3D tracking of laparoscopic instruments using statistical and geometric modeling

International audienceDuring a laparoscopic surgery, the endoscope can be manipulated by an assistant or a robot. Several teams have worked on the tracking of surgical instruments, based on methods ranging from the development of specific devices to image processing methods. We propose to exploit the instruments' insertion points, which are fixed on the patients abdominal cavity, as a geometric constraint for the localization of the instruments. A simple geometric model of a laparoscopic instrument is described, as well as a parametrization that exploits a spherical geometric grid, which offers attracting homogeneity and isotropy properties. The general architecture of our proposed approach is based on the probabilistic Condensation algorithm

Spatially Coherent Activation Maps for Electrocardiographic Imaging

International audienceObjective: Cardiac mapping is an important diagnostic step in cardiac electrophysiology. One of its purposes is to generate a map of the depolarization sequence. This map is constructed in clinical routine either by directly analyzing cardiac electrograms (EGM) recorded invasively or an estimate of these EGMs obtained by a non-invasive technique. Activation maps based on noninvasively estimated EGMs often show artefactual jumps in activation times. To overcome this problem we present a new method to construct the activation maps from reconstructed unipolar EGMs. Methods: On top of the standard estimation of local activation time from unipolar intrinsic deflections, we propose to mutually compare the EGMs in order to estimate the delays in activation for neighboring recording locations. We then describe a workflow to construct a spatially coherent activation map from local activation times and delay estimates in order to create more accurate maps. The method is optimized using simulated data and evaluated on clinical data from 12 different activation sequences. Results: We found that the standard methodology created lines of artificially strong activation time gradient. The proposed workflow enhanced these maps significantly. Conclusion: Estimating delays between neighbors is an interesting option for activation map computation in ECGi

Accuracy of Lead Removal vs Linear Interpolation in Non-Invasive Electrocardiographic Imaging (ECGI)

International audienceThis study examines the effect of missing body surface potentials on inverse solutions, and determines if linear interpolation can regain information lost. Using simulated and experimental data, electrograms (EGMs) were reconstructed after 1) removing and 2) interpolating 'broken' signals. Results showed that losing body surface potentials over the chest can reduce inverse reconstruction accuracy. Linear interpolation did not improve, and could further deteriorate reconstruction accuracy

VT Scan: Towards an Efficient Pipeline from Computed Tomography Images to Ventricular Tachycardia Ablation

International audienceNon-invasive prediction of optimal targets for efficient radio-frequency ablation is a major challenge in the treatment of ventricular tachycardia.Most of the related modelling work relies on magnetic resonance imaging of the heart for patient-specific personalized electrophysiology simulations.In this study, we used high-resolution computed tomography images to personalize an Eikonal model of cardiac electrophysiology in seven patients, addressed to us for catheter ablation in the context of post-infarction arrhythmia.We took advantage of the detailed geometry offered by such images, which are also more easily available in clinical practice, to estimate a conduction speed parameter based on myocardial wall thickness.We used this model to simulate a propagation directly on voxel data, in similar conditions to the ones invasively observed during the ablation procedure.We then compared the results of our simulations to dense activation maps that recorded ventricular tachycardias during the procedures.We showed as a proof of concept that realistic re-entrant pathways responsible for ventricular tachycardia can be reproduced using our framework, directly from imaging data

Do we need to enforce the homogeneous Neumann condition on the torso for solving the inverse electrocardiographic problem?

International audienceRobust calculations of the inverse electrocardiographicproblem may require accurate specification of boundaryconditions at the torso and cardiac surfaces. In particular,the numerical specification of the no-flux condition onthe torso is difficult because surface normals must be computed,and because the torso may alternatively be consideredinfinitely far away from the heart. Using the method offundamental solutions (MFS), this boundaryconditions can be taken into account in different manners.Specifically, the no-flux condition on the torso can beignored, or weighted with respect to the Dirichlet boundarycondition associated to the torso data, or can bestrongly enforced through a saddle-point problem.In this work we provide a preliminary comparison ofthese different strategies

