Medical datasets are continuously increasing in size. Although larger models may be available for certain research purposes, in the common clinical practice the models are usually of up to \(512 \times 512 \times 2000\) voxels. These resolutions exceed the capabilities of conventional GPUs, the ones usually found in the medical doctors’ desktop PCs. Commercial solutions typically reduce the data by downsampling the dataset iteratively until it fits the available target specifications. The data loss reduces the visualization quality and this is not commonly compensated with other actions that might alleviate its effects. In this paper, we propose adaptive transfer functions, an algorithm that improves the transfer function in downsampled multiresolution models so that the quality of renderings is highly improved. The technique is simple and lightweight, and it is suitable, not only to visualize huge models that would not fit in a GPU, but also to render not-so-large models in mobile GPUs, which are less capable than their desktop counterparts. Moreover, it can also be used to accelerate rendering frame rates using lower levels of the multiresolution hierarchy while still maintaining high-quality results in a focus and context approach. We also show an evaluation of these results based on perceptual metrics.

Optical technologies for measuring the human body shape without contact have gained popularity in the recent years. In particular, techniques based on fringe projection have demonstrated a good performance for generating three-dimensional (3D) topographies of the human body. For the 3D digitization of the human body, the technique has found various applications in different fields, including relevant cosmetic and medical applications such as 3D back shape detection in scoliosis [1], 3D shape measurement of pectus excavatum [2], 3D intra-oral dental measurements [3], or 3D measurement of the topography of human skin [4, 5, 6]. In the latter, optical measurement of the skin surface by means of fringe projection provides a less invasive, faster and more accurate result than the obtained with traditional methods established in the cosmetic industry based on skin replicas of silicone, which are applied along several minutes on the person, and therefore are more sensitive to errors associated with unintentional movements of the person due to breathing or muscle contractions.

Endoscopic interventions in the abdominal and thoracic cavity are often hampered by the difficulty to orient in the endoscopic view. This is due to the small field of view and the inhomogeneous illumination, but also because abdominal organs are highly deformable and subject to complex movements. The use of flexible endoscopes further complicates these issues. In the context of a multidisciplinary project involving clinical and technical teams, we report the definition of clinical requirements and surgical workflow of abdominal endoscopic interventions, and present the design and implementation of a planning and navigation system. Some of the implemented features include: segmentation, tracking, landmark-based navigation, and combined surface and volume rendering. Our system is based on open source libraries, and is flexible and applicable to other types of interventions.

Agar plates are widely used in the biomedical field as a medium in which to artificially grow bacteria, algae or fungi. Agar plates (Petri dishes) are used routinely in microbiology laboratories in order to identify the type of micro-organism responsible for infections. Such diagnoses are based on counting the number and type of bacterial colonies growing in the Petri dish. The count of bacterial colonies is a time consuming task prone to human error, so interest in automated counting systems has increased in the recent years. One of the difficulties of automatizing the counting process is the presence of markers and annotations made in the lower part of the agar plate. Efficient removal of such markers can increase the accuracy of the bacterial counting system. This article introduces a fast method for detection, segmentation and removal of annotations in agar plates that improves the results of existing bacterial colony counting algorithms.

Cochlear implantation is a surgical technique which aims to restore hearing in people with deep hearing loss. However, outcomes of the surgery still exhibit a large variability between patients. Among the factors that contribute to variability the most important are morphological differences in anatomical structures between patients and incorrect implant placements. In order to address these issues, it would be desirable to have a functional model of the cochlea which incorporates inter-patients variability and simulate electrode placement. To this end, we present a finite element model which captures the interaction between the cochlear partition, modeled as an elastic solid with finite deformation, and the perilymph fluid, modeled as a compressible, viscous fluid. Numerical results show that the membrane responds to changes in the stimulation frequencies.

Delayed Enhancement Magnetic Resonance Imaging can be used to non-invasively differentiate viable from non-viable myocardium within the Left Ventricle in patients suffering from myocardial diseases. Automated segmentation of scarified tissue can be used to accurately quantify the percentage of myocardium affected. This paper presents a method for cardiac scar detection and segmentation based on supervised learning and level set segmentation. First, a model of the appearance of scar tissue is trained using a Support Vector Machines classifier on image-derived descriptors. Based on the areas detected by the classifier, an accurate segmentation is performed using a segmentation method based on level sets.

