patient's CT-scan and a numerical model of a stem, RP3D aims at providing mechanical criteria indicative of the achievable primary stability. We investigate variations of the modal response of the stem to changes of area and apparent stiffness of the bone-implant interface.

Assessment of trabecular bone tissue elasticity with resonant ultrasound spectroscopy.

The material properties of the trabeculae (tissue-level properties), together with the trabecular architecture and the bone volume fraction determine the apparent millimetre-scale bone mechanical properties. We present a novel method to measure trabecular tissue elastic modulus E using resonant ultrasound spectroscopy (RUS). The first mechanical resonance frequency f of a freestanding cuboid specimen is measured and used to back-calculate E.