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Now showing 1 - 8 of 8
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    Semi-Automatic Vessel Boundary Detection in Cardiac 4D PC-MRI Data Using FTLE fields
    (The Eurographics Association, 2016) Behrendt, Benjamin; Köhler, Benjamin; Gräfe, Daniel; Grothoff, Matthias; Gutberlet, Matthias; Preim, Bernhard; Stefan Bruckner and Bernhard Preim and Anna Vilanova and Helwig Hauser and Anja Hennemuth and Arvid Lundervold
    Four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) is a method to non-invasively acquire in-vivo blood flow, e.g. in the aorta. It produces three-dimensional, time-resolved datasets containing both flow speed and direction for each voxel. In order to perform qualitative and quantitative data analysis on these datasets, a vessel segmentation is often required. These segmentations are mostly performed manually or semi-automatically, based on three-dimensional intensity images containing the maximal flow speed over all time steps. To allow for a faster segmentation, we propose a method that, in addition to intensity, incorporates the flow trajectories into the segmentation process. This is accomplished by extracting Lagrangian Coherent Structures (LCS) from the flow data, which indicate physical boundaries in a dynamical system. To approximate LCS in our discrete images, we employ Finite Time Lyapunov Exponent (FTLE) fields to quantify the rate of separation of neighboring flow trajectories. LCS appear as ridges or valleys in FTLE images, indicating the presence of either a flow structure boundary or physical boundary. We will show that the process of segmenting low-contrast 4D PC-MRI datasets can be simplified by using the generated FLTE data in combination with intensity images.
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    A Survey of Perceptually Motivated 3D Visualization of Medical Image Data
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Preim, Bernhard; Baer, Alexandra; Cunningham, Douglas; Isenberg, Tobias; Ropinski, Timo; Ross Maciejewski and Timo Ropinski and Anna Vilanova
    This survey provides an overview of perceptually motivated techniques for the visualization of medical image data, including physics-based lighting techniques as well as illustrative rendering that incorporate spatial depth and shape cues. Additionally, we discuss evaluations that were conducted in order to study the perceptual effects of these visualization techniques as compared to conventional techniques. These evaluations assessed depth and shape perception with depth judgment, orientation matching, and related tasks. This overview of existing techniques and their evaluation serves as a basis for defining the evaluation process of medical visualizations and to discuss a research agenda.
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    Illustrative PET/CT Visualisation of SIRT-Treated Lung Metastases
    (The Eurographics Association, 2016) Merten, Nico; Glaßer, Sylvia; Lassen-Schmidt, Bianca; Großer, Oliver Stephan; Ricke, Jens; Amthauer, Holger; Preim, Bernhard; Stefan Bruckner and Bernhard Preim and Anna Vilanova and Helwig Hauser and Anja Hennemuth and Arvid Lundervold
    We present an illustrative rendering pipeline which combines anatomical information from CT scans with functional information from PET scans. To treat lung metastases with Selective Internal Radiation Therapies (SIRTs), combined PET/CT recordings are used for treatment planning and intervention validation. We firstly extract surface meshes from the lung lobes and trachea from the CT scan. In addition, the radiation activity of the therapeutic agent 90Y is acquired from the PET data. To convey all this information in one view, we use illustrative rendering techniques, combining Order-Independent Transparencies with Boundary Enhancements and Silhouettes. Our methods are evaluated by clinical and visualisation domain experts. This study indicates an excellent spatial perception and evaluation of tumor position, metabolic and therapeutic agent activity, when transparencies and boundary enhancements are used to render the surrounding lung lobes.
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    Semi-automatic Vortex Flow Classification in 4D PC-MRI Data of the Aorta
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Meuschke, Monique; Köhler, Benjamin; Preim, Uta; Preim, Bernhard; Lawonn, Kai; Kwan-Liu Ma and Giuseppe Santucci and Jarke van Wijk
    We present an Aortic Vortex Classification (AVOCLA) that allows to classify vortices in the human aorta semi-automatically. Current medical studies assume a strong relation between cardiovascular diseases and blood flow patterns such as vortices. Such vortices are extracted and manually classified according to specific, unstandardized properties. We employ an agglomerative hierarchical clustering to group vortex-representing path lines as basis for the subsequent classification. Classes are based on the vortex' size, orientation and shape, its temporal occurrence relative to the cardiac cycle as well as its spatial position relative to the vessel course. The classification results are presented by a 2D and 3D visualization technique. To confirm the usefulness of both approaches, we report on the results of a user study. Moreover, AVOCLA was applied to 15 datasets of healthy volunteers and patients with different cardiovascular diseases. The results of the semi-automatic classification were qualitatively compared to a manually generated ground truth of two domain experts considering the vortex number and five specific properties.
