VCBM: Eurographics Workshop on Visual Computing for Biomedicine

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Browsing VCBM: Eurographics Workshop on Visual Computing for Biomedicine by Subject "and texture"

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    Coherence Maps for Blood Flow Exploration
    (The Eurographics Association, 2016) Englund, Rickard; Ropinski, Timo; Hotz, Ingrid; Stefan Bruckner and Bernhard Preim and Anna Vilanova and Helwig Hauser and Anja Hennemuth and Arvid Lundervold
    Blood flow data from direct measurements (4D flow MRI) or numerical simulations opens new possibilities for the understanding of the development of cardiac diseases. However, before this new data can be used in clinical studies or for diagnosis, it is important to develop a notion of the characteristics of typical flow structures. To support this process we developed a novel blood flow clustering and exploration method. The method builds on the concept of coherent flow structures. Coherence maps for crosssectional slices are defined to show the overall degree of coherence of the flow. In coherent regions the method summarizes the dominant blood flow using a small number of pathline representatives. In contrast to other clustering approaches the clustering is restricted to coherent regions and pathlines with low coherence values, which are not suitable for clustering and thus are not forced into clusters. The coherence map is based on the Finite-time Lyapunov Exponent (FTLE). It is created on selected planes in the inflow respective outflow area of a region of interest. The FTLE value measures the rate of separation of pathlines originating from this plane. Different to previous work using FTLE we do not focus on separating extremal lines but on local minima and regions of low FTLE intensities to extract coherent flow. The coherence map and the extracted clusters serve as basis for the flow exploration. The extracted clusters can be selected and inspected individually. Their flow rate and coherence provide a measure for their significance. Switching off clusters reduces the amount of occlusion and reveals the remaining part of the flow. The non-coherent regions can also be explored by interactive manual pathline seeding in the coherence map.
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    Combining Pseudo Chroma Depth Enhancement and Parameter Mapping for Vascular Surface Models
    (The Eurographics Association, 2017) Behrendt, Benjamin; Berg, Philipp; Preim, Bernhard; Saalfeld, Sylvia; Stefan Bruckner and Anja Hennemuth and Bernhard Kainz and Ingrid Hotz and Dorit Merhof and Christian Rieder
    The presence of depth cues in a visualization can be a great aid in understanding the structure and topology of a vessel tree. Pseudo Chromadepth is a well-known technique for enhancing depth perception in vascular 3D models. Since it strongly relies on the color channel to convey its depth cues, it is traditionally not suited for combined visualizations comprising color-encoded surface parameters. In this paper, we present and evaluate the use of a modified form of Pseudo Chromadepth that supports displaying additional surface parameters using the color channel while still increasing depth perception. This technique has been designed for the visualization of cerebral aneurysm models. We have combined a discretized color scale to visualize the surface parameter with the Pseudo Chromadepth color scale to convey depth using a Fresnel-inspired blending mask. To evaluate our approach, we have conducted two consecutive studies. The first was performed with 104 participants from the general public and the second with eleven experts in the fields of medical engineering and flow simulation. These studies show that Pseudo Chromadepth can be used in conjunction with color-encoded surface attributes to support depth perception as long as the color scale is chosen appropriately.
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    Interactive Position-dependent Customization of Transfer Function Classification Parameters in Volume Rendering
    (The Eurographics Association, 2015) Brix, Tobias; Scherzinger, Aaron; Völker, Andreas; Hinrichs, Klaus; Katja Bühler and Lars Linsen and Nigel W. John
    In direct volume rendering (DVR) and related techniques a basic operation is the classification of data values by mapping (mostly scalar) intensities to color values using a transfer function. However, in some cases this kind of mapping might not suffice to achieve satisfying rendering results, for instance when intensity homogeneities occur in the volume data due to technical restrictions of the scanner technology. In this case it might be desirable to customize one or more parameters of the visualization depending on the position within the volume. In this paper we propose a novel approach for an interactive position-dependent customization of arbitrary parameters of the transfer function classification. Our method can easily be integrated into existing volume rendering pipelines by incorporating an additional operation during the classification step. It allows the user to interactively modify the rendering result by specifying reference points within the data set and customizing their associated visualization parameters while receiving direct visual feedback. Since the additional memory requirements of our method do not depend on the size of the visualized data our approach is applicable to large data sets, for instance in the field of ultra microscopy.