Detlev Stalling - Academia.edu (original) (raw)

Papers by Detlev Stalling

Journal of Visualization, Sep 1, 2004

... One important hemodynamic parameter implicated in the aneurysm growth and rupture is wall she... more ... One important hemodynamic parameter implicated in the aneurysm growth and rupture is wall shear stress. ... With the recent development of the 3D medical imaging it is now possible to reliably simulate blood flow in anatomically realistic vessel geometries. ...

Physics in Medicine and Biology, 1998

Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition fo... more Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition for various applications in radiation oncology, especially for planning purposes in hyperthermia. We have developed the three following algorithms for contour generation and implemented them in an editor of the HyperPlan hyperthermia planning system. Firstly, a manual contour input with numerous correction and editing options. Secondly, a volume growing algorithm with adjustable threshold range and minimal region size. Thirdly, a watershed transformation in two and three dimensions. In addition, the region input function of the Helax commercial radiation therapy planning system was available for comparison. All four approaches were applied under routine conditions to two-dimensional computed tomographic slices of the superior thoracic aperture, mid-chest, upper abdomen, mid-abdomen, pelvis and thigh; they were also applied to a 3D CT sequence of 72 slices using the three-dimensional extension of the algorithms. Time to generate the contours and their quality with respect to a reference model were determined. Manual input for a complete patient model required approximately 5 to 6 h for 72 CT slices (4.5 min/slice). If slight irregularities at object boundaries are accepted, this time can be reduced to 3.5 min/slice using the volume growing algorithm. However, generating a tetrahedron mesh from such a contour sequence for hyperthermia planning (the basis for finite-element algorithms) requires a significant amount of postediting. With the watershed algorithm extended to three dimensions, processing time can be further reduced to 3 min/slice while achieving satisfactory contour quality. Therefore, this method is currently regarded as offering some potential for efficient automated model generation in hyperthermia. In summary, the 3D volume growing algorithm and watershed transformation are both suitable for segmentation of even low-contrast objects. However, they are not always superior to user-friendly manual programs for contour generation. When the volume growing algorithm is used, the contours have to be postprocessed with suitable filters. The watershed transformation has a large potential if appropriately developed to 3D sequences and 3D interaction features. After all, the practicality and feasibility of every segmentation method critically depend on various details of the user software as pointed out in this article.

International Journal of Radiation Oncology*Biology*Physics, 2000

A prototype of the hyperthermia treatment planning system (HTPS) HyperPlan for the SIGMA-60 appli... more A prototype of the hyperthermia treatment planning system (HTPS) HyperPlan for the SIGMA-60 applicator (BSD Medical Corp., Salt Lake City, Utah, USA) has been evaluated with respect to clinical practicability and correctness. HyperPlan modules extract tissue boundaries from computed tomography (CT) images to generate regular and tetrahedral grids as patient models, to calculate electric field (E-field) distributions, and to visualize three-dimensional data sets. The finite difference time-domain (FDTD) method is applied to calculate the specific absorption rate (SAR) inside the patient. Temperature distributions are calculated by a finite-element code and can be optimized. HyperPlan was tested on 6 patients with pelvic tumors. For verification, measured SAR values were compared with calculated SAR values. Furthermore, intracorporeal E-field scans were performed and compared with calculated profiles. The HTPS can be applied under clinical conditions. Measured absolute SAR (in W/kg), as well as relative E-field scans, correlated well with calculated values (+/-20%) using the contour-based FDTD method. Values calculated by applying the FDTD method directly on the voxel (CT) grid, were less well correlated with measured data. The HyperPlan system proved to be clinically feasible, and the results were quantitatively and qualitatively verified for the contour-based FDTD method.

L'invention concerne un systeme de visualisation client-serveur a traitement de donnees hybri... more L'invention concerne un systeme de visualisation client-serveur a traitement de donnees hybride, comprenant un processeur de donnees numeriques de serveur, qui permet un rendu d'image cote serveur et un traitement de donnees d'image, et des processeurs de donnees numeriques de clients connectes simultanement au serveur, qui recoit des messages des clients, cree des images rendues d'ensembles de donnees ou d'autres resultats de traitement de donnees et envoie ces images rendues et ces resultats aux clients pour un affichage ou un traitement ulterieur. L'execution de certaines operations de rendu d'images sur l'un ou l'autre du serveur ou du client en fonction de celui qui est le mieux adapte pour les tâches demandees par l'utilisateur a tout moment, et eventuellement le reglage dynamique de cette partie de travail, ameliorent la vitesse de rendu et la reactivite de l'application sur les clients.

