421 research outputs found

    The Haemodynamics of a Stented Arteriovenous Fistula through Experiments and Flow Modelling

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    The arteriovenous fistula (AVF) is a vasculature created for end-stage renal disease patients who undergo haemodialysis. This vasculature is often affected by stenosis in the juxta-anastomotic (JXA) region and the presence of disturbed haemodynamics within the vessel is known to initiate such diseased conditions. A novel treatment involving the implantation of a flexible stent in the JXA region has shown potential for retaining healthy AVFs. Only a limited number of experimental studies have been conducted to understand the disturbed flow conditions, while the impact of stent implantation on the haemodynamics within the AVF is yet to be explored. The study was initiated by developing a benchtop patient-specific AVF model to conduct a Tomographic Particle Image Velocimetry (Tomo-PIV) measurement. The subsequent temporally resolved volumetric velocity field was phase-averaged to quantify fluctuations occurring over the inlet pulsatile conditions. It was noted that high turbulent kinetic energy (TKE) was generated at the JXA region. To study the effects of the stent implantation, Large Eddy Simulations (LES) comparing the AVF geometry with and without the presence of the stent implantation were conducted. The trajectory of the flow in the stented case was funnelled within the stent encapsulated region which in turn, contained the disturbed flow within the stent lumen while mitigating the generation of turbulence. Consequently, the distribution of adverse wall shear stress (WSS) in the stented region was much lower compared to that of the `stent-absent' case. Simulations were also conducted on the diseased patient AVF, before the stent implantation, to make an overall assessment of the effect of treatment. Larger and persistent regions of high TKE were noted in the vessel downstream of the stenosis despite the lower velocity of flow in the diseased model. In summary, the stent implantation in the patient AVF showed the ability to funnel flow disturbances away from the vessel wall, thereby leading to lower adverse WSS distributions. The presence of the stent also mitigated turbulence generation. These findings provide valuable insight into the favourable haemodynamic effects of this novel endovascular procedure, thus, substantiating this treatment strategy to treat vascular disease in AVFs

    The Historical and Archaeological Analysis of the Swords of La Belle

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    ABSTRACT This research involves the conservation, historical and archaeological analysis of a cache of swords recovered from the 17th-century French shipwreck La Belle. The central premise of my research model is the incorporation of the theories and methodologies of several convergent disciplines; concentrating on the material and cultural aspect of these weapons, and the technical processes involved with their conservation. The integration of the conservation process and research results with the archaeological evidence, both objects and context, can lead to new methods of archaeological inquiry. The details of materials composition and structure, sequence of processing, properties, performance, or use should define the way modern material culture research is conducted. This research approach seeks to answer such relevant questions as what is the past and current history of the sword types recovered from La Belle? What materials, technology or skilled craft aided in the production of these swords and their individual components? What was the practical and symbolic function of these edged weapons? Subsequently, the data lead to interpretations of the finds and their broader meaning within the context of the shipwreck itself. I am convinced that the research presented in this dissertation will help to facilitate a wider dialogue about swords and other edged weapons among weapons historians and archaeologists. The conservator is dedicated to maintaining the long-term preservation of cultural artifacts through examination, documentation, treatment, and preventive care and research. Conservation is an interdisciplinary field involving knowledge and skills acquired from a number of diverse disciplines in the arts and sciences. As a result, conservators must have a working knowledge of materials technology, chemistry, biology, physics, art history, and archaeology. The results of the case studies discussed in chapter six, though limited in scope, proved most promising, indicating that there are always viable alternatives to the methods and materials used by artifact conservation and preservation. The collaboration between conservators and experts in other related fields, such as conservation science, computer science, radiography, digital imaging, and rapid-prototyping technology is critical to the successful practice of artifact conservation and interpretation

    Three--dimensional medical imaging: Algorithms and computer systems

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    This paper presents an introduction to the field of three-dimensional medical imaging It presents medical imaging terms and concepts, summarizes the basic operations performed in three-dimensional medical imaging, and describes sample algorithms for accomplishing these operations. The paper contains a synopsis of the architectures and algorithms used in eight machines to render three-dimensional medical images, with particular emphasis paid to their distinctive contributions. It compares the performance of the machines along several dimensions, including image resolution, elapsed time to form an image, imaging algorithms used in the machine, and the degree of parallelism used in the architecture. The paper concludes with general trends for future developments in this field and references on three-dimensional medical imaging

    Automatic segmentation and reconstruction of traffic accident scenarios from mobile laser scanning data

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    Virtual reconstruction of historic sites, planning of restorations and attachments of new building parts, as well as forest inventory are few examples of fields that benefit from the application of 3D surveying data. Originally using 2D photo based documentation and manual distance measurements, the 3D information obtained from multi camera and laser scanning systems realizes a noticeable improvement regarding the surveying times and the amount of generated 3D information. The 3D data allows a detailed post processing and better visualization of all relevant spatial information. Yet, for the extraction of the required information from the raw scan data and for the generation of useable visual output, time-consuming, complex user-based data processing is still required, using the commercially available 3D software tools. In this context, the automatic object recognition from 3D point cloud and depth data has been discussed in many different works. The developed tools and methods however, usually only focus on a certain kind of object or the detection of learned invariant surface shapes. Although the resulting methods are applicable for certain practices of data segmentation, they are not necessarily suitable for arbitrary tasks due to the varying requirements of the different fields of research. This thesis presents a more widespread solution for automatic scene reconstruction from 3D point clouds, targeting street scenarios, specifically for the task of traffic accident scene analysis and documentation. The data, obtained by sampling the scene using a mobile scanning system is evaluated, segmented, and finally used to generate detailed 3D information of the scanned environment. To realize this aim, this work adapts and validates various existing approaches on laser scan segmentation regarding the application on accident relevant scene information, including road surfaces and markings, vehicles, walls, trees and other salient objects. The approaches are therefore evaluated regarding their suitability and limitations for the given tasks, as well as for possibilities concerning the combined application together with other procedures. The obtained knowledge is used for the development of new algorithms and procedures to allow a satisfying segmentation and reconstruction of the scene, corresponding to the available sampling densities and precisions. Besides the segmentation of the point cloud data, this thesis presents different visualization and reconstruction methods to achieve a wider range of possible applications of the developed system for data export and utilization in different third party software tools

