Visual Haptic Feedback for Training of Robotic Suturing.

Current surgical robotic systems are teleoperated and do not have force feedback. Considerable practice is required to learn how to use visual input such as tissue deformation upon contact as a substitute for tactile sense. Thus, unnecessarily high forces are observed in novices, prior to specific robotic training, and visual force feedback studies demonstrated reduction of applied forces. Simulation exercises with realistic suturing tasks can provide training outside the operating room. This paper presents contributions to realistic interactive suture simulation for training of suturing and knot-tying tasks commonly used in robotically-assisted surgery. To improve the realism of the simulation, we developed a global coordinate wire model with a new constraint development for the elongation. We demonstrated that a continuous modeling of the contacts avoids instabilities during knot tightening. Visual cues are additionally provided, based on the computation of mechanical forces or constraints, to support learning how to dose the forces. The results are integrated into a powerful system-agnostic simulator, and the comparison with equivalent tasks performed with the da Vinci Xi system confirms its realism.

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.

Simulation of lipofilling reconstructive surgery using coupled Eulerian fluid and deformable solid models.

We present a method to simulate the outcome of reconstructive facial surgery based on fat-filling. Facial anatomy is complex: the fat is constrained between layers of tissues which behave as walls along the face; in addition, connective tissues that are present between these different layers also influence the fat-filling procedure. To simulate the end result, we propose a method which couples a 2.5D Eulerian fluid model for the fat and a finite element model for the soft tissues. The two models are coupled using the computation of the mechanical compliance matrix. Two contributions are presented in this paper: a solver for fluids which couples properties of solid tissues and fluid pressure, and an application of this solver to fat-filling surgery procedure simulation.

Preconditioner-based contact response and application to cataract surgery.

In this paper we introduce a new method to compute, in real-time, the physical behavior of several colliding soft-tissues in a surgical simulation. The numerical approach is based on finite element modeling and allows for a fast update of a large number of tetrahedral elements. The speed-up is obtained by the use of a specific preconditioner that is updated at low frequency. The preconditioning enables an optimized computation of both large deformations and precise contact response. Moreover, homogeneous and inhomogeneous tissues are simulated with the same accuracy. Finally, we illustrate our method in a simulation of one step in a cataract surgery procedure, which require to handle contacts with non homogeneous objects precisely.

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.

Volumetric modeling and interactive cutting of deformable bodies.

A new approach for the interactive simulation of viscoelastic object cutting is presented. Two synchronized geometrical models at different resolutions are used, both derived from medical images. In contrast with most previous approaches, the blade deforms the object, and cutting occurs once a contact pressure threshold is exceeded. Moreover, we achieve interactive simulation rates by embedding a high-resolution geometry within a regular grid with arbitrary resolution. This allows to trade off accuracy for speed in the computation of deformations. The input data is a high-resolution volumetric model of the objects. The surface model of the object, used for rendering as well as collision detection and response, is a polygonal level set of the volumetric data. It is embedded in the volume model using barycentric coordinates. Cutting is performed by removing voxels at the fine level, and updating the surface and volume models accordingly. We introduce a new data structure, which we call a Dynamic Branched Grid, in order to preserve the fine-level topology at the coarse level. When an element of the coarse volumetric model is cut, it is replaced by a number of superimposed elements with the same size and at the same rest position as the original one. Each new element is assigned a part of material contained in the original one, and the mass and stiffness are recomputed accordingly. The well-known problem of creating small, ill-shaped finite elements while remeshing is thus completely avoided.

Fiber-based fracture model for simulating soft tissue tearing.

In this paper, we propose a novel approach for simulating soft tissue tearing, using a model that takes into account the existence of fibers within the tissue. These fibers influence the deformation by introducing anisotropy, and impact the direction of propagation for the fracture during tearing. We describe our approach for simulating, in real-time, the deformation and fracture of anisotropic membranes, and we illustrate our method with the simulation of capsulorhexis, one of the critical steps of cataract surgery.

Toward real-time simulation of blood-coil interaction during aneurysm embolization.

Over the last decade, remarkable progress has been made in the field of endovascular treatment of aneurysms. Technological advances continue to enable a growing number of patients with cerebral aneurysms to be treated with a variety of endovascular strategies, essentially using detachable platinum coils. Yet, coil embolization remains a very complex medical procedure for which careful planning must be combined with advanced technical skills in order to be successful. In this paper we propose a method for computing the complex blood flow patterns that take place within the aneurysm, and for simulating the interaction of coils with this flow. This interaction is twofold, first involving the impact of the flow on the coil during the initial stages of its deployment, and second concerning the decrease of blood velocity within the aneurysm, as a consequence of coil packing. We also propose an approach to achieve real-time computation of coil-flow bilateral influence, necessary for interactive simulation. This in turns allows to dynamically plan coil embolization for two key steps of the procedure: choice and placement of the first coils, and assessment of the number of coils necessary to reduce aneurysmal blood velocity and wall pressure.

Real-time modeling of vascular flow for angiography simulation.

Interventional neuroradiology is a growing field of minimally invasive therapies that includes embolization of aneurysms and arteriovenous malformations, carotid angioplasty and carotid stenting, and acute stroke therapy. Treatment is performed using image-guided instrument navigation through the patient's vasculature and requires intricate combination of visual and tactile coordination. In this paper we present a series of techniques for real-time high-fidelity simulation of angiographic studies. We focus in particular on the computation and visualization of blood flow and blood pressure distribution patterns, mixing of blood and contrast agent, and high-fidelity simulation of fluoroscopic images.