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  • Contenido colónico fisiológico medido por resonancia magnética

     Bendezú, Álvaro; Merino, Xavi; Accarino Garaventa, Anna María; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Azpiroz Vidaur, Fernando
    Gastroenterologia y Hepatologia
    Date of publication: 2014-03
    Journal article

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  • Contributions to the Interactive Visualization of Medical Volume Models in Mobile Devices

     Campoalegre Vera, Lazaro
    Defense's date: 2014-07-11
    Universitat Politècnica de Catalunya
    Theses

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    Los adelantos actuales en imagenes médicas están permitiendo a los especialistas obtener información cada vez más precisa de las estructuras anatómicas del organismo humano. Mediante la utilización de diferentes técnicas de visualización, los expertos pueden obtener imágenes de calidad para los huesos, tejidos blandos y torrente sanguíneo, entre otros. Los actuales algoritmos de procesamiento de imágenes garantizan el equilibrio entre la resolución y la exactitud de la información. Paralelamente, los médicos están más familiarizados con las estructuras tridimensionales reconstruidas a partir de imágenes en dos dimensiones.Por otro lado, los hospitales están incorporando la tele-medicina y el tele-diagnóstico entre sus soluciones técnicas. Las aplicaciones cliente-servidor permiten estas funcionalidades.En ocasiones el uso de dispositivos móviles es necesario debido a su fácil mantenimiento y a su portabilidad. Sin embargo, el tiempo de transmisión de la información volumétrica así como el bajo rendimiento del hardware en estos dispositivos, hacen que el diseño de sistemas eficientes de visualización sea todavía una tarea compleja.El objetivo principal de esta tesis es enriquecer la experiencia del usuario en la visualización interactiva de modelos volumétricos de medicina en dispositivos de bajo rendimiento.Para conseguir esto, se ha puesto en práctica la implementación de un mecanismo de compresión/descompresión que depende de funciones de transferencia para optimizar la transmisión, reconstrucción y la visualización en estos dispositivos. Esta tesis, por lo tanto, propone varios esquemas para aprovechar el uso de las funciones de transferencia (TFs) e incrementar el ratio de compresión del volumen durante la transmisión a los dispositivos móviles. De acuerdo con nuestros conocimientos, ninguna de las técnicas descritas en los trabajos presentados anteriormente ha considerado esta posibilidad.El esquema de compresión de volumen basado en Wavelets para la visualización remota, es una propuesta para compresión que tiene en cuenta la función de transferencia. Permite la inspección de modelos de volumen complejos con máximos niveles de detalles en regiones de interés seleccionados. El rendering ejecuta un ray-casting adaptado a modelos con regiones de interés orientado a la GPU en el cliente con una cantidad de información muy limitada que se envía por la red.La otra contribución de esta tesis es la implementación de un esquema para la exploración remota de modelos volumétricos mediante Gradient Octrees. Esta técnica codifica de manera eficiente datos de volumen mientras garantiza visualizaciones de alta calidad con funciones de transferencias predefinidas en un determinado conjunto. La actual implementación permite codificiar hasta 10 materiales diferentes en los datos de Volumen.Gradient Octrees es una técnica multi-resolución, permite la transmisión progresiva y evita los cálculos del gradiente en el dispositivo cliente. En efecto, esta aproximación codifica gradientes previamente calculados para reducir el coste de los cálculos en la GPU del cliente y garantizar el ray-casting con iluminación en la GPU del dispositivo. En comparación con las propuestas estudiadas la pérdida de la calidad visual en los Gradient Octrees es mínima. La estructura del octree es compacta, compuesta de un pequeño vector de volumen y un conjunto de vectores de texturas codificadas, que utilizan solo 1 bit por nodo del octree. El esquema soporta además secciones planas de volumen que contienen información de alta resolución, además de la extrusión de estructuras en los modelos visualizados.

  • Advanced interaction techniques for medical models

     Monclús Lahoya, Eva
    Defense's date: 2014-07-15
    Universitat Politècnica de Catalunya
    Theses

