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Item Viewpoint Selection for Intervention Planning(The Eurographics Association, 2007) Muehler, Konrad; Neugebauer, Mathias; Tietjen, Christian; Preim, Bernhard; K. Museth and T. Moeller and A. YnnermanViewpoint selection is crucial for medical intervention planning. The interactive exploration of a scene with 3d objects involves the systematic analysis of several anatomic structures. Viewpoint selection techniques enhance the display of the currently selected structure. For animations in collaborative intervention planning and surgical education, the authoring process may be significantly enhanced if good' viewpoints for important objects as well as for the whole scene are chosen automatically.We describe a viewpoint selection technique guided by parameters like size of unoccluded surface, importance of occluding objects, preferred region and viewpoint stability. The influence of these parameters may be flexibly adjusted by weights. Parameter maps indicate the influence of the current parameter settings on the viewpoints. For selected applications, the weights may be predefined and reused for other cases. We also describe an informal user study which was accomplished to understand if our viewpoint selection strategies produce adequate results from the users' point of view.Item Illustrative Visualization(The Eurographics Association, 2005) Viola, Ivan; Gröller, Meister E.; Hadwiger, Markus; Bühler, Katja; Preim, Bernhard; Ebert, David; Ming Lin and Celine LoscosThe tutorial presents state-of-the-art visualization techniques inspired by traditional technical and medical illustrations. Such techniques exploit the perception of the human visual system and provide effective visual abstractions to make the visualization clearly understandable. Visual emphasis and abstraction has been used for expressive presentation from prehistoric paintings to nowadays scientific and medical illustrations. Many of the expressive techniques used in art are adopted in computer graphics, and are denoted as illustrative or non-photorealistic rendering. Different stroke techniques, or brush properties express a particular level of abstraction. Feature emphasis or feature suppression is achieved by combining different abstraction levels in illustrative rendering. Challenges in visualization research are very large data visualization as well as multi-dimensional data visualization. To effectively convey the most important visual information there is a significant need for visual abstraction. For less relevant information the dedicated image space is reduced to enhance more prominent features. The discussed techniques in the context of scientific visualization are based on iso-surfaces and volume rendering. Apart from visual abstraction, i.e., illustrative representation, the visibility of prominent features can be achieved by illustrative visualization techniques such as cut-away views or ghosted views. The structures that occlude the most prominent information are suppressed in order to clearly see more interesting parts. Another smart way to provide information on the data is using exploded views or other types of deformation. Illustrative visualization is demonstrated via application-specific tasks in medical visualization. An important aspect as compared to traditional medical illustrations is the interactivity and real-time manipulation of the acquired patient data. This can be very useful in anatomy education. Another application area is surgical planning which is demonstrated with two case studies: neck dissection and liver surgery planning.Item Advanced Algorithms in Medical Computer Graphics(The Eurographics Association, 2008) Klein, Jan; Bartz, Dirk; Friman, Ola; Hadwiger, Markus; Preim, Bernhard; Ritter, Felix; Vilanova, Anna; Zachmann, Gabriel; Theoharis Theoharis and Philip DutreAdvanced algorithms and efficient visualization techniques are of major importance in intra-operative imaging and image-guided surgery. The surgical environment is characterized by a high information flow and fast decisions, requiring efficient and intuitive presentation of complex medical data and precision in the visualization results. Regions or organs that are classified as risk structures are in this context of particular interest. This paper summarizes advanced algorithms for medical visualization with special focus on risk structures such as tumors, vascular systems and white matter fiber tracts. Algorithms and techniques employed in intra-operative situations or virtual and mixed reality simulations are discussed. Finally, the prototyping and software development process of medical visualization algorithms is addressed.Item Advanced GPU Volume Rendering for Virtual Endoscopy(The Eurographics Association, 