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In gynecologic cancer imaging, multiple magnetic resonance imaging (MRI) sequences are acquired per patient to reveal different tissue characteristics. However, after image acquisition, the anatomical structures can be misaligned in the various sequences due to changing patient location in the scanner and organ movements. The co-registration process aims to align the sequences to allow for multi-sequential tumor imaging analysis. However, automatic co-registration often leads to unsatisfying results. To address this problem, we propose the web-based application MuSIC (Multi-Sequential Interactive Co-registration). The approach allows medical experts to co-register multiple sequences simultaneously based on a pre-defined segmentation mask generated for one of the sequences. Our contributions lie in our proposed workflow. First, a shape matching algorithm based on dual annealing searches for the tumor position in each sequence. The user can then interactively adapt the proposed segmentation positions if needed. During this procedure, we include a multi-modal magic lens visualization for visual quality assessment. Then, we register the volumes based on the segmentation mask positions. We allow for both rigid and deformable registration. Finally, we conducted a usability analysis with seven medical and machine learning experts to verify the utility of our approach. Our participants highly appreciate the multi-sequential setup and see themselves using MuSIC in the future. Best Paper Honorable Mention at VCBM2022 publishedVersion

International audience; We present Multiscale Unfolding, an interactive technique for illustratively visualizing multiple hierarchical scales of DNA in a single view, showing the genome at different scales and demonstrating how one scale spatially folds into the next. The DNA's extremely long sequential structure---arranged differently on several distinct scale levels---is often lost in traditional 3D depictions, mainly due to its multiple levels of dense spatial packing and the resulting occlusion. Furthermore, interactive exploration of this complex structure is cumbersome, requiring visibility management like cutaways. In contrast to existing temporally controlled multiscale data exploration, we allow viewers to always see and interact with any of the involved scales. For this purpose we separate the depiction into constant-scale and scale transition zones. Constant-scale zones maintain a single-scale representation, while still linearly unfolding the DNA. Inspired by illustration, scale transition zones connect adjacent constant-scale zones via level unfolding, scaling, and transparency. We thus represent the spatial structure of the whole DNA macro-molecule, maintain its local organizational characteristics, linearize its higher-level organization, and use spatially controlled, understandable interpolation between neighboring scales. We also contribute interaction techniques that provide viewers with a coarse-to-fine control for navigating within our all-scales-in-one-view representations and visual aids to illustrate the size differences. Overall, Multiscale Unfolding allows viewers to grasp the DNA's structural composition from chromosomes to the atoms, with increasing levels of "unfoldedness," and can be applied in data-driven illustration and communication.

International audience; We present ScaleTrotter, a conceptual framework for an interactive, multi-scale visualization of biological mesoscale data and, specifically, genome data. ScaleTrotter allows viewers to smoothly transition from the nucleus of a cell to the atomistic composition of the DNA, while bridging several orders of magnitude in scale. The challenges in creating an interactive visualization of genome data are fundamentally different in several ways from those in other domains like astronomy that require a multi-scale representation as well. First, genome data has intertwined scale levels---the DNA is an extremely long, connected molecule that manifests itself at all scale levels. Second, elements of the DNA do not disappear as one zooms out---instead the scale levels at which they are observed group these elements differently. Third, we have detailed information and thus geometry for the entire dataset and for all scale levels, posing a challenge for interactive visual exploration. Finally, the conceptual scale levels for genome data are close in scale space, requiring us to find ways to visually embed a smaller scale into a coarser one. We address these challenges by creating a new multi-scale visualization concept using a scale-dependent camera model that controls the visual embedding of the scales into their respective parents, the rendering of a subset of the scale hierarchy, and the location, size, and scope of the view. In traversing the scales, ScaleTrotter is roaming between 2D and 3D visual representations that are depicted in integrated visuals. We discuss, specifically, how this form of multi-scale visualization is a consequence of the specific characteristics of the genome data and describe its implementation. Finally, we discuss the implications of our work to the general illustrative depiction of multi-scale data.

