Christian Duriez

GPU-based Real-Time Soft Tissue Deformation with Cutting and Haptic Feedback

This article describes a series of contributions in the field of real-time simulation of soft tissue biomechanics. These contributions address various requirements for interactive simulation of complex surgical procedures. In particular, this article presents results in the areas of soft tissue deformation, contact modelling, simulation of cutting, and haptic rendering, which are all relevant to a variety of medical interventions. The contributions described in this article share a common underlying model of deformation and rely on GPU implementations to significantly improve computation times. This consistency in the modelling technique and computational approach ensures coherent results as well as efficient, robust and flexible solutions.

Virtual Reality Interaction and Physical Simulation: Interactive physically-based simulation of catheter and guidewire

For over 20 years, interventional methods have improved the outcomes of patients with cardiovascular disease or stroke. However, these procedures require an intricate combination of visual and tactile feedback and extensive training periods. An essential part of this training relates to catheter or guidewire manipulation. In this paper, we propose a composite model to realistically simulate a catheter, a guidewire or a combination of both. Where a physics-based simulation of both devices would be computationally prohibitive and would require to deal with a large number of contacts, we propose to address this problem by replacing both objects by a composite model. This model has a dual visual representation and can dynamically change its material properties to locally describe a combination of both devices. Results show that the composite model exhibits the same characteristics of a catheter/guidewire combination while maintaining real-time interaction.

SOFA: A Multi-Model Framework for Interactive Physical Simulation

Simulation Open Framework Architecture (SOFA) 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.

Real-time simulation of contact and cutting of heterogeneous soft-tissues

This paper presents a numerical method for interactive (real-time) simulations, which considerably improves the accuracy of the response of heterogeneous soft-tissue models undergoing contact, cutting and other topological changes. We provide an integrated methodology able to deal both with the ill-conditioning issues associated with material heterogeneities, contact boundary conditions which are one of the main sources of inaccuracies, and cutting which is one of the most challenging issues in interactive simulations. Our approach is based on an implicit time integration of a non-linear finite element model. To enable real-time computations, we propose a new preconditioning technique, based on an asynchronous update at low frequency. The preconditioner is not only used to improve the computation of the deformation of the tissues, but also to simulate the contact response of homogeneous and heterogeneous bodies with the same accuracy. We also address the problem of cutting the heterogeneous structures and propose a method to update the preconditioner according to the topological modifications. Finally, we apply our approach to three challenging demonstrators: (i) a simulation of cataract surgery (ii) a simulation of laparoscopic hepatectomy (iii) a brain tumor surgery.

Control of elastic soft robots based on real-time finite element method

In this paper, we present a new method for the control of soft robots with elastic behavior, piloted by several actuators. The central contribution of this work is the use of the Finite Element Method (FEM), computed in real-time, in the control algorithm. The FEM based simulation computes the nonlinear deformations of the robots at interactive rates. The model is completed by Lagrange multipliers at the actuation zones and at the end-effector position. A reduced compliance matrix is built in order to deal with the necessary inversion of the model. Then, an iterative algorithm uses this compliance matrix to find the contribution of the actuators (force and/or position) that will deform the structure so that the terminal end of the robot follows a given position. Additional constraints, like rigid or deformable obstacles, or the internal characteristics of the actuators are integrated in the control algorithm. We illustrate our method using simulated examples of both serial and parallel structures and we validate it on a real 3D soft robot made of silicone.

Constraint-Based Haptic Rendering of Multirate Compliant Mechanisms

The paper is dedicated to haptic rendering of complex physics-based environment in the context of surgical simulation. A new unified formalism for modeling the mechanical interactions between medical devices and anatomical structures and for computing accurately the haptic force feedback is presented. The approach deals with the mechanical interactions using appropriate force and/or motion transmission models named compliant mechanisms. These mechanisms are formulated as a constraint-based problem that is solved in two separate threads running at different frequencies. The first thread processes the whole simulation including the soft-tissue deformations, whereas the second one only deals with computer haptics. This method builds a bridge between the so-called virtual mechanisms (that were proposed for haptic rendering of rigid bodies) and intermediate representations (used for rendering of complex simulations). With this approach, it is possible to describe the specific behavior of various medical devices while relying on a unified method for solving the mechanical interactions between deformable objects and haptic rendering. The technique is demonstrated in interactive simulation of flexible needle insertion through soft anatomical structures with force feedback.

Contact Model for Haptic Medical Simulations

In surgery simulation, precise contact modeling is essential to obtain both realistic behavior and convincing haptic feedback. When instruments create deformations on soft tissues, they modify the boundary conditions of the models and will mainly modify their behavior. Yet, most recent work has focused on the more precise modeling of soft tissues while improving efficiency; but this effort is ruined if boundary conditions are ill-defined. In this paper, we propose a novel and very efficient approach for precise computation of the interaction between organs and instruments. The method includes an estimation of the contact compliance of the concerned zones of the organ and of the instrument. This compliance is put in a buffer and is the heart of the multithreaded local model used for haptics. Contact computation is then performed in both simulation and haptic loops. It follows unilateral formulation and allows realistic interactions on non-linear models simulated with stable implicit scheme of time integration. An iterative solver, initialized with the solution found in the simulation, allows for fast computation in the haptic loop. We obtain realistic and physical results for the simulation and stable haptic rendering.

Interactive Simulation of Embolization Coils: Modeling and Experimental Validation

Coil embolization offers a new approach to treat aneurysms. This medical procedure is namely less invasive than an open-surgery as it relies on the deployment of very thin platinum-based wires within the aneurysm through the arteries. When performed intracranially, this procedure must be particularly accurate and therefore carefully planned and performed by experienced radiologists. A simulator of the coil deployment represents an interesting and helpful tool for the physician by providing information on the coil behavior. In this paper, an original modeling is proposed to obtain interactive and accurate simulations of coil deployment. The model takes into account geometric nonlinearities and uses a shape memory formulation to describe its complex geometry. An experimental validation is performed in a contact-free environment to identify the mechanical properties of the coil and to quantitatively compare the simulation with real data. Computational performances are also measured to insure an interactive simulation.

New approaches to catheter navigation for interventional radiology simulation

For over 20 years, interventional methods have improved the outcomes of patients with cardiovascular disease. However, these procedures require an intricate combination of visual and tactile feedback and extensive training periods. In this paper, we describe a series of novel approaches that have lead to the development of a high-fidelity simulation system for interventional neuroradiology. In particular we focus on a new approach for real-time deformation of devices such as catheters and guidewires during navigation inside complex vascular networks. This approach combines a real-time incremental Finite Element Model, an optimization strategy based on substructure decomposition, and a new method for handling collision response in situations where the number of contacts points is very large. We also briefly describe other aspects of the simulation system, from patient-specific segmentation to the simulation of contrast agent propagation and fast volume rendering techniques for generating synthetic X-ray images in real-time.

Interactive Simulation of Flexible Needle Insertions Based on Constraint Models

This paper presents a new modeling method for the insertion of needles and more generally thin and flexible medical devices into soft tissues. Several medical procedures rely on the insertion of slender medical devices such as biopsy, brachytherapy, deep-brain stimulation. In this paper, the interactions between soft tissues and flexible instruments are reproduced using a set of dedicated complementarity constraints. Each constraint is positionned and applied to the deformable models without requiring any remeshing. Our method allows for the 3D simulation of different physical phenomena such as puncture, cutting, static and dynamic friction at interactive frame rate. To obtain realistic simulation, the model can be parametrized using experimental data. Our method is validated through a series of typical simulation examples and new more complex scenarios.