• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 35
  • 7
  • 4
  • 2
  • Tagged with
  • 58
  • 58
  • 10
  • 10
  • 9
  • 9
  • 7
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Método de alta resolução em imageamento acústico. / High resolution method for acoustic imaging.

Flavio Guimarães Caduda 29 April 2011 (has links)
O estudo concentra-se na localização de fontes de ruídos em aeroacústica, através do processamento digital de sinais. O objetivo em aeroacústica é localizar fontes de ruído em estruturas aerodinâmicas (e.g.: aerofólios, slats, flaps e trens de pouso), motores e turbinas. Isto se faz possível utilizando arranjos de microfones, ou simplesmente arrays, cujos sinais são processados para localizar as fontes. Ao utilizar o beamforming clássico para processar os sinais vindos do array, este é incapaz de localizar as fontes de ruído de forma satisfatória. O 2D-ESPRIT é um método de alta resolução que é apresentado como alternativa. Nas simulações, é possível perceber que o 2D-ESPRIT tem melhor desempenho que o beamforming clássico, conseguindo localizar fontes próximas com arrays quadrados e com um número reduzido de amostras de sinal. / This study focuses on locating sources of noise in aeroacoustics, through digital signal processing. An objective in aeroacoustics is to locate sources of noise in aerodynamic structures (e.g.: airfoils, slats, flaps and landing gears), engines and fans. This is possible using microphone arrays, whose signals are processed to locate the sources. Using classical beamforming as the processing scheme for these signals, it is shown that it is incapable of locating sources satisfactorily in many of the practical scenarios. 2D-ESPRIT is a high resolution processing scheme that is presented as an alternative. Simulations show that 2D-ESPRIT outperfoms classical beamforming, locating closely positioned sources with the simple URA and with a reduced number of signal samples.
32

Método de alta resolução em imageamento acústico. / High resolution method for acoustic imaging.

Caduda, Flavio Guimarães 29 April 2011 (has links)
O estudo concentra-se na localização de fontes de ruídos em aeroacústica, através do processamento digital de sinais. O objetivo em aeroacústica é localizar fontes de ruído em estruturas aerodinâmicas (e.g.: aerofólios, slats, flaps e trens de pouso), motores e turbinas. Isto se faz possível utilizando arranjos de microfones, ou simplesmente arrays, cujos sinais são processados para localizar as fontes. Ao utilizar o beamforming clássico para processar os sinais vindos do array, este é incapaz de localizar as fontes de ruído de forma satisfatória. O 2D-ESPRIT é um método de alta resolução que é apresentado como alternativa. Nas simulações, é possível perceber que o 2D-ESPRIT tem melhor desempenho que o beamforming clássico, conseguindo localizar fontes próximas com arrays quadrados e com um número reduzido de amostras de sinal. / This study focuses on locating sources of noise in aeroacoustics, through digital signal processing. An objective in aeroacoustics is to locate sources of noise in aerodynamic structures (e.g.: airfoils, slats, flaps and landing gears), engines and fans. This is possible using microphone arrays, whose signals are processed to locate the sources. Using classical beamforming as the processing scheme for these signals, it is shown that it is incapable of locating sources satisfactorily in many of the practical scenarios. 2D-ESPRIT is a high resolution processing scheme that is presented as an alternative. Simulations show that 2D-ESPRIT outperfoms classical beamforming, locating closely positioned sources with the simple URA and with a reduced number of signal samples.
33

