CeVis
  1. Center of Complex Systems and Visualization
  2. Lehre
  3. Oberseminar

In dem regelmäßig stattfindenden Oberseminar tragen Gäste aus aller Welt über Forschungsarbeiten zu Themen vor, die mit der Arbeit von CeVis und MeVis in Verbindung stehen, und Mitarbeiter von CeVis und MeVis präsentieren ihre neusten Ergebnisse.

Program for the Winter-Semester 2006-2007

19.10.2006, 11:00
Generalized Rigid Image Registration and Interpolation by Optical Flow using Contrast Invariant Intensity Scaling
Date: 19.10.2006
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Mag. Dr. Stephen Keeling
Karl-Franzens-Universität Graz
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Generalized Rigid Image Registration and Interpolation by Optical Flow using Contrast Invariant Intensity Scaling

A generalization of rigid image registration and interpolation is achieved variationally by penalizing a departure from rigidity of an optical flow. The image similarity measure is based upon the difference between scaled intensities. This similarity measure achieves contrast invariance purely by composition with scaling functions, while other contrast invariant measures are based upon differential formulations. Such rescaling is additionally found to have a smoothing effect on noisy images. Results obtained by Tikhonov regularization of scaling functions are superior to those obtained by a restricted set of basis functions. It is found that the computational cost for the implementation of scaling functions is very small, and yet the resulting image similarity can provide a match between images which is closer than that obtained by a sum of squared differences alone. The optical flow approach is investigated theoretically and numerically as well as with respect to a geometric multigrid solution process. For computations, a lumped finite element Eulerian discretization is used to solve the optimality system for the optical flow under natural boundary conditions. Also, a Lagrangian integration of the intensity along optical flow trajectories has the advantage of prohibiting diffusion among trajectories which would otherwise blur interpolated images. For the solution of the optimality system determining the optical flow, it is shown that the Hackbusch convergence criteria are met. Specifically, the Galerkin formalism is used together with a multi-colored ordering of unknowns to permit vectorization of a symmetric Gauss-Seidel relaxation on image processing systems. The procedure is shown to be independence of image order. Also, it is shown that non-autonomous optical flows are theoretically possible, but that autonomous flows may be used in practice to achieve a great computational savings. This work is motivated by applications in histological reconstruction and in dynamic medical imaging, and results are shown for such realistic examples.

Mag. Dr. Stephen Keeling , Karl-Franzens-Universität Graz
19.10.2006, 14:00
Methodische Entwicklung zur Perfusionsquantifizierung in der dynamischen MRT
Boris Keil , Universitätklinik Marburg
20.10.2006, 11:00
Nonparametric Deconvolution Approaches for Dynamic Contrast Enhanced Magnetic Resonance Imaging and a Proposed Theory of Tracer Transport
Date: 20.10.2006
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Mag. Dr. Stephen Keeling
Karl-Franzens-Universität Graz
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Nonparametric Deconvolution Approaches for Dynamic Contrast Enhanced Magnetic Resonance Imaging and a Proposed Theory of Tracer Transport

Efforts to perform nonparametric deconvolution for the determination of tissue transport properties led to a proposed revision of the theory of tracer transport. Counterexamples are used to motivate the revision of the established theory. Then dynamic contrast enhanced magnetic resonance imaging in particular is conceptualized in terms of a fully distributed convection-diffusion model from which a widely used convolution model is derived using, alternatively, compartmental discretizations or semigroup theory. On this basis, applications and limitations of the convolution model are identified. For instance, it is proved that perfusion and tissue exchange states cannot be identified on the basis of a single convolution equation alone. Yet under certain assumptions, particularly that flux is purely convective at the boundary of a tissue region, physiological parameters such as mean transit time, effective volume fraction, and volumetric flow rate per unit tissue volume can be deduced from the kernel. On this basis,a deconvolution framework is developed which constrains the convolution kernel to be non-increasing. Under this constraint it is proved that kernel estimates have bounded variation and thus readily manifest a well known staircasing effect. Further regularization is implemented by the choice of a function basis. Both spline bases and exponential bases are investigated. For exponential bases a condition for monotonicity is derived which is a considerable generalization over a previous condition implying complete monotonicity. Spline bases are found to be better suited for reconstructing kernels corresponding to plug flow, but exponential bases are found to be better suited to typical physiological data. Therefore the exponential approach is applied to dynamic contrast enhanced magnetic resonance imaging data to determine physiological parameters pixelwise to visualize a cerebral tumor, and the results are compared favorably with those of the standard Truncated Singular Value Decomposition approach.

