Towards an Interactive Electromechanical Model of the Heart

International audienceIn this work, we develop an interactive framework for rehearsal and training in the context of cardiac catheter ablation, and for planning in the context of Cardiac Resynchronization Therapy (CRT). To this end, an interactive and real-time electrophysiology model of the heart is developed to fit patient-specific data. The proposed interactive framework relies on two main contributions. An efficient implementation of cardiac electrophysiology is first proposed using latest GPU computing techniques. Second, a mechanical simulation is then coupled to the electrophysiological signals to produce realistic motion of the heart. We demonstrate that pathological mechanical and electrophysiological behaviour can be simulated

Fast porous visco-hyperelastic soft tissue model for surgery simulation: Application to liver surgery

International audienceUnderstanding and modeling liver biomechanics represents a significant challenge due to its complex nature. In this paper, we tackle this issue in the context of real time surgery simulation where a compromise between biomechanical accuracy and computational efficiency must be found. We describe a realistic liver model including hyperelasticity, porosity and viscosity that is implemented within an implicit time integration scheme. To optimize its computation, we introduce the Multiplicative Jacobian Energy Decomposition (MJED) method for discretizing hyperelastic materials on linear tetrahedral meshes which leads to faster matrix assembly than the standard Finite Element Method. Viscohyperelasticity is modeled by Prony series while the mechanical eff ect of liver perfusion is represented with a linear Darcy law. Dynamic mechanical analysis has been performed on 60 porcine liver samples in order to identify some visco-elastic parameters. Finally, we show that liver deformation can be simulated in real-time on a coarse mesh and study the relative eff ects of the hyperelastic, viscous and porous components on the liver biomechanics

Evaluation of Personalised Canine Electromechanical Models

International audienceCardiac modelling aims at understanding cardiac diseases and predicting cardiac responses to therapies. By generating the elec-trical propagation, the contraction and the mechanical response, we are able to simulate cardiac motion from non-invasive imaging techniques. Four healthy canine clinical data (left ventricles) were provided by the STACOM'2014 challenge. Our study is based on Bestel-Clement-Sorine mechanical modelling, while the electrophysiological phenomena is driven by an Eikonal model. Our model has been calibrated by a quantitative sensitivity study as well as a personalized automatic calibration. Results and comparison with clinical measures are shown in terms of left ventricular volume, flow, pressure and ejection fraction

SOFA: A Multi-Model Framework for Interactive Physical Simulation

International audienceSOFA (Simulation Open Framework Architecture) is an open-source C++ library primarily targeted at interactive computational medical simulation. SOFA facilitates collaborations between specialists from various domains, by decomposing complex simulators into components designed independently and organized in a scenegraph data structure. Each component encapsulates one of the aspects of a simulation, such as the degrees of freedom, the forces and constraints, the differential equations, the main loop algorithms, the linear solvers, the collision detection algorithms or the interaction devices. The simulated objects can be represented using several models, each of them optimized for a different task such as the computation of internal forces, collision detection, haptics or visual display. These models are synchronized during the simulation using a mapping mechanism. CPU and GPU implementations can be transparently combined to exploit the computational power of modern hardware architectures. Thanks to this flexible yet efficient architecture, \sofa{} can be used as a test-bed to compare models and algorithms, or as a basis for the development of complex, high-performance simulators

Interactive Electromechanical Model of the Heart for Patient-Specific Therapy Planning and Training using SOFA

International audienceThe contributions of this work are twofold. First, we developed an electrophysiological training simulator in SOFA which tackles the interactive issue in the context of cardiac arrhythmias. Coupled with this electrophysiology, we developed a mechanical model of the heart that can be personalized from MRI datasets. Our simulations are based on the SOFA platform. SOFA is an open-source framework targeted at real-time simulation with an emphasis on medical simulation, mainly developed at Inria. A large choice of efficient solvers, hyperelastic or viscous material laws are already implemented in SOFA. Moreover, it enables interactivity during the simulation (pacing, surgery planning, ...) and gives a good trade-off between accuracy and computational efficiency

Non linear Biomechanical Model of the Liver: Hyperelastic Constitutive Laws for Finite Element Modeling

International audienceUnderstanding and modeling the liver biomechanics represent a significant challenge due to its complex nature. While many studies have been performed to fit hyperelastic constitutive laws on rheological experiments, they tend to agree about the importance of strain rate in the liver mechanical behavior. Furthermore, as the liver is heavily perfused with blood, its constitutive behavior is greatly porous. Supported by these observations, we developed a porous visco-hyperelastic model as a liver parenchyma material. More precisely, visco-hyperelasticity is obtained through Prony series while the mechanical effect of liver perfusion is represented with a linear Darcy's law. Since this mechanical model is developed in the context of real time surgery simulation, a compromise between biomechanical accuracy and computational efficiency must be found. We propose the Multiplicative Jacobian Energy Decomposition method (MJED) to obtain a fast assembly of stiffness matrices on linear tetrahedral elements

Fast Parameter Calibration of a Cardiac Electromechanical Model from Medical Images based on the Unscented Transform

International audiencePatient-specific cardiac modelling can help in understanding pathophysiology and predict therapy planning. However, it requires to personalize the model geometry, kinematics, electrophysiology and mechanics. Calibration aims at providing proper initial values of parameters before performing the personalization stage which involves solving an inverse problem. We propose a fast automatic calibration method of the mechanical parameters of a complete electromechanical model of the heart based on a sensitivity analysis and the Unscented Transform algorithm. A new implementation of the complete Bestel-Clement-Sorine (BCS) cardiac model is also proposed, in a modular and efficient framework. A complete sensitivity analysis is performed that reveals which observations on the volume evolution are significant to characterize the global behaviour of the myocardium. We show that the calibration method gives satisfying results by optimizing up to 5 parameters of the BCS model in only one iteration. This method was evaluated synthetically as well as on 7 volunteers with a mean relative error from the real data of 10 %. This calibration is designed to replace manual parameter estimation as well as initialization steps that precede automatic personalization algorithms based on images