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    Els avenços en la investigació en el camp de recerca de Medical Visualization permeten l'anàlisi de models volumètrics tridimensionals d'estructures anatòmiques obtinguts a partir d'imatges mèdiques capturades mitjançant diferents tècniques, essent la Tomografia Computeritzada (TC) una de les més habituals.Generalment, les aplicacions informàtiques d'ajuda al diagnòstic, la simulació, etc. , permeten l¿exploració interactiva d'aquests tipus de models, una tasca que pot anar precedida d¿un procés d¿identificació (segmentació) de les estructures anatòmiques per tal de possibilitar la seva exploració.L¿objectiu d¿aquesta tesi és millorar l'eficiència i l'experiència de l'usuari, tant de la tasca de segmentació com d¿exploració. Per tal d'assolir-ho, s'han desenvolupat diversos algorismes dissenyats sota una perspectiva centrada en l¿usuari i fent servir els darrers avenços tecnològics de las targes gràfiques, el que ens permet obtenir resultats visuals de màxima qualitat en temps real. Respecte de la tasca de segmentació, ens hem centrat en la identificació d¿ossos ubicats en les articulacions, en models capturats mitjançant TC. La identificació d¿aquests ossos fent servir les tècniques clàssiques de segmentació pot arribar a ser molt feixuga i costosa. La recerca realitzada en el marc de la tesi s'ha enfocat en assolir la màxima automatització possible del procés sencer. La tècnica proposada empra una malla triangular d¿exemple de l¿os que es vol segmentar, que es fará servir per guiar tot el procés de segmentació. L¿algorisme deforma de forma local i adaptativa aquesta malla, adaptant-la a la informació present en el model volumètric en les parts que de forma inambigua és pot determinar la seva frontera, mentre que en les zones en el que el model volumètric presenta incertesa, la malla preserva al màxim la seva forma original. Per altra banda, en la pràctica clínica pot ser de molta utilitat oferir a l'usuari una previsualització ràpida del model volumètric que ha d'inspeccionar. En aquesta tesi elaborem una nova tècnica que permet obtenir en un temps acceptable un conjunt de vistes representatives d'un model volumètric, així com la generació automàtica d'una animació a l'entorn del model que facilita a l'usuari una ràpida comprensió del mateix. La tècnica desenvolupada utilitza una formulació de l'entropia multiescala per la obtenció de bones vistes i la distància de compressió normalitzada, una mètrica del camp de la teoria de la complexitat, per establir el conjunt de vistes representatives. En l'exploració de models mèdics pot ser difícil la visualització simultània d'estructures internes i externes. Per abordar aquest problema s'ha desenvolupat una nova tècnica d'interacció anomenada Virtual Magic Lantern, pensada per a facilitar la inspecció d'aquests models en entorns de realitat virtual. Aquesta metàfora d'interacció es comporta com una llanterna. El seu feix de llum determina una regió d'interès del model, que serà visualitzada emprant una funció de transferència específica permetent la visualització de les estructures internes sense eliminar el context de tot el model.Per últim, s'ha desenvolupat una nova metàfora d'interacció per entorns de realitat virtual, que permet la selecció de punts en un model volumètric no necessàriament segmentat. Aquesta tècnica es basa en l'ús d'un raig originat en la mà de l'usuari, sobre el que es visualitzen els punts d'intersecció amb les estructures anatòmiques que travessa. Donat que la superfície d'aquestes estructures no està explícitament definida, s'ha requerit desenvolupar especialment un càlcul ràpid i precís de les seves interseccions amb el raig. Per tal de facilitar la visió dels punts interiors a superfícies opaques i enriquir la visualització global, s'afegeix sobre dos plans auxiliars la visió del volum tallat garantint la visibilitat total del conjunt de punts.

  • Medición no invasiva del gas intestinal en pacientes con distensión abdominal

     Bendezú, Álvaro; Barba, Elisabeth; Accarino Garaventa, Anna María; Quiroga, Sergi; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Azpiroz Vidaur, Fernando
    Congrés de la Societat Catalana de Digestologia
    Presentation's date: 2014-01-31
    Presentation of work at congresses

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    La distensión abdominal se presenta en general de forma episódica y los pacientes habitualmente atribuyen sus síntomas a un exceso de gas intestinal. OBJETIVO: Determinar si la distensión abdominal se asocia a una acumulación de gas en el tubo digestivo. MATERIAL Y MÉTODOS: En 93 pacientes que se quejaban de distensión abdominal (mediana de 38,5 años, 19-74 años; 86 mujeres, 6 hombres) se realizó un TAC en un momento en que se encontraban bien (condiciones basales sin distensión) y en 76 pacientes se realizó otro TAC durante un episodio de distensión. Además se estudiaron 42 sujetos sanos (mediana de 51 años, 19-62 años; 31 mujeres, 11 hombres) como grupo control. La identificación y medición del gas intestinal se realizó mediante un programa de análisis original desarrollado y previamente validado en nuestro laboratorio. RESULTADOS: En pacientes en condiciones basales la cantidad total de gas abdominal fue de 110 ± 9 mL, distribuida de forma uniforme a lo largo del tubo digestivo (12 ± 1 mL en estómago, 16 ± 2 mL intestino delgado, 16 ± 2 mL colon ascendente, 32 ± 4 mL transverso, 16 ± 2 mL descendente y 18 ± 2 mL pélvico). El volumen y la distribución de gas en los distintos compartimentos del tubo digestivo fue similar que en sujetos sanos (total 119 ± 12 mL: 16 ± 2 mL en estómago, 19 ± 3 mL intestino delgado, 13 ± 2 mL colon ascendente, 33 ± 7 mL transverso, 11 ± 2 mL descendente y 27 ± 5 mL pélvico). Durante los episodios de distensión abdominal los pacientes presentaron un aumento del volumen de gas, pero la diferencia real fue relativamente pequeña y sobre todo debida a un aumento del gas en colon (total 172 ± 19 mL; p < 0,005 vs. condiciones basales y sujetos sanos: 23 ± 8 mL en estómago, 22 ± 5 mL intestino delgado, 26 ± 3 mL colon ascendente, 46 ± 6 mL transverso, 28 ± 4 mL descendente y 25 ± 3 mL pélvico). En ninguno de los grupos se detectaron diferencias relacionadas con edad o sexo. CONCLUSIONES: La distensión abdominal se asocia con un aumento reproducible, pero relativamente pequeño, del volumen de gas intestinal, que en si no justifica un aumento del volumen intraabdominal.