Mag. Dr. Stephen Keeling , Karl-Franzens-Universität Graz
23.10.2006, 11:00
An overview of LiverCAD research in Gifu University
Dr. Xuejun Zhang , Graduate School of Medicine, Gifu University
23.10.2006, 15:30
Overview of CAD research at Fujita Lab. in Gifu University
Prof. Hiroshi Fujita , Graduate School of Medicine, Gifu University
25.10.2006, 11:00
Extremal properties of (epi)sturmian sequences and distribution modulo 1
Date: 25.10.2006
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Prof. Dr. J. P. Allouche
CNRS, LRI, Paris XI, France

Extremal properties of (epi)sturmian sequences and distribution modulo 1

We survey recent results by Dubickas about distribution modulo 1 of sequences {ξαn}. In particular we show that a recent result of Bugeaud and Dubickas (Fractional parts of powers and Sturmian words, C. R. Acad. Sci., 341 (2005) 69-74) is based upon a proposition on Sturmian sequences that was (re)discovered several times - sometimes in disguised form.

Prof. Dr. J. P. Allouche , CNRS, LRI, Paris XI, France
25.10.2006, 14:30
Automated segmentation of liver region and its surrounding organs
Dr. Xuejun Zhang , Graduate School of Medicine, Gifu University
01.11.2006, 11:00
Blind deconvolution – ill-posedness and regularization aspects
Date: 01.11.2006
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Dr. Lutz Justen
ZETEM, Universität Bremen

Blind deconvolution – ill-posedness and regularization aspects

Abstract as PDF-File

Dr. Lutz Justen , ZETEM, Universität Bremen
06.11.2006, 15:00
Investigation of respiratory organ motion using 4D MR imaging
Date: 06.11.2006
Time: 15:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Prof. Dr. Gabor Szekely
Medical Image Analysis and Visualization Group, ETH Zürich

Investigation of respiratory organ motion using 4D MR imaging

Respiratory organ motion is a key problem in various treatments. Whilst the commonly used imaging methods rely on simplified breathing patterns to acquire one breathing cycle, we propose a method which allow to study irregularities in organ motion during free breathing over tens of minutes. The approach does not assume a constant breathing depth or even strict periodicity and does not depend on an external gating signal.

We reconstruct time resolved 3D image sequences by retrospective stacking of dynamic 2D MR images using internal image-based gating. The generic method is tested by acquiring the motion of the liver and the lung. The quantitative evaluation of the gating accuracy demonstrate several advantages over one-dimensional gating signals. Dense deformation fields describing the respiratory motion were estimated from the reconstructed volumes using non-rigid 3D registration. All obtained motion fields showed variations in the range of minutes such as drifts and deformations, which changed both the exhalation position of the liver and the breathing pattern.

We used the obtained motion data to evaluate the effect of breathing on radiation therapy like comparing proton therapy planning with actual dose delivery and analyze its sensitivity to organ motion. In addition, we report about first studies in evaluating the efficiency of standard gating techniques for motion compensation

Prof. Dr. Gabor Szekely , Medical Image Analysis and Visualization Group, ETH Zürich
08.11.2006, 11:00
Der Coding Style Guide für MeVis Research – Überblick und Diskussion
Stephan Kuhagen , MeVis Research
15.11.2006, 11:00
Self-organized symmetry in frame cellular automata
Date: 15.11.2006
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Prof. Dr. A. Barbe
Katholieke Universiteit Leuven

Self-organized symmetry in frame cellular automata

Abstract as PDF-File

Prof. Dr. A. Barbe , Katholieke Universiteit Leuven
23.11.2006, 14:00
Klassifikation von MR Spektren von Brustgewebsbiopsaten - Probleme und Methoden
Date: 23.11.2006
Time: 14:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Markus Wenzel
MeVis Research

Klassifikation von MR Spektren von Brustgewebsbiopsaten - Probleme und Methoden

Dieser Arbeitsbericht soll neben einer sehr (!) kurzgefaßte Einführung in die Methode der MR-Spektroskopischen Meßtechnik zunächst einige grundsätzliche Probleme der Messungen beschreiben. Einige gebräuchliche Lösungsmöglichkeiten und Methoden der Arbeit mit solchen Spektren werden vorgestellt, bevor die Ideen, Methoden und Ergebnisse, die die MeVis-Spektroskopiker in den letzten Wochen hatte bzw. einsetzten, vorgestellt werden. Der Fokus liegt dabei auf dem Ziel der automatischen Klassifikation von Spektren.

