Segmentação e simulação de contornos em imagens através de processos físicos

O objectivo principal deste trabalho é, a partir de duas imagens de um mesmo objecto em dois instantes distintos, simular as formas intermédias que o objecto assume quando o seu comportamento é guiado por princípios físicos. Para tal, é preciso começar por segmentar o objecto nas duas imagens em questão extraindo o seu contorno, após definição manual de um contorno inicial em cada uma delas. Seguidamente, cada um dos contornos definidos evoluirá automaticamente ao longo de um processo iterativo até alcançar a fronteira do objecto desejado. Para isso, é construído um modelo deformável para cada um dos contornos usando o método dos elementos finitos. Posteriormente, a evolução temporal do modelo físico até ao contorno final desejado é obtida resolvendo a equação de equilíbrio dinâmico que contrabalança as forças externas e internas virtualmente aplicadas no objecto modelizado.Para simular a deformação entre os dois contornos obtidos na segmentação, é utilizada análise modal complementada com técnicas de optimização para estabelecer a correspondência entre os dados pontuais dos mesmos. Após esta fase de emparelhamento, o campo dos deslocamentos entre os dois contornos é simulado através da equação de equilíbrio dinâmico

Determination of objects contours using physical principles

Segmentation, the identification of an object represented in a static image or along image sequences,is one of the most common and complex tasks in the domain of Computational Vision. Usually,whenever we intend to extract higher level information from images, we need to start by segmentingthem.The main goal of this work is to segment an object represented in an image by extracting its contourafter defining an initial contour for it; this coarse contour will evolve along an iterative process untilit reaches the frontier of the desired object, figure 1. For that purpose, a deformable model is used,whose behaviour is driven by physical principles

Numerical and experimental study of sandwich plates with metallic foam cores

World-wide vehicles safety experts agree that significant further reductions in fatalities and injuries can be achieved as a result of the use of new energy absorbing materials. In this field, passive safety systems still have great potential to reduce fatalities and injuries, as in the case of using new lightweight energy-absorbing materials. On this work, the authors present the development of a procedure able to perform reliable panels of sandwich sheets with metallic foam cores for industrial applications. The mathematical model used to describe the behavior of sandwich shells with metal cores form is presented and some numerical examples are included. The numerical results are validated using the experimental results obtained from the mechanical experiments. Using the crushable foam constitutive model, available on ABAQUS, a set of different mechanical tests were simulated

The human otitis media with effusion: a numerical-based study

Otitis media is a group of inflammatory diseases of the middle ear. Acute otitis media and otitis media with effusion (OME) are its two main types of manifestation. Otitis media is common in children and can result in structural alterations in the middle ear which will lead to hearing losses. This work studies the effects of an OME on the sound transmission from the external auditory meatus to the inner ear. The finite element method was applied on the present biomechanical study. The numerical model used in this work was built based on the geometrical information obtained from The visible ear project. The present work explains the mechanisms by which the presence of fluid in the middle ear affects hearing by calculating the magnitude, phase and reduction of the normalized umbo velocity and also the magnitude and phase of the normalized stapes velocity. A sound pressure level of 90 dB SPL was applied at the tympanic membrane. The harmonic analysis was performed with the auditory frequency varying from 100 Hz to 10 kHz. A decrease in the response of the normalized umbo and stapes velocity as the tympanic cavity was filled with fluid was obtained. The decrease was more accentuated at the umbo.info:eu-repo/semantics/publishedVersio

New enhanced strain elements for incompressible problems

A new enhanced strain element, based on the definition of extra compatibles modes of deformation added to the standard four-node finite element, is initially presented. The element is built with the objective of addressing incompressible problems and avoiding locking effects. By analysing at the element level the deformation modes which form a basis for the incompressible subspace the extra modes of deformation are proposed in order to provide the maximum possible dimension to that subspace. Subsequently another new element with more degrees of freedom is formulated using a mixed method. This is done by including an extra field of variables related to the derivatives of the displacement field of the extra compatible modes defined previously. The performance of the elements proposed is assessed in linear and non-linear situations. Copyright (C) 1999 John Wiley & Sons, Ltd

Study of the middle ear behavior considering the presence of fluid

O objetivo deste trabalho foi estudar a influência de diferentes fluidos dentro e fora da cavidade timpânica no comportamento biomecânico do ouvido médio. O modelo computacional 3 D da cadeia tímpano‐ossicular foi construído através de imagens de tomografia axial computorizada (TAC). Após a construção do modelo da cadeia tímpano‐ossicular, para a parte interna da membrana timpânica foi criada a caixa timpânica, que inclui toda a cadeia ossicular, e para a parte externa da membrana foi criada uma passagem, simulando o canal auditivo externo. A discretização do modelo foi feita utilizando o método dos elementos finitos, com base no software ABAQUS. As propriedades mecânicas foram extraídas de trabalhos anteriores. Foram obtidos os deslocamentos do umbo e de um ponto central da platina do estribo, para um nível de pressão sonora de 105 dB aplicada na membrana timpânica, comparando a cadeia tímpano‐ossicular e os diferentes níveis de pressão externa e interna do ouvido médio (fluido líquido e fluido gasoso). Os resultados demonstram que o comportamento biomecânico do ouvido médio é diferente para os diferentes níveis de pressões testadas neste modelo. Quando utilizada uma pressão de fluido líquido, os deslocamentos são de amplitude inferior quando comparados com os resultados obtidos com pressão de ar.The objective of this work is to study the influence of different fluids of the tympanic cavity into the biomechanical behavior of the middle ear. The 3 D computer model of the tympanic ossicular chain was built using images from computed tomography (CT). After construction of the tympanic ossicular chain model, it was adapted the simulation by placing the passage to the external auditory canal and to the tympanic cavity. The discretization of the model was made using the finite element method based on ABAQUS software. The mechanical properties were extracted from previous works. The umbo and the stapes footplate displacements, for a sound pressure level of 105 dB applied in tympanic membrane were obtained, comparing the tympanic ossicular chain and the different levels of external and internal pressure in the middle ear (liquid and air). The results demonstrate that the biomechanical behavior of the middle ear is different for different levels of pressure tested in this model. When using liquid, displacements are of lower amplitude when compared with the results obtained with air.Peer Reviewe

Métodos de segmentação para modelação 3D do ouvido a partir de imagens

O objectivo principal deste artigo centra-se na apresentação de métodos de segmentação de imagem adequados para a construção de modelos geométricos 3D das estruturas do ouvido a partir de imagens médicas de Tomografia Computorizada (TC), sendo discutidas as vantagens e desvantagens de cada um. Os métodos são classificados de acordo com as técnicas utilizadas; nomeadamente, em métodos de thresholding, de clustering e de modelos deformáveis. Neste artigo, são também apresentados e discutidos resultados experimentais de segmentação das estruturas do ouvido em imagens de TC

A review on the current segmentation algorithms for medical images

This paper makes a review on the current segmentation algorithms used for medical images. Algorithms are divided into three categories according to their main ideas: the ones based on threshold, the ones based on pattern recognition techniques and the ones based on deformable models. The main tendency of each category with their principle ideas, application field, advantages and disadvantages are discussed. For each considered type some typical algorithms are described. Algorithms of the third category are mainly focused because of the intensive investigation on deformable models in the recent years. Possible applications of these algorithms on segmenting organs and tissues contained in the pelvic cavity are also discussed through several preliminary experiments