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The role of expressive surface visualizations in rendering vascular structures has seen an increased impact over the last years. Surface visualizations provide an overview of complex anatomical structures and support treatment planning as well as medical education. To support decision-making, physicians need visualizations that depict anatomical structures and their spatial relations to each other, i.e., well perceivable visual encodings of egocentric and endocentric distances. We give an overview of common techniques for encoding distance information of 3D vessel surfaces. We also provide an implementation of all the visualizations presented as a starting point for other researchers. Therefore, we provide a Unity environment for each visualization, as well as implementation instructions. Thirteen different visualizations are included in this work, which can be divided into fundamental, surface-based, auxiliary and illustrative visualizations., Narrative, Education, and Virtual Reality (VR), Jan Hombeck, Monique Meuschke, Simon Lieb, Nils Lichtenberg, Rabi Datta, Michael Krone, Christian Hansen, Bernhard Preim, and Kai Lawonn

Data are often subject to some degree of uncertainty, whether aleatory or epistemic. This applies both to experimental data acquired with sensors as well as to simulation data. Displaying these data and their uncertainty faithfully is crucial for gaining knowledge. Specifically, the effective communication of the uncertainty can influence the interpretation of the data and the users' trust in the visualization. However, uncertainty-aware visualization has gotten little attention in molecular visualization. When using the established molecular representations, the physicochemical attributes of the molecular data usually already occupy the common visual channels like shape, size, and color. Consequently, to encode uncertainty information, we need to open up another channel by using feature lines. Even though various line variables have been proposed for uncertainty visualizations, they have so far been primarily used for two-dimensional data and there has been little perceptual evaluation. Therefore, we conducted a perceptual study to determine the suitability of the line variables sketchiness, dashing, grayscale, and width for distinguishing several uncertainty values on molecular surfaces., Uncertainties, Ensembles, and Comparisons, Anna Sterzik, Nils Lichtenberg, Michael Krone, Douglas W. Cunningham, and Kai Lawonn