  • Mechanisms of abdominal distension in severe intestinal dysmotility: abdomino-thoracic response to gut retention

     Barba, Elisabeth; Quiroga Gómez, Sergi; Accarino Garaventa, Anna María; Monclús Lahoya, Eva; Malagelada Prats, Carolina; Burri, Emanuel; Navazo Alvaro, Isabel; Malagelada Benapres, Juan Ramon; Azpiroz Vidaur, Fernando
    Neurogastroenterology and motility
    Date of publication: 2013
    Journal article

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    BACKGROUND: We previously showed that abdominal distension in patients with functional gut disorders is due to a paradoxical diaphragmatic contraction without major increment in intraabdominal volume. Our aim was to characterize the pattern of gas retention and the abdomino-thoracic mechanics associated with abdominal distension in patients with intestinal dysmotility. METHODS: In 15 patients with manometrically proven intestinal dysmotility, two abdominal CT scans were performed: one during basal conditions and other during an episode of severe abdominal distension. In 15 gender- and age-matched healthy controls, a basal scan was performed. KEY RESULTS: In basal conditions, patients exhibited more abdominal gas than healthy subjects, particularly in the small bowel, and the volume significantly increased during an episode of distension. During episodes of abdominal distension, the increase in abdominal content was associated with increased girth and antero-posterior abdominal diameter, as well as a cephalic displacement of the diaphragm, which reduced the height of the lung. The consequent reduction in the air volume of the lung was attenuated by an increase in the antero-posterior diameter of the chest. CONCLUSIONS & INFERENCES: Abdominal distension in patients with severe intestinal dysfunction is related to marked pooling of gut contents, particularly in the small bowel. This increase in content is accommodated within the abdominal cavity by a global and coordinated abdomino-phreno-thoracic response, involving an accommodative ascent of the diaphragm and a compensatory expansion of the chest wall.

  • Interactive visualization of medical volume models in mobile devices

     Campoalegre, Lazaro; Brunet, Pere; Navazo Alvaro, Isabel
    Personal and ubiquitous computing
    Date of publication: 2013-10
    Journal article

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    Interactive visualization of volume models in standard mobile devices is a challenging present problem with increasing interest from new application fields like telemedicine. The complexity of present volume models in medical applications is continuously increasing, therefore increasing the gap between the available models and the rendering capabilities in low-end mobile clients. New and efficient rendering algorithms and interaction paradigms are required for these small platforms. In this paper, we propose a transfer function-aware compression and interaction scheme, for client-server architectures with visualization on standard mobile devices. The scheme is block-based, supporting adaptive ray-casting in the client. Our two-level ray-casting allows focusing on small details on targeted regions while keeping bounded memory requirements in the GPU of the client. Our approach includes a transfer function-aware compression scheme based on a local wavelet transformation, together with a bricking scheme that supports interactive inspection and levels of detail in the mobile device client. We also use a quantization technique that takes into account a perceptive metrics of the visual error. Our results show that we can have full interaction with high compression rates and with transmitted model sizes that can be of the order of a single photographic image.

    Interactive visualization of volume models in standard mobile devices is a challenging present problem with increasing interest from new application fields like telemedicine. The complexity of present volume models in medical applications is continuously increasing, therefore increasing the gap between the available models and the rendering capabilities in low-end mobile clients. New and efficient rendering algorithms and interaction paradigms are required for these small platforms. In this paper, we propose a transfer function-aware compression and interaction scheme, for client-server architectures with visualization on standard mobile devices. The scheme is block-based, supporting adaptive ray-casting in the client. Our two-level ray-casting allows focusing on small details on targeted regions while keeping bounded memory requirements in the GPU of the client. Our approach includes a transfer function-aware compression scheme based on a local wavelet transformation, together with a bricking scheme that supports interactive inspection and levels of detail in the mobile device client. We also use a quantization technique that takes into account a perceptive metrics of the visual error. Our results show that we can have full interaction with high compression rates and with transmitted model sizes that can be of the order of a single photographic image.

  • Best Student paper award of the International Conference on Computer Graphics Theory and Applications

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Award or recognition

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  • Generalized haptic relief atlas for rendering surface detail

     Theoktisto Colmenares, Victor Arturo; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel
    International Conference on Computer Graphics Theory and Applications and International Conference on Information Visualization Theory and Applications
    Presentation's date: 2013-02
    Presentation of work at congresses

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    A fast global approach that encodes haptic surface relief detail using an image-based Hybrid Rugosity Me-sostructure Atlas (HyRMA) shell is presented. It is based on a depth/normal texture computed from surface differences of the same mesh object at different resolutions (a dense one with thousands/millions of triangles, and a highly decimated version). Per-face local depth differences are warped from volume space into tangent space, and stored in a sorted relief atlas. Next, the atlas is sampled by a vertex/fragment shader pair, unwarped, displacing the pixels at each face of the decimated mesh to render the original mesh detail with quite fewer triangles. We achieve accurate correspondence between visualization of surface detail and perception of its fine features without compromising rendering framerates, with some loss of detail at mesostructure "holes".

  • DAAPMed: a data-aware anchor point selection tool for medical Models in VR environments

     Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications
    Presentation's date: 2013-02-22
    Presentation of work at congresses

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  • Enhanced Perception in Volume Visualization  Open access

     Díaz Iriberri, José
    Defense's date: 2013-04-26
    Universitat Politècnica de Catalunya
    Theses

