Dissertations / Theses: 'Ultrasonic imaging'

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Sikdar, Siddhartha. "Ultrasonic imaging of flow-induced vibrations in tissue /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6100.

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Zemp, Roger James. "Detection theory in ultrasonic imaging /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

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Goode, Ashley Harford. "High resolution ultrasonic imaging system." Thesis, University of Portsmouth, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329278.

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Wylie, Stephen Robert. "An underwater ultrasonic imaging system." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266220.

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Hutt, Timothy David. "Towards next generation ultrasonic imaging." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9759.

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Recently the use of ultrasonic arrays for imaging defects in metal components has become economically attractive in Non-Destructive Testing. Given a certain array, the image quality strongly depends on how the measurements are process into an image. The current state-of-the-art imaging algorithm in actual use is delay-and-sum beamforming, which has a resolution capability that is fundamentally limited by the physical approximation used to describe how waves interact with matter. This thesis explores the practical use of alternative non-linear “super-resolution” imaging algorithms that use more accurate physical models, and can theoretically achieve unlimited resolution. This is made possible by utilising additional sources of information contained within the measurements, in particular the small amplitude multiply scattered signals. The distribution of information contained in the measurements, and utilised by the imaging algorithms is studied in the context of information capacity of signals. We discover some insights into the limits of imaging which depend on the signal-to-noise ratio. The accuracy of non-linear imaging algorithms can be strongly dependent on the accuracy of the measurements. Therefore several experiments are performed to assess their performance in practice. The experimental implementation of these methods poses a number of challenges, including removal of the incident field, and compensating for array element directivity. Super-resolution capability is demonstrated in a highly attenuative medium for the first time. To further improve the image quality we explore the possibility of using mirror reflections. This gives an increase in the effective aperture. We perform simulated and experimental reconstructions of a complex scatterer and find that the completeness of the image is improved. The mirror interface also allows quantitative speed-of-sound imaging of penetrable scatterers using the HARBUT algorithm. This is tested experimentally for the first time.

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York, George W. P. "Architecture and algorithms for a fully programmable ultrasound system /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/5931.

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Mehra, Sumat. "Frequency modulated pulse for ultrasonic B-scan imaging in attenuating medium /." Online version of thesis, 1991. http://hdl.handle.net/1850/11641.

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Baylosis, Benito E. "Acoustic imaging of ultrasonic wave propagation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA290390.

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Weaver, J. M. R. "The ultrasonic imaging of plastic deformation." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375316.

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Wu, Chung Hao. "DETERMINATION OF BLADDER VOLUMES BY MICROPROCESSOR BASED ULTRASONIC SYSTEM." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275392.

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11

Levine, Ross M. "Ultrasonic guided wave imaging via sparse reconstruction." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51829.

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Structural health monitoring (SHM) is concerned with the continuous, long-term assessment of structural integrity. One commonly investigated SHM technique uses guided ultrasonic waves, which travel through the structure and interact with damage. Measured signals are then analyzed in software for detection, estimation, and characterization of damage. One common configuration for such a system uses a spatially-distributed array of fixed piezoelectric transducers, which is inexpensive and can cover large areas. Typically, one or more sets of prerecorded baseline signals are measured when the structure is in a known state, with imaging methods operating on differences between follow-up measurements and these baselines. Presented here is a new class of SHM spatially-distributed array algorithms that rely on sparse reconstruction. For this problem, damage over a region of interest (ROI) is considered to be sparse. Two different techniques are demonstrated here. The first, which relies on sparse reconstruction, uses an a priori assumption of scattering behavior to generate a redundant dictionary where each column corresponds to a pixel in the ROI. The second method extends this concept by using multidimensional models for each pixel, with each pixel corresponding to a "block" in the dictionary matrix; this method does not require advance knowledge of scattering behavior. Analysis and experimental results presented demonstrate the validity of the sparsity assumption. Experiments show that images generated with sparse methods are superior to those created with delay-and-sum methods; the techniques here are shown to be tolerant of propagation model mismatch. The block-sparse method described here also allows the extraction of scattering patterns, which can be used for damage characterization.

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Barkefors, Annea. "3D Synthetic Aperture Technique for Ultrasonic Imaging." Thesis, Uppsala University, Signals and Systems Group, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121022.

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The group for non-destructive testing at Uppsala University has recently implemented the phase shift migration method, which is a method to focus images acquired unfocused using ultrasound. However, their work has been limited to 2D data, while for many applications the gathered data is 3D. This project has extended the old implementation to 3D data. The new implementation has been done in two different ways, giving one algorithm that works fast but needs much RAM, and one algorithm that takes long time but works on smaller computers, not demanding as much memory. The fast algorithm works faster than the time it takes to acquire the raw data, which makes real-time use realistic. To test the performance of the two algorithms with respect to image improvement, both against each other and against the previous 2D implementation, a number of experiments were carried out, which showed that, apart from processing time, the two new algorithms were equal in performance. The experiments also showed that the obtained resolution in both x- and y-directions matched the theoretical discussion.

