Made available in DSpace on 2015-10-06T13:03:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-12-03. Added 1 bitstream(s) on 2015-10-06T13:18:56Z : No. of bitstreams: 1 000847380.pdf: 806327 bytes, checksum: f7d3032d99de2e92c79e98f58dfe233a (MD5) / Foi realizado estudo transversal, descritivo e observacional de 38 nervos ulnares de pacientes com hanseníase multibacilar, com idades entre 20 e 59 anos, com diagnóstico realizado na disciplina de dermatologia da Faculdade de Medicina de Botucatu (FMB-UNESP). Estes pacientes foram submetidos à palpação, exames de eletroneurografia e ultrassonografia dos nervos ulnares direito e esquerdo com o objetivo de estudar o comprometimento do nervo pela doença e comparar os resultados dos exames. Dos nervos estudados, nove (23,68%) não apresentaram nenhuma alteração nos resultados dos exames. Os que apresentaram alteração em um ou mais dos exames realizados, somaram 29 (76,32%). Os resultados foram comparados, e os que apresentaram alterações de normalidade em dois ou mais, foram denominados compatíveis. Houve compatibilidade de 20,68% entre clínica, eletroneurografia e ultrassonografia. Observou-se que esse fato ocorreu quando o exame ultrassonográfico mostrou valores próximos do dobro da normalidade. Não houve significância estatística entre os resultados apresentados; no entanto, deve-se considerar a correspondência entre os exames clínico, eletroneurográficos e ultrassonográficos / A cross-sectional, descriptive, observational study of 38 ulnar nerves of multibacillary patients, aged 20 to 59 years, with diagnosis made in Dermatology course of the Faculty of Medicine of Botucatu (FMB-UNESP). These patients underwent palpation, ultrasound exams and electroneurography ulnar nerve left and right in order to study the nerve disease involvement and compare the test results. The nerves studied, nine (23.68%) showed no change in the results of the examinations. Those who had alterations in one or more of the tests performed, totaled 29 (76.32%). The results were compared, and those with normal changes in two or more, were called compatible. There was 20.68% compatibility between clinical, electroneurography and ultrasound. It was observed that this actually occurred when the ultrasound examination showed values close to double the normal. There was no statistical significance between the results presented; however, one must consider the correlation between the clinical, electroneurographic and ultrasonography

This thesis presents the design and analysis for development of a Capacitive Micromachined Ultrasonic Transducer (CMUT), a novel sensor and actuator, aimed at replacing the conventional piezoelectric transducers for air-coupled ultrasonic imaging applications. These CMUTs are fabricated using the silicon micromachining technology wherein all fabrication is done on the surface of a silicon wafer by means of thin-film depositions, patterning with photolithography and etching. The main emphasis of this study is on developing analytical models that serve as effective design tools for the development of these devices. A desirable goal of such study is to create reasonable mathematical models, obtain analytical solutions, wherever possible, for various measures of transducer performance and provide design aids. A logical start is the lumped parameter modeling wherein the explicit dependence of the physical parameters on the spatial extent of the device is ignored. The system lumped parameters, such as the equivalent stiffness, the equivalent mass, and the equivalent damping are extracted from reasonable analytical or numerical models and subsequently used in the static and dynamic analysis of the device. Useful predictions are made with regard to the key transducer parameters, such as, the pull-in voltage, the static deflection, the dynamic response and the acoustic field produced. The modeling work presented embodies two main objectives: (i) it serves to provide direction in the design phase, and, (ii) it serves to aid in the extraction of critical parameters which affect the device behavior. Comparison of the results with the more rigorous FEM simulations as well as with those present in the existing literature assure that the developed models are accurate enough to serve as useful design tools. The distributed parameter modeling is presented next. Analysis of MEMS devices which rely on electrostatic actuation is complicated due to the fact that the structural deformations alter the electrostatic forces, which redistribute and modify the applied loads. Hence, it becomes imperative to consider the electro-elastic coupling aspect in the design of these devices. An approximate analytical solution for the static deflection of a thin, clamped circular plate caused by electrostatic forces which are inherently nonlinear, is presented. The model is based on the Kirchhoff-Love assumptions that the plate is thin and the deflections and slopes are small. The classical thin-plate theory is adequate when the ratio of the diameter to thickness of the plate is very large, a situation commonly prevalent in many MEMS devices, especially the CMUTs. This theory is used to determine the static deflection of the CMUT membrane due to a DC bias voltage. The thin-plate electro-elastic equation is solved using the Galerkin weighted residual technique under the assumption that the deflections are small in comparison to the thickness of the plate. The results obtained are compared to those obtained from ANSYS simulations and an excellent agreement is observed between the two. The pull-in voltage predicted by our model is close to the value predicted by ANSYS simulations. A simple analytical formula, which gives fairly accurate results (to within 3% of the value predicted by ANSYS simulations) for determination of the pull-in voltage, is also presented. As stated, this formula accounts for the elastic deflection of the membrane due to the coupled interaction with the electrostatic field. The effect of vacuum sealing the backside cavity of a CMUT is investigated in some detail. The presence or absence of air inside the cavity has a marked effect upon the system parameters, such as the natural frequency and the pull-in voltage. The possibility of using sealed CMUT cavities with air inside at ambient pressure is explored. In order to estimate the transducer loss due to the presence of air in the sealed cavity, the squeeze film forces resulting from the compression of the trapped air film are evaluated. Towards this end, the linearized Reynolds equation is solved in conjunction with the appropriate boundary conditions, taking the flexure of the membrane into account. From this analysis, it is concluded that, for a sealed CMUT cavity, the presence of air does not cause any squeeze film damping even when the flexure of the membrane is taken into account (the case of a rigid plate is already known). Although the emphasis of the study undertaken here is not on the physical realization of a working CMUT, a single cell as well as a linear array based on the design presented here, were fabricated (in a foundry elsewhere) in order to verify some of the most fundamental device parameters from experimental measurements. The fabricated devices have been characterized for their resonant frequency, quality factor, and structural integrity. These tests were conducted using the laser Doppler vibrometer and the Focused Ion Beam milling. Having investigated thoroughly the behavior of a single cell, we proceed to demonstrate how these cells can be arranged optimally in the form of an array to provide a comprehensive ultrasonic imaging system. A thorough analysis of the requirements for the array architecture is undertaken to determine the optimal configuration. The design constraints that need to be taken into account for CMUT arrays, especially for NDE applications, are presented. The main issue of designing an array consisting of a large number of CMUT cells required for producing a pressure wave of sufficient strength which is detectable upon reflection from the desired location even after suffering severe attenuation resulting from propagation in various media is addressed. A scalable annular array architecture of CMUT cells is recommended based on the analysis carried out.

