Breccia Pipe Estimation: a new approach using non-stationary covariances

International audienceThe El Teniente mine is famous not only as one of the largest known porphyry-copper ore bodies but also, among geologists, for its typical breccia pipe named “Braden”, an almost vertical poorly mineralized cone, located at the center of the mine and surrounded by early-stage mineralizations. As the edge of the pipe constitutes the limit of the deposit and of the mining operation, estimating it accurately is important. In this paper, we are interested in estimation of the elevation of the pipe surface using a geostatistical approach based on non-stationary covariances. Previous approaches have been applied on this dataset by Séguret and Celhay (2013). The proposed estimation method offers an integrated treatment of all aspects of non-stationarity (mean, variance, spatial continuity) in the modelling process. The proposed method has revealed an increased prediction accuracy when compared to standard stationary method, and demonstrated the ability to extract the underlying non-stationarity from a single realization. A comparison of predictions and prediction standard deviations maps indicates that the proposed non-stationary method captures some varying spatial features (such as locally varying anisotropy) in the data that are not present using the stationary method, the outcome appears more realistic

Antenatal Diagnosis and Management of Nuchal Cystic Hygroma: A Case Report in the Yaounde Central Maternity, Cameroon

Ultrasonographic evaluation, as a routine component of antenatal care, has significantly contributed to in utero assessment of pregnancy status. The detection of fetal abnormalities by ultrasound, however, has raised clinical questions and created parental dilemmas concerning the outcomes of such pregnancies. A relatively frequent anomaly observed on routine ultrasonographic examination is the posterior nuchal cystic hygroma. Most cases of cystic hygromas are associated with chromosomal abnormalities. Only 2–3% survival rate is reported when fetal cystic hygromas are diagnosed in utero. This information should be helpful when counseling patients whose pregnancies involve fetuses with this anomaly. We report a case of nuchal cystic hygroma diagnosed in the second trimester of pregnancy with the aid of an ultrasonographic morphological analysis. The parents requested termination of the pregnancy.Keywords antenatal; diagnosis; cystic hygrom

Estimation of Space Deformation Model for Non-stationary Random Functions

Stationary Random Functions have been successfully applied in geostatistical applications for decades. In some instances, the assumption of a homogeneous spatial dependence structure across the entire domain of interest is unrealistic. A practical approach for modelling and estimating non-stationary spatial dependence structure is considered. This consists in transforming a non-stationary Random Function into a stationary and isotropic one via a bijective continuous deformation of the index space. So far, this approach has been successfully applied in the context of data from several independent realizations of a Random Function. In this work, we propose an approach for non-stationary geostatistical modelling using space deformation in the context of a single realization with possibly irregularly spaced data. The estimation method is based on a non-stationary variogram kernel estimator which serves as a dissimilarity measure between two locations in the geographical space. The proposed procedure combines aspects of kernel smoothing, weighted non-metric multi-dimensional scaling and thin-plate spline radial basis functions. On a simulated data, the method is able to retrieve the true deformation. Performances are assessed on both synthetic and real datasets. It is shown in particular that our approach outperforms the stationary approach. Beyond the prediction, the proposed method can also serve as a tool for exploratory analysis of the non-stationarity.Comment: 17 pages, 9 figures, 2 table

A Generalized Convolution Model and Estimation for Non-stationary Random Functions

Standard geostatistical models assume second order stationarity of the underlying Random Function. In some instances, there is little reason to expect the spatial dependence structure to be stationary over the whole region of interest. In this paper, we introduce a new model for second order non-stationary Random Functions as a convolution of an orthogonal random measure with a spatially varying random weighting function. This new model is a generalization of the common convolution model where a non-random weighting function is used. The resulting class of non-stationary covariance functions is very general, flexible and allows to retrieve classes of closed-form non-stationary covariance functions known from the literature, for a suitable choices of the random weighting functions family. Under the framework of a single realization and local stationarity, we develop parameter inference procedure of these explicit classes of non-stationary covariance functions. From a local variogram non-parametric kernel estimator, a weighted local least-squares approach in combination with kernel smoothing method is developed to estimate the parameters. Performances are assessed on two real datasets: soil and rainfall data. It is shown in particular that the proposed approach outperforms the stationary one, according to several criteria. Beyond the spatial predictions, we also show how conditional simulations can be carried out in this non-stationary framework.Comment: 24 pages, 10 figures, 2 table

Contributions à la modélisation et à l'inférence des fonctions aléatoires non-stationnaires de second ordre