RADStation3G is a software platform for cardiovascular image analysis and surgery planning. It provides image visualization and management in 2D, 3D and 3D+t; data storage (images or operational results) in a PACS (using DICOM); and exploitation of patients' data such as images and pathologies. Further, it provides support for computationally expensive processes with grid technology. In this article we first introduce the platform and present a comparison with existing systems, according to the platform's modules (for cardiology, angiology, PACS archived enriched searching and grid computing), and then RADStation3G is described in detail.

This paper surveys global illumination algorithms for environments including participating media and accounting for multiple scattering. The objective of this survey is the characterization of those methods: Identification of their base techniques, their assumptions, limitations and range of utilization. To this end, the algorithms are grouped into functional categories and each method is briefly reviewed, with a discussion of its complexity and its pros and cons. We finish by discussing some applications as well as remaining areas for investigation.

Thresholding is perhaps one of the most basic techniques in image processing. The Insight Toolkit (ITK) includes several threshold filters ranging from simple ones to Otsu based thresholding. Deep into the implementation of the Canny edge detection filter, ITK includes an implementation of hysteresis thresholding, but unfortunately this method can not be used as a generic filter. This paper presents an implementation of the hysteresis thresholding filter that can be used as a standalone ITK filter.

We have developed a system for computer-assisted surgical planning of tracheal surgeries. The system allows to plan the intervention based on CT images of the patient, and includes a virtual database of commercially available prostheses. Automatic segmentation of the trachea and apparent pathological structures is obtained using a modified region growing algorithm. A method for automatic adaptation of a finite element mesh allows to build a patient-specific biomechanical model for simulation of the expected performance of the implant under physiological movement (swallowing, sneezing). Laboratory experiments were performed to characterise the tissues present in the trachea, and movement models were obtained from fluoroscopic images of a patient. Results are reported on the planning and biomechanical simulation of two patients that underwent surgery at our hospital.

BACKGROUND & AIMS:Abdominal bloating is a frequent symptom in various categories of patients; however, its origin is unclear. Our aim was to establish the mechanisms of abdominal bloating.METHODS:The study evaluated 56 patients whose predominant symptom was abdominal bloating. Of these, 47 (44 female and 3 male; aged 19-74 years) were diagnosed with functional intestinal disorder by Rome II criteria and 9 (7 female and 2 male; aged 18-64 years) were diagnosed with intestinal dysmotility by gastrointestinal manometry. Computed tomographic scans were obtained before (basal level) and during a severe bloating episode. Control scans were also obtained from 12 healthy subjects (11 female and 1 male; aged 19-62 years). Morpho-volumetric differences between basal and severe bloating scans were measured using an original computer analysis program.RESULTS:During severe bloating, patients with dysmotility exhibited anterior wall protrusion (23 +/- 4 mm; P < .001 vs basal) associated with a marked increase in total abdominal volume (1.4 +/- 0.3 L; P = .002 vs basal) and with cephalic displacement of the diaphragm. By contrast, in patients with functional intestinal disorder, total abdominal volume barely increased (0.3 +/- 0.1 L; P < .001 vs dysmotility); in these patients, abdominal distention (14 +/- 2 mm anterior wall protrusion; P < .001 vs basal) was related to diaphragmatic descent (-12 +/- 3 mm; R = -0.62; P < .001).CONCLUSIONS:Abdominal distention might be caused by an increase in intra-abdominal volume or abdomino-phrenic displacement and ventro-caudal redistribution of contents.

BACKGROUND AND AIM: We previously showed that colonic gas infusion increases the girth and modifies the muscular activity of the anterior abdominal wall. We hypothesized that abdominal accommodation to volume loads is an active process instrumented by the coordinated activity of the anterior wall and the diaphragm.METHODS: To increase intraabdominal volume in healthy subjects, a gas was infused into the colon (1.44 L in 1 h) while measuring girth (by tape measure) and electromyography (EMG) activity of the anterior wall (via four pairs of surface electrodes) and the diaphragm (via six ring electrodes over an esophageal tube in the hiatus). After preliminary feasibility studies (N = 12), postural activity (N = 6) and responses to colonic gas loads, both with the trunk erect (N = 8) and in supine position (N = 8), were studied. A morphometric analysis was performed by computed tomography, image analysis (N = 8).RESULTS: In the erect position, anterior wall tone was higher and diaphragmatic tone was lower than in the supine position. With the trunk erect, gas infusion induced diaphragmatic relaxation (by 21 +/- 3%; P < 0.05) and anterior wall contraction (16 +/- 4% EMG increment; P < 0.05). By contrast, in the supine position, it induced diaphragmatic contraction (15 +/- 6%, P < 0.05), while the anterior wall, in the absence of postural tone, showed no change (3 +/- 2%, NS). Gas infusion was associated with girth increase (7.3 +/- 1.0 mm with the trunk erect and 8.6 +/- 1.4 mm in the supine position) and diaphragmatic ascent (17.6 +/- 5.2 mm; P < 0.05).CONCLUSION: The degree of abdominal distension produced by intraabdominal volume increments results from posture-related abdomino-phrenic muscular responses.