Acoustic Imaging of Bruises

Prabhakara, Sandeep 22 May 2006 (has links)
Ultrasound is a valuable tool to monitor wound healing. In this report, ultrasound is used to determine the features in the B-scans that correspond to a bruise. High frequency ultrasound scans show clear and distinct features that correspond to a laceration or a late stage pressure ulcer. This is because of the extensive damage and the rupture of the epidermis in both the cases. This study assumes significance because it is an effort to find such artifacts in the ultrasound scans of bruises caused by blunt forces where the epidermis remains intact. In this study, the structure of the skin was visualized using a 20 MHz ultrasound scanner. Skin thickness and echogenicity changes may result due to blood extravasations or edema. The thickness and the echogenicity values are plotted against time to determine the trend in the variation of these parameters. We see an intraday and a daily fluctuation of skin thickness and echogenicity albeit with no distinct trend on a day to day basis or between subjects. The results also give us a good estimation of the variation observable in these parameters in the event of an injury. A snapshot analysis is also performed, which describes qualitatively the structural changes in the B-scan of the bruise site compared to the control site. There are six different types of qualitative changes which can appear in the B-scan of a bruised site compared to the control. In the event of an injury, usually, more than one of these changes is manifested in the scan of a bruise. Skin thickness and echogenicity vary considerably due to a number of physiological factors which can seldom be controlled. Therefore, these parameters can give conclusive evidence of a bruise only if the change between a bruised region and a control region is much greater than the daily, normal variations. Snapshot analysis can help detect a bruise or a deep tissue injury. Further work involves the application of pattern recognition or face recognition algorithms to automate the detection.
34

Time-frequency methods for the analysis of multistatic acoustic scattering of elastic shells in shallow water.

Anderson, Shaun David 26 January 2011 (has links)
The development of low-frequency sonar systems, using for instance a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e. when the source and receiver are widely separated) allowing for multiple viewpoints of the target of interest. Time-frequency analysis, in particular Wigner-Ville analysis, takes advantage of the evolution time dependent aspect of the echo spectrum to differentiate a man-made target (e.g. elastic spherical shell) from a natural one of the similar shape (e.g. solid). A key energetic feature of fluid loaded and thin spherical shell is the coincidence pattern, or mid-frequency enhancement echoes (MFE), that result from antisymmetric Lamb-waves propagating around the circumference of the shell. This thesis investigates numerically the bistatic variations of the MFE (with respect to the monostatic configuration) using the Wigner-Ville analysis. The observed time-frequency shifts of the MFE are modeled using a previously derived quantitative ray theory for spherical shell's scattering. Additionally, the advantage of an optimal array beamformer, based on joint time delays and frequency shifts (over a conventional time-delay beamformer) is illustrated for enhancing the detection of the MFE recorded across a bistatic receiver array.
35

Ultrasound and photoacoustic imaging to guide and monitor photothermal therapy

Shah, Jignesh Mukesh, 1979- 02 October 2012 (has links)
Photothermal cancer therapy is a potential alternative to surgery and involves selective tissue destruction using thermal energy. Targeted photoabsorbers, used in conjunction with matching a continuous wave laser, make photothermal therapy both noninvasive and tumor-specific. However, to become clinically relevant, there is a need to develop an imaging technique to identify tissue composition and to detect the presence of photoabsorbers in the tumor volume before therapy; to monitor the temperature rise during therapy; and to assess the tumor damage after therapy. In this study, a combined ultrasound and photoacoustic imaging system was designed to assist photothermal therapy. The imaging system was tested on tissue mimicking phantoms, ex-vivo porcine tissue samples, ex-vivo mice and in-vivo mice. First, ultrasound imaging was utilized to differentiate between water-based and lipidbearing tissue. A combined ultrasound and photoacoustic imaging system was then assembled to identify the presence and spatial location of gold nanoparticles. Multiwavelength photoacoustic imaging was used to further confirm the presence of nanoparticles. Temperature monitoring algorithms, using both temperature-dependent time shifts in ultrasound signals and amplitude changes in photoacoustic signals, were developed. Finally, photothermal therapy was carried out on tumor-bearing nude mice using in-vivo ultrasound and photoacoustic imaging to identify the tumor boundary, detect the nanoparticles and monitor the temperature elevation. The results of the studies show that ultrasound and photoacoustic imaging provide complementary and clinically relevant information. Overall, there is potential of using the ultrasound and photoacoustic imaging system to plan, guide and monitor photothermal therapy. / text
36