International audience

Spatial selections are a ubiquitous concept in visualization. By localizing particular features, they can be analysed and compared in different views. However, the semantics of such selections often depend on specific parameter settings and it can be difficult to reconstruct them without additional information. In this paper, we present the concept of contextual snapshots as an effective means for managing spatial selections in visualized data. The selections are automatically associated with the context in which they have been created. Contextual snapshots can also be used as the basis for interactive integrated and linked views, which enable in-place investigation and comparison of multiple visual representations of data. Our approach is implemented as a flexible toolkit with well-defined interfaces for integration into existing systems. We demonstrate the power and generality of our techniques by applying them to several distinct scenarios such as the visualization of simulation data, the analysis of historical documents and the display of anatomical data. publishedVersion

This paper describes the concept of A-space. A-space is the space where visualization algorithms reside. Every visualization algorithm is a unique point in A-space. Integrated visualizations can be interpreted as an interpolation between known algorithms. The void between algorithms can be considered as a visualization opportunity where a new point in A-space can be reconstructed and new integrated visualizations can be created.

This paper proposes a novel technique to measure fabrication artifacts through direct comparison of a reference surface model with the corresponding industrial CT volume. Our technique uses the information from the surface model to locate corresponding points in the CT dataset. We then compute various comparison metrics to measure differences (fabrication artifacts) between the two datasets. The differences are presented to the user both visually as well as quantitatively. Our comparison techniques are divided into two groups, namely geometry-driven comparison techniques and visual-driven comparison techniques. The geometry-driven techniques provide an overview, while the visual-driven techniques can be used for a localized examination.

Virtual endoscopy can be used for preoperative planning, for training and intraoperatively. Surface rendering displays the inner lumen very well. Volume rendering has to be used if the external structures are of interest. For certain applications, e.g. endoluminal biopsy, it is of great advantage to be able to use both techniques at once. In this work we describe an approach that allows using these two methods in combination on a low-end standard personal computer. Since image generation is done in a preprocessing step, any high quality volume or polygonal rendering technique can be used and mixed together without any loss in performance at run-time. This work extends a previous image based rendering system for virtual bronchoscopy to include tracking of a rigid or flexible endoscope and finding one's way in the tracheal tree by displaying the endoscope's position in a top-view map of the trachea. Natural landmarks, i.e. bifurcations in the bronchial tree, are used for registration. Properties of the technique are explored on a phantom data set.

Proceedings of Graphics Interface 2001, Ottawa, Ontario, Canada, Canada, 7 - 9 June 2001, 209-216, In this paper an interactive volume rendering technique is presented which is based on a novel visualization model. We call the basic method ''bubble model'' since iso-surfaces are rendered as thin semi-transparent membranes similarly to blown soap bubbles. The primary goal is to develop a fast previewing technique for volumetric data which does not require a time-consuming transfer function specification to visualize internal structures. Our approach uses a very simple rendering model controlled by only two parameters. We also present an interactive rotation technique which does not rely on any specialized hardware, therefore it can be widely used even on low-end machines. Due to the interactive display, fine tuning is also supported since the modification of the rendering parameters has an immediate visual feedback.

In recent years the Hessian matrix and its eigenvalues became important in pattern recognition. Several algorithms based on the information they provide have been introduced. We recall the relationship between the eigenvalues of Hessian matrix and the 2nd order edge detection filter, show the usefulness of treating them separately and exploit these facts to design a combined threshold operation to generate sparse data sets.

The Fast Hartley Transform (FHT), a discrete version of the Hartley Transform (HT), has been studied in various papers and shown to be faster and more convenient to implement and handle than the corresponding Fast Fourier Transform (FFT). As the HT is not as nicely separable as the Fourier Transform (FT), a multidimensional version of the HT needs to perform a final correction step to convert the result of separate HTs for each dimension into the final multi-dimensional transform. Although there exist algorithms for two and three dimensions, no generalization to arbitrary dimensions can be found in the literature. We demonstrate an easily comprehensible and efficient implementation of the fast HT and its multi-dimensional extension. By adapting this algorithm to volume rendering by the projection-slice theorem and by the use for filter analysis in frequency domain we further demonstrate the importance of the HT in this application area.