Acknowledgements The work described in this thesis has been carried out from 1995 to 1998 at the ... more Acknowledgements The work described in this thesis has been carried out from 1995 to 1998 at the department of Scientific Visualization at the Konrad-Zuse-Zentrum Berlin (ZIB). First of all, I would like to thank my tutors Prof. Dr. Peter Deuflhard and Hans-Christian Hege for the opportunity to graduate. They introduced me into an interesting new field between mathematics, computer science, and art, namely scientific visualization. Without their constant support and encouragement this work would not have been possible. I am also very grateful to Prof. Dr. Thomas Ertl for reviewing this thesis. I deeply appreciated the creative atmosphere at ZIB and enjoyed many fruitful and inspiring discussions. Malte Zöckler deserves special thanks for helping me to develop and implement many ideas presented in this work. Moreover, I would like to thank all other members and ex-members of the department of Scientific Visualization at ZIB for many suggestions and practical help offered every day. Line integral convolution of a 2D Hamiltonian system.

Introduction In this lecture we will discuss how line integral convolution can be generalized to ... more Introduction In this lecture we will discuss how line integral convolution can be generalized to depict vector fields defined on surfaces in 3D. The surfaces are assumed to be topologically equivalent to a 2D plane -- at least in a local neighbourhood. In principle, any 2D imaging technique can be applied to such a surface as well. In particular, it is possible to map standard 2D LIC images onto the surface to visualize directional information. This is very similar to conventional texture mapping in computer graphics. Applying LIC on surfaces implies a number of interesting questions, e.g. how to compute field lines on a surface, how to define a suitable input noise, or how to perform the texture mapping in detail. Different methods have been proposed to solve these problems. Basically, surface LIC algorithms can be divided into two groups depending on whether they operate in parameter space or in physical space. After introducing tangent curves on surfaces mathematically, we wil

We present a new technique for generating surface meshes from a uniform set of discrete samples. ... more We present a new technique for generating surface meshes from a uniform set of discrete samples. Our method extends the well-known marching cubes algorithm used for computing polygonal isosurfaces. While in marching cubes each vertex of a cubic grid cell is binary classified as lying above or below an isosurface, in our approach an arbitrary number of vertex classes can be specified. Consequently the resulting surfaces consist of patches separating volumes of two different classes each. Similar to the marching cubes algorithm all grid cells are traversed and classified according to the number of different vertex classes involved and their arrangement. The solution for each configuration is computed on base of a model that assigns probabilities to the vertices and interpolates them. We introduce an automatic method to find a triangulation which approximates the boundary surfaces- implicitly given by our model- in a topological correct way. Look-up tables guarantee a high performance ...

Introduction Line integral convolution is a nice technique, being of interest in visualization as... more Introduction Line integral convolution is a nice technique, being of interest in visualization as well as in computer graphics and art. An essential prerequisite for its practical use is interactive speed. Furthermore, enlarged flexibility and functions for zooming or texture animation are required. In the following we will discuss algorithmic ideas that allow us to meet these requirements. The lecture is intended for both practioners, who want a deeper understanding of LIC algorithms, and programmers, aiming on implementing or modifying LIC code. According the landmark paper of Brian Cabral and Casey Leedom [4], LIC basically means convolution of an input texture along lines that are defined by a vector field. For simplicity we call these lines "convolution lines". The main idea we are building upon in this lecture is to separate the computation of convolution lines from that of convolution, [14]. Thereby we are able to exploit economies and to provide wider fu

Recently a new method for interactive image segmentation called Intelligent Scissors has been pro... more Recently a new method for interactive image segmentation called Intelligent Scissors has been proposed by Mortensen and Barrett. Based on optimal path searching in a graph network, the method has a number of advantages over previous approaches. It is fast, robust, and very intuitively to use. Originally designed as a general-purpose tool for image manipulation, we have applied the method for medical image segmentation within an interactive contour editor. In this paper we describe some results and conclusions from our work. We also suggest a number of modifications of the original algorithm improving both, quality and performance of the method. A common requirement is to obtain smooth contours, i.e. contours free of sudden directional changes. Such smoothness constraints are quite difficult to implement using traditional edge costs, but may be achieved easily using a simple graph pruning strategy. This method not only avoids acute angles but also implies a 25% performance gain. Alth...

Line Integral Convolution (LIC) is a powerful technique for generating striking images and animat... more Line Integral Convolution (LIC) is a powerful technique for generating striking images and animations from vector data. Introduced in 1993, the method has rapidly found many application areas, ranging from computer arts to scientific visualization. Based upon locally filtering an input texture along a curved stream line segment in a vector field, it is able to depict directional information at high spatial resolutions. We present a new method for computing LIC images. It employs simple box filter kernels only and minimizes the total number of stream lines to be computed. Thereby it reduces computational costs by an order of magnitude compared to the original algorithm. Our method utilizes fast, error-controlled numerical integrators. Decoupling the characteristic lengths in vector field grid, input texture and output image, it allows computation of filtered images at arbitrary resolution. This feature is of significance in computer animation as well as in scientific visualization, w...

A new technique for interactive vector field visualization using large numbers of properly illumi... more A new technique for interactive vector field visualization using large numbers of properly illuminated stream lines is presented. Taking into account ambient, diffuse, and specular reflection terms as well as transparency, we employ a realistic shading model which significantly increases quality and realism of the resulting images. While many graphics workstations offer hardware support for illuminating surface primitives, usually no means for an accurate shading of line primitives are provided. However, we show that proper illumination of lines can be implemented by exploiting the texture mapping capabilities of modern graphics hardware. In this way high rendering performance with interactive frame rates can be achieved. We apply the technique to render large numbers of integral curves in a vector field. The impression of the resulting images can be further improved by making the curves partially transparent. We also describe methods for controlling the distribution of stream lines...

The speaker and his co-workers in Scientific Computing and Visualization have established a close... more The speaker and his co-workers in Scientific Computing and Visualization have established a close cooperation with medical doctors at the Rudolf-Virchow-Klinikum of the Humboldt University in Berlin on the topic of regional hyperthermia. In order to permit a patient-specific treatment planning, a special software system (HyperPlan) has been developed. A mathematical model of the clinical system (radio frequency applicator with 8 antennas, water bolus, individual patient body) involves Maxwell's equations in inhomogeneous media and a so-called bio-heat transfer PDE describing the temperature distribution in the human body. The electromagnetic field and the thermal phenomena need to be computed at a speed suitable for the clinical environment. An individual geometric patient model is generated as a quite complicated tetrahedral "coarse" grid (several thousands of nodes). Both Maxwell's equations and the bioheat transfer equation are solved on that 3D-grid by means of adaptive multilevel finite element methods, which automatically refine the grid where necessary in view of the required accuracy. Finally optimal antenna parameters for the applicator are determined. All steps of the planning process are supported by powerful visualization methods. Medical images, contours, grids, simulated electromagnetic fields and temperature distributions can be displayed in combination. A number of new algorithms and techniques had to be developed and implemented. Special emphasis has been put on advanced 3D interaction methods and user interface issues.

HyperPlan is a software system for performing 3D-simulations and treatment planning in regional h... more HyperPlan is a software system for performing 3D-simulations and treatment planning in regional hyperthermia. It allows the user to understand the complex effects of electromagnetic wave propagation and heat transport inside a patient's body. Optimized power amplitudes and phase settings can be calculated for the BSD radiowave applicators Sigma 60 and Sigma 2000 (eye-applicator). HyperPlan is built on top of the modular, object-oriented visualization system Amira. This system already contains powerful algorithms for image processing, geometric modelling and 3D graphics display. HyperPlan provides a number of hyperthermia-specific modules, allowing the user to create 3D tetrahedral patient models suitable for treatment planning. In addition, all numerical simulation modules required for hyperthermia simulation are part of HyperPlan. This guide provides a step-by-step introduction to hyperthermia planning using HyperPlan. It also describes the usage of the underlying visualization...

Journal of Visualization, Sep 1, 2004

Physics in Medicine and Biology, 1998

International Journal of Radiation Oncology*Biology*Physics, 2000