Fast Personalized Electrophysiological Models from CT Images for Ventricular Tachycardia Ablation Planning

International audienceAims Clinical application of patient-specific cardiac computer models requires fast and robust processing pipelines that can be seamlessly integrated into clinical workflows. We aim at building such a pipeline from computed tomography (CT) images to personalised cardiac electrophysiology (EP) model. The simulation output could be useful in the context of post-infarct ventricular tachycardia (VT) radio-frequency ablation (RFA) planning for pre-operative targets prediction

Local Conduction Velocity Mapping for Electrocardiographic Imaging

International audienceSlow conduction is a well-known pro-arrhythmic feature for tachycardia and fibrillation. Cardiac conduction velocity (CV) mapping can be extremely helpful for investigating unusual activation patterns. Although methods have been developed to estimate velocity vector field, from ex-vivo preparations (e.g. from optical mapping recordings), the estimation from in-vivo electrograms (EGMs) remains challenging. This paper presents a new method specifically designed for EGMs reconstructed non-invasively from body surface potentials using electrocardiographic imaging (ECGi). The algorithm is based on cardiac activation maps and assumes either a linear or quadratic wavefront shape. The proposed methodology was performed on computed and experimental data for epicardial pacing on healthy tissue. The results were compared with reference velocity vector fields and evaluated by analyzing the errors of direction and speed. The outcomes indicate that a linear wavefront is the most suited for cardiac propagation in healthy tissue

Early Repolarization Syndrome: Diagnostic and Therapeutic Approach

An early repolarization pattern can be observed in 1% up to 13% of the overall population. Whereas, this pattern was associated with a benign outcome for many years, several more recent studies demonstrated an association between early repolarization and sudden cardiac death, so-called early repolarization syndrome. In early repolarization syndrome patients, current imbalances between epi- and endo-cardial layers result in dispersion of de- and repolarization. As a consequence, J waves or ST segment elevations can be observed on these patients' surface ECGs as manifestations of those current imbalances. Whereas, an early repolarization pattern is relatively frequently found on surface ECGs in the overall population, the majority of individuals presenting with an early repolarization pattern will remain asymptomatic and the isolated presence of an early repolarization pattern does not require further intervention. The mismatch between frequently found early repolarization patterns in the overall population, low incidences of sudden cardiac deaths related to early repolarization syndrome, but fatal, grave consequences in affected patients remains a clinical challenge. More precise tools for risk stratification and identification of this minority of patients, who will experience events, remain a clinical need. This review summarizes the epidemiologic, pathophysiologic and diagnostic background and presents therapeutic options of early repolarization syndrome

New Mathematical approaches in Electrocardiography Imaging inverse problem

International audienceImprove ECGI inverse problem reconstruction Introduce new mathematical approches to the field of the ECGI inverse problem Compare the performance of the new mathematical approaches to the state-of-the-art methods, mainly the MFS method used in commercial devices. In silico validation of the new approches. Assessment of some simplification hypothesis: Torso inhomogeneity Propose some uncertainty quantification apronches to deal with measurements errors Context and objectives Optimal control approach Mathematical model In silico gold standard Results Torso Heterogeneity effect Conclusions Forward model If we know the heart potential we can compute the electrical potential Inverse problem If we know the electrical potential and the current density at the outer boundary of the torso and we look for the electrical potential at the heart surface Computational heart and torso anatomical models + electrodes position Computational torso meshes: 250 nodes mesh (blue). More accurate FE mesh with 6400 nodes (green) Remarks Introducing the torso heterogeneity is natural with FEM. also anisotropy could be introduced The error is more important in the left ventricle Main results and perspectives New mathematical approches for solving the inverse problem in electrocardiography imaging based on optimal control Over all the 20 cases used in this study the optimal control method performs better than the MFS both in terms of relative error and correlation coefficient: Acknowledgment: This work was partially supported by an ANR grant part of "Investissements d'Avenir" program with reference ANR-10-IAHU-04. It is also supported by the LIRIMA international lab thought the EPICARD tea

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation