Browsing by Author "Jorge, Renato N."
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- An introduction to the level set methods and its applicationsPublication . Reis, Ilda; Tavares, João Manuel R.S.; Jorge, Renato N.Finding a mathematical model which describes the evolution of an interface (in this context, an interface is understood as the boundary between two separate and closed regions, each one having a volume measure different from zero) over the time, like a burning flame or breaking waves, can be a challenging problem. The main difficulties arise when sharp corners appear or different parts of the interface are split or merged, [1]. That kind of interface can be modeled as the embedded zero level set of an implicit time-dependent function. So, the evolving interface can be followed by tracking the zero level set of that implicit function. The above briefly described technique, known as the Level Set Method was introduced by Osher and Sethian, [2]. The idea behind this method [3] is to start with a closed curve, in two dimensions (or a surface in three dimensions) and allow the curve to move perpendicularly to itself from an initial speed, F. If the sign speed is preserved, the location of the propagating front is computed as the arrival time T(x, y) of the front as it crosses the point (x, y). In this case, the equation that describes this arrival time is given as: |∇T| F = 1, T = 0 on. In the general case, the interface can not be considered as the level set of a spacial-dependent function because the arrival time is not a single-valued function. The way to address this difficulty is to represent the initial curve implicitly as a zero level set of a function in one higher dimension. So, at any time, the front is given by the zero level set of the time-dependent function, , referred to as the level set function. Mathematically, the set written as: {x(t) : (x(t), t) = 0} represents the interface at time t. Applying the chain rule and some algebraic manipulation, we can obtain the level set equation: t + |∇ | F = 0, (x(0), 0) = . This method is a powerful mathematical and computational tool for tracking the evolution of curves/surfaces along image sequences. The main advantage came from a different approach similar to the Eulerian formulation. Instead of tracking a curve through time, the Level Set Method evolves a curve by updating the level set function at fixed coordinates through time, [4]. This approach [3], which handles topological merging and breaking in a natural way, is easily generalized to any other dimensional space and do not require that the moving front behaves as an explicit function. The Level Set Method has been widely applied in different areas [3] like geometry, grid generation, image enhancement and noise removal in image processing, shape detection and recognition in image analysis, combustion and crystal growth analysis, among others. Our purpose is to use this approach in the segmentation of structures represented in medical images. This task is very important for an adequate medical diagnosis, for example, in the location of anatomical structures or even in the analysis of its motion. The main difficulties [4] are due to the large variability in the structure shapes and the considerable quantity of noise that acquired images can have. We designed a computational platform in C++, using Visual Studio .NET 2005 environment, and integrated in it the computational library OpenCV (http://sourceforge.net/projects/opencvlibrary) that gave us the possibility for using a great quantity of basic algorithms available for image processing and analysis. Now, we are implementing the above described technique to segment anatomical structures represented in medical images. Our final goal is to estimate the material properties of anatomical structures segmented and tracked along image sequences. In this presentation, we are going to describe the Level Set methodology, exhibit some of its possible applications, present our segmentation method under development and show some of its experimental results.
- Computational model to predict the temperature distribution produced by bone cementPublication . Oliveira, Vânia C.C.; Fonseca, E.M.M.; Oliveira, A.F.; Belinha, Jorge; Rua, Cláudia C.; Piloto, P.A.G.; Jorge, Renato N.Bone is the third frequent location for haematogenous dissemination of malignant tumors. Patients with multiple bone metastases are exponentially growing. Bone metastases, which are frequently diagnosed late, are associated to imminent and pathological bone fractures. Metastatic disease translates an advanced tumor stage and it has a high impact in patients’ quality of life and survival. The main objective is to study the thermal effect induced by the bone cement polymerization, in the bone metastatic tumor reduction and to understand the role of such procedure and its biomechanical stabilization. To assess the clinical effect, it is important to test this methodology before its application and obtain sustained results. In this work, a computational model was developed to predict the temperature distribution produced by cement polymerization, and verify the reduction of the metastatic tumor area due the thermal effect. Different simulations produced to evaluate the necrosis effect for two cement amount sizes introduced in a cortical and spongy bone tumor. The same computational models were reproduced introducing an endomedular nail in titanium and a femoral stem in cobalt-chrome material in pathological bone fractures.
- Drilling of bone: numerical and experimental investigationsPublication . Fernandes, M.G.A.; Fonseca, E.M.M.; Jorge, Renato N.Implant failures and post-operative problems may occur after implant placement as a result of the inappropriate conditions during drilling. The analysis of different materials and drilling parameters is crucial to reduce the bone damage and contribute to the success of this medical interventions. In this research, the effect of drilling parameters on the generated stresses and temperatures in the bone during the process was investigated.
- Drilling of bone: numerical and experimental investigationsPublication . Fernandes, M.G.A.; Fonseca, E.M.M.; Jorge, Renato N.Implant failures and post-operative problems may occur after implant placement as a result of the inappropriate conditions during drilling. The analysis of different materials and drilling parameters is crucial to reduce the bone damage and contribute to the success of this medical interventions. Motivation: Contribute towards the application of optimum drilling parameters that will minimise the bone damage due invasive procedures.
