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Multiple change point detection with application to physiological signals

le 29 novembre 2018
14h00

Soutenance de thèse de Charles Truong (CMLA, CognacG)

TRUONG_Ch1.jpg

TRUONG_Ch1.jpg

This work addresses the problem of detecting multiple change points in (univariate or multivariate) physiological signals. Well-known examples of such signals include electrocardiogram (ECG), electroencephalogram (EEG), inertial measurements (acceleration, angular velocities, etc.). The objective of this thesis is to provide change point detection algorithms that (i) can handle long signals, (ii) can be applied on a wide range of real-world scenarios, and (iii) can incorporate the knowledge of medical experts. In particular, a greater emphasis is placed on fully automatic procedures which can be used in daily clinical practice. To that end, robust detection methods as well as supervised calibration strategies are described, and a documented open-source Python package is released.

The first contribution of this thesis is a sub-optimal change point detection algorithm that can accommodate time complexity constraints while retaining most of the robustness of optimal procedures. This algorithm is sequential and alternates between the two following steps: a change point is estimated then its contribution to the signal is projected out. In the context of mean-shifts, asymptotic consistency of estimated change points is obtained. We prove that this greedy strategy can easily be extended to other types of changes, by using reproducing kernel Hilbert spaces. Thanks this novel approach, physiological signals can be handled without making assumption of the generative model of the data. Experiments on real-world signals show that those approaches are more accurate than standard sub-optimal algorithms and faster than optimal algorithms.

The second contribution of this thesis consists in two supervised algorithms for automatic calibration. Both rely on labelled examples, which in our context, consist in segmented signals. The first approach learns the smoothing parameter for the penalized detection of an unknown number of changes. The second procedure learns a non-parametric transformation of the representation space, that improves detection performance. Both supervised procedures yield finely tuned detection algorithms that are able to replicate the segmentation strategy of an expert. Results show that those supervised algorithms outperform unsupervised algorithms, especially in the case of physiological signals, where the notion of change heavily depends on the physiological phenomenon of interest.

All algorithmic contributions of this thesis can be found in "ruptures", an open-source Python library, available online. Thoroughly documented, "ruptures" also comes with a consistent interface for all methods

Détection de ruptures multiples - application aux signaux physiologiques

Ce projet de recherche veut apporter des réponses mathématiques à des problématiques biomédicales, plus particulièrement dans le domaine de la recherche clinique. Les chercheurs du CMLA et de Cognac G collaborent pour améliorer les diagnostics et rendre plus efficaces les traitements.

Pour cela, je chercherai à créer des nouvelles méthodes pour traiter automatiquement des données médicales issues de capteurs non intrusifs, par exemple l'accélération des membres d'un sujet qui marche. Des algorithmes statistiques isoleront alors des phases (accélération, décélération, demi tour,...) et extrairont des informations pertinentes (quantifier le mouvement du bassin, la claudication,...).

D'un point de vue mathématique, ce problème est celui de la détection de rupture pour des signaux multivariés, sujet dans lequel la recherche est encore balbutiante. Les approches classiques basées sur des changements de moyenne ou de variance ont des limites flagrantes sur des signaux complexes. Pour la segmentation de ces données hétérogènes et non stationnaires, on développera alors des méthodes basées sur des tests d'égalité de distributions statistiques.


Type :
Thèses - HDR
Lieu(x) :
Campus de Cachan
Salle des conférences, Pavillon des Jardins

Collaboration de recherche






Composition du Jury

Directeurs de thèse :
Nicolas Vayatis
(CMLA, ENS Paris-Saclay)
Laurent Oudre
(Univ. Paris 13, L2TI)

Rapporteurs :
Zaid Harchaoui
(University of Washington)
Fabrice Rossi
(Univ. Paris 1 Panthéon-Sorbonne)

Examinateurs :
Patrick Gallinari
(UPMC)
Celine Lévy-Leduc
(AgroParisTech)

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