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    Debido a la naturaleza de los datos científicos, visualizarlos correctamente puede ser una tarea complicada, pero crucial para interpretarlos de forma adecada. Cuando se trabaja con modelos de volumen complejos, como es el caso de los modelos anatómicos, es importante generar imágenes precisas, ya que una mala interpretación de las mismas puede producir errores graves en el diagnóstico de enfermedades o en la planificación de operaciones quirúrgicas. En estos casos, mejorar la percepción de las zonas de interés, facilita la comprensión de la información inherente a los datos.Durante décadas, los investigadores se han centrado en el desarrollo de técnicas para mejorar la visualización de datos volumétricos. Por ejemplo, los métodos que permiten definir buenas funciones de transferencia son clave, ya que éstas determinan cómo se clasifican los materiales. Otros ejemplos son las técnicas que simulan modelos de iluminación realista, que permiten percibir mejor la distribución espacial de los elementos del volumen, o bien los que imitan efectos ilustrativos, que proporcionan el nivel de abstracción necesario para interpretar correctamente los datos.El trabajo presentado en esta tesis se centra en mejorar la percepción de los elementos del volumen, ya sea modificando el modelo de iluminación aplicado en la visualización, o simulando efectos ilustrativos. Aprovechando la capacidad de cálculo de los nuevos procesadores gráficos, se describen un conjunto de algoritmos que permiten obtener los resultados en tiempo real.Para mejorar la percepción de detalles locales, proponemos modificar el modelo de iluminación utilizando una conocida herramienta de procesado de imágenes (unsharp masking). Iluminando aquellos detalles que sobresalen de las superfícies y oscureciendo las zonas profundas, se mejora el contraste local de la imagen, con lo que se consigue realzar los detalles de superfície.También se presentan diferentes técnicas para mejorar la percepción de la profundidad en Direct Volume Rendering. Concretamente, se propone modificar la iluminación teniendo en cuenta la oclusión ambiente de dos maneras diferentes: la primera utiliza los valores de profundidad en espacio imagen para calcular el factor de oclusión del entorno de cada píxel, mientras que la segunda utiliza los valores de densidad del volumen para aproximar dicha oclusión. Además de estas dos técnicas, también se propone mejorar la percepción espacial y de la profundidad de ciertas estructuras mediante la generación de halos.La técnica conocida como Maximum Intensity Projection (MIP) permite visualizar los elementos de mayor intensidad del volumen, pero no aporta ningún tipo de información contextual. Para mejorar la percepción de la profundidad, proponemos una nueva técnica basada en cambiar la forma en la que se acumula la intensidad en MIP. También se describe un esquema de color para mejorar la percepción espacial de los elementos visualizados.La última contribución de la tesis es una herramienta de manipulación directa de los datos, que permite preservar la información contextual cuando se realizan cortes en el modelo de volumen. Basada en efectos ilustrativos tradicionales, esta técnica permite al usuario estirar las estructuras visibles en las secciones de los cortes. Como resultado, las estructuras de interés se visualizan a diferentes alturas sobre la sección, lo que permite al observador percibirlas correctamente.

    Due to the nature of scientic data sets, the generation of convenient visualizations may be a difficult task, but crucial to correctly convey the relevant information of the data. When working with complex volume models, such as the anatomical ones, it is important to provide accurate representations, since a misinterpretation can lead to serious mistakes while diagnosing a disease or planning surgery. In these cases, enhancing the perception of the features of interest usually helps to properly understand the data. Throughout years, researchers have focused on different methods to improve the visualization of volume data sets. For instance, the definition of good transfer functions is a key issue in Volume Visualization, since transfer functions determine how materials are classified. Other approaches are based on simulating realistic illumination models to enhance the spatial perception, or using illustrative effects to provide the level of abstraction needed to correctly interpret the data. This thesis contributes with new approaches to enhance the visual and spatial perception in Volume Visualization. Thanks to the new computing capabilities of modern graphics hardware, the proposed algorithms are capable of modifying the illumination model and simulating illustrative motifs in real time. In order to enhance local details, which are useful to better perceive the shape and the surfaces of the volume, our first contribution is an algorithm that employs a common sharpening operator to modify the lighting applied. As a result, the overall contrast of the visualization is enhanced by brightening the salient features and darkening the deeper regions of the volume model. The enhancement of depth perception in Direct Volume Rendering is also covered in the thesis. To do this, we propose two algorithms to simulate ambient occlusion: a screen-space technique based on using depth information to estimate the amount of light occluded, and a view-independent method that uses the density values of the data set to estimate the occlusion. Additionally, depth perception is also enhanced by adding halos around the structures of interest. Maximum Intensity Projection images provide a good understanding of the high intensity features of the data, but lack any contextual information. In order to enhance the depth perception in such a case, we present a novel technique based on changing how intensity is accumulated. Furthermore, the perception of the spatial arrangement of the displayed structures is also enhanced by adding certain colour cues. The last contribution is a new manipulation tool designed for adding contextual information when cutting the volume. Based on traditional illustrative effects, this method allows the user to directly extrude structures from the cross-section of the cut. As a result, the clipped structures are displayed at different heights, preserving the information needed to correctly perceive them.