- Dynamic numerical simulation of different drill bit diameter on the polyurethane foams drillingPublication . Fernandes, M.G.A.; Fonseca, E.M.M.; Teixeira, Tiago A.S.; Jorge, Renato N.Drilling is one of the most common processes involved in different cutting operations and may affect the mechanical properties of the workpiece by creating residual stresses around the opened hole and highly stressed on the newly formed surface. Nevertheless, when it comes to the living tissues, drilling assumes more attention to guarantee a non-invasive procedure. Drilling of bone is common in orthopaedic surgical process, to produce a hole to screw insertion to fix the fractured members for immobilization, or even in dental implant interventions. This work describes a conventional drilling process performed on solid rigid polyurethane foams blocks with similar mechanical properties to the human bone. A dynamic and numerical study was conducted to evaluate the use of different drill diameters (4, 5 and 6mm) on the stresses generated during the process.
- Dynamic numerical simulation of different drill bit diameter on the polyurethane foams drillingPublication . Fernandes, M.G.A.; Fonseca, E.M.M.; Teixeira, Tiago A.S.; Jorge, Renato N.Drilling is one of the most common processes involved in different cutting operations and may affect the mechanical properties of the workpiece by creating residual stresses around the opened hole and highly stressed on the newly formed surface.
- Effect of drill speed on bone damage during drillingPublication . Fernandes, M.G.A.; Azevedo, Lucas D.; Jorge, Renato N.; Fonseca, E.M.M.; Ribeiro, J.E.The boné drilling is a common surgical procedure in clinicai intei-ventions including the dentistry. Although not a novelty in medicine, the penetration of a sharp tool in the boné tissue continues to be a clinicai and surgical challenge, as many pertinent questions still remain without solutions. Mechanical damage to the boné tissue is one of the common complication associafed with the drilling process [l]. An excessive force generated by a cutting tool can lead to the formation of microcracks and fractures, and even cause permanent damage in the boné tissue that, in tum, can delay postoperative recovery [2]. The main goal of this paper is to investigate the effect of drill speed on mechanical damage during drilling of solid rigid foam materiais, with similar mechanical properties to the human boné. Experimental tests were performed on biomechanical blocks instrumented with strain gauges in different surface positions during the drilling process. Finite element (FE) simulations were performed to simulate the drilling process and validated with experimental results.
- Effect of drill speed on the strain distribution during drilling of bovine and human bonesPublication . Fernandes, M.G.A.; Fonseca, E.M.M.; Jorge, Renato N.; Manzanares, Cristina; Dias, Maria Isabel RibeiroDrilling is an operation commonly required in orthopaedic surgery for insertion of screws and internal fixation of bone fractures. Induced damage is one of the undesired effects of drilling mainly due to the use of inadequate drilling parameters. During the recent years, scientists have been trying to describe the relationship between drilling parameters and bone injury. However, no studies have examined the level of strain generated in the bone during the drilling process. This paper focuses on the analysis of different drill speeds during drilling of fresh bovine femora and human cadaveric tibiae. The main contribution of this work is to determine how differences in applied drill speeds affect the strain of cortical tissue near the drilling site and the drill bit temperature.
- Estudo térmico numérico em sarcomas ósseosPublication . Rua, Cláudia C.; Oliveira, Vânia C.C.; Piloto, P.A.G.; Fonseca, E.M.M.; Belinha, Jorge; Jorge, Renato N.; Vasconcelos, José C.Com a evolução da ciência e das novas tecnologias de diagnóstico, foi possível observar uma melhoria contínua nos tratamentos em geral e no auxílio da qualidade de vida dos doentes. Os tumores podem ser benignos, podendo verificar-se um crescimento anormal de células sem capacidade de invadir outros tipos de tecidos e órgãos (metástase) ou malignos, em que as células crescem mais rápido e invadem outros tecidos. Podem ainda ser primários ou metastáticos, devido à disseminação de células cancerígenas sistémicas.
- Estudo térmico numérico em sarcomas ósseosPublication . Rua, Cláudia C.; Oliveira, Vânia C.C.; Piloto, P.A.G.; Fonseca, E.M.M.; Belinha, Jorge; Jorge, Renato N.; Vasconcelos, José C.Os sarcomas são tumores heterogéneos que se formam no tecido ósseo, tecido conjuntivo, tecido cartilageneo, tecido muscular, tecido adiposo, nervos periféricos e vasos sanguíneos, geralmente nas extremidades. A cimentação é uma técnica utilizada por exemplo, em procedimentos percutâneos como vertebroplastia, cifoplastia, osteoplastia e sacroplastia. Os cimentos ósseos são biomateriais sintéticos compostos por um polímero (pó) e um componente líquido (monómero). A introdução de cimento ósseo no tecido tem como objetivo tratar ou prevenir fraturas patológicas vertebrais e extraespinhais, aliviar a dor em doentes com osteoporose e metástases, por exemplo.
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