Parametric Modelling of Multivariate Count Data Using Probabilistic Graphical Models

Multivariate count data are defined as the number of items of different categories issued from sampling within a population, which individuals are grouped into categories. The analysis of multivariate count data is a recurrent and crucial issue in numerous modelling problems, particularly in the fields of biology and ecology (where the data can represent, for example, children counts associated with multitype branching processes), sociology and econometrics. We focus on I) Identifying categories that appear simultaneously, or on the contrary that are mutually exclusive. This is achieved by identifying conditional independence relationships between the variables; II)Building parsimonious parametric models consistent with these relationships; III) Characterising and testing the effects of covariates on the joint distribution of the counts. To achieve these goals, we propose an approach based on graphical probabilistic models, and more specifically partially directed acyclic graphs

Estimation of Discrete Partially Directed Acyclic Graphical Models in Multitype Branching Processes

International audienceWe address the inference of discrete-state models for tree-structured data. Our aim is to introduce parametric multitype branching processes that can be efficiently estimated on the basis of data of limited size. Each generation distribution within this macroscopic model is modeled by a partially directed acyclic graphical model. The estimation of each graphical model relies on a greedy algorithm for graph selection. We present an algorithm for discrete graphical model which is applied on multivariate count data. The proposed modeling approach is illustrated on plant architecture datasets

Détection de motifs disruptifs au sein de plantes : une approche de quotientement/classification d'arborescences

National audienceMultiple change-point models for path-indexed data are transposed to tree-indexed data. The objective of multiple change-point models is to partition a heterogeneous tree into homogeneous subtrees. Since optimal algorithms for segmenting sequences cannot be transposed to trees, we propose here an efficient heuristic for tree segmentation. Segmented subtrees are grouped together in a post-processing phase since similar disjoint patches are often observed in tree canopy. Application of such models is illustrated on mango tree where subtrees are assimilated to plant patches and clusters of patches to patch types (e.g. vegetative, flowering or resting patch).Les modèles de détection de ruptures multiples pour séquences sont transposés aux arborescences. L'objectif est de quotienter une arborescence en sous-arborescences homogènes. Comme les algorithmes optimaux de segmentation de séquences ne peuvent être transposés aux arborescences, nous proposons ici une méthode heuristique permettant de segmenter efficacement une arborescence. Les sous-arborescences obtenues sont ensuite groupées dans une phase de post-traitement car des sous-arborescences disjointes relativement similaires sont observées dans les canopées d'arbre. Ces modèles sont illustrés par le cas du manguier où les collections de sous-arborescences permettent d'identifier les motifs disruptifs (juxtaposition de sous-arborescences végétatives, florifères ou en pause) observés dans les canopées

Automatic quality control of digitally reconstructed radiograph computation and comparison with standard methods

12 pagesInternational audienceConformal radiotherapy helps to deliver an accurate and effective cancer treatment by exactly targeting the tumor. In this purpose, softwares of the treatment planning system (TPS) compute every geometric parameters of the treatment. It is essential to control the quality of them because the TPS performances are directly connected with the precision on the treated region. The standard method to control them is to use physical test objects (PTOs).1,2 The use of PTOs introduces uncertainties in the quality assessment because of the CT scan. Another method to assess the quality of these softwares is to use digital test objects (DTOs).3-5 DTOs are exactly known in a continuous and a discrete way. Thus the assessment of the TPS quality can be more accurate and faster. The fact that the DTO characteristics are well known allows to calculate a theoretical result. The comparison of the TPS and this theoretical results leads to a quantitative assessment of the TPS softwares quality. This work presents the control of major quality criteria of digitally reconstructed radiograph (DRR) computation: ray divergence, ray incidence and spatial resolution. Fully automated methods to control these points have been developed. The same criteria have been tested with PTO and the quality assessments by the two methods have been compared. The DTO methods appeared to be much more accurate because computable

Deciphering mango tree asynchronisms using Markov tree and probabilistic graphical models

ISBN 978-951-651-408-9International audienceTree development is often characterised by complex dependencies between daughter growth units (GUs) deriving from a given mother GU, the so-called sister GUs. These dependencies directly affect the reproductive and vegetative phenological patterns that are at the origin of asynchronisms between adjacent GUs, eventually leading to within-canopy patchiness. These phenomena are rather common on tropical fruit-trees. We introduce new parsimonious statistical models to identify such dependencies. The proposed approach is illustrated on mango tree, a tropical species with a particularly complex timing of development. We focus especially on differences on fates and dates of burst between the daughter GUs issued from a same mother GU

Secured and progressive transmission of compressed images on the Internet: application to telemedicine

International audienceWithin the framework of telemedicine, the amount of images leads first to use efficient lossless compression methods for the aim of storing information. Furthermore, multiresolution scheme including Region of Interest (ROI) processing is an important feature for a remote access to medical images. What is more, the securization of sensitive data (e.g. metadata from DICOM images) constitutes one more expected functionality: indeed the lost of IP packets could have tragic effects on a given diagnosis. For this purpose, we present in this paper an original scalable image compression technique (LAR method) used in association with a channel coding method based on the Mojette Transform, so that a hierarchical priority encoding system is elaborated. This system provides a solution for secured transmission of medical images through low-bandwidth networks such as the Internet

Le LAR aux Mojettes

National audienceLes faibles bandes passantes de réseaux type Internet comparées aux volumes de données associées aux images, ont rendu nécessaire l'utilisation de méthodes de compression efficaces, afin de réduire la quantité d'information à transmettre. A l'opposé, la perte potentielle de paquets sur ce type de réseau peut exiger l'ajout de redondance garantissant partiellement ou totalement le recouvrement de l'information. Ce papier présente une solution globale de codage conjoint source-canal, permettant une compression d'images avec une redondance à priorité. La méthode de compression LAR (Locally Adaptive Resolution) permet un codage progressif d'images, hiérarchisant l'importance des flux. La transformée Mojette est ensuite appliquée sur chacun de ces flux en particularisant la redondance qui y est associée

Digital phantoms for the evaluation of a software used for an automatic analysis of the Winston-Lutz test in image guided radiation therapy

11 pagesInternational audienceAccurate isocentre positioning of the treatment machine is essential for the radiation therapy process, especially in stereotactic radio surgery and in image guided radiation therapy. We present in this paper a new method to evaluate a software which is used to perform an automatic analysis of the Winston-Lutz1, 2 test used in order to determine position and size of the isocentre. The method consists of developing digital phantoms that simulate mechanical distortions of the treatment machine as well as misalignments of the positioning laser targeting the isocentre. These Digital Test Objects (DTOs) offer a detailed and profound evaluation of the software and allow determining necessary adjustments which lead to high precision and therefore contributes to a better treatment targeting

Integrative models for analyzing jointly shoot growth and branching patterns

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitièresISBN 978-951-651-408-9International audienceThe branching pattern of a shoot may be influenced by numerous factors varying along the shoot such as the internode length, the leaf surface or the local curvature. We introduce a generalization of hidden semi-Markov chains for categorical response variables that incorporates explanatory variables varying with the index parameter. Using this model, we demonstrate the influence of the growth pattern of a shoot on its immediate branching

Mémoires en Bits

Dossier - Flous de Mémoire ISSN 1954-1872Article de vulgarisation scientifique pour Têtes Chercheuses, Actualité et culture des sciences en Pays de la Loire, numéro