L'objectif de la caractérisation des tissus par ultrasons ou ‘Quantitative Ultrasound (QUS)’ est de différencier les tissus pathologiques en associant les paramètres d’un modèle aux caractéristiques physiques du tissu. L'usage exclusif des ultrasons pour obtenir un diagnostic peut garantir que le patient ne subira pas une procédure invasive (e.g. une biopsie), utilisant des rayonnements ionisants (e.g. la tomographie) ou même inconfortable et coûteuse (e.g. IRM). Les méthodes de QUS extraient des informations sur la microstructure du tissu à partir du contenu spectral ou temporel des signaux ultrasonores. Le signal temporel radiofréquence (RF) et son enveloppe sont d'intérêt à cause du speckle crée par l’interférence des ondes, qui peut être modélisé par des distributions statistiques. Ce travail propose d'explorer la possibilité d'obtenir des estimations QUS fiables en utilisant des distributions statistiques comme modèles pour le speckle ultrasonore. Les estimations sont constituées des paramètres des distributions respectives et dépendent de la densité de diffuseurs dans le milieu. L’évaluation s’effectue sur des images simulées, des fantômes de particules et des biofantômes. Dans la première partie, la distribution Gaussienne Généralisée est utilisée pour modéliser le signal RF, et la distribution de Nakagami est utilisée pour modéliser son enveloppe. Les deux distributions sont limitées à discriminer les milieux avec une faible densité de diffuseurs, parce que les valeurs de leurs paramètres de forme saturent pour un speckle pleinement développé. Par conséquent, puisque la formation du speckle pleinement développé dépend de la résolution du système d'imagerie, la caractérisation peut se faire seulement à de très hautes résolutions, correspondant à des hautes fréquences qui ne sont pas communes en échographie clinique. Une application du modèle de Nakagami sur l’image crée par la seconde harmonique montre le potentiel du paramètre de forme de Nakagami en tant que mesure de la nonlinéarité du milieu. Dans la deuxième partie, l'enveloppe a été modélisée en utilisant la distribution K-Homodyne. Le paramètre de regroupement des diffuseurs α permet de discriminer entre les milieux denses jusqu’à une limite supérieure à celle du paramètre de Nakagami. Pourtant, cette limite est difficile à estimer avec précision, parce que les valeurs caractéristiques pour le speckle pleinement développé sont affectées par un biais et une variance élevés. Le biais et la variance peuvent être améliorés en augmentant la quantité de données utilisée pour l’estimation. Dans la dernière partie, une technique de déconvolution spécialement conçue pour la caractérisation des tissus a été évaluée. Des essais exhaustifs ont montré qu’elle n’est pas suffisamment robuste pour une application clinique, puisque les images déconvoluées ne sont pas fidèles à la réflectivité originale du milieu / The purpose of ultrasound tissue characterization or Quantitative Ultrasound (QUS) is to differentiate between tissue pathologies by associating model parameters to physical tissue features. The exclusive use of ultrasound for diagnosis would guarantee that the patient does not undergo a procedure that is invasive (e.g. a biopsy), using ionizing radiation (e.g. tomography) or simply uncomfortable and expensive (e.g. MRI). QUS methods extract information on the tissue microstructure from the temporal or spectral content of the acquired ultrasound signals. The temporal radiofrequency (RF) signal and its envelope are of interest because of the speckle patterns created by wave interference, which can be modeled by statistical distributions. The present work proposes to explore the possibility of obtaining reliable QUS estimates by using statistical distributions as models for ultrasound speckle. The estimates consist in the parameters of the respective distributions and are indicators of the scatterer density in the medium. The evaluation is conducted on simulated images, particle phantoms and biophantoms. In the first part, the Generalized Gaussian distribution is used to model the RF signal, and the Nakagami distribution is used to model its envelope. The two distributions show limitations in discriminating media with high scatterer densities, as the values of their shape parameters saturate in the fully developed speckle regime. Therefore, since the formation of fully developed speckle depends on the resolution of the imaging system, characterization can be done only at very high resolutions, corresponding to high frequencies that are not common in clinical ultrasound. An application of the Nakagami model on the second harmonic image shows the potential of the Nakagami shape parameter as a measure of the nonlinearity of the medium. In the second part, the echo envelope was modeled using the Homodyned-K distribution. The scatterer clustering parameter α allows the discrimination of dense media up to a concentration that is higher than the one that limits the Nakagami distribution. However, this limit is difficult to estimate precisely, because the values of α that are characteristic for fully developed speckle suffer from large estimation bias and variance. The bias and the variance can be improved by performing the estimation on a very large amount of data. In the final part, a deconvolution technique designed specifically for ultrasound tissue characterization has been analyzed. Extensive testing has shown it to not be sufficiently robust for clinical applications, since the deconvolved images are not reliable in terms of fidelity to the original reflectivity of the medium