2009) Krüger, Arno; Kubisch, Christoph; Strauß, Gero; Preim, Bernhard; K. Bühler and D. BartzFor difficult cases in endoscopic sinus surgery, a careful planning of the intervention is necessary. Virtual endoscopy enables the visualization of the operating field and additional information, such as risk structures and target structures to be removed. The Sinus Endoscopy system provides the functional range of a virtual endoscopic system with special focus on a realistic representation. Furthermore, by using direct volume rendering, we avoid time-consuming segmentation steps for the use of individual patient datasets. However, the image quality of the endoscopic view can be adjusted in a way that a standard computer with a modern standard graphics card achieves interactive frame rates with low CPU utilization. Thereby, characteristics of the endoscopic view are systematically used for the optimization of the volume rendering speed. As a small standalone application it can be instantly used for surgical planning and patient education. The system was used for preoperative planning in 102 cases, provides useful information for intervention planning (e.g., anatomic variations of the Rec. Frontalis), and closely resembles the intraoperative situation.Item Combining Map Displays and 3D Visualizations for the Analysis of Scalar Data on Cerebral Aneurysm Surfaces(The Eurographics Association and Blackwell Publishing Ltd., 2009) Neugebauer, Mathias; Gasteiger, Rocco; Beuing, Oliver; Diehl, Volker; Skalej, Martin; Preim, Bernhard; H.-C. Hege, I. Hotz, and T. MunznerCerebral aneurysms result from a congenital or evolved weakness of stabilizing parts of the vessel wall and potentially lead to rupture and a life-threatening bleeding. Current medical research concentrates on the integration of blood flow simulation results for risk assessment of cerebral aneurysms. Scalar flow characteristics close to the aneurysm surface, such as wall shear stress, form an important part of the simulation results. Aneurysms exhibit variable surface shapes with only few landmarks. Therefore, the exploration and mental correlation of different surface regions is a difficult task. In this paper, we present an approach for the intuitive and interactive overview visualization of near wall flow data that is mapped onto the surface of a 3D model of a cerebral aneurysm. We combine a multi-perspective 2D projection map with a standard 3D visualization and present techniques to facilitate the correlation between a 3D model and a related 2D map. An informal evaluation with 4 experienced radiologists has shown that the map-based overview actually improves the surface exploration. Furthermore, different color schemes were discussed and, as a result, an appropriate color scheme for the visual analysis of the wall shear stress is presented.Item Enhancing Slice-based Visualizations of Medical Volume Data(The Eurographics Association, 2006) Tietjen, Christian; Meyer, Björn; Schlechtweg, Stefan; Preim, Bernhard; Hertel, Ilka; Strauß, Gero; Beatriz Sousa Santos and Thomas Ertl and Ken JoySlice-based visualizations of CT and MRI data are frequently used for diagnosis, intervention planning and intraoperative navigation since they allow a precise analysis and localization. We present new techniques to enhance the visualization of cross sectional medical image data. Our work is focussed on intervention planning and intraoperative navigation. We address the following problems of slice-based visualization in these areas: the lack of a graphical overview on the positions of anatomic structures, the localization of a target structure and the display of safety zones around pathologic structures. To improve the overview, we introduce LIFTCHARTs, attached as vertical bars to a slice-based visualization. For localizing target structures, we introduce halos. These techniques restrict the occlusion of the original data to a minimum and avoid any modification of the original data. To demonstrate the usability of these visualization techniques, we show two application scenarios in which the techniques come into operation.Item Interactive Visualization for Neck-Dissection Planning(The Eurographics Association, 2005) Krüger, Arno; Tietjen, Christian; Hintze, Jana; Preim, Bernhard; Hertel, Ilka; Strauß, Gero; Ken Brodlie and David Duke and Ken JoyIn this paper, we present visualization techniques for neck dissection planning. These interventions are carried out to remove lymph node metastasis in the neck region. 