A Sketch-Based Interface for Annotation of 3D Brain Vascular Reconstructions

Within the medical imaging community, 3D models of anatomical structures are now widely used in order to establish more accurate diagnoses than those based on 2D images. Many research works focus on an automatic process to build such 3D models. However automatic reconstruction induces many artifacts if the anatomical structure exhibits tortuous and thin parts (such as vascular networks) and the correction of these artifacts involves 3D-modeling skills and times that radiologists do not have. This article presents a semi-automatic approach to build a correct topology of vascular networks from 3D medical images. The user interface is based on sketching; user strokes both defines a command and the part of geometry where the command is applied to. Moreover the user-gesture speed is taken into account to adjust the command: a slow and precise gesture will correct a local part of the topology while a fast gesture will correct a larger part of the topology. Our system relies on an automatic segmentation that provides a initial guess that the user can interactively modify using the proposed set of commands. This allows to correct the anatomical aberrations or ambiguities that appear on the segmented model in a few strokes.Dans le domaine de l'imagerie médicale, la modélisation 3D de structures anatomiques est maintenant largement utilisée dans l'optique d'é}tablir des diagnostics plus précis qu'avec des données basées sur des images 2D. Aujourd'hui, de nombreux travaux mettent l'accent sur les méthodes automatique de reconstruction de modèles 3D mais ces méthodes induisent de nombreuses erreurs. Avec une structure anatomique (réseau cérébral) présente des parties assez fines et tortueuses, des erreurs sont introduites, cela nécessitent de la correction du modèle 3D, mais aussi des compétences et des heures que les radiologistes ne possèdent pas. Cet article présente une approche semi-automatique de reconstruction d'une topologie correcte de réseaux vasculaires issus d'images médicales en 3D. Notre système repose sur une segmentation automatique qui fournit une estimation initiale dont l'utilisateur peut modifier interactivement en utilisant un jeu proposé de commandes basées sur le croquis. Cela permet de corriger les aberrations anatomiques ou les ambiguïtés qui apparaissent sur le modèle segmenté en quelques traits

Asynchronous Interactive Physical Simulation

This document introduces a multi-agent framework for real-time physical simulation. Unlike classical physical simulators, no shared discrete time-line is imposed to simulated objects. Each simulated object is an autonomous agent that can maintain its simulation state, and possibly modify its behavior by checking its environment. Decision schemes are proposed that enable objects to locally adapt their computation time, in order to maintain approximate global synchronization. Results and measures are presented, especially regarding time management and simulation synchronization in regard of classical simulation methods. Examples are shown, outlining some of the practical advantages such a framework provides

Refining the 3D surface of blood vessels from a reduced set of 2D DSA images

International audienceNumerical simulations, such as blood flow or coil deployment in an intra-cranial aneurism, are very sensitive to the boundary conditions given by the surface of the vessel walls. Despite the undisputable high quality of 3D vascular imaging modalities, artifacts and noise still hamper the extraction of this surface with enough accuracy. Previous studies took the a priori that a homogeneous object was considered to make the reconstruction from the Xray images more robust. Here, an active surface approach is described, that does not depend on any particular image similarity criterion and grounds on high speed computation of the criterion derivatives. Mean square error and normalized cross-correlation are used to successfully demonstrate our algorithm on real images acquired on an anthropomorphic phantom. Preliminary results of coil deployment simulation are also given

A (Near) Real-Time Simulation Method of Aneurysm Coil Embolization

International audienceA (Near) Real-Time Simulation Method of Aneurysm Coil Embolizatio

Deformation-based Augmented Reality for Hepatic Surgery

International audienceIn this paper we introduce a method for augmenting the laparoscopic view during hepatic tumor resection. Using augmented reality techniques, vessels, tumors and cutting planes computed from pre-operative data can be overlaid onto the laparoscopic video. Compared to current techniques, which are limited to a rigid registration of the pre-operative liver anatomy with the intra-operative image, we propose a real-time, physics-based, non-rigid registration. The main strength of our approach is that the deformable model can also be used to regularize the data extracted from the computer vision algorithms. We show preliminary results on a video sequence which clearly highlights the interest of using physics-based model for elastic registration

Haptic Rendering of Interacting Dynamic Deformable Objects Simulated in Real-Time at Different Frequencies

International audienceThe dynamic response of deformable bodies varies significantly in dependence on mechanical properties of the objects: while the dynamics of a stiff and light object (e. g. wire or needle) involves high-frequency phenomena such as vibrations, much lower frequencies are sufficient for capturing dynamic response of an object composed of a soft tissue. Yet, when simulating mechanical interactions between soft and stiff deformable models, a single time-step is usually employed to compute the time integration of dynamics of both objects. However, this can be a serious issue when haptic rendering of complex scenes composed of various bodies is considered. In this paper, we present a novel method allowing for dynamic simulation of a scene composed of colliding objects modelled at different frequencies: typically, the dynamics of soft objects are calculated at frequency about 50 Hz, while the dynamics of stiff object is modeled at 1 kHz, being directly connected to the computation of haptic force feedback. The collision response is performed at both low and high frequencies employing data structures which describe the actual constraints and are shared between the high and low frequency loops. During the simulation, the realistic behaviour of the objects according to the mechanical principles (such as non-interpenetration and action-reaction principle) is guaranteed. Examples showing the scenes involving different bodies in interaction are given, demonstrating the benefits of the proposed method