    A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

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    This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

    3-D surface modelling of the human body and 3-D surface anthropometry

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    This thesis investigates three-dimensional (3-D) surface modelling of the human body and 3-D surface anthropometry. These are two separate, but closely related, areas. 3-D surface modelling is an essential technology for representing and describing the surface shape of an object on a computer. 3-D surface modelling of the human body has wide applications in engineering design, work space simulation, the clothing industry, medicine, biomechanics and animation. These applications require increasingly realistic surface models of the human body. 3-D surface anthropometry is a new interdisciplinary subject. It is defined in this thesis as the art, science, and technology of acquiring, modelling and interrogating 3-D surface data of the human body. [Continues.

    Application of X-ray Grating Interferometry to Polymer/Flame Retardant Blends in Additive Manufacturing

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    X-ray grating interferometry is a nondestructive tool for visualizing the internal structures of samples. Image contrast can be generated from the absorption of X-rays, the change in phase of the beam and small-angle X-ray scattering (dark-field). The attenuation and differential phase data obtained complement each other to give the internal composition of a material and large-scale structural information. The dark-field signal reveals sub-pixel structural detail usually invisible to the attenuation and phase probe, with the potential to highlight size distribution detail in a fashion faster than conventional small-angle scattering techniques. This work applies X-ray grating interferometry to the study of additively manufactured polymeric objects. Additively manufactured bunnies made from single material—acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA)—were studied by grating-based X-ray interferometric two-dimensional imaging and tomography. The dark-field images detected poor adhesion in the plane perpendicular to the build plate. Curvature analysis of the sample perimeter revealed a slightly higher propensity to errors in regions of higher curvature. Incorporation of flame-retardant molecules to near-surface regions of otherwise flammable objects through the fused deposition modeling additive manufacturing technique was also explored. The anticipated advantage was efficient use of the flame retardants while keeping them away from the surface for safety. To determine heat propagation effects, two-dimensional grating-based interferometry imaging at LSU CAMD was used to study heated samples. The focus was on the dark-field signals to highlight voids and gaps arising from layer delamination or gasification of chemical components. The resulting differential phase and dark-field x images were tainted by fringes attributed to inaccuracies in the grating-step position. Attempts to correct this will be presented. Interferometric tomography was also carried out on the heated samples using the W. M. Keck interferometric system at LSU. Grating-based interferometry was also used to probe scattering structure sizes of heated samples. Comparison of the data with the conventional small-angle x-ray scattering technique, SAXS, is being pursued. The results obtained so far from the above-mentioned experimental works are presented in this document

    The Historical and Archaeological Analysis of the Swords of La Belle

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    ABSTRACT This research involves the conservation, historical and archaeological analysis of a cache of swords recovered from the 17th-century French shipwreck La Belle. The central premise of my research model is the incorporation of the theories and methodologies of several convergent disciplines; concentrating on the material and cultural aspect of these weapons, and the technical processes involved with their conservation. The integration of the conservation process and research results with the archaeological evidence, both objects and context, can lead to new methods of archaeological inquiry. The details of materials composition and structure, sequence of processing, properties, performance, or use should define the way modern material culture research is conducted. This research approach seeks to answer such relevant questions as what is the past and current history of the sword types recovered from La Belle? What materials, technology or skilled craft aided in the production of these swords and their individual components? What was the practical and symbolic function of these edged weapons? Subsequently, the data lead to interpretations of the finds and their broader meaning within the context of the shipwreck itself. I am convinced that the research presented in this dissertation will help to facilitate a wider dialogue about swords and other edged weapons among weapons historians and archaeologists. The conservator is dedicated to maintaining the long-term preservation of cultural artifacts through examination, documentation, treatment, and preventive care and research. Conservation is an interdisciplinary field involving knowledge and skills acquired from a number of diverse disciplines in the arts and sciences. As a result, conservators must have a working knowledge of materials technology, chemistry, biology, physics, art history, and archaeology. The results of the case studies discussed in chapter six, though limited in scope, proved most promising, indicating that there are always viable alternatives to the methods and materials used by artifact conservation and preservation. The collaboration between conservators and experts in other related fields, such as conservation science, computer science, radiography, digital imaging, and rapid-prototyping technology is critical to the successful practice of artifact conservation and interpretation

    Advancements and Breakthroughs in Ultrasound Imaging

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    Ultrasonic imaging is a powerful diagnostic tool available to medical practitioners, engineers and researchers today. Due to the relative safety, and the non-invasive nature, ultrasonic imaging has become one of the most rapidly advancing technologies. These rapid advances are directly related to the parallel advancements in electronics, computing, and transducer technology together with sophisticated signal processing techniques. This book focuses on state of the art developments in ultrasonic imaging applications and underlying technologies presented by leading practitioners and researchers from many parts of the world
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