Automated quantification of retinal vessel morphometry in the UK Biobank Cohort

The following topics are dealt with: feature extraction; learning (artificial intelligence); image classification; image segmentation; computer vision; object detection; feedforward neural nets; image colour analysis; image representation; medical image processing

Automated retinal image quality assessment on the UK Biobank dataset for epidemiological studies.

Morphological changes in the retinal vascular network are associated with future risk of many systemic and vascular diseases. However, uncertainty over the presence and nature of some of these associations exists. Analysis of data from large population based studies will help to resolve these uncertainties. The QUARTZ (QUantitative Analysis of Retinal vessel Topology and siZe) retinal image analysis system allows automated processing of large numbers of retinal images. However, an image quality assessment module is needed to achieve full automation. In this paper, we propose such an algorithm, which uses the segmented vessel map to determine the suitability of retinal images for use in the creation of vessel morphometric data suitable for epidemiological studies. This includes an effective 3-dimensional feature set and support vector machine classification. A random subset of 800 retinal images from UK Biobank (a large prospective study of 500,000 middle aged adults; where 68,151 underwent retinal imaging) was used to examine the performance of the image quality algorithm. The algorithm achieved a sensitivity of 95.33% and a specificity of 91.13% for the detection of inadequate images. The strong performance of this image quality algorithm will make rapid automated analysis of vascular morphometry feasible on the entire UK Biobank dataset (and other large retinal datasets), with minimal operator involvement, and at low cost

Quantile regression analysis reveals widespread evidence for gene-environment or gene-gene interactions in myopia development

A genetic contribution to refractive error has been confirmed by the discovery of more than 150 associated variants in genome-wide association studies (GWAS). Environmental factors such as education and time outdoors also demonstrate strong associations. Currently however, the extent of gene-environment or gene-gene interactions in myopia is unknown. We tested the hypothesis that refractive error-associated variants exhibit effect size heterogeneity, a hallmark feature of genetic interactions. Of 146 variants tested, evidence of non-uniform, non-linear effects were observed for 66 (45%) at Bonferroni-corrected significance (P < 1.1 × 10−4) and 128 (88%) at nominal significance (P < 0.05). LAMA2 variant rs12193446, for example, had an effect size varying from −0.20 diopters (95% CI −0.18 to −0.23) to −0.89 diopters (95% CI −0.71 to −1.07) in different individuals. SNP effects were strongest at the phenotype extremes and weaker in emmetropes. A parsimonious explanation for these findings is that gene-environment or gene-gene interactions in myopia are pervasive

Temporary migrant workers programs "South-North". The experience of El Salvador and Honduras

Incluye bibliografí

Early Cycladic Potter's Marks from Mount Kynthos in Delos

Mac Gillivray J. A. Early Cycladic Potter's Marks from Mount Kynthos in Delos. In: Bulletin de correspondance hellénique. Volume 105, livraison 2, 1981. pp. 615-621

A numerical investigation of the February 1993 snowstorm

Despite considerable research in the study of explosively deepening oceanic storms, much less attention has been paid to coastal secondary cyclogenesis that is characterized by weak baroclinicity but heavy precipitation. In this thesis, the development of one such storm, the February 1993 cyclone, is investigated using a high-resolution version of the Canadian Regional Finite-element (RFE) model in which more realistic physical representations are incorporated. It is shown that the improved RFE model reproduces extremely well the timing and location of coastal secondary cyclogenesis along the Carolina coast, the evolution of the associated surface pressure perturbations and tropospheric baroclinic waves. The model also performs remarkably well in predicting the distribution and intensity of the storm's precipitation over the New England states, Quebec and the maritime provinces.It is found that the coastal secondary cyclogenesis occurs in response to the low-level inshore advection of warm and moist air from the maritime boundary layer and the approach of the midtropospheric short-wave trough associated with a decaying cyclone to the west. Rapid deepening of the cyclone ensues as intense precipitation falls along the warm and cold frontal zones.Diagnosis of a series of sensitivity simulations reveals that large-scale dry dynamics, latent heat release, air-sea interaction and surface characteristics act in concert to determine the cyclone's intensification and evolution. It is found that the low-level thermal advection contributes more to the cyclogenesis during the incipient stage, whereas the upper-level trough control the cyclone's rapid deepening at later stages. Overall, latent heat release accounts for about 50% of the total deepening. It is also found that ice microphysics (i.e., melting of snow) could indeed induce a thermally indirect circulation superposed onto the mean flow in the vicinity of the rain-snow boundary, but it has a weak negative impact on the cyclogenesis

Mount Kynthos in Delos. The Early Cycladic Settlement

Mac Gillivray J. A. Mount Kynthos in Delos. The Early Cycladic Settlement. In: Bulletin de correspondance hellénique. Volume 104, livraison 1, 1980. pp. 3-45