Non-Linear Anisotropic Elasticity for Real-Time Surgery Simulation

In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. A key problem with such a simulator is the physical modeling of soft tissues. We propose a new deformable model based on non-linear elasticity, anisotropic behavior, and the finite element method. This model is valid for large displacements, which means in particular that it is invariant with respect to rotations. This property improves the realism of the deformations and solves the problems related to the shortcomings of linear elasticity, which is only valid for small displacements. We also address the problem of volume variations by adding to our model incompressibility constraints. Finally, we demonstrate the relevance of this approach for the real-time simulation of laparoscopic surgical gestures on the liver

Improving Realism of a Surgery Simulator : Linear Anisotropic Elasticity, Complex Interactions and Force Extrapolation

In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed for performing laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that contribute to improve the overall realism of our simulator. First, we have developed bio-mechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behavior of anatomical models to "transversally isotropic" materials, i.e. materials having a different behavior in one given direction. We have also added to the volumetric model an external elastic membrane standing for the "liver capsule", a quite stiff skin surrounding the liver and creating a kind of "surface anisotropy". Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently , we are able to achieve a simulation frequency of 25Hz (visual real-time) with anatomical models of complex geometry and behavior. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300Hz (haptic real-time). Thus, we propose a force extrapolat- ion algorithm in order to reach haptic real-time

Improving realism of a surgery simulator: linear anisotropic elasticity, complex interactions and force extrapolation

International audienceIn this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed to perform laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that improve the overall realism of our simulator. First, we have developed biomechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behaviour of anatomical models to 'transversally isotropic' materials, i.e. materials having a different behaviour in a given direction. We have also added to the volumetric model an external elastic membrane representing the 'liver capsule', a rather stiff skin surrounding the liver, which creates a kind of 'surface anisotropy'. Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently, we are able to achieve a simulation frequency of 25 Hz (visual real time) with anatomical models of complex geometry and behaviour. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300 Hz (haptic real time). Thus, we propose a force extrapolation algorithm in order to reach haptic real time

Modèles géométriques et physiques pour la simulation d'interventions chirurgicales

In this thesis, we propose a set of tools necessary for the development of a surgery simulator. First, we define several real-time physically based deformable models allowing us to simulate the deformations and the cutting of human organs. These models are based on the theory of elasticity and the finite element method. We began with the improvement of the linear elastic model by generalizing it to materials having an anisotropic behavior, either because they contain fibers (muscles, tendons), or because they are surrounded by a skin (liver capsule). Nevertheless, the main shortcoming of linear elasticity is that it is only valid under the hypothesis of small displacements. Thus, we propose a new deformable model implementing the St Venant-Kirchhoff non-linear elasticity, which is also valid for large displacements. After having extended this model to anisotropic materials, we propose two optimization methods, either using an adaptive algorithm which combines linear and non-linear models, or implementing a new formulation. The second part of this work is dedicated to the simulation of the interactions between the surgical tools and the virtual organs. For this, we have modelized contacts and some special gestures like sliding, gripping, or cutting. Furthermore, we have addressed the problems related to the use of force feedback devices.Dans cette thèse, nous proposons un ensemble d'outils nécessaires à l'élaboration d'un simulateur de chirurgie. Dans un premier temps, nous définissons plusieurs modèles déformables physiques temps réels permettant de simuler les déformations et la découpe d'organes du corps humain. Ces modèles s'appuient sur la théorie de l'élasticité et la méthode des éléments finis. Nous avons tout d'abord travaillé sur l'enrichissement du modèle élastique linéaire en le généralisant au cas des matériaux dont le comportement est anisotrope, soit en raison de la présence de fibres (muscles, tendons), soit parce qu'ils sont entourés d'une peau (capsule de Glisson pour le foie). Cependant, la principale limitation de l'élasticité linéaire est de n'être valable que dans l'hypothèse de petits déplacements. Nous proposons donc un nouveau modèle déformable mettant en oeuvre l'élasticité non-linéaire de St Venant-Kirchhoff, qui reste valable pour les grands déplacements. Après avoir étendu ce modèle aux matériaux anisotropes, nous proposons plusieurs méthodes d'optimisation des calculs, soit en utilisant un algorithme adaptatif qui combine les modèles linéaires et non-linéaires, soit à partir d'une nouvelle formulation. La seconde partie de ces travaux porte sur la simulation des interactions entre les instruments chirurgicaux et les organes virtuels. Pour cela, nous avons modélisé les contacts, ainsi que certaines actions spécifiques comme le glissement, la préhension et la découpe. De plus, nous nous sommes intéressés aux problèmes liés à l'utilisation d'interfaces à retour d'effort