    Debido a la naturaleza de los datos científicos, visualizarlos correctamente puede ser una tarea complicada, pero crucial para interpretarlos de forma adecuada. Cuando se trabaja con modelos de volumen complejos, como es el caso de los modelos anatómicos, es importante generar imágenes precisas, ya que una mala interpretación de las mismas puede producir errores graves en el diagnóstico de enfermedades o en la planificación de operaciones quirúrgicas. En estos casos, mejorar la percepción de las zonas de interés, facilita la comprensión de la información inherente a los datos. Durante décadas, los investigadores se han centrado en el desarrollo de técnicas para mejorar la visualización de datos volumétricos. Por ejemplo, los métodos que permiten definir buenas funciones de transferencia son clave, ya que éstas determinan cómo se clasifican los materiales. Otros ejemplos son las técnicas que simulan modelos de iluminación realista, que permiten percibir mejor la distribución espacial de los elementos del volumen, o bien los que imitan efectos ilustrativos, que proporcionan el nivel de abstracción necesario para interpretar correctamente los datos. El trabajo presentado en esta tesis se centra en mejorar la percepción de los elementos del volumen, ya sea modificando el modelo de iluminación aplicado en la visualización, o simulando efectos ilustrativos. Aprovechando la capacidad de cálculo de los nuevos procesadores gráficos, se describen un conjunto de algoritmos que permiten obtener los resultados en tiempo real. Para mejorar la percepción de detalles locales, proponemos modificar el modelo de iluminación utilizando una conocida herramienta de procesado de imágenes (unsharp masking). Iluminando aquellos detalles que sobresalen de las superficies y oscureciendo las zonas profundas, se mejora el contraste local de la imagen, con lo que se consigue realzar los detalles de superficie. También se presentan diferentes técnicas para mejorar la percepción de la profundidad en Direct Volume Rendering. Concretamente, se propone modificar la iluminación teniendo en cuenta la oclusión ambiente de dos maneras diferentes: la primera utiliza los valores de profundidad en espacio imagen para calcular el factor de oclusión del entorno de cada pixel, mientras que la segunda utiliza los valores de densidad del volumen para aproximar dicha oclusión en cada vóxel. Además de estas dos técnicas, también se propone mejorar la percepción espacial y de la profundidad de ciertas estructuras mediante la generación de halos. La técnica conocida como Maximum Intensity Projection (MIP) permite visualizar los elementos de mayor intensidad del volumen, pero no aporta ningún tipo de información contextual. Para mejorar la percepción de la profundidad, proponemos una nueva técnica basada en cambiar la forma en la que se acumula la intensidad en MIP. También se describe un esquema de color para mejorar la percepción espacial de los elementos visualizados. La última contribución de la tesis es una herramienta de manipulación directa de los datos, que permite preservar la información contextual cuando se realizan cortes en el modelo de volumen. Basada en técnicas ilustrativas tradicionales, esta técnica permite al usuario estirar las estructuras visibles en las secciones de los cortes. Como resultado, las estructuras de interés se visualizan a diferentes alturas sobre la sección, lo que permite al observador percibirlas correctamente.

  • Distensión abdominal funcional ¿La causa está en el tórax?

     Barba, Elisabeth; Quiroga, Sergi; Accarino, Anna; Monclús Lahoya, Eva; Burri, Emanuel; Navazo Alvaro, Isabel; Malagelada Benapres, Juan Ramon; Azpiroz Vidaur, Fernando
    Reunión Nacional de la Asociación Española de Gastroenterología
    Presentation's date: 2013-03
    Presentation of work at congresses

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  • Gradient Octrees: A new scheme for remote interactive exploration of volume models

     Campoalegre Vera, Lazaro; Navazo Alvaro, Isabel; Brunet, Pere
    International Conference on Computer-Aided Design and Computer Graphics
    Presentation's date: 2013
    Presentation of work at congresses

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    Remote exploration of medical volume models is nowadays a challenging problem. Interactive visualization algorithms must be able to send and render in real-time the volume model at the maximum possible visual quality, while adapting to network bandwidth limitations and to hardware constraints in the client device. In this paper we present a transfer function-aware scheme for the remote interactive inspection of volume models in client-server architectures with the objectives of supporting multi-resolution, avoiding gradient computations in the client device and sending a very limited amount of information through the network. Gradient Octrees can be progressively transmitted to the clients in a strongly compact way while achieving a minimum loss of visual quality as compared to state of the art ray-casting renderings. Visual volume understanding can be complemented by showing 2D sections of the original volume data on demand. The approach is discussed and compared to standard ray-casting results on several examples.

  • Morpho-volumetric measurement tools for abdominal distension diagnose

     Monclús Lahoya, Eva; Muñoz Pandiella, Imanol; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Accarino Garaventa, Anna María; Barba, Elisabeth; Quiroga, Sergi; Azpiroz Vidaur, Fernando
    Congreso Español de Informática Gráfica
    Presentation's date: 2013-09-18
    Presentation of work at congresses

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    Digestive bloating is a very common disease, that, though tightly linked to other better known functional diseases such as functional dyspepsia and irritable intestine syndrome, often appears as isolated disfunction itself. Patients refer episodes of abdominal pressure that are difficult to explain. Through the analysis of CT captures of the patients, using a series of measuring tools developed ad-hoc, we have obtained a better comprehension of these functional digestive diseases that have lead to a proper diagnosis and treatment of such patients. In this paper we present the tools that have been developed to assist physicians in obtaining measures of different morpho-volumetric parameters of the abdominal and pulmonary structures and how these are used in the clinical practice to effectively diagnosing digestive bloating.

  • Adaptive cross-sections of anatomical models

     Díaz Iriberri, José; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Computer graphics forum
    Date of publication: 2012-09
    Journal article

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    Medical illustrations have been used for a long time for teaching and communicating information for diagnosis or surgery planning. Illustrative visualization systems create methods and tools that adapt traditional illustration techniques to enhance the result of renderings. Clipping the volume is a popular operation in volume rendering for inspecting the inner parts, though it may remove some information of the context that is worth preserving. In this paper we present a new editing technique based on the use of clipping planes, direct structure extrusion, and illustrative methods, which preserves the context by adapting the extruded region to the structures of interest of the volumetric model. We will show that users may interactively modify the clipping plane and edit the structures to highlight, in order to easily create the desired result. Our approach works with segmented volume models and non-segmented ones. In the last case, a local segmentation is performed on-the-fly. We will demonstrate the efficiency and utility of our method.

