Konstantinos N. Grivas

Application of an effective medium theory for modeling ultrasound wave propagation in healing long bones.

Quantitative ultrasound has recently drawn significant interest in the monitoring of the bone healing process. Several research groups have studied ultrasound propagation in healing bones numerically, assuming callus to be a homogeneous and isotropic medium, thus neglecting the multiple scattering phenomena that occur due to the porous nature of callus. In this study, we model ultrasound wave propagation in healing long bones using an iterative effective medium approximation (IEMA), which has been shown to be significantly accurate for highly concentrated elastic mixtures. First, the effectiveness of IEMA in bone characterization is examined: (a) by comparing the theoretical phase velocities with experimental measurements in cancellous bone mimicking phantoms, and (b) by simulating wave propagation in complex healing bone geometries by using IEMA. The original material properties of cortical bone and callus were derived using serial scanning acoustic microscopy (SAM) images from previous animal studies. Guided wave analysis is performed for different healing stages and the results clearly indicate that IEMA predictions could provide supplementary information for bone assessment during the healing process. This methodology could potentially be applied in numerical studies dealing with wave propagation in composite media such as healing or osteoporotic bones in order to reduce the simulation time and simplify the study of complicated geometries with a significant porous nature.

The effect of cortical bone porosity on ultrasonic backscattering parameters

Bone is a medium with a complex microstructure, consisting of a nonhomogeneous and anisotropic porous network. The numerical study of the ultrasound scattering by cancellous and cortical bone has attracted the interest of several research groups worldwide. In this work, we employed the boundary element method to perform numerical simulations of ultrasonic wave propagation in two-dimensional computational models of cortical bone. A plane wave of frequency 1 MHz was used to simulate ultrasound scattering due to the microstructure and porous nature of cortical bone. The magnitude of the radial scattering amplitude and the displacement at a distance of 20 mm above cortical cortex were calculated to investigate changes in cortical porosity and the occurrence of non-refilled resorption lacunae (RL). It was shown that the scattering amplitudes as well as the calculated displacements can reveal differences due to changes in cortical porosity from 0-16% as well as the occurrence of pores larger than the Haversian canals.

Computational Study of the Effect of Cortical Porosity on Ultrasound Wave Propagation in Healthy and Osteoporotic Long Bones

Computational studies on the evaluation of bone status in cases of pathologies have gained significant interest in recent years. This work presents a parametric and systematic numerical study on ultrasound propagation in cortical bone models to investigate the effect of changes in cortical porosity and the occurrence of large basic multicellular units, simply called non-refilled resorption lacunae (RL), on the velocity of the first arriving signal (FAS). Two-dimensional geometries of cortical bone are established for various microstructural models mimicking normal and pathological tissue states. Emphasis is given on the detection of RL formation which may provoke the thinning of the cortical cortex and the increase of porosity at a later stage of the disease. The central excitation frequencies 0.5 and 1 MHz are examined. The proposed configuration consists of one point source and multiple successive receivers in order to calculate the FAS velocity in small propagation paths (local velocity) and derive a variation profile along the cortical surface. It was shown that: (a) the local FAS velocity can capture porosity changes including the occurrence of RL with different number, size and depth of formation; and (b) the excitation frequency 0.5 MHz is more sensitive for the assessment of cortical microstructure.

A mathematical model for bone healing predictions under the ultrasound effect

The bone healing process involves a sequence of cellular actions and interactions, regulated by biochemical and mechanical signals. Experimental studies have shown that ultrasound accelerates bone solidification and enhances the underlying healing mechanisms. We present a mathematical model for deriving predictions of bone healing under the presence of ultrasound. The model consists of i) partial differential equations which describe the spatiotemporal evolution cells, growth factors, tissues and ultrasound acoustic pressure and ii) velocity equations of endothelial tip cells which determine the development of the blood vessel network. The results showed that ultrasound accelerates bone healing primarily by enhancing blood vessel growth. Thus the proposed model could be useful for the ultrasonic evaluation of bone fracture healing.

A mechano-regulatory model for bone healing predictions under the influence of ultrasound.

The bone healing process involves a sequence of cellular action and interaction, regulated by biochemical and mechanical signals. Experimental studies have shown that ultrasound accelerates bone solidification and enhances the underlying healing mechanisms. An integrated computational model is presented for deriving predictions of bone healing under the presence of ultrasound.