Extrapolation: A Solution for Force Feedback?

Using a force feedback device within the framework of deformable object simulation remains difficult because of the incompatibility between the computation time needed by realistic deformable models and high refresh frequencies necessary for real-time haptic rendering. Giving the user a good haptic sensation requires refreshing the applied forces at least ten times more often than for giving a good visual sensation. Even though visually interactive deformable models exists, they can not be directly used for haptic rendering. We suggest, in this paper, to extrapolate the forces computed by the deformable model to go beyond interactivity to haptic real-time

Modèles géométriques et physiques pour la simulation d'interventions chirurgicales

Dans cette thèse, nous proposons un ensemble d'outils nécessaires à l'élaboration d'un simulateur de chirurgie. Dans un premier temps, nous définissons plusieurs modèles déformables physiques temps réels permettant de simuler les déformations et la découpe d'organes du corps humain. Ces modèles s'appuient sur la théorie de l'élasticité et la méthode des éléments finis. Nous avons tout d'abord travaillé sur l'enrichissement du modèle élastique linéaire en le ge néralisant au cas des matériaux dont le comportement est anisotrope, soit en raison de la présence de fibres (muscles, tendons), soit parce qu'ils sont entourés d'une peau (capsule de Glisson pour le foie). Cependant, la principale limitation de l'élasticité linéaire est de n'être valable que dans l'hypothèse de petits déplacements. Nous proposons donc un nouveau modèle déformable mettant en oeuvre l'élasticité non-linéaire de St Venant-Kirchhoff, qui reste valable pour les grands déplacements. Après avoir étendu ce modèle aux matériaux anisotropes, nous proposons plusieurs méthodes d'optimisation des calculs, soit en utilisant un algorithme adaptatif qui combine les modèles linéaires et non-linéaires, soit à partir d'une nouvelle formulation. La seconde partie de ces travaux porte sur la simulation des interactions entre les instruments chirurgicaux et les organes virtuels. Pour cela, nous avons modélisé les contacts, ainsi que certaines actions spécifiques comme le glissement, la préhension et la découpe. De plus, nous nous sommes intéressés aux problèmes liés à l'utilisation d'interfaces à retour d'effort.NICE-BU Sciences (060882101) / SudocSudocFranceF

Non-Linear Anisotropic Elasticity for Real-Time Surgery Simulation

In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. A key problem with such a simulator is the physical modeling of soft tissues. We propose a new deformable model based on non-linear elasticity, anisotropic behavior, and the #nite element method. This model is valid for large displacements, which means in particular that it is invariant with respect to rotations. This property improves the realism of the deformations and solves the problems related to the shortcomings of linear elasticity, which is only valid for small displacements. We also address the problem of volume variations by adding to our model incompressibility constraints. Finally, we demonstrate the relevance of this approach for the real-time simulation of laparoscopic surgical gestures on the liver

Modèle déformable élastique non-linéaire pour la simulation de chirurgie en temps réel

National audienceno abstrac

Non-Linear Anisotropic Elasticity for Real-Time Surgery Simulation

International audienceno abstrac

Non-linear and anisotropic elastic soft tissue models for medical simulation

Best conference paper awardInternational audienceno abstrac