Lev Podshivalov

3D hierarchical geometric modeling and multiscale FE analysis as a base for individualized medical diagnosis of bone structure

This paper describes a new alternative for individualized mechanical analysis of bone trabecular structure. This new method closes the gap between the classic homogenization approach that is applied to macro-scale models and the modern micro-finite element method that is applied directly to micro-scale high-resolution models. The method is based on multiresolution geometrical modeling that generates intermediate structural levels. A new method for estimating multiscale material properties has also been developed to facilitate reliable and efficient mechanical analysis. What makes this method unique is that it enables direct and interactive analysis of the model at every intermediate level. Such flexibility is of principal importance in the analysis of trabecular porous structure. The method enables physicians to zoom-in dynamically and focus on the volume of interest (VOI), thus paving the way for a large class of investigations into the mechanical behavior of bone structure. This is one of the very few methods in the field of computational bio-mechanics that applies mechanical analysis adaptively on large-scale high resolution models. The proposed computational multiscale FE method can serve as an infrastructure for a future comprehensive computerized system for diagnosis of bone structures. The aim of such a system is to assist physicians in diagnosis, prognosis, drug treatment simulation and monitoring. Such a system can provide a better understanding of the disease, and hence benefit patients by providing better and more individualized treatment and high quality healthcare. In this paper, we demonstrate the feasibility of our method on a high-resolution model of vertebra L3.

Volumetric texture synthesis of bone micro-structure as a base for scaffold design

Bones consist of hierarchical biocomposite materials arranged in multi-scale structural geometry exhibiting complex behavior. This structure is vulnerable to various damaging factors that may cause its degradation, such as accidents, medical operations and diseases. Current technology cannot precisely reconstruct damaged bone tissue and can only roughly approximate such damaged structures. The aim of this research is to develop a method to identify the damaged regions and provide a best fitting scaffold to imitate the original structure, thus offering better rehabilitation.

Multiresolution 2D geometric meshing for multiscale finite element analysis of bone micro-structures

Bones are composed of hierarchical bio-composite materials characterized by complex multiscale structural geometry and behaviour. Currently, there is great interest within the biomedical community in developing accurate non-invasive techniques for analysing bone micro-structure. We propose a new approach of multiscale finite element analysis of bone micro-structure which can provide physicians with a ‘digital magnifying glass’ providing a continuous bi-directional transition between macro- and micro-scales. In the macro-scale, the material appears to be smoother and more homogeneous. The zooming-in process reveals additional details and the heterogeneity of the material. In this paper we deal with the 2D geometric aspects, demonstrating the feasibility of the proposed method, using a multiscale domain-based geometric model.

Geometric modeling and analysis of bone micro–structures as a base for scaffold design

Bones consist of hierarchical bio-composite materials arranged in multi scale structural geometry. This structure is vulnerable to various damaging factors that may cause its degradation, such as accidents, medical operations and diseases. Imaging techniques can already provide highly detailed micro-features of a bone or even its complete volumetric micro-structure. A three-dimensional model of the bone can then be reconstructed and analyzed. However, current technology cannot precisely fix damaged bone tissue and can only roughly approximate such damaged structures by using scaffolds with standard geometry. This paper proposes a new method for creating natural scaffolds that can adapt according to location, size and shape. The method is based on constructing the scaffold as a 3D volumetric texture that imitates the irregular textural behavior of its surroundings. The method has the ability to create a smooth and continuous structure according to topological and geometrical characteristics. Moreover, the texture captures the stochastic and porous nature of the bone micro-structure. The resulting scaffold texture is tested by applying mechanical analysis to the new synthesized structure, thus controlling the mechanical properties of the reconstructed bone. We believe our method will help in customizing the design and fabrication of scaffolds for bone micro structures. Moreover, such scaffolds can facilitate the process of rehabilitating damaged bone.

