Search results for "TORTUOSITY"

Filter Bank: a Directional Approach for Retinal Vessel Segmentation

2017

It is well known that retinal diseases are sometimes identified by tortuosity of the vessels, presence of exudates and hemorrhages while lesions of tissues are associated to diabetic retinopathy, retinopathy of prematurity and more general cerebrovascular problems. One of the main issues in this research field is detecting small curvilinear structures, thus the aim of this contribution is to introduce a non-supervised and automated methodology to detect features such as curvilinear structures in retinal images. The core of the proposed methodology consists in using an approach that resembles the “a trous” wavelet algorithm. With respect to the standard Gabor analysis our methodology is base…

From the Golgi-Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring a…

2007

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrai…

2020

Abstract. Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities and measure the permeability experimentally. The microstructure, namely effective porosity and effective specific surface, is investigated using image processing. We determine flow proper…

Combined numerical and experimental study of microstructure and permeability in porous granular media

2020

<div> <div> <div> <p>Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities, representing shallow depth crustal sediments. The microstructure, namely effective porosity …

Hybrid Endograft Solution for Complex Iliac Anatomy

2010

The purpose of this study was to evaluate single-center results with selective use of Gore Excluder limbs (W.L. Gore & Associates, Flagstaff, AZ) in a Cook Zenith body (Cook Inc, Bloomington, IN) for elective endovascular abdominal aortic aneurysm (AAA) repair. A prospectively held database for patients with AAA, who were treated endovascularly between March 1999 and July 2008, was queried for patients treated with a Cook Zenith body and one or two Gore Excluder limbs. Indication, technical success, late limb occlusion, and disconnection were evaluated. From 276 patients who were treated with a Zenith body, 29 underwent repair with hybrid graft components with, in total, 41 Gore Exclud…

Influence of carotid tortuosity on internal carotid artery access time in the treatment of acute ischemic stroke

2017

Purpose Carotid artery anatomy is thought to influence internal carotid artery access time (ICA-AT) in patients requiring mechanical thrombectomy for acute ischemic stroke. This study investigates the association between ICA-AT and carotid anatomy. Material and methods Computed tomography angiography (CTA) data of 76 consecutive patients presenting with acute ischemic stroke requiring mechanical thrombectomy for middle cerebral artery or carotid T occlusion were evaluated. The supraaortic extracranial vasculature was analyzed regarding take-off angles and curvature of the affected side. Digital subtraction angiography data were primarily analyzed regarding ICA-AT and secondarily regarding r…

Simulations of single-fluid flow in porous media

1998

Several results of lattice-gas and lattice-Boltzmann simulations of single-fluid flow in 2D and 3D porous media are discussed. Simulation results for the tortuosity, effective porosity and permeability of a 2D random porous medium are reported. A modified Kozeny–Carman law is suggested, which includes the concept of effective porosity. This law is found to fit well the simulated 2D permeabilities. The results for fluid flow through large 3D random fibre webs are also presented. The simulated permeabilities of these webs are found to be in good agreement with experimental data. The simulations also confirm that, for this kind of materials, permeability depends exponentially on porosity over…

Prepapillary venous loops and choroidal veins tortuosity

2003

A visual framework to create photorealistic retinal vessels for diagnosis purposes

2020

The methods developed in recent years for synthesising an ocular fundus can be been divided into two main categories. The first category of methods involves the development of an anatomical model of the eye, where artificial images are generated using appropriate parameters for modelling the vascular networks and fundus. The second type of method has been made possible by the development of deep learning techniques and improvements in the performance of hardware (especially graphics cards equipped with a large number of cores). The methodology proposed here to produce high-resolution synthetic fundus images is intended to be an alternative to the increasingly widespread use of generative ad…

Digital rock physics: Effect of fluid viscosity on effective elastic properties

2011

Abstract This paper is concerned with the effect of pore fluid viscosity on effective elastic properties using digitized rocks. We determine a significant velocity dispersion in wave propagation simulations by the variation of the pore fluid viscosity. Several attenuation regimes are considered which may contribute to this observation. Starting point is a virtual rock physics approach. Numerical simulations of effective transport and effective mechanical properties are applied to statistically representative rock samples. The rock microstructure is imaged by 3D X-ray tomography. Permeability values were estimated through Lattice-Boltzmann flow simulations. The dry rock moduli and the tortuo…