EuroVis13: Eurographics Conference on Visualization

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https://diglib.eg.org/handle/10.2312/13888

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AmniVis - A System for Qualitative Exploration of Near-Wall Hemodynamics in Cerebral Aneurysms
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Neugebauer, Mathias; Lawonn, Kai; Beuing, Oliver; Berg, Philipp; Janiga, Gabor; Preim, Bernhard; B. Preim, P. Rheingans, and H. Theisel
The qualitative exploration of near-wall hemodynamics in cerebral aneurysms provides important insights for risk assessment. For instance, a direct relation between complex flow patterns and aneurysm formation could be observed. Due to the high complexity of the underlying time-dependent flow data, the exploration is challenging, in particular for medical researchers not familiar with such data. We present the AmniVis-Explorer, a system that is designed for the preparation of a qualitative medical study. The provided features were developed in close collaboration with medical researchers involved in the study. This comprises methods for a purposeful selection of surface regions of interest and a novel approach to provide a 2D overview of flow patterns that are represented by streamlines at these regions. Furthermore, we present a specialized interface that supports binary classification of patterns and temporal exploration as well as methods for selection, highlighting and automatic 3D navigation to particular patterns. Based on eight representative datasets, we conducted informal interviews with two bordcertified radiologists and a flow expert to evaluate the system. It was confirmed that the AmniVis-Explorer allows for an easy selection, qualitative exploration and classification of near-wall flow patterns that are represented by streamlines.
Comparative Visualization of Tracer Uptake in In Vivo Small Animal PET/CT Imaging of the Carotid Arteries
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Diepenbrock, Stefan; Hermann, Sven; Schäfers, Michael; Kuhlmann, Michael; Hinrichs, Klaus; B. Preim, P. Rheingans, and H. Theisel
Cardiovascular diseases are the main cause of death in the western world. Medical research on atherosclerosis is therefore of great interest and a very active research topic. We present a visualization system that supports scientists in exploring plaque development and evaluating the applicability of PET tracers for early diagnosis of cardiovascular diseases. In our application case a cone shaped cuff has been implanted around the carotid artery of ApoE knockout mice, fed with a high cholesterol western type diet. As a result, vascular lesions develop upstream and downstream from the cuff. Tracer uptake induced by these lesions needs to be analyzed in order to evaluate the effectiveness of different PET tracers. We discuss the approach previously utilized to perform this kind of analysis, the problems arising from in vivo image acquisition (in contrast to ex vivo) and the design process of our application. In close cooperation with domain experts we have developed new visualization techniques that display PET activity in the vessel wall and surrounding tissue in a single image. We use the vessel wall detected in the CT image to perform a normalized circular projection which allows the user to judge PET signal distribution in relation to the deformed vessel. Based on this projection a quantitative analysis of a defined region adjacent to the vessel wall can be performed and compared to the artery without the cuff.
dPSO-Vis: Topology-based Visualization of Discrete Particle Swarm Optimization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Volke, Sebastian; Middendorf, Martin; Hlawitschka, Mario; Kasten, Jens; Zeckzer, Dirk; Scheuermann, Gerik; B. Preim, P. Rheingans, and H. Theisel
Particle swarm optimization (PSO) is a metaheuristic that has been applied successfully to many continuous and combinatorial optimization problems, e.g., in the fields of economics, engineering, and natural sciences. In PSO, a swarm of particles moves within a search space in order to find an optimal solution. Unfortunately, it is hard to understand in detail why and how changes in the design of PSO algorithms affect the optimization behavior. Visualizing the particle states could provide substantially better insight into PSO algorithms. Though in case of combinatorial optimization problems, it often raises the problem of illustrating the states within the discrete search space that cannot be embedded spatially. We propose a visualization approach to depict the optimization problem topologically using a landscape metaphor. This visualization is augmented by an illustration of the time-dependent states of the particles. Thus, the user of dPSO-Vis is able to analyze the swarm's behavior within the search space. In principle, our method can be used for any optimization algorithm where a swarm of individuals searches within a discrete search space. Our approach is verified with a case study for the PSO algorithm HelixPSO that predicts the secondary structure of RNA molecules.
HiFiVE: A Hilbert Space Embedding of Fiber Variability Estimates for Uncertainty Modeling and Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Schultz, Thomas; Schlaffke, Lara; Schölkopf, Bernhard; Schmidt-Wilcke, Tobias; B. Preim, P. Rheingans, and H. Theisel
