Julien Lenoir

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. In this paper, we describe a series of novel approaches that have led 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 (FEM), an optimization strategy based on substructure decomposition, and a new method for handling collision response in situations where the number of contact 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. Although currently targeted at stroke therapy, our results are applicable to the simulation of any interventional radiology procedure.

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.

A layered model of a virtual human intestine for surgery simulation.

In this paper, we propose a new approach to simulate the small intestine in a context of laparoscopic surgery. The ultimate aim of this work is to simulate the training of a basic surgical gesture in real-time: moving aside the intestine to reach hidden areas of the abdomen. The main problem posed by this kind of simulation is animating the intestine. The problem comes from the nature of the intestine: a very long tube which is not isotropically elastic, and is contained in a volume that is small when compared to the intestines length. It coils extensively and collides with itself in many places. To do this, we use a layered model to animate the intestine. The intestines axis is animated as a linear mechanical component. A specific sphere-based model handles contacts and self-collisions. A skinning model is used to create the intestines volume around the axis. This paper discusses and compares three different representations for skinning the intestine: a parametric surface model and two implicit surface models. The first implicit surface model uses point skeletons while the second uses local convolution surfaces. Using these models, we obtained good-looking results in real-time. Some videos of this work can be found in the online version at doi: 10.1016/j.media.2004.11.006 and at www-imagis.imag.fr/Publications/2004/FLAMCFC04.

A Suture Model for Surgical Simulation

In this paper, we propose a surgical thread model in order for surgeons to practice a suturing task. We first model the thread as a spline animated by continuous mechanics. The suture is simulated via so-called “sliding point” constraints, which allow the spline to move freely while constrained to pass through specific piercing points. The direction of the spline at these points can also be imposed. Moreover, to enhance realism, an adapted model of friction is proposed, which allows the thread to remain fixed at the piercing point or slides through it. Our model yields to good results showing realistic behavior, robust computation and interactive rates.

A physically-based virtual environment dedicated to surgical simulation

In this paper, we present a system dedicated to the simulation of various physically-based and mainly deformable objects. Its main purpose is surgical simulation where many models are necessary to simulate the organs and the users tools. In our system, we found convenient to decompose each simulated model in three units: The mechanical, the visual and the collision units. In practice, only the third unit is actually constrained, since we want to process collisions in a unified way. We choose to rely on a fast penalty-based method which uses approximation of the objects depth map by spheres. The simulation is sufficiently fast to control force feedback devices.

Mixing deformable and rigid-body mechanics simulation

This article presents a new method to achieve heterogeneous physical simulation, within the same global system, of both deformable and rigid-bodies objects, whatever their intrinsic nature. The proposed approach combines several mechanical formalisms in the same system and offers a common constraint management via Lagrange multipliers. This allows the simulation of a wide variety of models, including deformable and rigid pans linked by constraints. Some applications of this approach are presented to show its effectiveness

Adaptive resolution of 1D mechanical B-spline

This article presents an adaptive approach to B-spline curve physical simulation. We combine geometric refinement and coarsening techniques with an appropriate continuous mechanical model. We thus deal with the (temporal and geometric) continuity issues implied when mechanical adaptive resolution is used. To achieve real-time local adaptation of spline curves, some criteria and optimizations are shown. Among application examples, real-time knot tying is presented, and curve cutting is also pointed out as a nice side-effect of the adaptive resolution animation framework.

Interactive contacts resolution using smooth surface representation

Accurately describing interactions between medical devices and anatomical structures, or between anatomical structures themselves, is an essential step towards the adoption of computer-based medical simulation as an alternative to traditional training methods. However, while substantial work has been done in the area of real-time soft tissue modeling, little has been done to study the problem of contacts occurring during tissue manipulation. In this paper we introduce a new method for correctly handling complex contacts between various combination of rigid and deformable objects. Our approach verifies Signorinis law by combining Lagrange multipliers and the status method to solve unilateral constraints. Our method handles both concave and convex surfaces by using a displacement subdivision strategy, and the proposed algorithm allows interactive computation times even in very constrained situations. We demonstrate the efficiency of our approach in the context of interventional radiology, with the navigation of catheters and guidewires in tortuous vessels and with the deployment of coils to treat aneurysms.