M.Tech. / It is difficult to manage a pregnancy when fetal age, health status or potential pregnancy risks are not known. The aim of this study was to assess the impact of routine ultrasound screening as compared to selective use of ultrasound in the mid-trimester of pregnancy, on women using South African government health services. The three objectives investigated included assessment of the availability of reliable menstrual histories in the study population, the influence of ultrasound dating on obstetric management and the effect of ultrasound on pregnancy outcome due to the early detection of high risk pregnancies. A cluster randomised trial of 962 women was performed to test the hypothesis that midtrimester routine ultrasound screening in low risk pregnancies would result in improved antenatal care and perinatal outcome. Groups of eligible pregnant women were randomly selected to have either a routine scan followed by normal antenatal care or routine antenatal care which only allows for the selective use of ultrasound, in line with South African Antenatal Care Policy. Statistical analysis of the results confirmed that ultrasound dating is a more accurate predictor of the expected date of delivery when compared to other dating methods. Improved pregnancy dating resulted in a significant reduction in induction of labour for post-term pregnancy in the ultrasound screening group, suggesting a positive effect of ultrasound screening on obstetric management. No improvement was demonstrated in perinatal morbidity or mortality. The early detection of anomalous fetuses only led to one therapeutic abortion. The study did not possess the statistical power to demonstrate improved outcomes when multiple pregnancies were detected early in pregnancy. Currently there appears to be no urgent need to implement a routine antenatal screening programme in the Gauteng public health sector. In view of the fact that a third of the participants indicated that they were unsure of menstrual dates, and one third of the participants in the ultrasound screening group presented with an unreliable menstrual history, it is proposed that unsure dates be considered as a valid indication for the selective use of ultrasound in mid-trimester pregnancy.

Distributed Point Source Method (DPSM) was developed by Placko and Kundu 1, as a technique for modeling electromagnetic and elastic wave propagation problems. DPSM has been used for modeling ultrasonic, electrostatic and electromagnetic fields scattered by defects and anomalies in a structure. The modeling of such scattered field helps to extract valuable information about the location and type of defects. Therefore, DPSM can be used as an effective tool for Non-Destructive Testing (NDT). Anisotropy adds to the complexity of the problem, both mathematically and computationally. Computation of the Green's function which is used as the fundamental solution in DPSM is considerably more challenging for anisotropic media, and it cannot be reduced to a closed-form solution as is done for isotropic materials. The purpose of this study is to investigate and implement DPSM for an anisotropic medium. While the mathematical formulation and the numerical algorithm will be considered for general anisotropic media, more emphasis will be placed on transversely isotropic materials in the numerical example presented in this paper. The unidirectional fiber-reinforced composites which are widely used in today's industry are good examples of transversely isotropic materials. Development of an effective and accurate NDT method based on these modeling results can be of paramount importance for in-service monitoring of damage in composite structures.

A dissertation presented in partial compliance with the requirements for the Master's Degree in Technology: Chiropractic, Technikon Natal, 2001. / The purpose of this study was to determine the relative efficacy of chiropractic manipulation used in conjunction with detuned ultrasound over the gluteal muscles compared to manipulation used in conjunction with proprioceptive neuromuscular facilitation stretching of the gluteal muscle group in the treatment of sacroiliac syndrome. It was hypothesised that both treatment groups would be effective in the treatment of sacroiliac syndrome but that manipulation used in conjunction with proprioceptive neuromuscular facilitation of the gluteal musculature would be more effective than manipulation used in conjunction with detuned ultrasound, in terms of subjective and objective clinical findings. / M