BACKGROUND: It is unknown if abdominal bloating is attributable to excess abdominal gas or improved by a prokinetic agent.AIMS: To assess abdominal gas content in functional abdominal bloating and to ascertain the effect of a prokinetic agent on intestinal gas symptoms in these patients.METHODS: In 20 patients, intra-abdominal gas content and symptoms were quantified before and during treatment with pyridostigmine (30 mg/8 hp. o) in this randomized, placebo-controlled, double-blind study. Daily symptoms were quantified for 5 days before and 10 days during treatment, and abdominal gas volume was quantified by CT imaging before and at the fourth day of treatment. A CT scan was also obtained in 10 healthy subjects.RESULTS: Before treatment, the total volume of intestinal gas was similar in patients (112 +/- 18 mL) and in healthy controls (116 +/- 20 mL). The treatment-induced change in total and regional intestinal gas volume was not significantly different between pyridostigmine (-4 +/- 18 mL; mean +/- SEM) and placebo (0 +/- 15 mL). However, pyridostigmine reduced the severity of bloating from 3.3 +/- 0.3 to 2.6 +/- 0.4 (P < 0.05), whereas placebo did not (3.2 +/- 0.3 vs 3.0 +/- 0.4), although the change did not reach statistical difference across groups.CONCLUSION: In patients complaining of functional bloating, the volume and distribution of intestinal gas, measured on nonselected days, is comparable to asymptomatic subjects. Prokinetic stimulation improves bloating sensation without detectable changes in gas content.

BACKGROUND AND AIMS: Patients frequently complain of gas symptoms precipitated by meals, but the effect of early digestion on intestinal gas content remains unknown. Our aim was to determine the influence of meals on intestinal gas volume and distribution.METHODS: First, we developed a CT image analysis program, based on independent software modules, to measure gas content within the gut. The system was validated in nine healthy subjects by taking helical abdominal CT scans before and after rectal infusion of known volumes of air (100-400 mL). In 15 healthy subjects, intestinal gas distribution was measured in fast and early postcibal CT scans. The postcibal scan was taken 99 +/- 22 minutes after a 597 +/- 57 kcal meal.RESULTS: The volume of gas infused per rectum was detected with an accuracy of 100.4 +/- 3.0%. During fasting, intestinal gas volume was 94 +/- 7 mL (excluding two extreme outliers). After the meal, gas content within the gut increased by 64.7% (up to 149 +/- 21 mL, P < 0.01 vs fast) and the increment occurred in the colon (59 +/- 9 mL precibal vs 121 +/- 20 mL postcibal, P < 0.001), while other gut compartments remained unchanged.CONCLUSION: Ingestion of a meal activated gas metabolism and increased gas content within the gut. The increment occurred early, presumably prior to colonic fermentation of food substrates and was localized in the distal gut, suggesting that gas had a proximal origin and was propelled caudally.

Rendering participating media is important for a number of domains, ranging from commercial applications (entertainment, virtual reality) to simulation systems (driving, flying, and space simulators) and safety analyses (driving conditions, sign visibility). This article surveys global illumination algorithms for environments including participating media. It reviews both appearance-based and physically-based media methods, including the single-scattering and the more general multiple-scattering techniques. The objective of the survey is the characterization of all these methods: identification of their base techniques, assumptions, limitations, and range of utilization. It concludes with some reflections about the suitability of the methods depending on the specific application involved, and possible future research lines.