Fast Oriented Line Integral Convolution (FROLIC), which is a variant of LIC, illustrates 2D vector fields by approximating a streamlet by a set of disks with varying intensity. FROLIC does not only show the direction of the flow but also its orientation. This paper presents color-table animation of FROLIC images. Various color-table compositions are discussed in detail. When animating FROLIC images visual artifacts (pulsation, synchronization) must be avoided. Several strategies in this respect are dealt with. Color-table animation of FROLIC has been implemented as a Visual C++ application, whereby the calculation of the dynamical system is performed with Mathematica. This allows researchers from various disciplines to conveniently explore and investigate analytically defined 2D and 3D vector fields.

This work describes DynSys3D, a framework for testing and implementing visualization techniques in the area of three-dimensional dynamical systems. DynSys3D has been designed to meet requirements which allow a fast and modular investigation of dynamical systems. Such requirements are, e.g., extendability, interactivity, and symmetry. Some visualization examples realized with DynSys3D illustrate the flexibility of the system.

We present several terms and definitions related to the local analysis of dynamical systems. Multiple terms for one and the same thing that were found in literature are put together to provide a “dictionary” of terms and to avoid potential confusion due to misleading definitions. Additionally, some important concepts which are necessary to analyze a dynamical system are briefly discussed and a new procedure to locally analyze a dynamical system’s behavior near trajectory points is proposed. The paper should give computer graphics specialists working on the visualization of analytically defined dynamical systems a set of mathematically tools for a thorough investigation of the local behavior of such system.

The basic reqirement for the functions of an Iterated Function System (IFS for shor) is contractivity. Nevertheless the majority of recent scientific investigations is concentrating on IFSs defined through a set of contractive linear functions. Simpler handling of this kind of functions and a more predictable results is the main reason for this approach. In this work we use distorted grids (representing nonlinear functions) to specify an IFS with a higher degree of flexibility and a higher modeling capability. A program for modeling these grids with so-called high-level operations is presented. Attention is directed to the interactivity of designing the IFS and rendering its limit set. Therefore a z-Buffer for displaying the result of a stochastic algorithm is included. Example images designed with the implemented software system are presented.

An interactive program for visualizing the long term behavior of dynamical systems, e.g., attractors and bifurcation diagrams, is presented. The program allows an easy specification of a set of formulas and constants which describe a dynamical system. This set of equations is then used for displaying the geometrical structure of the long term development of the dynamical system. The user defines the assignment of variables of the dynamical system to at most three spatial axes and one color axis. Viewing parameters, e.g., point of view, zoom, rotation angle, can again be changed interactively. The program is intended to provide researchers working on dynamical systems with a fast visual analysis and experimentation tool.

Superquadrics are well known and often used 3D surface objects in computer graphics. They are used for modelling parts of scenes that are then rendered using photorealistic image synthesis algorithms (e.g., ray tracing). For some techniques like texturing, which are part of these rendering methods, the type of the parametrization of such a surface has to be chosen carefully and is not intuitively obvious at first sight. There are cases, where the straight forward extension of quadric parameterizations to superquadrics do not produce satisfying results. We therefore investigate a number of different parameterizations in combination with the corresponding formulas, and point out some significant differences between them.

Scan-line algorithms for visibility calculation exploit various types of coherence properties. Several scan-line algorithms for Constructive Solid Geometry (CSG)are discussed. In one approach CSG primitives are represented by polygonal approximations. Another technique processes CSG primitives as general quadric surfaces. We investigate the handling of frequently occuring quadric surfaces (cube, cone, sphere, cylinder)as distinct cases. Thus the differing properties of such objects can be used more efficiently than a uniform approach would allow. A so called eBRep (extended Boundary Representation) is defined for the frequently occuring quadric surfaces. An eBRep is an exact representation of of a quadric object and contains curved edges and faces. For each of the above mentioned quadric surfaces a different, geometry dependent eBRep is specified. A comparison between the polygon-based scan-line algorithm for CSG and our eBRep based approach is done. eBRep is a storage efficient exact representation of quadric surfaces, well suited for scan-line visibility determination.