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Descripción
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| Radio-frequency ablation is an evolving technology, currently established as the primary ablative modality at most institutions. It is used as a minimally invasive treatment for primary and metastatic liver tumors, and has become a promising alternative to other therapy forms. Although surgical resection is commonly used when the tumor is well-localized, radio-frequency ablation is preferred when the tumor is close to a key vessel, relatively big, or when malignant cells are already spread among the liver. Moreover, the risk of bleeding is minimum and big hepatic segments do not need to be removed. A typical radio-frequency ablation procedure takes place within the frequency range de need by 460 and 550 KHz. Here, an electrical voltage is applied by an electrically active probe, heating the tissue to 100 C for about 15 minutes. Previous simulations explored by other authors predict how big the ablation zone will be, and how much malignant tissue will be heated up. An optimal radio-frequency intervention is closely bound to the position of the probe, which can be monitored through Magnetic Resonance. To simulate an hepatic radio-frequency ablation, ANSYS commercial finite-element software has been used. ANSYS uses the bio-heat equation in order to carry out steady-state and transient thermal analysis. These analysis are performed on phantoms of varying complexity. The boundary conditions for the simulations are the convection induced by the blood perfusion, and the heating power of the needle, defined as a constant temperature. To observe a close heat distribution to what an actual one would be, hepatic tissue parameters are defined to perform the simulations. After a thermal analysis, ANSYS generates an unstructured grid with temperature information in its nodes. In order to take point-measurements, this unstructured grid needs to be converted to a structured space with a spacing the like of the underlying CT image. An initial approach was carried out using the Shepard's method, based on an inverse distance weighted function, which was already implemented by the Visualization Toolkit. Its results were incomplete, and so, an algorithm matching the finite element nature of the unstructured grid was implemented. This algorithm is based on a linear interpolation using barycentric coordinates. To display all data and results, a graphical user interface has been created to display simulation results, offer tools to aid clinical decisions, and validate experiments. To predict the size of the thermal lesion caused by the electrode, the thermal dose concept is presented. Laboratory experiments involving a copper rod and a gel were performed, to simulate heat distribution in the gel. This gel has been elaborated as a substitute for human tissue, to verify that the tissue parameters defined for the phantom experiments lead to obtain results matching the actual case. Measurements are taken through optical fiber, and then plotted and compared with simulated temperature values obtained in ANSYS to validate the tissue parameters. ANSYS experiments involve a liver mesh and a hepatic tumor, which can be located in different parts of the liver. | |
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Internacional
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Si |
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Entidad premiada
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Facultad de Informatica. UPM |
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Entidad concedente
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ACCENTURE |
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Fecha
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01/12/2011 |
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Lugar donde se premió
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Madrid |