Spatially-filtered continuous-wave acoustic tomography for breast cancer detection

McCaugherty, Kevin 15 January 2013 (has links)
The main objective of this master’s thesis is to investigate the possibility of applying spatially-filtered continuous-wave acoustic tomography to the detection of breast cancer. A continuous acoustic wave is transmitted through the specimen in this tomographic imaging method. Any scattered waves that do not positively contribute to the projection are filtered out using an aperture. There is evidence to suggest that cancerous lesions in the breast have a higher speed of sound than surrounding tissues. This imaging method produces two tomograms of the specimen simultaneously: one showing the internal speed of sound, and the other showing the internal acoustic attenuation coefficient. There is the possibility for a third imaging modality, acoustic dispersion tomography, to be applied to this imaging method. Two proof-of-concept prototype spatially-filtered continuous-wave acoustic tomography scanners were designed and built: one that uses a collimated beam to interrogate the specimen, and another that uses a confocal beam. A least-squares tomographic reconstruction algorithm was chosen to reconstruct the tomograms this method creates. A prostate phantom and a breast phantom were imaged with the confocal tomographic scanner. The tomograms of the prostate phantom show two 1 cm lesions which are consistent with information from the phantom manufacturer. Further work is required to properly validate the speed of sound and acoustic attenuation measurements this method produces. / Graduate
37

The spatial cross-correlation coefficient as an ultrasonic detection statistic

Cepel, Raina. January 2007 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 7, 2008) Includes bibliographical references.
38

The seabed as an acoustic mirror for suspended sediment /

Hamm, Craig A., January 1993 (has links)
Thesis (M.Sc.)--Memorial University of Newfoundland. / Typescript. Restricted until October 1994. Bibliography: l. 118-123. Also available online.
39

Ultrasound and photoacoustic imaging to guide and monitor photothermal therapy

Shah, Jignesh Mukesh, January 1900 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.
40

Imagerie ultrasonore 2D et 3D sur GPU : application au temps réel et à l'inversion de forme d'onde complète / 2D and 3D ultrasoundimaging using GPU : toward real-time and full waveform inversion

Bachmann, Etienne 07 October 2016 (has links)
Si les avancées majeures en imagerie ultrasonore ont longtemps été liées à la qualité de l'instrumentation, l'avènement de l'informatique a incontestablement changé la donne en introduisant des possibilités croissantes de traitement des données pour obtenir une meilleure image. Par ailleurs, les GPUs, composants principaux des cartes graphiques, offrent de par leur architecture des vitesses de calcul bien supérieures aux processeurs, y compris à des fins de calcul scientifique. Le but de cette thèse a été de tirer parti de ce nouvel outil de calcul, en ciblant deux applications complémentaires. La première est d'autoriser une imagerie en temps réel de meilleure qualité que les autres techniques d'imagerie échographique, en parallélisant le procédé d'imagerie FTIM (Fast Topological IMaging). La seconde est d'introduire l'imagerie quantitative et en particulier la reconstruction de la carte de vitesse du milieu inconnu, en utilisant l'inversion de la forme d'onde complète. / If the most important progresses in ultrasound imaging have been closely linked to the instrumentation's quality, the advent of computing science revolutionized this discipline by introducing growing possibilities in data processing to obtain a better picture. In addition, GPUs, which are the main components of the graphics cards deliver thanks to their architecture a significantly higher processing speed compared with processors, and also for scientific calculation purpose. The goal of this work is to take the best benefit of this new computing tool, by aiming two complementary applications. The first one is to enable real-time imaging with a better quality than other sonographic imaging techniques, thanks to the parallelization of the FTIM (Fast Tpological IMaging) imaging process. The second one is to introduce quantitative imaging and more particularly reconstructing the wavespeed map of an unknown medium, using Full Waveform Inversion.

Page generated in 0.0696 seconds