Active learning methods for remote sensing image classification

In this paper, we propose two active learning algorithms for semiautomatic definition of training samples in remote sensing image classification. Based on predefined heuristics, the classifier ranks the unlabeled pixels and automatically chooses those that are considered the most valuable for its improvement. Once the pixels have been selected, the analyst labels them manually and the process is iterated. Starting with a small and nonoptimal training set, the model itself builds the optimal set of samples which minimizes the classification error. We have applied the proposed algorithms to a variety of remote sensing data, including very high resolution and hyperspectral images, using support vector machines. Experimental results confirm the consistency of the methods. The required number of training samples can be reduced to 10% using the methods proposed, reaching the same level of accuracy as larger data sets. A comparison with a state-of-the-art active learning method, margin sampling, is provided, highlighting advantages of the methods proposed. The effect of spatial resolution and separability of the classes on the quality of the selection of pixels is also discussed.

Dépistage de la dépression chez des patients consultant pour une plainte physique en médecine de famille en Suisse romande : existe-t-il une différence selon le genre

Introduction¦La dépression est une maladie fréquente à travers le monde. D'un point de vue épidémiologique, une différence entre hommes et femmes a été observée, un diagnostic de dépression étant attribué à deux fois plus de femmes que d'hommes. Le médecin de famille est souvent le premier¦professionnel sollicité face à une dépression, cependant un grand nombre patients atteints de dépression consultent leur médecin de famille pour une plainte physique.¦Objectifs et méthodes¦L'objectif de ce travail est de déterminer s'il existe une différence entre hommes et femmes dans la prévalence de la dépression dépistée chez des patients consultant leur médecin de famille exclusivement pour une plainte d'ordre physique en Suisse romande. Afin d'y parvenir, nous avons effectué une sous-analyse de l'étude SODA (SOmatoform, Depression, Anxiety dont nous disposons de la base de données). Il s'agit d'une étude menée en Suisse romande qui a pour but de d'évaluer la prévalence des troubles anxieux, dépressif et somatoforme, à une année d'intervalle, chez des patients consultant leur médecin de famille exclusivement pour une plainte physique. Le Patient Health Questionnaire (PHQ) est le questionnaire utilisé dans l'étude SODA afin de déterminer le diagnostic de dépression.¦Résultats¦L'analyse statistique effectuée n'a pas permis de mettre en évidence une différence entre hommes et femmes dans la prévalence de la dépression au sein de l'étude SODA, que ce soit au moment de¦l'inclusion (t0, p=0.764), à une année d'intervalle (t1, p=0.9) ou dans l'évolution de la dépression.¦Conclusion¦Nous nous attendions à trouver une différence significative dans la prévalence de la dépression avec¦une prépondérance féminine comme le suggère la littérature. L'absence de différence significative¦entre hommes et femmes dans la prévalence de la dépression au sein de l'étude SODA pourrait provenir de certaines modalités de l'étude telles que le PHQ par exemple et du choix de ne considérer que les patients se présentant pour une plainte somatique. Ceci a peut être contribué à une meilleure détection de la dépression chez les hommes et ceci, peut-être, au détriment des femmes.

Les Chalcidiens (Hymenoptera, Chalcidoidea) associés au genre Ficus spp. (Moracee) du Sénégal : répartition, abondance et diversité

Cette étude est la première portant sur la biodiversité écologique des Chalcidiens associés au genre Ficus au Sénégal. Sur les 26 espèces de figuiers signalées au Sénégal, 11 ont été trouvées. Chaque espèce de Ficus possède une microfaune Chalcidienne caractéristique. La comparaison des niveaux d'infestation révèle une différence très significative entre espèces de Ficus (P<0.0001). Les figues de F.sycomorus du domaine Nord-Soudanien sont, en valeurs absolues, plus infestées que celles des domaines Sud-Soudanien et Soudanien Atlantique. Les tests statistiques révèlent une différence d'infestation non significative des figues de F.sycomorus entre les 3 domaines (P>0.05). Cependant, entre le domaine Nord-Soudanien et le domaine Soudanien Atlantique, cette différence est significative (P=0.0091).

