In this paper various algorithms for rendering gaseous phenomena are reviewed. In computer graphics such algorithms are used to model natural scenes containing clouds, fog, flames and so on. On the other hand it has become an important technique in scientific visualization to display three dimensional scalar datasets as cloudy objects. Our emphasis is on this latter subject of so-called {\em direct volume rendering}. All algorithms will be discussed within the framework of linear transport theory. The equation of transfer is derived. This equation is suitable to describe the radiation field in a participating medium where absorption, emission, and scattering of light can occur. Almost all volume rendering algorithms can be shown to solve special cases of the equation of transfer. Related problems like the mapping from data values to model parameters or possible parallelization strategies will be discussed as well.

To date, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve’s stagnant and recirculation zones. Optimization of valve design requires detailed flow field investigations. Usually, the regions that are more prone to thrombus formation can be estimated using a dye washout experiment. This successful experimental method was simulated using numerical methods. The proposed method was applied to three standard mechanical heart valves—Björk-Shiley, St-Jude, and Starr-Edwards valve. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time (HDT), which characterizes the blood residence time. The HDT in the best valve, the Starr-Edwards valve, was 0.0747 s. The HDT in the worst valve, the Björk-Shiley, was 0.0942 s. The analysis of the hemodynamic valve parameters (pressure drop, velocity magnitudes and turbulence) revealed that the best valve is the St-Jude valve. The Starr-Edwards valve displayed the worst hemodynamic parameters. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool for the flow characterization.

We present a set of coherent methods for the nearly automatic creation of 3D geometric models from large stacks of images of histological sections. Three-dimensional surface models facilitate the visual analysis of 3D anatomy. They also form a basis for standardized anatomical atlases that allow researchers to integrate, accumulate and associate heterogeneous experimental information, like functional or gene-expression data, with spatial or even spatio-temporal reference. Models are created by performing the following steps: image stitching, slice alignment, elastic registration, image segmentation and surface reconstruction. The proposed methods are to a large extent automatic and robust against inevitably occurring imaging artifacts. The option of interactive control at most stages of the modeling process complements automatic methods.

Until today, no ideal heart valve prosthesis for the replacement of a diseased natural valve or for use in ventricular assist devices exists. Valves still cause thromboembolic complications originating from thrombus formations in the valve’s stagnant zones. Optimization of valve design involves avoiding stagnation zones and zones of high shear stresses. This requires detailed flow field investigations. Usually, the regions which are more prone to thrombus formation can be estimated using a dye washout experiment. The method allows an assessment of regions with a high or low residence time that may in turn predict regions with a corresponding thrombus risk. This successful experimental method was simulated using numerical methods with a combination of the computational fluid dynamics program FLUENT (Fluent Inc., Lebanon, NH, U.S.A.) and of the visualization tool AMIRA (TGS Inc., San Diego, CA, U.S.A.). The numerical dye washout visualization was applied to four monoleaflet valves with varying valve housing geometries. The results show a significant difference in the washout processes of the examined valves. The dye washout was characterized by a time course of the gray value averaged over a defined region of interest. Finally, these curves were quantified by a half dye time. The half dye time in the best optimized valve was only 0.2753 s. The same time in the original valve was 0.6834 s. This study shows that the proposed numerical method of dye washout visualization can be used as an additional tool of the flow characterization in artificial organs.

Flow visualization in realistic models is very important for the study of pathological vessel enlargements (aneurysms). Furthermore, flow visualization may help in treatment decisions. However, the most interesting parameter, the wall shear stress, is difficult to measure in vivo. This parameter can be provided by computational fluid dynamics. However, the numerical methods don't visualize the results as does of the dye washout method - a method often used in flow studies. This experimental method simulates the cine angiograms acquired during contrast agent injection used in medicine. In this paper we present the dye washout visualization of CFD results and compare these results with the conventional dye washout experiments in the same aneurysm model under steady flow conditions.

Die Strömungseigenschaften in Blutgefäßen sind nur sehr schwer zugänglich, bzw. einige Eigenschaften sind auch gar nicht exakt messbar. Theoretische Strömungsmodelle und Berechnungen sind daher ein wertvolles Hilfsmittel für deren Erforschung. Die Strömungsberechnung ist sehr komplex und die Korrektheit der Berechnung ist von vielen Parametern abhängig. In diesem Beitrag stellen wir ein Verfahren vor, mit dem wir die berechnete Blutströmung in einem Gefäßsystem durch einen experimentellen Versuchsaufbau verifizieren. Der Vergleich von Experiment und Simulation erfolgt auf der Basis von Bildsequenzen, die mit Methoden der wissenschaftlichen Visualisierung aus der Simulation erzeugt werden.

By combining techniques of preparation, histology, confocal microscopy, data visualization and data processing, we have created and recently published a standard brain model for drosophila and honey bee brains. This report describes the algorithms and implementation of the corresponding software modules. At the same time it serves as a user's guide for scientist who want to reproduce the results for differerent species or mutants.

By combining techniques of preparation, histology, confocal microscopy,data visualization and data processing, we have created and recently publisheda Standard Brain model for drosophila and honey bee brains. Thisreport describes the algorithms and implementation of the correspondingsoftware modules. At the same time it serves as a users guide for scientistswho want to reproduce the results for di#erent species or mutants as wellas those who want to incorporate new data into the...