Stationary Random Functions have been sucessfully applied in geostatistical applications for decades. The underlying spatial dependence structure of the Random Function is represented by a stationary variogram or covariance. However, in some instances, there is little reason to expect the spatial dependence structure to be stationary over the whole region of interest. In this manuscript, two non-stationary modelling approaches for Random Functions are considered: space deformation and stochastic convolution. For each of them, we develop a statistical methodology for estimating the non-stationary spatial dependence structure, in the context of a single realization. Moreover, we also show how spatial predictions and conditional simulations can be carried out in this non-stationary framework. The developed inference methods allow to capture varying spatial structures while guaranteeing the global consistency of the final model. The assessment of their performance on both synthetic and real datasets show that they outperform stationary method, according to several criteria. Beyond the prediction, they can also serve as a tool for exploratory analysis of the non-stationarity.Les fonctions aléatoires stationnaires ont été utilisées avec succès dans les applications géostatistiques depuis plusieurs décennies. La structure de dépendance spatiale sous-jacente de la fonction aléatoire est alors représentée par un variogramme ou une covariance stationnaire. Cependant, dans certaines situations, il y a très peu de raisons de s'attendre à une structure de dépendance spatiale stationnaire sur l'ensemble du domaine d'intérêt. Dans cette thèse, deux approches de modélisation non-stationnaire de fonctions aléatoires sont considérées: déformation d'espace et convolution stochastique. Pour chacune d'elle, nous développons une méthodologie statistique d'estimation de la structure de dépendance spatiale non-stationnaire, dans le contexte d'une réalisation unique. Par ailleurs, nous montrons également comment dans ce cadre non-stationnaire, les prédictions spatiales et les simulations conditionnelles peuvent être menées. Les méthodes d'inférence développées permettent de capturer des structures de dépendance variables tout en garantissant la cohérence globale du modèle final. L'évaluation de leur performance selon plusieurs critères, sur des données synthétiques et réelles montre qu'elles donnent de meilleurs résultats de prédiction qu'une méthode stationnaire. Au delà de la prédiction, elles peuvent également servir comme outil pour une analyse exploratoire de la non-stationnarité

Hématométrie unilatérale sur utérus didelphe de découverte fortuite chez une multipare Camerounaise de 31 ans : à propos d’un cas et revue de la littérature

L’utérus didelphe est une malformation utérine par défaut de fusion des canaux de Müller entre la 10e et la 13e semaine de gestation, aboutissant à la persistance plus ou moins complète de la dualité de ces canaux. Certains types de malformations utérines ont des conséquences sur la vie reproductrice et exigent la chirurgie pour rétablir la continuité ou vider une collection des voies génitales si elles sont découvertes à temps. Nous vous présentons un cas d’hématométrie unilatérale sur utérus didelphe de découverte fortuite en per opératoire chez une multipare et traitée par hémi hystérectomie en urgence. La rareté de cette pathologie peut amener à omettre le diagnostic. Le diagnostic précoce et par conséquent une meilleure prise en charge permettent de diminuer les complications. L’hématométrie sur utérus didelphe est une urgence gynécologique dont la prise en charge exige la chirurgie. Les gestes doivent être moins mutilants chez les patientes souvent jeunes.Mots Clés hématométrie ; utérus didelphe ; hémihystérectomi

Non-Puerperal Uterine Inversion Following a Prolapsed Leiomyoma in a Cameroonian Woman

Non-puerperal uterine inversion is a rare condition that occurs as a complication of intrauterine tumors, especially giant submucosal leiomyomas. This condition can cause severe pain and hemorrhage. Management can consist of manual repositioning through the cervical ring, or surgical corrective measures. We report here a case of uterine inversion following the prolapse of a submucosal leiomyoma, managed by laparotomy. We also discuss alternative therapeutic approaches.Keywords uterine inversion; non-puerperal; leiomyom

Prevalence and associated factors of HIV infection among pregnant women attending antenatal care at the Yaoundé central hospital