Direct Fourier Tomographic Reconstruction Image-To-Image Filter

We present an open-source ITK implementation of a directFourier method for tomographic reconstruction, applicableto parallel-beam x-ray images. Direct Fourierreconstruction makes use of the central-slice theorem tobuild a polar 2D Fourier space from the 1D transformedprojections of the scanned object, that is resampled intoa Cartesian grid. Inverse 2D Fourier transform eventuallyyields the reconstructed image. Additionally, we providea complex wrapper to the BSplineInterpolateImageFunctionto overcome ITKâeuro?s current lack for image interpolatorsdealing with complex data types. A sample application ispresented and extensively illustrated on the Shepp-Loganhead phantom. We show that appropriate input zeropaddingand 2D-DFT oversampling rates together with radial cubicb-spline interpolation improve 2D-DFT interpolationquality and are efficient remedies to reducereconstruction artifacts.

Weight status, body image and bullying among adolescents in the Seychelles.

We investigated the relationship between being bullied and measured body weight and perceived body weight among adolescents of a middle-income sub Saharan African country. Our data originated from the Global School-based Health Survey, which targets adolescents aged 13-15 years. Student weights and heights were measured before administrating the questionnaire which included questions about personal data, health behaviors and being bullied. Standard criteria were used to assess thinness, overweight and obesity. Among 1,006 participants who had complete data, 16.5% (95%CI 13.3-20.2) reported being bullied ≥ 3 days during the past 30 days; 13.4% were thin, 16.8% were overweight and 7.6% were obese. Categories of actual weight and of perceived weight correlated only moderately (Spearman correlation coefficient 0.37 for boys and 0.57 for girls; p < 0.001). In univariate analysis, both actual obesity (OR 1.76; p = 0.051) and perception of high weight (OR 1.63 for "slightly overweight"; OR 2.74 for "very overweight", both p < 0.05) were associated with being bullied. In multivariate analysis, ORs for categories of perceived overweight were virtually unchanged while ORs for actual overweight and obesity were substantially attenuated, suggesting a substantial role of perceived weight in the association with being bullied. Actual underweight and perceived thinness also tended to be associated with being bullied, although not significantly. Our findings suggest that more research attention be given to disentangling the significant association between body image, overweight and bullying among adolescents. Further studies in diverse populations are warranted.

Three-dimensional magnetic resonance myocardial motion tracking from a single image plane.

Three-dimensional imaging for the quantification of myocardial motion is a key step in the evaluation of cardiac disease. A tagged magnetic resonance imaging method that automatically tracks myocardial displacement in three dimensions is presented. Unlike other techniques, this method tracks both in-plane and through-plane motion from a single image plane without affecting the duration of image acquisition. A small z-encoding gradient is subsequently added to the refocusing lobe of the slice-selection gradient pulse in a slice following CSPAMM acquisition. An opposite polarity z-encoding gradient is added to the orthogonal tag direction. The additional z-gradients encode the instantaneous through plane position of the slice. The vertical and horizontal tags are used to resolve in-plane motion, while the added z-gradients is used to resolve through-plane motion. Postprocessing automatically decodes the acquired data and tracks the three-dimensional displacement of every material point within the image plane for each cine frame. Experiments include both a phantom and in vivo human validation. These studies demonstrate that the simultaneous extraction of both in-plane and through-plane displacements and pathlines from tagged images is achievable. This capability should open up new avenues for the automatic quantification of cardiac motion and strain for scientific and clinical purposes.

Bayesian image reconstruction with space-variant noise suppression

In this paper we present a Bayesian image reconstruction algorithm with entropy prior (FMAPE) that uses a space-variant hyperparameter. The spatial variation of the hyperparameter allows different degrees of resolution in areas of different statistical characteristics, thus avoiding the large residuals resulting from algorithms that use a constant hyperparameter. In the first implementation of the algorithm, we begin by segmenting a Maximum Likelihood Estimator (MLE) reconstruction. The segmentation method is based on using a wavelet decomposition and a self-organizing neural network. The result is a predetermined number of extended regions plus a small region for each star or bright object. To assign a different value of the hyperparameter to each extended region and star, we use either feasibility tests or cross-validation methods. Once the set of hyperparameters is obtained, we carried out the final Bayesian reconstruction, leading to a reconstruction with decreased bias and excellent visual characteristics. The method has been applied to data from the non-refurbished Hubble Space Telescope. The method can be also applied to ground-based images.