In dieser Arbeit wird sowohl die Entwicklung eines neuartigen Verfahrens zur Partikelinjektion in einen Tundish als auch die hydrodynamische Verbesserung der Einströmung in eine Bandgießanlage beschrieben. Sie besteht aus drei Teilen und beschäftigt sich im übergeordneten Sinne mit der Optimierung von Strömungen in der Gießereitechnik. Teil A stellt den gemeinsamen Teil beider Untersuchungen dar. Er gibt eine ausführliche Herleitung der dimensionslosen Kennzahlen, die eingehalten werden müssen, um einen Gießereiprozess mit einem Wassermodell nachzustellen (Ähnlichkeitstheorie). Auf dieser Grundlage wurde ein Versuchsstand (Wassermodell) aufgebaut, der eine maßstabsgetreue Stranggussanlage mit Tundish, Stopfen, Tauchrohr und Gießkokille nachbildet. Dieser Aufbau wurde dann modifiziert und somit für die zweite Reihe von Strömungsuntersuchungen in eine Bandgießanlage umgewandelt. Alle gemeinsamen Bauteile werden im Teil A vorgestellt, welcher zusätzlich die grundlegenden Verfahren zur Förderung von Feststoffen in Flüssigkeiten und die Gefahren beim Umgang mit feinen Pulvern erläutert. Im Teil B wird die Injektion von Additiven zur Herstellung von Legierungen im Tundish untersucht. Es werden Additive in Form von Partikeln untersucht deren Dichte sowohl größer ist als die der Schmelze und damit sinken sowie Additive deren Dichte geringe ist die der Schmelze und damit aussteigen. Es werden Möglichkeiten aufgezeigt, um Partikel (Additive) sehr nahe am Austritt des Tundishs und kurz vor der Erstarrung homogen zu vermischen. Hierzu bot sich die Zugabe durch den Stopfen bzw. im Stopfenbereich an. Damit werden die Freiheitsgrade bei der Legierungsarbeit im Vergleich zum Stand der Technik erweitert und es besteht die Möglichkeit zur Herstellung völlig neuer Stahl-Produkte mit völlig neuen Eigenschaften. Prinzipiell gelten die Ergebnisse dieser Forschungsarbeit auch für nicht-eisen Legierungen und deren Herstellungsverfahren im Strangguss. Damit ergeben sich die beiden Hauptziele für die Entwicklung des neuen Stahlgießverfahrens: (1) gleichmäßige und homogene Dosierung des Additivs und (2) Additivzugabe nahe der Stahlgusskokille und damit direkt in den Gießstrang, um weitere produktspezifische Vorteile zu erlangen. Der Versuchsstand, der zur Entwicklung des Prozesses diente, besteht zum größten Teil aus transparenten Bauteilen und kann die gleichen Strömungsverhältnisse des Hochtemperatur-Verfahrens bei Raumtemperatur nachbilden. Hinzu kommt der weitere Vorteil, dass in dem Wassermodell weniger gefährliche Substanzen, nämlich Wasser statt flüssigem Stahl und zum Beispiel PVC- statt Bleipartikel (Additiv mit höherer Dichte), zum Einsatz kommen. Von Anfang an wurde der Stopfen als Injektor der Partikel in die Flüssigkeit eingesetzt. Die Partikel wurden zuerst mit Hilfe eines Transportgases gefördert und danach gravimetrisch in den Stopfen eingetragen. Intensive Untersuchungen der Strömungsverhältnisse im Inneren des Stopfens erweiterten den Stopfen zu einer Partikel-Mischkammer. Somit wurde am Ende dieser Arbeit eine blasenfreie, homogene und zeitlich konstante Zugabe des Pulvers in die Kokille erreicht. Im Teil C wird die Einströmung durch ein Tauchrohr in eine Bandgießanlage untersucht. Acht verschiedene Tauchrohrgeometrien wurden geprüft, um eine schnelle Annährung der Stahlfließ-geschwindigkeit aus dem Tauchrohr an die Produktionsgeschwindigkeit des festen Knüppels zu erlangen. Dadurch werden die Spannungen, die beim Aushärten an den Rändern des Stranges entstehen, verringert und somit die Qualität des Produktes erhöht. Für die Beurteilung der Tauchrohrströmung in die Bandgießanlage wurden PIV-Messungen durchgeführt und die daraus ermittelten Geschwindigkeitsprofile miteinander verglichen. Somit konnten drei Vorzugsvarianten experimentell bestimmt werden. Die aus den PIV-Messungen entstandenen Daten bildeten im weiteren Verlauf die Grundlage der Validierung einer Strömungssimulation (CFD) mit der der Versuchsstand numerisch erweitert werden kann. Zuerst wurden Berechnungen an einer vereinfachten Geometrie, bestehend aus Tauchrohr und Caster durchgeführt. Nach unzureichender Übereinstimmung mit den experimentellen Daten, wurde die gesamte Versuchsstandsgeometrie, inklusive Tundish und Stopfen, simuliert. Gleichzeitig wurden zwei Turbulenzmodelle eingesetzt, welche die Drall-behaftete Strömung unterhalb des Stopfens unterschiedlich stark zeigen. Weiterführende Kreuzkorrelationen der Geschwindigkeitsprofile von PIV-Messungen und CFD konnten zum Schluss der Arbeit eine Empfehlung für das k-ω-SST Turbulenzmodell für diese Art der Strömung aussprechen., This work describes both the development of a novel method for particle injection into a tundish as well as the hydrodynamic improvement of the flow entering a twin-belt caster. It consists of three parts and, broadly speaking, deals with the optimization of flow in foundry technology. Part A relates the common part of both investigations. It gives a detailed derivation of the dimensionless numbers that must be adhered to in order to fully reproduce a foundry process using a water model (similarity theory). Based on this concept, a test facility (water model), which replicates a true-to-scale continuous-casting plant with tundish, stopper, submerged entry nozzle, and casting mould, was set up for the analysis and development of the particle injection process. This same setup was then modified and thus converted into a twin-belt caster for the second set of flow investigations. All common components are presented in Part A. Furthermore, this part of the work also details the basic processes involved in conveying solids within liquids and the dangers involved in handling fine powders. Part B investigates the addition of additives in the tundish, a process required in the production of alloys. This investigation takes both particles (additives) with a density higher and lower than that of the molten metals, causing them to sink or float, respectively. Here, various particle addition possibilities are presented. Particles are added very close to the outlet of the tundish and shortly before solidification, aiming to homogenously incorporate the particles into the mixture. To this end, injecting particles either through the stopper or into the stopper area proved suitable. This extends the degrees of freedom in the production of alloys compared to the state of the art, creating possibilities for novel steel products with entirely new properties. In principle, the results of this research work also apply to non-ferrous alloys and their continuous casting manufacturing processes. This results in the two main objectives for the development of the novel steel casting process: (1) uniform and homogeneous additive dosing and (2) additive addition close to the steel casting mold and therefore directly into the casting strand in order to obtain further product-specific advantages. The test facility employed in the development of this novel process consists mostly of transparent components and replicates the flow conditions present in the high-temperature process, yet at room temperature. Furthermore, the water model has the added advantage that less dangerous substances are used, namely water instead of liquid steel and PVC instead of lead particles (higher density additive). From the beginning, the stopper was used to inject the particles into the liquid. The particles were first conveyed with the aid of a transport gas and then entered into the stopper gravimetrically. Intensive investigations of the flow conditions inside the stopper expanded the use of the stopper to that of a particle-mixing chamber. Thus, at the end of this work, a bubble-free, steady state, and homogeneously distributed addition of the powder into the mold was achieved. In part C, the inflow through a submerged nozzle into a twin-belt caster is examined. Eight different submerged entry nozzle geometries were tested in order to achieve a rapid approximation between the steel flow rate exiting the submerged entry nozzle and the production rate of the solid billet. This reduces the stresses that arise at the edges of the strand during hardening and therefore increases the quality of the product. PIV measurements were carried out to assess the submerged nozzle flow into the twin-belt caster. The resulting velocity profiles were compared with one another, allowing three preferred variants to be experimentally determined. The data resulting from the PIV measurements subsequently formed the basis for the validation of a numerical model. First, flow simulations (CFD) were carried out on a simplified geometry consisting of the submerged nozzle and the caster. After observing inadequate agreement with the experimental data, the entire test facility geometry was simulated, including the tundish and the stopper. Two turbulence models were used, both of which revealed a strong swirling flow below the stopper, yet to varying degrees. Further cross-correlations between the velocity profiles of the PIV measurements and the CFD enabled a final recommendation of the k-ω-SST turbulence model for this type of flow.