Multi-Scale Finite-Element Analysis as a Base for a 3D Computerized Virtual Biopsy System

This paper proposes a novel multi-scale approach for three-dimensional non-invasive analysis of 3d bone models reconstructed from μCT/μMRI images. The feasibility of the proposed method is demonstrated on 2D models representing a simple 2D trabecular bone tissue structure. First, a fundamental domain decomposition method is applied to solve these models. Then, a numerical zoom technique is utilized for local solution enhancement. The proposed new multi-scale FE method has the potential to provide new insights into bone structure and behavior as a component of a computerized virtual biopsy system.Copyright

Patient-Specific Diagnosis and Visualization of Bone Micro-Structures

Bone is a hierarchical bio-material whose architecture differs at each level of hierarchy and whose mechanical properties can vary considerably, even on the same specimen, due to bone heterogeneity. Because of their complexity and large number of details, these models are considered to be large-scale models. Modeling, visualization and diagnosis of such models is challenging, since a large amount of data must be processed rapidly. Moreover, if physically based modeling is required, material properties are also included in the computational model in addition to geometrical data, making the task more difficult. Therefore, advanced technology and computational methods are required for efficient, reliable and robust visualization and diagnosis. In this chapter we describe state-of-the-art technologies and methods that facilitate the processing of bone structure at the micro-scale. Specifically, we relate to computational methods that enable structural analysis of this highly detailed structure for medical diagnosis.

A NEURAL NETWORK TECHNIQUE FOR RE-MESHING OF BONE MICRO-STRUCTURE

Today there is major interest within the biomedical community in developing accurate non-invasive means for evaluation of bone micro-structure and bone quality. Recent improvements in 3D imaging technology, among them development of micro-CT and micro-MRI scanners, allow in-vivo 3D high-resolution scanning and reconstruction of large specimens or even whole bone models. Thus, the tendency today is to evaluate bone features using 3D assessment techniques rather than traditional 2D methods. For this purpose high quality meshing methods are required. However, the 3D meshes produced from current commercial systems usually are of low quality with respect to analysis and rapid prototyping. 3D model reconstruction of bone is difficult due to the complexity of bone micro-structure. The small bone features lead to a great deal of neighborhood ambiguity near each vertex. The relatively new Neural Network method for mesh reconstruction has the potential to create or remesh 3D models accurately and quickly. A Neural Network (NN), which resembles an artificial intelligence (AI) algorithm, is a set of interconnected neurons, where each neuron is capable of making an autonomous arithmetic calculation. Moreover, each neuron is affected by its surrounding neurons through the structure of the network. This paper proposes an extension of the Growing Neural Gas Neural Network (GNG NN) technique for remeshing a triangular manifold mesh that represents bone micro structure. This method has the advantage of reconstructing the surface of an n-genus freeform object without a priori knowledge regarding the original object, its topology, or its shape.

Performance Assessment of Hexahedral Meshing Methods for Design and Mechanical Analysis of Composite Materials

Composite materials can be designed and modeled as material volumes with inclusions of several materials. These multiple inclusions are randomly distributed in a unit cube volume according to the material parameters (density, dimensions, orientation etc.). Then, the finite element (FE) analysis method is applied on the resulting structure to estimate the equivalent material properties. Therefore, these models should to be meshed prior to mechanical FE analysis.Automatic high quality hexahedral meshing is considered a very complex task. Hence, despite extensive research, currently there are no robust methods that can handle grain-based geometry. Meshing a composite material modeled by multiple inclusions presents a number of challenges: (a) the meshing needs to be robust to dimensions, position and orientation of the inclusions; (b) mesh continuity must be achieved on the boundaries between the volume (also known as the matrix) and the inclusions; (c) the mesh needs to approximate the original geometric model with high accuracy; and (d) high quality mesh elements are required for mechanical analysis.Structured and unstructured meshing methods can be used for handling this task. In this research two meshing methods were developed to generate high quality meshes: (a) structured meshing created by warping the grid according to the model’s geometry, and (b) unstructured meshing created by projecting the nodes onto the boundaries of the inclusions to achieve exact geometric representation.The performance of these methods was then evaluated and compared on composite materials with ellipsoidal inclusions. Among the performance criteria for these methods are mesh element quality, geometry approximation error, stress concentrations near the boundaries, and computational complexity.The results indicate that the proposed methods can be used for design and mechanical analysis of composite materials. Moreover, in homogenization applications the structured warped mesh is compatible in terms of performance and element quality to the unstructured mesh.Copyright