  • Example-guided segmentation

     Chica Calaf, Antonio; Monclús Lahoya, Eva; Brunet Crosa, Pere; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Graphical models
    Date of publication: 2012-11
    Journal article

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  • Efficient selection of representative views and navigation paths for volume data exploration

     Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    Date of publication: 2012
    Book chapter

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    The ViRVIG institute  Open access

     Andujar Gran, Carlos A.; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Patow, Gustavo Ariel; Pueyo, Xavier
    SBC Journal on 3D interactive systems
    Date of publication: 2011-11-16
    Journal article

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    In this paper we present the ViRVIG Institute, a recently created institution that joins two well-known research groups: MOVING in Barcelona, and GGG in Girona. Our main research topics are Virtual Reality devices and interaction techniques, complex data models, realistic materials and lighting, geometry processing, and medical image visualization. We briefly introduce the history of both research groups and present some representative projects. Finally, we sketch our lines for future research.

  • Avances en realidad virtual para aplicaciones punteras

     Lligadas Rodriguez, Xavier; Susin Sanchez, Antonio; Brunet Crosa, Pere; Vinacua Pla, Alvaro; Fairen Gonzalez, Marta; Andujar Gran, Carlos A.; Monclús Lahoya, Eva; Vazquez Alcocer, Pere Pau; Campoalegre Vera, Lazaro; Argelaguet Sanz, Fernando; Pelechano Gomez, Nuria; Díaz Iriberri, José; Chica Calaf, Antonio; Cervero Abello, Maria Angels; Ojeda Contreras, Jesus; Beacco Porres, Alejandro; Navazo Alvaro, Isabel
    Participation in a competitive project

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  • GPU collision detection in conformal geometric space

     Roa, Eduardo; Theoktisto, Víctor; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel
    Ibero-American Symposium in Computer Graphics
    Presentation's date: 2011-06-02
    Presentation of work at congresses

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  • A volume approach to model repair and smoothing

     Brunet, Pere; Chica Calaf, Antonio; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Geometric Modeling (Dagstuhl Seminar 11211)
    Presentation's date: 2011
    Presentation of work at congresses

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  • Real-time ambient occlusion and halos with Summed Area Tables

     Díaz Iriberri, José; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel; Duguet, Florent
    Computers & graphics
    Date of publication: 2010-08
    Journal article

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  • Hybrid Rugosity Mesostructures (HRMs) for fast and accurate rendering of fine haptic detail

     Theoktisto, Victor; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel
    CLEI electronic journal
    Date of publication: 2010
    Journal article

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  • Visualization of large-scale urban models through multi-level relief impostors

     Andujar Gran, Carlos A.; Brunet Crosa, Pere; Chica Calaf, Antonio; Navazo Alvaro, Isabel
    Computer graphics forum
    Date of publication: 2010-12
    Journal article

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    In this paper, we present an efficient approach for the interactive rendering of large-scale urban models, which can be integrated seamlessly with virtual globe applications. Our scheme fills the gap between standard approaches for distant views of digital terrains and the polygonal models required for close-up views. Our work is oriented towards city models with real photographic textures of the building facades. At the heart of our approach is a multi-resolution tree of the scene defining multi-level relief impostors. Key ingredients of our approach include the pre-computation of a small set of zenithal and oblique relief maps that capture the geometry and appearance of the buildings inside each node, a rendering algorithm combining relief mapping with projective texture mapping which uses only a small subset of the pre-computed relief maps, and the use of wavelet compression to simulate two additional levels of the tree. Our scheme runs considerably faster than polygonal-based approaches while producing images with higher quality than competing relief-mapping techniques. We show both analytically and empirically that multi-level relief impostors are suitable for interactive navigation through large urban models.

  • A hybrid rugosity mesostructure (HRM) for rendering fine haptic detail

     Fairen Gonzalez, Marta; Navazo Alvaro, Isabel
    Date: 2009-02
    Report

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  • GRUP DE RECERCA EN VISUALITZACIO, REALITAT VIRTUAL I INTERACCIO GRAFICA (VIRVIG)

     Vinacua Pla, Alvaro; Chica Calaf, Antonio; Vazquez Alcocer, Pere Pau; Díaz Iriberri, José; Susin Sanchez, Antonio; Monclús Lahoya, Eva; Cervero Abello, Maria Angels; Ojeda Contreras, Jesus; Andujar Gran, Carlos A.; Fairen Gonzalez, Marta; Lligadas Rodriguez, Xavier; Argelaguet Sanz, Fernando; Campoalegre Vera, Lazaro; Pelechano Gomez, Nuria; Navazo Alvaro, Isabel; Brunet Crosa, Pere
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    The Virtual Magic Lantern: an interaction metaphor for enhanced medical data inspection  Open access

     Monclús Lahoya, Eva; Díaz Iriberri, José; Vazquez Alcocer, Pere Pau; Navazo Alvaro, Isabel
    ACM Symposium on Virtual Reality Software and Technology
    Presentation's date: 2009-11-19
    Presentation of work at congresses

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    In this paper we present the Virtual Magic Lantern (VML), an interaction tool tailored to facilitate volumetric data inspection. It behaves like a lantern whose virtual illumination cone provides the focal region which is visualized using a secondary transfer function or different rendering style. This may be used for simple visual inspection, surgery planning, or injure diagnosis. The VML is a particularly friendly and intuitive interaction tool suitable for an immersive Virtual Reality setup with a large screen, where the user moves a Wanda device, like a lantern pointing to the model. We show that this inspection metaphor can be efficiently and easily adapted to a GPU ray casting volume visualization algorithm. We also present the Virtual Magic Window (VMW) metaphor as an efficient collateral implementation of the VML, that can be seen as a restricted case where the lantern illuminates following the viewing direction, through a virtual window created as the intersection of the virtual lantern (guided by the Wanda device) and the bounding box of the volume.