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    Robust Cardiac Function Assessment in 4D PC‐MRI Data of the Aorta and Pulmonary Artery
    (Copyright © 2016 The Eurographics Association and John Wiley & Sons Ltd., 2016) Köhler, Benjamin; Preim, Uta; Grothoff, Matthias; Gutberlet, Matthias; Fischbach, Katharina; Preim, Bernhard; Chen, Min and Zhang, Hao (Richard)
    Four‐dimensional phase‐contrast magnetic resonance imaging (4D PC‐MRI) allows the non‐invasive acquisition of time‐resolved, 3D blood flow information. Stroke volumes (SVs) and regurgitation fractions (RFs) are two of the main measures to assess the cardiac function and severity of valvular pathologies. The flow rates in forward and backward direction through a plane above the aortic or pulmonary valve are required for their quantification. Unfortunately, the calculations are highly sensitive towards the plane's angulation since orthogonally passing flow is considered. This often leads to physiologically implausible results. In this work, a robust quantification method is introduced to overcome this problem. Collaborating radiologists and cardiologists were carefully observed while estimating SVs and RFs in various healthy volunteer and patient 4D PC‐MRI data sets with conventional quantification methods, that is, using a single plane above the valve that is freely movable along the centerline. By default it is aligned perpendicular to the vessel's centerline, but free angulation (rotation) is possible. This facilitated the automation of their approach which, in turn, allows to derive statistical information about the plane angulation sensitivity. Moreover, the experts expect a continuous decrease of the blood flow volume along the vessel course. Conventional methods are often unable to produce this behaviour. Thus, we present a procedure to fit a monotonous function that ensures such physiologically plausible results. In addition, this technique was adapted for the usage in branching vessels such as the pulmonary artery. The performed informal evaluation shows the capability of our method to support diagnosis; a parameter evaluation confirms the robustness. Vortex flow was identified as one of the main causes for quantification uncertainties.Four‐dimensional phase‐contrast magnetic resonance imaging (4D PC‐MRI) allows the non‐invasive acquisition of time‐resolved, 3D blood flow information. Stroke volumes (SVs) and regurgitation fractions (RFs) are two of the main measures to assess the cardiac function and severity of valvular pathologies. The flow rates in forward and backward direction through a plane above the aortic or pulmonary valve are required for their quantification. Unfortunately, the calculations are highly sensitive towards the plane's angulation since orthogonally passing flow is considered.
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    Semi-Immersive 3D Sketching of Vascular Structures for Medical Education
    (The Eurographics Association, 2016) Saalfeld, Patrick; Stojnic, Aleksandar; Preim, Bernhard; Oeltze-Jafra, Steffen; Stefan Bruckner and Bernhard Preim and Anna Vilanova and Helwig Hauser and Anja Hennemuth and Arvid Lundervold
    We present a semi-immersive 3D User Interface to sketch complex vascular structures and vessel pathologies by drawing centerlines in 3D. Our framework comprises on-the-fly reconstruction of the corresponding vessel surface and subsequent local surface compression and expansion. Additionally, we allow the enrichment with an illustrative, plausible blood flow visualization. Our framework is designed for medical educators and students to support anatomy and pathology education. Anatomy educators can realize the step-by-step process of creating and explaining complex spatial relationships of interlinked vascular structures and blood flow behavior. Students can view this process and explore the created structures, which helps them in reproducing and memorizing them. To create a surface model based on the sketched centerlines, we employ implicit surfaces. This allows for easy adding, editing, and removing vessel branches and achieve continuous surfaces with smooth transitions at branchings. The blood flow can be interactively added and is realized with a topology-aware particle simulation. We qualitatively evaluated our framework and demonstrate the applicability and usability of our approach.
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    How to Evaluate Medical Visualizations on the Example of 3D Aneurysm Surfaces
    (The Eurographics Association, 2016) Glaßer, Sylvia; Saalfeld, Patrick; Berg, Philipp; Merten, Nico; Preim, Bernhard; Stefan Bruckner and Bernhard Preim and Anna Vilanova and Helwig Hauser and Anja Hennemuth and Arvid Lundervold
    For the evaluation of medical visualizations, a ground truth is often missing. Therefore, the evaluation of medical visualizations is often restricted to qualitative comparisons w.r.t user preferences but neglects more objective measures such as accuracies or task completion times. In this work, we provide a pipeline with statistical tests for the evaluation of the user performance within an experimental setup. We demonstrate the adaption of the pipeline for the specific example of cerebral aneurysm surface visualization. Therefore, we developed three visualization techniques to compare the aneurysm volumes. Then, we present a single-factor, within-subject user study, which allows for the evaluation of these visualization techniques as well as the identification of the most suitable one. The evaluation includes a qualitative as well as a comprehensive quantitative analysis to determine statistically significant differences. As a result, a color-coded map surface view is identified as best suited to depict the aneurysm volume changes. The presentation of the different stages of the evaluation pipeline allows for an easy adaption to other application areas of medical visualization. As a result, we provide orientation to enrich qualitative evaluations by the presented quantitative analyses.
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    On the Evaluation of a Semi-Automatic Vortex Flow Classification in 4D PC-MRI Data of the Aorta
    (The Eurographics Association, 2016) Meuschke, Monique; Köhler, Ben; Preim, Bernhard; Lawonn, Kai; Kai Lawonn and Mario Hlawitschka and Paul Rosenthal
    In this paper, we report on our experiences that we made during our contributions in the field of the visualization of flow characteristics. Mainly, we focused on the vortex flow classification in 4D PC-MRI as current medical studies assume a strong correlation between cardiovascular diseases and blood flow patterns such as vortices. For further analysis, medical experts are asked to manually extract and classify such vortices according to specific properties. We presented and evaluated techniques that enable a fast and robust vortex classification [MLK 16,MKP 16] that supports medical experts. The main focus in this paper is a report that describes our conversations with the domain experts. The dialog was the fundament that gave us the direction of what the experts need. We derived several requirements that should be fulfilled by our tool. From this, we developed a prototype that supports the experts. Finally, we describe the evaluation of our framework and discuss currently limitations.