The principle of operation of a novel rotating disk ultrasonic intensity meter is studied. Its characteristics are explained by a competition between acoustic radiation pressure and viscous drag on the disk. Acoustic streaming does not play a significant role in the operation of this meter as it is now configured. Experiments are described which were done to find the optimum dimensions and position for a nylon disk. In this optimum configuration, the rotation rate of the disk is related to the ultrasonic intensity by a power law. This relationship is theoretically predicted and found to hold as the ultrasonic intensity varies by a factor of at least ten. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Heart disease is the leading cause of death globally. Early diagnosis is the key to successful treatment. By providing noninvasive, non-ionizing, and real-time imaging, echocardiography plays a critical role in identifying heart disease. Compared to other imaging modalities, ultrasound has unparalleled temporal resolution. High frame-rate imaging has enabled the development of new metrics to characterize myocardial mechanics. Strain imaging measures the heart's deformation throughout the cardiac cycle, providing a quantitative assessment of cardiac health. The intention of this dissertation is to bring Myocardial Elastography (ME) closer to clinical realization. ME is a high frame-rate strain imaging technique for transthoracic and intracardiac echocardiography. This work consists of four Aims. There is a fundamental trade-off between spatial and temporal resolution in strain imaging. In Aim 1, the optimal transmit sequence that generates the most accurate and precise strain estimate was determined. Two common approaches to coherent compounding (full and partial aperture) were compared in simulation and in transthoracic imaging of healthy human subjects (n=5). The optimized subaperture compounding sequence (25-element subperture, 90° angular aperture, 10 virtual sources, 300 Hz frame rate) was compared to the optimized steered compounding sequence (60° angular aperture, 15° tilt, 10 virtual sources, 300 Hz frame rate) and was found to measure strain in healthy human subjects with equivalent precision. The optimal compounding configuration was then evaluated against two other high-frame rate transmit strategies, ECG-gated focused imaging, and wide-beam imaging, in simulation and in healthy subjects (n=7). Achieving the highest level of strain precision, ECG-gated focused imaging was determined to be the preferred imaging approach in patients capable of sustaining a breath hold, with compounding preferred in those unable to do so. Rapid diagnosis is essential to successful treatment of myocardial infarction. In Aim 2, ME's ability to track infarct formation and recovery, and localize infarct using regional strain measurments, was investigated in a large animal survival model (n=11). Infarcts were generated via ligation of the left anterior descending, imaging regularly for up to 28 days. A radial strain-based metric, percentage of healthy myocardium by strain (PHM_ε), was developed as a marker for healthy myocardial tissue. PHM_ε was strongly linearly correlated with actual infarct size as determined by gross pathology (R2 = 0.80). ME was capable of diagnosing individual myocardial segments as non-infarcted or infarcted with high sensitivity (82%), specificity (92%), and precision (85%) (ROC AUC = 0.90), and tracked infarct recovery from collateral reperfusion through time. Noninvasive strain imaging at rest can improve pre-test probability accuracy, and reduce unnecessary stress testing. In Aim 3, ME's potential to provide early diagnosis of coronary artery disease was investigated in an ongoing study. Patients undergoing myocardial perfusion imaging were recruited (n=126). Perfusion scores were used as the reference standard. Morphological transformations were integrated into the processing pipeline to reduce variability in the strain measurements. PHM_ε was reintroduced and used to differentiate between patients with and without coronary artery disease. ME was capable of distinguishing between normal patients and those with significant ischemia or infarct (subjects with perfusion defects at rest) with statistical significance (p < 0.05), although a greater sample size is needed to confirm the results. One of the most common treatments for arrhythmia, catheter ablation, can fail if the lesion line intended to terminate the abnormal rhythm is non-contiguous. In Aim 4, the gap resolution and clinical feasibility of Intracardiac Myocardial Elastography (IME) strain imaging, an ablation monitoring technique, was investigated. Lesion size estimation and gap resolution was evaluated in an open chest canine model (n=3), wherein lesion lines consisting of three lesions and two gaps were generated in each canine left ventricle via epicardial ablation. All gaps were resolvable. Average lesion and gap areas were measured with high agreement (33 ± 14 mm2 and 30 ± 15 mm2, respectively) when compared against gross pathology (34 ± 19 mm2 and 26 ± 11 mm2, respectively). Gaps as small as 11 mm2 (3.6 mm on epicardial surface) were identifiable. Patients undergoing ablation to treat typical cavotricuspid isthmus atrial flutter (n=5) were imaged throughout the procedure. In all patients, strain decreased in the cavotricuspid isthmus after ablation (mean paired difference of -17 ± 11 %, p < 0.05). Together, these Aims intend to translate a promising imaging method from research to clinical reality.