    Postprint (author’s final draft)

  • A hybrid rugosity mesostructure (HRM) for faster rendering of fine haptic detail

     Theoktisto, Victor; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel
    Latin American Informatics Conference
    Presentation's date: 2009
    Presentation of work at congresses

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    We propose a faster method for surface haptic rendering using image-based Hybrid Rugosity Mesostructures (HRMs), paired maps with per-face height eld displacements and normalmaps, which are layered on top of a much decimated mesh. The haptic probe's force response algorithm is modulated using the blended HRM coat to render surface features at much lower costs. The proposed method solves typical problems at edge crossings, concave foldings and texture transitions. To prove the wellness of the approach, a usability testbed framework was built to measure and compare experimental results of haptic rendering approaches. Trial results of user testing evaluations show the goodness of the proposed HRM technique, rendering accurate 3D surface detail at high sampling rates, deriving useful modeling and perception thresholds for this technique.

  • Massive mesh hole repair minimizing user intervention

     Brunet Crosa, Pere; Chica Calaf, Antonio; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Computing
    Date of publication: 2009-10
    Journal article

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    Automatic generation of exploration paths for medical models  Open access

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Herrero Jover, Javier; López, Jordi
    International journal of computer assisted radiology and sugery (Online)
    Date of publication: 2008
    Journal article

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    Although the visualization techniques are becoming faster and faster, the datasets also increase, and the time the radiologists are able to devote to a single analysis is limited. In this sense, we propose some techniques to help the specialists to find adequate views of the datasets in an efficient way.

    Postprint (author’s final draft)

  • S3Dc: a 3Dc-based volume compression algorithm

     Yela, H; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Congreso Español de Informática Gráfica
    Presentation's date: 2008
    Presentation of work at congresses

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    Volumes acquired for medical purposes are continuously increasing in size, faster than graphic cards memory capacity. Large volumetric datasets do not fit into GPU memory and therefore direct rendering is not possible. Even large volumes that still fit into GPU memory make frame rates decay. In order to reduce the size of large volumetric models, we present a new compression scheme. In this paper we present S3Dc, a lossy volume compression algorithm suitable for scalar values. It is inspired in hardware-accelerated 3Dc normal compression technique. S3Dc allows us to compress the volume in CPU up to a 4:1 or 8:1 ratio, while still yielding good quality results. We provide details on the compression scheme and show how to render directly from a S3Dc compressed texture. Furthermore, we analyze the image quality theoretical error and the average error with several images in order to assess the results.

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    Representative views and paths for volume models  Open access

     Vazquez Alcocer, Pere Pau; Monclús Lahoya, Eva; Navazo Alvaro, Isabel
    International Symposium on Smart Graphics
    Presentation's date: 2008
    Presentation of work at congresses

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    Volume data models are becoming larger and larger as the capture technology improves. Thus, their visualization requires high computational power. The automatic presentation of volume models through representative images and/or exploration paths becomes more and more useful. Representative views are also useful for document illustration, fast data quality evaluation, or model libraries documentation. Exploration paths are also useful for video demonstrations and previsualization of captured data. In this paper we present a fast, adaptive method for the selection of representative views and the automatic generation of exploration paths for volume models. Our algorithm is based on multi-scale entropy and algorithmic complexity. These views and paths reveal informative parts of a model given a certain transfer function. We show that our method is simple and easy to incorporate in medical visualization tools.

    Postprint (author’s final draft)

  • MTCut: real time marching tetra cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Theory and Practice of Computer Graphics
    Presentation's date: 2008
    Presentation of work at congresses

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    Isosurface construction and rendering based on tetrahedral grids has been adequately implemented on programmable graphics hardware. In this paper we present MTCut: a volume cutting algorithm that is able to cut isosurfaces obtained by a Marching Tetrahedra algorithm on volume data. It does not require a tetrahedal representation and runs in real time for complex meshes of up to 1.8M triangles. Our algorithm takes as input the isosurface to be cut, and produces the cut geometry in response to the user interaction with a haptic device. The result is a watertight manifold model that can be interactively recovered back to CPU upon user request.

  • A 3D virtual model for training in endoscopical repair of subcondylar fractures of the mandible

     Hueto, J A; Díaz Iriberri, José; Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Raspall, G
    International journal of computer assisted radiology and sugery
    Date of publication: 2008-09
    Journal article

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    Conventional treatment of the subcondylar fractures of the mandible is challenging because of the medial and anterior displacement of the condylar fragment and the limited surgical field. Proximity of facial nerve, carotid artery branches, parotid gland, and ear canal are risk factors to open surgical procedures. In these fractures a proper reduction and osteosynthesis are always difficult, even if using open procedures. The recent endoscopic approach allows a perfect control and vision of the fragments, and it also permits an anatomic reduction and plating of the fracture avoiding risks associated to the open surgery. Surgical training for these endoscopic procedures is difficult, especially in those cases in which surgeons are not familiar with endoscopic interventions and they still don’t have skills to work while looking at the screen. Simulators are friendly and risk free systems to train surgeons to operate with endoscopes.

