Combining atlas based segmentation and intensity classification with nearest neighbor transform and accuracy weighted vote

1361-8423 (Electronic) 1361-8415 (Linking) Journal Article Research Support, Non-U.S. Gov'tIn this paper, different methods to improve atlas based segmentation are presented. The first technique is a new mapping of the labels of an atlas consistent with a given intensity classification segmentation. This new mapping combines the two segmentations using the nearest neighbor transform and is especially effective for complex and folded regions like the cortex where the registration is difficult. Then, in a multi atlas context, an original weighting is introduced to combine the segmentation of several atlases using a voting procedure. This weighting is derived from statistical classification theory and is computed offline using the atlases as a training dataset. Concretely, the accuracy map of each atlas is computed and the vote is weighted by the accuracy of the atlases. Numerical experiments have been performed on publicly available in vivo datasets and show that, when used together, the two techniques provide an important improvement of the segmentation accuracy

A Sharp Sufficient Condition for B-Spline Vector Field Invertibility. Application to Diffeomorphic Registration and Interslice Interpolation.

International audienceIn this paper, a new sufficient condition for the invertibility of a B-spline vector field as well as its extension to spatio-temporal vector fields are presented. The new condition, while guaranteeing that the vector field is diffeomorphic, is sharp enough to allow large deformations. The complexity of the constraint is also discussed. A new diffeomorphic registration algorithm using this condition and its application to interslice interpolation are presented and evaluated on synthetic images and in vivo magnetic resonance T2 images of the brain. The registration method has also been compared to some state-of-the-art registration methods

Diffeomorphic B-Spline Vector Fields With a Tractable Set of Inequalities

International audienceB-spline diffeomorphic vector fields are objects of great interest in image processing and analysis, more specifically for the registration of medical images. In this paper, several conditions on the B-spline coefficients ensuring that a given B-spline vector field is a diffeomorphism are proposed. Some properties of vector fields satisfying these conditions are established showing that they are not too restrictive while having a reasonable computational complexity. This work opens the way to the development of practical image registration algorithms in two and three dimensions whose unknowns would be such diffeomorphic B-spline vector fields

A Fast Nonrigid Image Registration With Constraints on the Jacobian Using Large Scale Constrained Optimization

International audienceThis paper presents a new nonrigid monomodality image registration algorithm based on-splines. The deformation is described by a cubic-spline field and found by minimizing the energy between a reference image and a deformed version of a floating image. To penalize noninvertible transformation, we propose two different constraints on the Jacobian of the transformation and its derivatives. The problem is modeled by an inequality constrained optimization problem which is efficiently solved by a combination of the multipliers method and the L-BFGS algorithm to handle the large number of variables and constraints of the registration of 3-D images. Numerical experiments are presented on magnetic resonance images using synthetic deformations and atlas based segmentation

Automatic Detection of the Spinal Cord Centerline using Machine Learning and Global Nonlinear Optimization

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Nonrigid registration of multiple sclerosis brain images using lesion inpainting for morphometry or lesion mapping.

International audienceMorphometric studies of medical images often include a nonrigid registration step from a subject to a common reference. The presence of white matter multiple sclerosis lesions will distort and bias the output of the registration. In this article, we present a method to remove this bias by filling such lesions to make the brain look like a healthy brain before the registration. We finally propose a dedicated method to fill the lesions and present numerical results showing that our method outperforms current state of the art method

Boundary conditions for Young - van Vliet recursive filtering

International audienceYoung and van Vliet have designed computationally efficient methods for approximating Gaussian-based convolutions by running a recursive infinite-impulse-response (IIR) filter forward over the input signal, then running a second IIR filter backward over the first filter's output. To transition between the two filters, they use a suboptimal heuristic that produces significant amplitude and phase distortion for all points within about three standard deviations of the right-hand boundary. In this correspondence, a simple linear transition rule that eliminates this distortion is derived

Simulation de la dynamique du système de déplacements urbains : une plate-forme de modélisation

Recherche réalisée pour le compte de la DRAST, décision de subvention n° 00 MT 61, Ministère de l'Equipement, des Transports, du Logement, du Tourisme et de la Mer.Rapport final. Février 2003. Version 1.21.02.03. 164 p.Rapport disponible à cette url : http://www.innovations-transports.fr/IMG/pdf/210-R00MT61.pdf (lien consulté le 13 septembre 2006)Synthèse disponible à cette url : http://www.innovations-transports.fr/IMG/pdf/210-S00MT61.pdf (lien consulté le 13 sepRapport de recherchePROBLEMATIQUEL'objectif du travail de recherche proposé est de :1. Développer une plate-forme méthodologique renouvelée de simulation des déplacements urbains, reliant différentes " briques " de modèles (socio-démographiques, motorisation, mobilité, localisations d'activités, choix modal, etc.).2. Contribuer au développement d'une expertise française en simulation des systèmes de déplacements à l'échelle des agglomérations urbaines.Cette démarche mène en parallèle l'organisation conceptuelle des différents mécanismes de rétroaction, l'intégration de briques de modèles déjà calées par ailleurs, et des investigations complémentaires sur les données pour caler les autres modèles nécessaires.METHODOLOGIELe terrain privilégié est celui de l'agglomération lyonnaise, l'horizon temporel est le moyen, voire le long terme (10 ans et plus). On utilise un logiciel spécialisé dans la conception et la simulation de modèles de dynamique de systèmes (Vensim).La construction du système de modèles vise à croiser les effets de contexte socio-économique (croissance des revenus), socio-démographiques (vieillissement, étapes dans le cycle de vie), de localisation interne à l'agglomération, d'offre de transport distinguée selon les différentes liaisons. L'architecture du système de modèles est elle-même objet de la recherche.L'architecture est décomposée en trois phases :1. Conception générale de l'architecture du système, description verbale du phénomène, liens de causalité, rétroactions, etc., identification des blocs-modèles élémentaires ;2. Intégration des modèles élémentaires déjà prêts, premiers tests de simulation, retour sur l'architecture, et calages requis pour les modèles non existants ;3. Intégration finale des modèles, tests, retours sur l'architecture, exercices de simulation sous différentes hypothèses du contexte exogène.RESULTATSLe rapport final décrit l'architecture d'ensemble et le développement de 3 modèles : un modèle de régulation financière de l'offre de transports collectifs ; un modèle de choix d'heure de départ couplé à un algorithme de choix d'itinéraire sur un réseau routier ; un modèle de répartition modale de type " prix-temps ", adapté à une configuration urbaine et calé pour le motif domicile-travail sur l'agglomération lyonnaise. Enfin, le couplage entre le modèle de répartition modale et celui du choix d'heure de départ et d'affectation a été réalisé et testé sur des configurations simplifiées d'offre et de demande