Conference PaperPDF Available
11th World Congress on Computational Mechanics (WCCM XI)
5th European Conference on Computational Mechanics (ECCM V)
6th European Conference on Computational Fluid Dynamics (ECFD VI)
July 20–25, 2014, Barcelona, Spain
Michael Roland1, Tim Dahmen2, Thorsten Tjardes3, Robin Otchwemah3,
Philipp Slusalleck2and Stefan Diebels1
1Saarland University, Chair of Applied Mechanics, Campus A4 2, 66123 Saarbr¨ucken, and
2DFKI GmbH, Agents and Simulated Reality, Campus D3 2, 66123 Saarbr¨ucken, and
3Kliniken der Stadt K¨oln gGmbH, Neufelder Strae 34, 51067 K¨oln, and
Key words: patient–specific implants, segementation, volume mesh generation, finite
element simulation
Today fractures of the long bones, i.e. tibia or femur, are treated surgically. This means
that implants are used that allow early post operative weight bearing and physiotherapy
of the injured limb. However, the implants currently used in orthopaedic trauma surgery
do not account for individual specificities of the patient and of the fracture.
A personalized approach to fracture therapy necessitates the integration of knowledge
and techniques from mechanics, orthopaedic trauma surgery, computer science and image
processing. Here, we will merge the relevant knowledge from these disciplines into an
integrated workflow.
Routinely acquired computed tomography data sets are subjected to an automated seg-
mentation procedure using edge–enhancing nonlinear anisotropic diffusion (EED) filter-
ing. Thereafter, a volume mesh is generated using an adaptive, octree based scheme that
allows a locally heterogeneous resolution exploiting the concept of hanging nodes.
Mechanical FEM simulations are used to compute the stresses and strains arising in the
implant and the bone structure. Based on the results of the FEM simulations, new
therapeutic approaches for revision surgery are developed. With the help of optimisation
algorithms, a blue print of the mechanically optimal configuration of the cancellous bone
transplantation is computed to achieve fracture fusion.
Using these results the surgeon will be able to use a targeted approach with surgical inter-
vention only in those areas of the non union where load peaks of the bone–implant system
occur. With iterative automated optimisations and mechanical simulations we generate
also an patient specific implant model. The process integrates the biomechanical needs,
M. Roland, T. Dahmen, T. Tjardes, R. Otchwemah, P.Slusalleck and S. Diebels
i.e. optimal neutralisation of torsion loads, and the anatomical needs, i.e. minimally
invasive surgical technique, into the implant.
The resulting FEM model represents the individual patient fracture including the implant
that have been used to fix the fracture initially. This model will support the surgeon in
answering the key questions of a personalised therapeutic concept:
How much fusion area is necessary for the fracture?
Is the implant suitable for the fracture?
Does the patient need a customised implant?
Figure 1: Individual slice of the original computed tomography image (left); results of the segmentation
process of the same slice (middle); cut through the octree based volume mesh with hanging nodes structure
Figure 2: patient–specific volume mesh with implant and fracture area (left); von Mises stress of the
bone–implant system (right).
[1] J. Weickert. Anisotropic Diffusion in Image Processing. Teubner, 2005.
[2] J. M¨obius and L. Kobbelt. OpenFlipper: An Open Source Geometry Processing and
Rendering Framework. volume 6920 of Lecture Notes in Computer Science, Springer
Berlin / Heidelberg, 2012.
ResearchGate has not been able to resolve any citations for this publication.
In this work a scale-space framework has been presented which does not require any monotony assumption (comparison principle). We have seen that, besides the fact that many global smoothing scale-space properties are maintained, new possibilities with respect to image restoration appear. Rather than deducing a unique equation from first principles, we have analyzed well-posedness and scale-space properties of a general family of regularized anisotropic diffusion filters. Existence and uniqueness results, continuous dependence of the solution on the initial image, maximum-minimum principles, invariances, Lyapunov functionals, and convergence to a constant steady state have been established. The large class of Lyapunov functionals permits to regard these filters in numerous ways as simplifying, information-reducing transformations. These global smoothing properties do not contradict seemingly opposite local effects such its edge enhancement. For this reason it is possible to design scale-spaces with restoration properties giving segmentation-like results. Prerequisites have been stated under which one can prove well-posedness and scale-space results in the continuous, semidiscrete and discrete setting. Each of these frameworks stands on its own and does not require the others. On the other hand, the prerequisites in all three settings reveal many similarities and, as a consequence, representatives of the semidiscrete class can be obtained by suitable spatial discretizations of the continuous class, while representatives of the discrete class may arise from time discretizations of semidiscrete filters. The degree of freedom within the proposed class of filters can be used to tailor the filters towards specific restoration tasks. Therefore, these scale-spaces do not need to be uncommitted; they give the user the liberty to incorporate a-priori knowledge, for instance concerning size and contrast of especially interesting features. The analyzed class comprises linear diffusion filtering and the nonlinear isotropic model of Catté, Lions, Morel, Coll and Whitaker and Pizer, but also novel approaches have been proposed: The use of diffusion tensors instead of scalar-valued diffusivities puts us in a position to design real anisotropic diffusion processes which may reveal advantages at noisy edges. Last but not least, the fact that these filters are steered by the structure tensor instead of the regularized gradient allows to adapt them to more sophisticated tasks such as the enhancement of coherent flow-like structures. In view of these results, anisotropic diffusion deserves to be regarded as much more than all ad-hoc strategy for transforming a degraded image into a more pleasant looking one. It is a flexible and mathematically sound class of methods which ties the advantages of two worlds: scale-space analysis and image restoration.
Conference Paper
In this paper we present OpenFlipper, an extensible open source geometry processing and rendering framework. OpenFlipper is a free software toolkit and software development platform for geometry processing algorithms. It is mainly developed in the context of various academic research projects. Nevertheless some companies are already using it as a toolkit for commercial applications. This article presents the design goals for OpenFlipper, the central usability considerations and the important steps that were taken to achieve them. We give some examples of commercial applications which illustrate the flexibility of OpenFlipper. Besides software developers, end users also benefit from this common framework since all applications built on top of it share the same basic functionality and interaction metaphors.