Publications of Christoph Paulus

Publications HAL de paulus de la structure shacra;mimesis

2017

Conference papers

titre
Face-based Smoothed Finite Element Method for Real-time Simulation of soft tissue
auteur
Andrea Mendizabal, Rémi Duparc, Huu Phuoc Bui, Christoph Paulus, Igor Peterlik, Stéphane Cotin
article
SPIE Medical Imaging, Feb 2017, Orlando, United States. SPIE Medical Imaging
resume
In soft tissue surgery, a tumor and other anatomical structures are usually located using the preoperative CT or MR images. However, due to the deformation of the concerned tissues, this information suffers from inaccuracy when employed directly during the surgery. In order to account for these deformations in the planning process, the use of a bio-mechanical model of the tissues is needed. Such models are often designed using the finite element method (FEM), which is, however, computationally expensive, in particular when a high accuracy of the simulation is required. In our work, we propose to use a smoothed finite element method (S-FEM) in the context of modeling of the soft tissue deformation. This numerical technique has been introduced recently to overcome the overly stiff behavior of the standard FEM and to improve the solution accuracy and the convergence rate in solid mechanics problems. In this paper, a face-based smoothed finite element method (FS-FEM) using 4-node tetrahedral elements is presented. We show that in some cases, the method allows for reducing the number of degrees of freedom, while preserving the accuracy of the discretization. The method is evaluated on a simulation of a cantilever beam loaded at the free end and on a simulation of a 3D cube under traction and compression forces. Further, it is applied to the simulation of the brain shift and of the kidney’s deformation. The results demonstrate that the method outperforms the standard FEM in a bending scenario and that has similar accuracy as the standard FEM in the simulations of brain shift and kidney deformation.
Accès au texte intégral et bibtex
https://hal.inria.fr/hal-01444595/file/SPIE2017.pdf BibTex

Theses

titre
Topological Changes in Simulations of Deformable Objects
auteur
Christoph Paulus
article
Modeling and Simulation. University of Strasbourg, 2017. English
resume
Virtual cutting of deformable objects is at the core of many applications in interactive simulation and especially in computational medicine. The ability to simulate surgical cuts, soft tissue tearing or fractures, is essential for augmenting the capabilities of existing or future simulation systems. In this thesis, we present a new remeshing algorithm based on the finite element method. For tetrahedral elements with linear shape functions, we combined remeshing algorithm with the movement of the nodes to the cutting surface, called snapping in the literature. Our approach shows benefits when evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. When applying our remeshing algorithm to quadratic shape functions, we observe similar results. Due to the curved surfaces of the elements, when using quadratic shape functions, the snapping of nodes entails higher challenges. Thus, to investigate into the snapping, experience has been gathered on triangular shell elements, simulating fractures. Beyond the simulation of fractures, our remeshing approach for tetrahedral elements is generic enough to support a large variety of applications. In this work, we are the first to present results on the detection of topological changes, such as fractures, tearing and cutting, from a monocular video stream. Ex amples with highly elastic silicone bands, in-vivo livers and ex-vivo kidneys show the robustness of our detection algorithm, which is combined with the remeshing approach, in different scenarios. Finally, the augmentation of internal organ structures highlights the clinical potential and importance of the conducted work.
Accès au texte intégral et bibtex
https://hal.inria.fr/tel-01516170/file/PhD%20Thesis%20Christoph%20Joachim%20PAULUS%202017.pdf BibTex

2016

Journal articles

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titre
Handling Topological Changes during Elastic Registration: Application to Augmented Reality in Laparoscopic Surgery
auteur
Christoph Joachim Paulus, Nazim Haouchine, Seong-Ho Kong, Renato Vianna Soares, David Cazier, Stéphane Cotin
article
International Journal of Computer Assisted Radiology and Surgery (IJCARS), Springer, 2016
resume
Purpose: Locating the internal structures of an organ is a critical aspect of many surgical procedures. Minimally invasive surgery, associated with augmented reality techniques, offers the potential to visualize inner structures, allowing for improved analysis, depth perception or for supporting planning and decision systems. Methods: Most of the current methods dealing with rigid or non-rigid augmented reality make the assumption that the topology of the organ is not modified. As surgery relies essentially on cutting and dissection of anatomical structures, such methods are limited to the early stages of the surgery. We solve this shortcoming with the introduction of a method for physics-based elastic registration using a single view from a monocular camera. Singularities caused by topological changes are detected and propagated to the pre-operative model. This significantly improves the coherence between the actual laparoscopic view and the model, and provides added value in terms of navigation and decision-making, e.g. by overlaying the internal structures of an organ on the laparoscopic view. Results: Our real time augmentation method is assessed on several scenarios, using synthetic objects and real organs. In all cases, the impact of our approach is demonstrated, both qualitatively and quantitatively. Conclusion: The presented approach tackles the challenge of localizing internal structures throughout a complete surgical procedure, even after surgical cuts. This information is crucial for surgeons to improve the outcome for their surgical procedure and avoid complications.
Accès au texte intégral et bibtex
https://hal.inria.fr/hal-01397409/file/ijcars2016.pdf BibTex