3d visualization is intended to explore and to quantify anatomic and pathologic structures and thus support decisions concerning the surgical strategy. For this purpose we developed and combined visualization and interaction techniques such as cutaway views, silhouettes and colorcoded distances. In addition, a standardized procedure for processing and visualization of the patient data is presented.Item Reconstruction of Blood Vessels from Neck CT Datasets using Stable 3D Mass-Spring Models(The Eurographics Association, 2008) Dornheim, Jana; Lehmann, Dirk J.; Dornheim, Lars; Preim, Bernhard; Strauß, Gero; Charl Botha and Gordon Kindlmann and Wiro Niessen and Bernhard PreimPreoperative neck dissection planning benefits from a smooth, organic visualization of the main blood vessels of the neck, in particular the carotid artery and jugular vein. While most reconstruction techniques for vasculature are designed for segmenting the complete vessel tree, our goal is to isolate these specific blood vessels of the neck from the CT dataset, and to exclude irrelevant vasculature from the visualization. Pure threshold- and iso value-based reconstruction techniques do not allow such a selective segmentation and often lead to undersegmentation at the lower parts of the blood vessels, due to inhomogeneous contrast agent diffusion. In order to avoid staircase artifacts in the visualizations of the reconstructed vascular structures, a subvoxel accuracy of the reconstruction technique is also required. We present a model-based reconstruction technique to isolate blood vessels from neck CT datasets using Stable 3D Mass-Spring Models. The results can be visualized directly without staircase artifacts. The interaction needed for the reconstruction is reduced substantially to only a few clicks along the blood vessels. The presented method was evaluated with 30 blood vessels from 14 CT datasets of the neck and could be shown to be accurate, while leading to smooth visualizations of the neck blood vessels.Item A Four-level Focus + Context Approach to Interactive Visual Analysis of Temporal Features in Large Scientific Data(The Eurographics Association and Blackwell Publishing Ltd., 2008) Muigg, Philipp; Kehrer, Johannes; Oeltze, Steffen; Piringer, Harald; Doleisch, Helmut; Preim, Bernhard; Hauser, Helwig; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerIn this paper we present a new approach to the interactive visual analysis of time-dependent scientific data - both from measurements as well as from computational simulation - by visualizing a scalar function over time for each of tenthousands or even millions of sample points. In order to cope with overdrawing and cluttering, we introduce a new four-level method of focus+context visualization. Based on a setting of coordinated, multiple views (with linking and brushing), we integrate three different kinds of focus and also the context in every single view. Per data item we use three values (from the unit interval each) to represent to which degree the data item is part of the respective focus level. We present a color compositing scheme which is capable of expressing all three values in a meaningful way, taking semantics and their relations amongst each other (in the context of our multiple linked view setup) into account. Furthermore, we present additional image-based postprocessing methods to enhance the visualization of large sets of function graphs, including a texture-based technique based on line integral convolution (LIC). We also propose advanced brushing techniques which are specific to the timedependent nature of the data (in order to brush patterns over time more efficiently). We demonstrate the usefulness of the new approach in the context of medical perfusion data.Item Model-free Surface Visualization of Vascular Trees(The Eurographics Association, 2007) Schumann, Christian; Oeltze, Steffen; Bade, Ragnar; Preim, Bernhard; Peitgen, H.- O.; K. Museth and T. Moeller and A. YnnermanExpressive and efficient visualizations of complex vascular structures are essential for medical applications, such as diagnosis and therapy planning. A variety of techniques has been developed which provide smooth high-quality visualizations of vascular structures based on rather simple model assumptions. For diagnostic applications, these model assumptions and the resulting deviations from the actual vessel surface are not acceptable. We present a model-free approach which employs the binary result of a prior vessel segmentation as input. Instead of directly converting the segmentation result into a surface, we compute a point cloud which is adaptively refined at thin structures, where aliasing effects are particularly obvious and artifacts may occur. The point cloud is transformed into a surface representation by means of MPU Implicits, which provide a smooth piecewise quadratic approximation. Our method has been applied to a variety of datasets including pathologic cases. The generated visualizations are considerably more accurate than model-based approaches. Compared to other model-free approaches, our method produces smoother results.