Single View Augmentation of 3D Elastic Objects

International audienceThis paper proposes an efficient method to capture and augment highly elastic objects from a single view. 3D shape recovery from a monocular video sequence is an underconstrained problem and many approaches have been proposed to enforce constraints and resolve the ambiguities. State-of-the art solutions enforce smoothness or geometric constraints, consider specific deformation properties such as inextensibility or ressort to shading constraints. However, few of them can handle properly large elastic deformations. We propose in this paper a real-time method which makes use of a me chanical model and is able to handle highly elastic objects. Our method is formulated as a energy minimization problem accounting for a non-linear elastic model constrained by external image points acquired from a monocular camera. This method prevents us from formulating restrictive assumptions and specific constraint terms in the minimization. The only parameter involved in the method is the Young's modulus where we show in experiments that a rough estimate of its value is sufficient to obtain a good reconstruction. Our method is compared to existing techniques with experiments conducted on computer-generated and real data that show the effectiveness of our approach. Experiments in the context of minimally invasive liver surgery are also provided

Réalité augmentée pour la chirurgie minimalement invasive du foie utilisant un modèle biomécanique guidé par l'image

National audienceCet article présente une méthode de réalité augmentée pour la chirurgie minimalement invasive du foie. Le réseau vasculaire et les tumeurs internes reconstruites à partir des données pré-opératoires (IRM ou CT) peuvent ainsi être visualisées dans l'image laparoscopique afin de guider les gestes du chirurgien pendant l'opération. Cette méthode est capable de propager les déformations 3D de la surface du foie à ses structures internes grâce à un modèle biomécanique sous-jacent qui prend en compte l'anisotropie et l'hétérogénéité du tissu hépatique. Des résultats sont montrés sur une vidéo in-vivo d'un foie humain acquise pendant une opération et sur un foie en silicone

Vision-Based Sensing of External Forces Acting on Soft Robots Using Finite Element Method

International audienceIn this paper, we propose a new framework of external force sensing for soft robots based on the fusion of vision-based measurements and Finite Element Model (FEM) techniques. A precise mechanical model of the robot is built using real-time FEM to describe the relationship between the external forces acting on the robot and the displacement of predefined feature points. The position of these feature points on the real robot is measured using a vision system and is compared with the equivalent feature points in the finite element model. Using the compared displacement, the intensities of the external forces are computed by solving an inverse problem. Based on the developed FEM equations, we show that not only the intensities but also the locations of the external forces can be estimated. A strategy is proposed to find the correct locations of external forces among several possible ones. The method is verified and validated using both simulation and experiments on a soft sheet and a parallel soft robot (both of them have non-trivial shapes). The good results obtained from the experimental study demonstrate the capability of our approach

Introducing interactive inverse FEM simulation and its application for adaptive radiotherapy

International audienceWe introduce a new methodology for semi-automatic deformable registration of anatomical structures, using interactive inverse simulations. The method relies on non-linear real-time Finite Element Method (FEM) within a constraint-based framework. Given a set of few registered points provided by the user, a real-time optimization adapts the boundary conditions and(/or) some parameters of the FEM in order to obtain the adequate geometrical deformations. To dramatically fasten the process, the method relies on a projection of the model in the space of the optimization variables. In this reduced space, a quadratic programming problem is formulated and solved very quickly. The method is validated with numerical examples for retrieving Young's modulus and some pressures on the boundaries. Then, we apply the approach for the registration of the parotid glands during the radiotherapy of the head and neck cancer. Radiotherapy treatment induces weight loss that modifi es the shape and the positions of these structures and they eventually intersect the target volume. We show how we could adapt the planning to limit the radiation of these glands.Nous introduisons une nouvelle méthode de recalage déformable semi-automatique de structures anatomiques, à l'aide de simulations inverses interactives. La méthode est basée sur la méthode des éléments finis(FEM) et revient à résoudre un système de contraintes. Etant donné un ensemble de quelques points fournies par l'utilisateur, une optimisation en temps réel adapte les conditions aux limites et(/ou) des paramètres de la FEM dans le but d'obtenir les déformations géométriques adéquates. Pour accélérer les calculs de manière conséquente, la méthode repose sur une projection du modèle dans l'espace des variables d'optimisation. Dans cet espace réduit, un problème de programmation quadratique est formulé et résolu très rapidement. La méthode est validée par des exemples numériques (récupérer le module de Young et des pressions à appliquer sur le modèle). Ensuite, nous appliquons l'approche pour le recalage des glandes parotides pendant la radiothérapie de la tête et du cou. Un traitement de radiothérapie induit généralement une perte de poids chez le patient qui modifie la forme et la position de ces structures. Structures qui finissent par entrer dans le volume cible. Nous montrons comment nous pourrions adapter la planification afin de limiter le rayonnement de ces glandes