2015

Journal articles

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titre
Virtual Cutting of Deformable Objects based on Efficient Topological Operations
auteur
Christoph Paulus, Lionel Untereiner, Hadrien Courtecuisse, Stephane Cotin, David Cazier
article
Visual Computer, Springer Verlag, 2015, 31 (6-8), pp.831-841. <10.1007/s00371-015-1123-x>
resume
Virtual cutting of deformable objects is at the core of many applications in interactive simulation and especially in computational medicine. The ability to simulate surgical cuts, dissection, soft tissue tearing ormicro-fractures is essential for augmenting the capabilities of existing or future simulation systems. To support such features,we combine a new remeshing algorithm with a fast finite element approach. The proposed method is generic enough to support a large variety of applications. We show the benefits of our approach evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. These points are crucial to ensure accurate and stable real-time simulations.
Accès au texte intégral et bibtex
https://hal.archives-ouvertes.fr/hal-01162099/file/2015CGI.pdf BibTex

Conference papers

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titre
Surgical Augmented Reality with Topological Changes
auteur
Christoph Paulus, Nazim Haouchine, David Cazier, Stéphane Cotin
article
Medical Image Computing and Computer Assisted Interventions, Oct 2015, München, Germany. <http://miccai2015.org/>
resume
The visualization of internal structures of organs in minimally invasive surgery is an important avenue for improving the perception of the surgeon, or for supporting planning and decision systems. However, current methods dealing with non-rigid augmented reality only provide augmentation when the topology of the organ is not modified. In this paper we solve this shortcoming by introducing a method for physics-based non-rigid augmented reality. Singularities caused by topo-logical changes are detected and propagated to the pre-operative model. This significantly improves the coherence between the actual laparascopic view and the model, and provides added value in terms of navigation and decision making. Our real time augmentation algorithm is assessed on a video showing the cut of a porcine liver’s lobe in minimal invasive surgery.
Accès au texte intégral et bibtex
https://hal.inria.fr/hal-01184498/file/2015MICCAI.pdf BibTex
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titre
Augmented Reality during Cutting and Tearing of Deformable Objects
auteur
Christoph Paulus, Nazim Haouchine, David Cazier, Stephane Cotin
article
The 14th IEEE International Symposium on Mixed and Augmented Reality, Sep 2015, Fukuoka, Japan. pp.6
resume
Current methods dealing with non-rigid augmented reality only provide an augmented view when the topology of the tracked object is not modified, which is an important limitation. In this paper we solve this shortcoming by introducing a method for physics-based non-rigid augmented reality. Singularities caused by topological changes are detected by analyzing the displacement field of the underlying deformable model. These topological changes are then applied to the physics-based model to approximate the real cut. All these steps, from deformation to cutting simulation, are performed in real-time. This significantly improves the coherence between the actual view and the model, and provides added value.
Accès au texte intégral et bibtex
https://hal.inria.fr/hal-01184495/file/2015ISMAR.pdf BibTex
titre
Virtual Cutting of Deformable Objects based on Efficient Topological Operations
auteur
Christoph Paulus, Lionel Untereiner, Hadrien Courtecuisse, Stéphane Cotin, David Cazier
article
Computer Graphics International, 2015, Strasbourg, France. 2015
resume
Virtual cutting of deformable objects is at the core of many applications in interactive simulation and especially in computational medicine. The ability to simulate surgical cuts, dissection, soft tissue tearing ormicro-fractures is essential for augmenting the capabilities of existing or future simulation systems. To support such features,we combine a new remeshing algorithm with a fast finite element approach. The proposed method is generic enough to support a large variety of applications. We show the benefits of our approach evaluating the impact of cuts on the number of nodes and the numerical quality of the mesh. These points are crucial to ensure accurate and stable real-time simulations.
Accès au bibtex
BibTex