  • Pressing: Smooth Isosurfaces with Flats from Binary Grids

     Chica Calaf, Antonio; Williams, J; Andujar Gran, Carlos A.; Brunet Crosa, Pere; Navazo Alvaro, Isabel; Rossignac, J; Vinacua Pla, Alvaro
    Computer graphics forum
    Date of publication: 2008-01
    Journal article

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  • MTCut: GPU-based Marching Tetra Cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Date: 2007-01
    Report

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  • MTCut: GPU-based Marching Tetra Cuts

     Monclús Lahoya, Eva; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau
    Date: 2007-01
    Report

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  • Modelado, visualización, animación y análisis de entornos 3D altamente complejos en sistemas interactivos de realidad virtual

     Navazo Alvaro, Isabel; Andujar Gran, Carlos A.
    Participation in a competitive project

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  • Modelado, visualizacion, animacion y analisis de entornos 3d altamente complejos en sistemas interactivos de realidad virtual

     Navazo Alvaro, Isabel; Susin Sanchez, Antonio; Fairen Gonzalez, Marta
    Participation in a competitive project

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  • Buque Autónomo Polivalente para la Pesca 2020 (BAIP 2020)

     González Blanco, Ricardo; Garcia Espinosa, Julio; Mari Sagarra, Ricardo; Brunet Crosa, Pere; Vinacua Pla, Alvaro; Navazo Alvaro, Isabel
    Participation in a competitive project

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  • The eurographics association

     Navazo Alvaro, Isabel
    Collaboration in journals

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  • Registro 3D y 4D de imágenes cardíacas SPECT

     Murillo, Santiago; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Congreso Español de Informática Gráfica
    Presentation's date: 2007-09
    Presentation of work at congresses

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    Los estudios de cardiología nuclear provenientes de captaciones cardíacas 4D gated SPECT (Single Photon Emission Computed Tomographic) aportan información sobre la perfusión del ventrículo izquierdo en diferentes fases del ciclo cardíaco. Para el pronóstico de la viabilidad del miocardio es importante comparar la perfusión del miocardio con el paciente en estado de reposo y en esfuerzo. En este artículo presentamos un método de registro para imágenes cardíacas SPECT, basado en la Información Mutua (IM) como medida de similitud, que utiliza toda la información contenida en la captación. Ésta puede representar un instante del ciclo cardíaco (registro 3D) o una serie temporal de captaciones (registro 4D). La propuesta se basa en un nuevo método de interpolación que es especialmente significativo en el registro de imágenes de baja resolución. La utilización de toda la información disponible en la captación junto con el nuevo método de interpolación, conducen a un método de registro efciente y de alta precisión.

  • Data-driven tetrahedral mesh subdivision

     Rodriguez Pérez, Lyudmila Odalina; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Computer graphics forum
    Date of publication: 2007-12
    Journal article

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    Given a tetrahedral mesh immersed in a voxel model, we present a method to refine the mesh to reduce the discrepancy between interpolated values based on either scheme at arbitrary locations. An advantage of the method presented is that it requires few subdivisions and all decisions are made locally at each tetrahedron. We discuss the algorithm’s performance and applications.

  • Omni-directional relief impostors

     Andujar Gran, Carlos A.; Boo, J; Brunet Crosa, Pere; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel; Vazquez Alcocer, Pere Pau; Vinacua Pla, Alvaro
    Computer graphics forum
    Date of publication: 2007-07
    Journal article

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  • IST-027731 PRESENCCIA coordinació

     Slater, Melvyn; Navazo Alvaro, Isabel; Brunet Crosa, Pere; Vinacua Pla, Alvaro; Andujar Gran, Carlos A.
    Participation in a competitive project

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    Volume cardiac SPECT image registration  Open access

     Murillo, Santiago; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    International Conference on Medical Information Visualization
    Presentation's date: 2006
    Presentation of work at congresses

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    The registration of cardiac images is relevant for the diagnosis of cardiac pathologies. In the case of SPECT (Single Photon Emission Computer Tomography) datasets, this is difficult because of the low resolution of the images. In this paper we present a new registration method for 3D images with poor resolution. Our method is based on the maximization of the mutual information (MI) using a new interpolation method which significantly improves the result of an MI-based strategy on low resolution images. We also use a different optimization strategy than other MI-based algorithms, typically achieving errors of the order of one pixel. We also discuss experimental results of our method.

  • Data-driven tetrahedral mesh subdivision

     Rodriguez, Lyudmila; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Ibero-American Symposium on Computer Graphics
    Presentation's date: 2006-07
    Presentation of work at congresses

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    Given a tetrahedral mesh immersed in a voxel model, we present a method to refine the mesh to reduce the discrepancy between interpolated values based on either scheme at arbitrary locations. An advantage of the method presented is that it requires few subdivisions and all decisions are made locally at each tetrahedron. We discuss the algorithm’s performance and applications.

  • Access to the full text
    A topological comparison of surface extraction algorithms  Open access

     Andujar Gran, Carlos A.; Brunet Crosa, Pere; Fairen Gonzalez, Marta; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Date: 2006-01
    Report

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    In many application areas, it is useful to convert the discrete information stored in the nodes of a regular grid into a continuous boundary model. Isosurface extraction algorithms di er on how the discrete information in the grid is generated, on what information does the grid store and on the properties of the output surface.

  • Pressing: Smooth Isosurfaces with Flats from Binary Grids

     Andujar Gran, Carlos A.; Brunet Crosa, Pere; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Date: 2006-02
    Report

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  • Data-driven Tetrahedral Mesh Subdivision

     Rodriguez Pérez, Lyudmila Odalina; Navazo Alvaro, Isabel; Vinacua Pla, Alvaro
    Date: 2006-09
    Report

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