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The objective of this thesis is the development of algorithms for the simulation of the light transport in general environments to render high quality still images. To this end, first we have analyzed the existing methods able to render participating media, more concretely those that account for multiple scattering within the media. Next, we have devised a couple of two pass methods for the computation of those images. For the first step we have proposed algorithms to cope with the scenes we want to deal with. The second step uses the coarse solution of the first step to obtain the final rendered image. The structure of the dissertation is briefly presented below. In the first chapter the motivation of the thesis and its objectives are discussed. It also summarizes the contributions of the thesis and its organization. In the second chapter the principles of global illumination for general environments are reviewed, with the most important equations---the rendering equation and the transport equation---whose solution constitutes the global illumination problem. In order to solve the global illumination problem, a certain number of multi-pass methods exist. Their objective is to be able to skip restrictions on the number of types of light paths that could be dealt with a single technique, or increase efficiency and/or accuracy. We have opted to follow this philosophy, and a pair of two pass methods have been developed for general environments. The third chapter includes the study of the methods that perform the single scattering approximation, and also the study of the ones that take into account multiple scattering. The fourth chapter is devoted to our first pass method, which computes a rough estimate of the global illumination. Knowing the benefits of hierarchical approaches, two concrete algorithms based on hierarchies have been extended to be more generic: Hierarchical Radiosity with Clustering and Hierarchical Monte Carlo Radiosity. Our second pass is considered in the next chapter. Using the coarse solution obtained by the first pass, our second pass computes a high quality solution from a given viewpoint. Radiances and source radiances are estimated using Monte Carlo processes in the context of path tracing acceleration and also for final gather. Probability density functions (PDFs) are created at ray intersection points. For such a task, we initially used constant basis functions for the directional domain. After realizing of their limitations we proposed the Link Probabilities (LPs), which are objects with adaptive PDFs in the links-space. In order to take advantage of the effort invested for the construction of the LPs, we have devised two closely related progressive sampling strategies. In the second pass, instead of sampling each pixel individually, only a subset of samples is progressively estimated across the image plane. Our algorithms are inspired by the work of Michael D. McCool on anisotropic diffusion using conductance maps. The final chapter presents the conclusions of the thesis. Also possible lines of further research are suggested. El objetivo de esta tesis es el desarrollo de algoritmos para la simulación del transporte de la luz en los entornos genéricos para generar imágenes de la alta calidad. Con este fin, primero hemos analizado los métodos existentes capaces de visualizar medios participativos, más concretamente los que tienen en cuenta la dispersión múltiple en los medios. Después, hemos ideado un par de métodos de dos pasos para el cómputo de esas imágenes. Para el primer paso hemos propuesto algoritmos que hacen frente a las escenas que deseamos tratar. El segundo paso utiliza la solución aproximada del primer paso para obtener la imagen final. La estructura de la disertación se presenta brevemente en lo que sigue. En el primer capítulo se discuten la motivación de la tesis y sus objetivos. También se resumen las contribuciones de la tesis y su organización. En el segundo capítulo se repasan los principios de la iluminación global para los ambientes genéricos, con las ecuaciones-más importantes (la ecuación de rendering y la ecuación de transporte) cuya solución constituye el problema global de iluminación. Para solucionar el problema global de iluminación, cierto número de métodos de múltiples pasos existen. Su objetivo es poder eliminar restricciones en el número de tipos de caminos de luz que se podrían tratar con una sola técnica, o aumentar su eficacia y/o exactitud. Hemos optado seguir esta filosofía, desarrollando un par de métodos de dos pasos para entornos genéricos. El tercer capítulo incluye el estudio de los métodos que utilizan la aproximación de dispersión simple, y también el estudio de los que consideran la dispersión múltiple. El cuarto capítulo está dedicado a nuestro método de primer paso, que computa un cálculo aproximado de la iluminación global. Conociendo las ventajas de los métodos jerárquicos, dos algoritmos concretos basados en jerarquías se han ampliado para ser más genéricos: radiosidad jerárquica con clustering y radiosidad jerárquica usando Monte Carlo. Nuestro segundo paso se considera en el capítulo siguiente. Usando la solución aproximada obtenida por el primer paso, el segundo paso computa una solución de la alta calidad para un punto de vista dado. Se estiman las radiancias usando procesos de Monte Carlo en el contexto de la aceleración de trazadores de rayos y también para final gather. Las funciones de densidad de probabilidad (PDFs) se crean en los puntos de interacción de los rayos. Para tal tarea, utilizamos inicialmente funciones constantes como base para el dominio direccional. Después de comprender sus limitaciones, propusimos establecer probabilidades directamente sobre los enlaces (link probabilities, o LPs), usando objetos con PDFs adaptativos en el espacio de los enlaces. Para aprovechar el esfuerzo invertido en la construcción de los LPs, hemos ideado dos estrategias de muestreo progresivas. En el segundo paso, en vez de muestrear cada pixel individualmente, solamente se estima progresivamente un subconjunto de muestras a través del plano de imagen. Nuestros algoritmos han sido inspirados en el trabajo de Michael D. McCool en la difusión anisotrópica usando mapas de conductancia. El capítulo final presenta las conclusiones de la tesis, y también sugiere las líneas posibles de investigación futura.