Ultrasound propagation in cortical bone: Axial transmission and backscattering simulations

Cortical bone is a heterogeneous, composite medium with a porosity from 5-10%. The characterization of cortical bone using ultrasonic techniques is a complicated procedure especially in numerical studies as several assumptions must be made to describe the concentration and size of pores. This study presents numerical simulations of ultrasound propagation in two-dimensional numerical models of cortical bone to investigate the effect of porosity on: a) the propagation of the first arriving signal (FAS) velocity using the axial transmission method, and b) the displacement and scattering amplitude in the backward direction. The excitation frequency 1 MHz was used and different receiving positions were examined to provide a variation profile of the examined parameters along cortical bone. Cortical porosity was simulated using ellipsoid scatterers and the concentrations of 0-10% were examined. The results indicate that the backscattering method is more appropriate for the evaluation of cortical porosity in comparison to the axial transmission method.

Augmented Home Inventories

Normally, households comprise of people and their material possessions, where persons exercise exclusive agency. The digital augmentation of domestic environment transforms the constitution of households, populating them with new types of entities, namely connected and ‘smart’ objects/devices and distributed services. These new “players” operating within the household, are complex in nature, responsive, adaptive, blurring the given distinction between household members and their stuff, and evading a simplified classification. We consider the augmented home environment as an ecosystem which humans occupy among other interacting entities or parties which are actively affiliated to other networks and environments. Starting with the premise that a household inventory is one way to formally describe and define the household, we examine the contents and structure of traditional home inventories, and then elaborate on the potential evolution of the augmented home inventories as new types of interacting entities are introduced. Thus, we observe a shift from static and place-bound to dynamic classifications, allowing for diverse groupings of home-stuff. We contemplate on the possibility of integrating all parts of the household ecosystem into one unified classification and ontological system. We, also, acknowledge that the exponential growth of IoT will put increasing pressure for managing the huge volumes of data generated from connected households, on which an effective, meaningful, and socially compatible classification system is required. Finally, we highlight several challenges to the augmented home inventory.

In-silico evaluation of cortical porosity by tangential axial transmission

The role of quantitative ultrasound as a diagnostic and monitoring tool in bone pathologies has been widely investigated both experimentally and numerically. Recently, the numerical studies have focused on the exploitation of high-resolution imaging data of bones microarchitecture in order to develop more realistic computational models of osteoporotic bones. In this work, we present numerical simulations of ultrasonic wave propagation in two-dimensional computational models of cortical bone to investigate the effect of cortical porosity and the occurrence of non-refilled basic multicellular unit (BMU) on the propagation of the first arriving signal (FAS) velocity. Calculations are conducted in the tangential direction and the central excitation frequencies of 0.5 and 1 MHz are used. It was shown that the FAS velocity can detect changes in cortical porosity and capture the occurrence of BMU, indicating a potential region for the future evolution of osteoporosis. Also, the examined frequencies were found to be sensitive to changes in the distribution of normal and large pores.

Mapping Interactions in a Pervasive Home Environment

This work focuses on the visualisation of interactions in a pervasive home environment. Home as a space and as an activity container is traditionally linked to the habitual acts of the inhabitants. However, the infiltration of wireless connectivity, throughout the home and external to it, suggests that, in contrast to the traditional notion of hominess, we as inhabitants do not have the means to perceive significant data connections that take place throughout our home. These connections may range from simple data transfer to sensing and decision making, all taking place around our home and unseen. To this end we have tried to find the means to represent these connections in a visual way, in order to provide a tool that will help to reveal the structure, form and perplexity of digital connections to the inhabitants of a pervasive home environment. The study concludes that in order to visualise all this data, maps have to be formed that include both the material and immaterial infrastructure of home, as well as the connection between them and the rest of the world. These maps are bound to have the characteristics of centralised, distributed and decentralised networks, rendering them as hybrid maps, depending on the type of information they deal with.

A meshless Local Boundary Integral Equation (LBIE) method for cell proliferation predictions in bone healing

Bone healing involves a series of complicated cellular and molecular mechanisms that result in bone formation. Several mechanobiological models have been developed to simulate these cellular mechanisms via diffusive processes. In most cases solution to diffusion equations is accomplished using the Finite Element Method (FEM) which however requires global remeshing in problems with moving or new born surfaces or material phases. This limitation is addressed in meshless methods in which no background cells are needed for the numerical solution of the integrals. In this study a new meshless Local Boundary Integral Equation (LBIE) method is employed for deriving predictions of cell proliferation during bone healing. First a benchmark problem is presented to assess the accuracy of the method. Then the LBIE method is utilized for the solution of cell diffusion problem in a two-dimensional (2D) model of fractured model. Our findings indicate that the proposed here LBIE method can successfully predict cell distributions during fracture healing.