Markus Wenzel , MeVis Research
06.12.2006, 10:30
Quantitative Analyse der Thrombuslast in der CT-Diagnostik der akuten Lungenarterienembolie
Dr. med. Dipl.-Phys. Christian Riedel , Universitätsklinikum Schleswig-Holstein, Campus Kiel
07.12.2006, 09:30
Von chirurgischen Workflows zu Standards in der Chirurgie
Dr.-Ing. Oliver Burgert , Innovation Center Computer Assisted Surgery, Leipzig
13.12.2006, 14:00
Parameter Estimation for Plant Growth Analysis
Dr. Hanno Scharr , Forschungszentrum Jülich
12.01.2007, 11:00
Feature Extraction and Visualization of (Large) Medical Imaging Data
Date: 12.01.2007
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Prof. Dr. Lars Linsen
Jacobs University Bremen

Feature Extraction and Visualization of (Large) Medical Imaging Data

The purpose of this talk is to present past and on-going research efforts as well as ideas for future directions of our research group in the context of visualization in medicine. One focus is the extraction of features,typically in form of boundary surfaces. Among others, novel aspects and extensions to isosurface extraction and levels sets approaches are discussed. Another focus is how to handle large data, for example when dealing with cryosections or multivariate data. Adaptive multiresolution schemes and visualization methods operating on them are presented. Finally, new ideas in visualization of diffusion-based imaging data are introduced.

Prof. Dr. Lars Linsen , Jacobs University Bremen
24.01.2007, 10:30
Workshop-Bericht Molecular Imaging in Dementia
Date: 24.01.2007
Time: 10:30:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Bernd Merkel
MeVis Research

Workshop-Bericht Molecular Imaging in Dementia

In diesem Vortrag geht es um einen Bericht über den Workshop "Molecular Imaging in Dementia" (MIND), der im letzten Monat vom Klinikum rechts der Isar (TU München) unter der Leitung der Abteilungen Nuklearmedizin sowie Psychatrie durchgeführt wurde. Ich möchte einen kurzen Abriß der dort vorgestellten und relevanten Vorträge geben und Möglichkeiten aufzeigen, welche Rolle die molekulare Bildgebung bei Demenz-Erkrankungen spielt. Zusätzlich sollen etwas umfassendere Erklärungen zum Thema Demenz im Allgemeinen meinen Vortrag abrunden.

Bernd Merkel , MeVis Research
07.02.2007, 11:00
CSO – Contour Segmentation Objects
Date: 07.02.2007
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Olaf Konrad
MeVis Research

CSO – Contour Segmentation Objects

Demonstration und Diskussion

Olaf Konrad , MeVis Research
08.02.2007, 11:00
VTK and its Integration into MeVisLab
Wolf Spindler , MeVis Research
12.02.2007, 14:15
Molecular Imaging
PD Dr. Fabian Kiessling , DKFZ Heidelberg
13.02.2007, 11:00
Vascular Imaging with MRT and CT
PD Dr. Fabian Kiessling , DKFZ Heidelberg
15.03.2007, 16:00
Hochdimensionale konvexe Optimierung am Beispiel der Strahlentherapieplanung
Alexander Scherrer , ITWM Kaiserslautern
16.03.2007, 10:30
Hochdimensionale semiinfinite Optimierung am Beispiel der optimalen Zerlegung von Edelsteinen
Anton Winterfeld , ITWM Kaiserslautern
22.03.2007, 11:00
Particle Systems for Efficient and Accurate High-Order Finite Element Visualization
Date: 22.03.2007
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Prof. Dr. R. M. Kirby
SCI, University of Utah, USA

Particle Systems for Efficient and Accurate High-Order Finite Element Visualization

Visualization has become an important component of the simulation pipeline, providing scientists and engineers a visual intuition of their models. However, simulations that make use of the high-order finite element method for spatial subdivision present a challenge to conventional isosurface visualization techniques. High-order finite element isosurfaces are defined by basis functions in reference space, which give rise to a world space solution through a coordinate transformation, which does not necessarily have a closed-form inverse. Thereforeworld-space isosurface rendering methods such as marching cubes and raytracing must perform a nested root finding,which is computationally expensive. We thus propose visualizing these isosurfaces with a particle system. We present a framework that allows particles to sample an isosurface in reference space, avoiding the costly inverse mapping of positions from world space when evaluating the basis functions. The distribution of particles across the reference space isosurface is controlled by geometric information from the world space isosurface, such as the surface gradient and curvature. The resulting particle distributions can be distributed evenly or adapted to accommodate world-space surface features. This provides compact, efficient, and accurate isosurface representations of these challenging data sets.