Underground pipelines are used in various process piping systems to transport gasses or fluids and are usually subjected to the effects of external corrosion. Corrosion can be defined as the deterioration of a material due to a reaction with its environment or the destruction of the material by means that are not mechanical (Fontana and Greene, 1967:2). External corrosion, due to the interaction between the pipe and the soil, is generally a slow process and the corrosion rate is influenced by a variety of external factors. Some of these factors include the ambient pH and salinity, the presence of moisture and bacteria, temperature, the electrical potential difference between the pipe and other structures and the implementation of preventative measures (such as cathodic protection and wrapping). Although the external corrosion of underground pipelines is generally a slow process in mild environments, pipe degradation as a result of external corrosion remains one of the prevalent reasons for the failure of underground pipelines. As with many mechanical systems that are prone to fail at one time or the other, the high costs involved with unforeseen failure necessitate some quantitative (or qualitative) indication of the condition of the pipe system. Some of the costs that can be expected as a result of unforeseen pipeline failure are, amongst others: • costs as a result of the failure of dependent systems; • costs as a result of the loss of production; • costs as a result of the loss of product (in distribution networks); • the cost of unscheduled maintenance (logistical costs); • costs as a result of damage to public property; • fines imposed by customers (in distribution networks); • costs related to pollution control, and • the loss of life The single most important parameter associated with the condition of a system is its profitable remaining life. This is the time during which a sub-system contributes to the well-being of a larger system and the organisation. Therefore, it is necessary to determine, with reasonable accuracy, the extent of the remaining life of a system so that managerial decisions (i.e. investments, cash-flow analyses, maintenance task scheduling and replacement programmes), based on this figure, can be made. Done correctly, this can directly lead to a decrease in maintenance costs and subsequently to an increase in profit. The extent of a corrosive attack on the pipeline might be highly localised or might be fairly uniform over the length of the installation. The fact of the matter is that, since the pipe is buried, it is very difficult to quantify the external damage caused by corrosion. A variety of techniques are in use to survey pipelines and detect anomalies. However, for large pipelines, most of these techniques are either inefficient or too expensive. There will always remain some uncertainty regarding the integrity of the pipeline. The work presented in this study is explained with valid generic examples and aims: 1. to provide the reader with sufficient background information so that the need for determining the integrity of a pipeline becomes apparent; 2. to indicate why a reliability-centred approach is necessary (Chapter 1); 3. to explain the basic principles of corrosion and the electrochemical nature of corrosion (Chapter 2); 4. to indicate areas, based on the basic principles of corrosion, where severe corrosion can be expected (Chapters 2 and 7); 5. to provide and elaborate on information regarding pipe surveillance techniques that are currently available (Chapter 3); 6. to establish the criteria for pipeline failure, in the form of a limit state Junction, for pipes that are subjected to near-constant internal pressures (static failure domain) as well as for pipes subjected to varying internal pressures (fatigue domain) (Chapters 5 and 6); 7. to indicate the sensitivity of the fatigue domain solution to changes in the system variables and to indicate that a significant reduction in the system variables does not necessarily reduce the solution accuracy (Chapter 6), and 8. to integrate the above-mentioned into a practical and workable guideline that can be used to determine the remaining life of an underground pipe network (Chapter 7). / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2002. / Mechanical and Aeronautical Engineering / unrestricted

Research has been completed in order to rapidly manufacture spacecraft thermal control technologies embedded in spacecraft structural panels using ultrasonic consolidation. This rapid manufacturing process enables custom thermal control designs in the time frame necessary for responsive space. Successfully embedded components include temperature sensors, heaters, wire harnessing, pre-manufactured heat pipes, and custom integral heat pipes. High conductivity inserts and custom integral pulsating heat pipes were unsuccessfully attempted. This research shows the viability of rapid manufacturing of spacecraft structures with embedded thermal control using ultrasonic consolidation.