Unsupervised spatiotemporal video clustering a versatile mean-shift formulation robust to total object occlusions

International audienceIn this paper, we propose a mean-shift formulation allowing spatiotemporal clustering of video streams, and possibly extensible to other multivariate evolving data. Our formulation enables causal or omniscient filtering of spatiotemporal data, which is robust to total object occlusions. It embeds a new clustering algorithm within the filtering procedure that will group samples and reduce their number over the iterations. Based on our formulation, we express similar approaches and assess their robustness on real video sequences

LOCALLY CONTROLLED REGULARIZED SPATIOTEMPORAL ANISOTROPIC DIFFUSION

International audienceIn this paper, we propose a new anisotropic diffusion formulation allowing non-linear spatiotemporal filtering of image sequences. We first formulate a multidimensional spatiotemporal diffusion equation based on Barash’s iterative form, processing independently both spatial, temporal and intensity dimensions with their own diffusion functions and scale parameters. We then introduce a local regularization term designed to smooth the remaining spike noise. Experimental results processed on synthetic data and real MR images show that considering the temporal information and the regularization term improves the filtering quality. The method is also shown to be robust to noise, blur and temporal intensity evolution. Results are compared to the BM3D method with MSE and SSIM evaluation metrics

Unsupervised time-series clustering of distorted and asynchronous temporal patterns

International audienceMost time-series clustering methods, such as k-means or k-medoids, are initialized by prior knowledge about the number of classes or by a learning step. We propose an unsupervised clustering technique based on spatiotemporal mean-shift and optimal time series warping using dynamic time warping (DTW). Our main contribution consists in combining a spatiotemporal filtering technique, which gathers similar and synchronized temporal patterns in image sequences, with a clustering algorithm that applies a trajectory constraint on the DTW associations, thereby discriminating between similar time-series that are temporally shifted or warped. We assess the method's robustness on synthetic data, and demonstrate its versatility on brain magnetic resonance and multispectral satellite image sequences

Unsupervised spatio-temporal filtering of image sequences. A mean-shift specification

International audienceA new spatio-temporal filtering scheme based on the mean-shift procedure, which computes unsupervised spatio-temporal filtering for univariate feature evolution, is proposed in this paper. Our main contributions are on one hand the modification of the spatial/range domains to appropriately integrate the temporal feature into the mean-shift iterative form and on the other hand the addition of a trajectory constraint in the feature space with the use of the infinity norm. Therefore, only the samples living the same life in the feature space will converge. Major assets of the standard mean-shift framework such as convergence and bandwidth parameters adjustment are preserved. In this paper, we study the relative importance of the bandwidth parameters and the efficiency of the proposed method is assessed on synthetic data and compared to the standard mean-shift framework for spatio-temporal data filtering. The obtained results have allowed us to undertake a first study on real data, which has led to encouraging results in identifying spatio-temporal evolution of multiple sclerosis lesions appearing on T2-weighted MR images

Classification of multiple sclerosis lesion evolution patterns a study based on unsupervised clustering of asynchronous time-series

International audienceBased on weekly up to monthly follow-up of MS patients over one year with T2-weighted magnetic resonance images, a new clustering scheme is proposed to automatically identify lesions sharing similar temporal behaviors. The proposed method, based on spatiotemporal mean-shift and dynamic time warping, allows to detect intra and inter-patient similarities in lesion evolution patterns, which provides a quantitative approach towards the understanding of lesion evolution heterogeneity

New insight in perivenular lesion formation in multiple sclerosis on weekly susceptibility weighted images

International audienceIn this paper, we take advantage of a unique longitudinal MRI dataset acquired at weekly intervals on untreated multiple sclerosis patients. We study the signal dynamics of relapsing-remitting multiple sclerosis lesions on SWI MRI and show, thanks to an unsupervised spatiotemporal clustering algorithm, that specific signal intensity behaviors exist between the veins and the lesions that are synchronous with contrast enhancement on gadolinium-enhanced T1-weighted MRI. Our study shows that vein narrowing depicted on SWI is an early event that appears to precede blood-brain barrier disruption signified by contrast-enhancement

Analyse dynamique hebdomadaire du développement péri-veinulaire des lésions actives de SEP par imagerie de susceptibilité magnétique

International audienceIntroductionLe développement péri-veinulaires des lésions de SEP est un phénomène bien connu 0035, 0040 and 0045. Cependant, même si certains auteurs ont rapporté une sténose des veinules [4] intra-lésionnelles, aucune étude n’a caractérisé de manière dynamique ce phénomène. Dans cette étude, nous proposons d’analyser la cinétique ainsi que la localisation de la sténose des veinules dans les lésions actives de SEP.Matériel et méthodesUn suivi hebdomadaire a été mené pendant 8 semaines sur cinq patients non traités atteints d’une forme rémittente de SEP en IRM cérébrale 3 T 0055 and 0060 avec une exploration par imagerie de susceptibilité magnétique (SWI) et 3DT1 après injection de gadolinium. La sélection des lésions impliquait leur localisation sur une veine de diamètre supérieur à deux voxels et une prise de contraste comprise entre les première et dernière acquisitions exclues. Au total 3 lésions répondaient à ces critères. L’analyse des dynamiques d’interactions veine/lésion a été faite sur des régions d’intérêt (ROI) grâce à un algorithme7 regroupant automatiquement les voxels dont le signal évolue de manière similaire.RésultatsParmi les 3 lésions, un hypersignal transitoire a été mis en évidence en SWI au sein de la veinule centrale concomitant avec la prise de contraste, objectivé par une évolution commune du signal des voxels situés au cœur de la lésion (Fig. 1) Ces évolutions particulières du signal aux interfaces veine/lésion apparaissent au même moment ( and ) ou antérieurement (Fig. 4) à la prise de contraste.ConclusionNous avons mis en évidence une modification transitoire du signal à l’interface veine/lésion compatible avec une sténose des veinules synchronisée à la rupture de la barrière hémato-encéphalique, probablement en relation avec le manchon inflammatoire décrit histologiquement. L’idéal serait de pouvoir généraliser ces résultats sur un effectif plus grand même si cela pose des problèmes de faisabilité (de moins en moins de patients non traités, injections répétées de gadolinium)