Prof. Dr. R. M. Kirby , SCI, University of Utah, USA
28.03.2007, 11:00
HWT – Hybrid Watershed Transform: Optimal Combination of Hierarchical Interactive and Automated Image Segementation
Date: 28.03.2007
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Dr. Horst Hahn
MeVis Research

HWT – Hybrid Watershed Transform: Optimal Combination of Hierarchical Interactive and Automated Image Segementation

In quantitative medical imaging and therapy planning, the optimal combination of automated and interactively defined information is crucial for image segmentation methods to be both efficient and effective. We propose to combine an efficient hierarchical region merging scheme that collects per-region statistics across hierarchy levels with a trainable classification engine that facilitates automated region labeling based on an arbitrary number of reference segmentations. When applying the classification engine, we propose to use a corridor of non-classified regions resulting in a sparse labeling with extremely low false-classification rate, and to attribute labels to the remaining basins through successive merging with ready-labeled basins. The proposed hierarchical region merging scheme also permits to efficiently include interactively defined labels. We denominate this general approach as Hybrid Hierarchical Interactive Image Segmentation Scheme (HIS²). More specifically, we present an extension of the Interactive Watershed Transform, which we combine with a trainable two-class Support Vector Machine based on Gaussian radial basis functions. Finally, we present a novel asymmetric marker scheme, which provides a powerful means of regionally correcting remaining inaccuracies while preserving full detail of the automatic labeling procedure. We denominate the complete algorithm as Hybrid Watershed Transform (HWT), which we apply to one challenging segmentation problem in clinical imaging, namely efficient bone removal in large computed tomography angiographic data sets. Efficiency and accuracy of the proposed methodology is evaluated on multi-slice images from nine different sites. As a result, its ability to rapidly and automatically generate robust and precise segmentation results in combination with a versatile manual correction mechanism could be proven without requiring specific anatomical or geometrical models.

Dr. Horst Hahn , MeVis Research
30.03.2007, 11:00
Flow Sensitive 4D Magnetic Resonance Imaging - Analysis of 3D Blood Flow Characteristics in the Human Vascular System
Date: 30.03.2007
Time: 11:00:00
Place: CeVis/MeVis, Seminarraum Mandelbrot, UNI 29
Speaker: Dr. Michael Markl
Universitätklinik Freiburg

Flow Sensitive 4D Magnetic Resonance Imaging - Analysis of 3D Blood Flow Characteristics in the Human Vascular System

Magnetic Resonance Imaging (MRI) techniques provide a non-invasive method for the highly accurate anatomic depiction of the heart and vessels. In addition, the intrinsic sensitivity of MRI to flow, motion and diffusion offers the unique possibility to acquire spatially registered functional information simultaneously with the morphological data within a single experiment. Characterizations of the dynamic components of blood flow and cardiovascular function provide insight into normal and pathological physiology and have made considerable progress in recent years.

The potential of ECG synchronized and respiration controlled flow sensitive time-resolved 3D MR-Imaging using 3-directional velocity encoding for the detection and visualization of global and local blood flow characteristics in targeted vascular regions (aorta, cranial arteries, peripheral arteries) is presented. Blood flow characteristics in normal vascular geometries as well as for common aortic pathologies were investigated using advanced computer aided data analysis which empowered the reader to take full advantage of the 4D nature (3 spatial and one temporal dimension) of the data.

The comparison of vascular hemodynamics in volunteers and patients illustrates that even small pathological geometric changes such as mild aneurysms or prosthesis repair bear a major impact on local vascular hemodynamics and severely alter blood flow characteristics. Further quantification and analysis of derived vessel wall parameters may allow for a regional analysis of the impact of vascular pathologies on the vessel wall.

Dr. Michael Markl , Universitätklinik Freiburg

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