In this paper, we make contributions to the visualization of vascular structures. Based on skeletal input data, we provide a combined 2D and implicit 3D visualization of vasculature, that is parameterized on-the-fly for illustrative visualization. We use an efficient algorithm that creates a distance field volume from triangles and extend it to handle skeletal tree data. Spheretracing this volume allows to visualize the vasculature in a flexible way, without the need to recompute the volume. Illustrative techniques, that have been frequently applied to vascular visualizations often require texture coordinates. Therefore, modifying an object-based algorithm, we propose an image-based, hierarchical optimization process that allows to derive periodic texture coordinates in a frame-coherent way and suits the implicit representation of the vascular structures. In addition to the 3D surface visualization, we propose a simple layout algorithm that applies a 2D parameterization to the skeletal tree nodes. This parameterization can be used to color-code the vasculature or to plot a 2D overview-graph, that highlights the branching topology of the skeleton. We transfer measurements, done in 3D space, to the 2D plot in order to avoid visual clutter and self occlusions in the 3D representation. A visual link between the 3D and 2D views is established via color codes and texture patterns. The potential of our pipeline is shown in several prototypical application scenarios., Eurographics Workshop on Visual Computing for Biology and Medicine, Blood Flow and Vascular Visualization, 265, 278, Nils Lichtenberg, Bastian Krayer, Christian Hansen, Stefan Müller, and Kai Lawonn

The study and visualization of vascular structures, using 3D models obtained from medical data, is an active field of research. Illustrative visualizations have been applied to this domain in multiple ways. Researchers have tried to make the geometric properties of vasculature more comprehensive and to augment the surface with representations of multivariate clinical data. Techniques that head beyond the application of color-maps or simple shading approaches require a sort of surface parameterization, i.e., texture coordinates, in order to overcome locality. When extracting 3D models, the computation of texture coordinates on the mesh is not always part of the data processing pipeline. We combine existing techniques to a simple, yet effective, parameterization approach that is suitable for tree-like structures. The parameterization is done w.r.t. to a pre-defined source vertex. For this, we present an automatic algorithm, that detects the root of a tree-structure. The parameterization is partly done in screen-space and recomputed per frame. However, the screen-space computation comes with positive features that are not present in object-space approaches. We show how the resulting texture coordinates can be used for varying hatching, contour parameterization, the display of decals, as an additional depth cue and feature extraction., Eurographics Workshop on Visual Computing for Biology and Medicine, Surfaces, 145, 155, Nils Lichtenberg and Kai Lawonn, CCS Concepts: Computing methodologies --> Non-photorealistic rendering; Mesh geometry models

User studies are often required in biomedical visualization application papers in order to provide evidence for the utility of the presented approach. An important aspect is how well depth information can be perceived, as depth encoding is important to enable an understandable representation of complex data. Unfortunately, in practice there is often little time available to perform such studies, and setting up and conducting user studies may be labor-intensive. In addition, it can be challenging to reach enough participants to support the contribution claims of the paper. In this paper, we propose a system that allows biomedical visualization researchers to quickly generate perceptual task-based user studies for novel surface visualizations, and to perform the resulting experiment via a web interface. This approach helps to reduce effort in the setup of user studies themselves, and at the same time leverages a web-based approach that can help researchers attract more participants to their study. We demonstrate our system using the specific application of depth judgment tasks to evaluate vascular surface visualizations, since there is a lot of recent interest in this area. However, the system is also generally applicable for conducting other task-based user studies in biomedical visualization., Eurographics Workshop on Visual Computing for Biology and Medicine, Interaction and Evaluation, 33, 44, Monique Meuschke, Noeska N. Smit, Nils Lichtenberg, Bernhard Preim, and Kai Lawonn, CCS Concepts: Human-centered computing --> Visualization systems and tools; Visualization design and evaluation methods; Computing methodologies --> Scientific visualization