Obtaining reproducible fiber direction estimates from diffusion MRI is crucial for successful fiber tracking. Modeling and visualizing the probability distribution of the inferred fiber directions is an important step in evaluating and comparing different acquisition schemes and fiber models. However, this distribution is usually strongly dominated by its main direction, which makes it difficult to examine when plotted naively. In this work, we propose a new visualization of the fiber probability distribution. It is based on embedding the probability measure into a particular reproducing kernel Hilbert space. This permits a decomposition into an embedded delta peak, representing the main direction, and a non-negative residual. They are then combined into a new glyph representation which visually enhances the residual, in order to highlight even subtle differences. Moreover, the magnitude of the delta peak component quantifies precision of the main fiber direction. We demonstrate that our new glyph provides a more detailed impression of the uncertainty than the current standard method, cones that contain 95% of the estimated directions. We use our new method to contribute to the validation of different ways of resampling the data (bootstrapping), and to visualize the differences between alternative acquisition schemes and models for high angular resolution diffusion imaging (HARDI).
An Interactive Analysis and Exploration Tool for Epigenomic Data
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Younesy, Hamidreza; Nielsen, Cydney B.; Möller, Torsten; Alder, Olivia; Cullum, Rebecca; Lorincz, Matthew C.; Karimi, Mohammad M.; Jones, Steven J. M.; B. Preim, P. Rheingans, and H. Theisel
In this design study, we present an analysis and abstraction of the data and tasks related to the domain of epigenomics, and the design and implementation of an interactive tool to facilitate data analysis and visualization in this domain. Epigenomic data can be grouped into subsets either by k-means clustering or by querying for combinations of presence or absence of signal (on/off) in different epigenomic experiments. These steps can easily be interleaved and the comparison of different workflows is explicitly supported. We took special care to contain the exponential expansion of possible on/off combinations by creating a novel querying interface. An interactive heat map facilitates the exploration and comparison of different clusters. We validated our iterative design by working closely with two groups of biologists on different biological problems. Both groups quickly found new insight into their data as well as claimed that our tool would save them several hours or days of work over using existing tools.
VisRuption: Intuitive and Efficient Visualization of Temporal Airline Disruption Data
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Rosenthal, Paul; Pfeiffer, Linda; Müller, Nicholas H.; Ohler, Peter; B. Preim, P. Rheingans, and H. Theisel
The operation of an airline is a very complex task and disruptions to the planned operation can occur on very short notice. Already a small disruption like a delay of some minutes can cost the airline a tremendous amount of money. Hence, it is crucial to proactively control all operations of the airline and efficiently prioritize and handle disruptions. Due to the complex setting and the need for ad hoc decisions this task can only be carried out by human operation controllers. In the field of airline operations control there exists already a vast variety of different software in productive use. We analyze the different approaches from two of the market leaders and identify problematic design choices. We take into account this analysis and develop a set of rules for an intuitive visualization of airline disruption data. Finally, we introduce our tool for visualizing such data which complies to these rules. The visualization enables the user to gain a fast overview over the current problem situation and to intuitively prioritize different problems and problem hierarchies. The efficiency of the design is evaluated with the help of a user study which shows that the new system significantly outperforms the current state of the art.
Visual Explanation of the Complexity in Julia Sets
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Schrijvers, Okke; Wijk, Jarke J. van; B. Preim, P. Rheingans, and H. Theisel
Julia sets based on quadratic polynomials have a very simple definition, yet a highly intricate shape. Our contribution is to provide a visual explanation for this complexity. To this end we show the construction of Julia sets as a dynamic process, in contrast to showing just a static image of the set itself. Our method is based on the Inverse Iteration Method (IIM). We start with a disk, which is successively distorted. The crucial step is to show an animation of the effect of taking a root of a subset of the complex plane. We present four different approaches for this, using a Riemann surface, a corkscrew, a fan, and disks as metaphors. We packaged our results in an interactive tool with a simple interface, such that everybody can view and inspect these for different Julia sets. The results are useful for teaching complex analysis, promoting mathematics, entertainment, and, above all, as a visual explanation for the complexity of Julia sets.

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