Background: HIV infection affects millions of people worldwide, especially in sub-Saharan Africa. Transmission occurs by several means including the transmission from mother to child. The objective of this study was to determine the prevalence and factors associated with HIV infection in women attending antenatal care at the Yaoundé Central Hospital.Methods: We conducted an analytical cross-sectional study at the Obstetrics and Gynecologic Unit of the Yaoundé Central Hospital from 6th October 2015 to 30th June 2016. The sampling was consecutive. We included 360 pregnant women. Testing was done by a sensitive test and a specific test if the first was positive. Data analysis was done through Excel 2007 software EpiData Analysis Version 3.2 and STATA version 12.0 (Texas USA 2001). Statistical significance was accepted for a value of P <0.05.Results: The average age of our population was 27.99±5.63 years, ranging from 15 and 47 years. HIV prevalence in this population was 13.1% (47/360). Factors associated with HIV were the primary level of study (OR=7.97; 95% CI=2.23 to 28.49, P=0.001) and multiple sexual partners (OR=4.82; CI 95%=2.24 to 10.38, P=0.002).Conclusions: HIV prevalence in pregnant women at the Maternity of HCY is 13.1%. The low level of education and multiple sexual partners were significantly associated with HIV infection. We suggest the education of the girls who is a key factor in the empowerment of women

Risk factors of intrauterine fetal death: a case control study at the maternity of Yaoundé Central Hospital

Background: Intrauterine fetal death (IUFD) is the death before the beginning of the work of the fetus from the 28th week of pregnancy or a fetus of weight greater than or equal to 1000g. It occurs in 98% in poor countries, particularly in sub-Saharan Africa. The aim of this study was to identify the risk factors for IUFD in low-income countries.Methods: All the women with preeclampsia from 30 weeks onwards were enrolled in the study. The umblical artery (UA) Systolic-diastolic (S/D) ratio >2 standard deviation (SD) or UA-pulsatility index (PI) and UA-resistive index (RI) >2 SD were taken as abnormal. The middle cerebral artery (MCA) was visualised and cerebroumblical PI ratio calculated. MCA-RI<2SD was taken as abnormal.Results: Independent risk factors for IUFD are age over 30 years (ORa = 2.1, P = 0.052), (ORa = 2.4497, p = 0.01), household occupation (ORa = 2.0097, p = 0.0282), hypertension disorders (ORa = 2.11, p = 0.0176), antepartal haemorrhage (ORa = 3.9635, p = 0.000), multiparity (ORa = 13.3089, p = 0.0056).Conclusions: The main risk factors for IUFD identified in our study are maternal age greater than 30 years, hypertension, antepartal haemorrhage, multiparity, and the household profession. Any pregnant woman who has one of these factors should be follow-up closely during pregnancy with a weekly assessment of fetal well-being by the 28th week

Fetal outcome of HIV positive pregnant women taking highly active antiretroviral therapy at Yaoundé Central Hospital: a cross sectional analytic study

Background: HIV infection in pregnant women is delicate both for the mother and her child. With the adoption of option B+ treatment plan by Cameroon’s ministry of public health, there has been a marked decrease in the vertical transmission of HIV from mothers to their babies. There is a dearth of evidence in sub-Saharan Africa, especially in Cameroon, on the effects of highly active antiretroviral therapy (HAART) on pregnancy and foetal outcomes with respect to the time from onset of treatment. We therefore carried out this study to determine the foetal outcome of women on HAART. We hypothesized that the foetal outcome is poorer for pregnant women starting HAART during pregnancy compared to those starting HAART prior to conception.Methods: We carried out an analytic cross-sectional study which spanned from the 1st February to 30th April 2017 at the Yaoundé Central Maternity. We included consenting hospitalised HIV infected women who just terminated a pregnancy (abortion or delivery), and who started HAART at least four weeks before termination of pregnancy. Data was analysed using EPI info 7.2.1.0. SPSS version 20.0. Odds ratio (OR) was used to assess the degree of association that could exist between qualitative variables. The threshold of statistical significance was set at a p-value of 0.05.Results: A total of 121 participants were recruited in the present study. The mean age of the participants was 31.3±5.3 years for those who started HAART before pregnancy and 29.4±5.5 years for those who started during pregnancy (p=0.07). The viral loads means for those who started taking HAART before pregnancy 34.6±21.5 cells/mm3 and those who started during pregnancy 60±14 cells/mm3 (p = 0.01). Overall there were not any significant adverse fetal outcomes caused by taking HAART before or during pregnancy (p >0.05).Conclusions: Despite the fact that the viral load was more elevated in women starting HAART prior pregnancy compared to those started during pregnancy, there was no significant adverse foetal outcome related to time of initiation of HAART treatment by pregnant HIV positive in Yaoundé central Maternity. We suggest that the implementing of the test and treat strategy will have a positive impact on the vertical transmission of HIV