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Vyas, Nina. "Imaging dental ultrasonic cavitation and its effects." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7338/.

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Current methods of dental biofilm removal are predominantly mechanical and are not effective in removing it from irregular surfaces in the mouth. Cavitation occurs around dental ultrasonic scalers and may be a more efficient and less damaging technique. Previous work has failed to quantify the cavitation bubble dynamics around ultrasonic scalers and its effects. The aim was to develop imaging and analysis protocols to analyse the cavitation and to investigate its ability to disrupt biofilms and deliver sub-micron particles into dentine. High speed imaging was used to characterise cavitation. Its effect on biofilm removal and dentinal tubule occlusion was studied using electron microscopy and x-ray micro computed tomography. We are able to demonstrate that cavitation occurs at the free end of scaler tips and increases with power and vibration amplitude. Biofilm can effectively be removed from dental implant surfaces using this cavitation. It can also be used to transport sub-micron particles further into dentinal tubules. The results show that ultrasonic scalers could be optimised for non-contact use and improved removal of plaque from the teeth. The protocols established in this study can be applied to future studies for quantitative investigation of biofilm growth and removal and analysis of cavitation dynamics.

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Jeffery, Roland. "Diagnostic ultrasound imaging and its role within musculoskeletal medicine a dissertation submitted in partial fulfilment for the degree of Master of Health Science, Auckland University of Technology, March 2003." Full thesis, 2003.

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15

Yeung, Tin-wai, and 楊天慧. "Use of three-dimensional ultrasound in the prediction of homozygous alpha0-thalassemia." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41290616.

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Leung, Kwok-yin, and 梁國賢. "Prenatal ultrasound prediction of homozygous α⁰-thalassemia." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47454039.

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Homozygous α0-thalassemia is a serious autosomal recessive disorder with poor fetal outcome and severe maternal complications. Conventionally, prenatal diagnosis is performed by an invasive test. A non-invasive approach using serial ultrasonography can effectively reduce the need for invasive tests in unaffected pregnancies. For two-dimensional ultrasound prediction, a total of 777 at-risk fetuses were studied from 12 to 20 weeks between 1995 and 2006. At 12–15 weeks’ gestation, the highest sensitivity (98.3%) was achieved by the combination of fetal cardiothoracic ratio (CTR) and/or middle cerebral artery peak systolic velocity (MCA-PSV) at a false-positive rate of 15.8%. At 16–20 weeks’ gestation, the sensitivity of CTR was 100.0%, but the false-positive rate was 5.2%. In contrast, the false-positive rate of MCA-PSV alone was 1.4% and that of the combination of CTR and MCA-PSV was 0%, although their sensitivities were less than 65%. In a cross-sectional retrospective study of 546 samples at-risk and control (268 fetal and 278 neonatal cord blood), the degree of anemia was only mild in 27.5% of the affected fetuses (see chapter 3 for definition of mild anemia). Because MCA-PSV is not very predictive of mild anemia, this may be one of the reasons why MCA-PSV is not very sensitive in predicting an affected pregnancy. A total of 832 at-risk pregnancies were studied using same noninvasive approach at Maternal and Neonatal Hospital of Guangzhou (MNH) and Tsan Yuk Hospital (TYH). The overall sensitivity and specificity of the noninvasive approach was 100% and 95.6% respectively. At MNH, the need for an invasive test was reduced by 78.6%, and all the affected pregnancies were diagnosed before 24 weeks’ gestation. After adequate training and monitoring the quality of the subsequent ultrasound examinations, the results achieved at MNH were comparable to TYH, with at-risk pregnancies including the affected ones being seen at a more advanced gestation at MNH. In a retrospective review of 361 women at risk of carrying an affected fetus, 311 (86.2%) opted for the non-invasive approach using CTR and/or placenta. The cost saving of this non-invasive approach was relatively small (HK$ 2,651) in comparison to the cost of the whole prenatal screening program. On the other hand, the non-invasive approach was more expensive than the direct invasive approach for low MCV couples, as well as couples discordant for α-thalassemia and β-thalassemia. ages. These results support the adoption of non-invasive approach in which routine invasive test or karyotyping is no longer performed. A total of 106 at-risk pregnancies and normal controls were prospectively studied using three-dimensional ultrasonography. Placental volume (PV) at 11-14 weeks, and PV/CRL quotient at 9-14 weeks’ gestation of affected pregnancies were significantly greater than unaffected pregnancies (P<0.05). Using a cut-off point of 1.2ml/mm for PV/CRL quotient to predict an affected pregnancy, the sensitivity, and specificity was 96.2%, and 100.0% respectively.
published_or_final_version
Obstetrics and Gynaecology
Master
Doctor of Medicine

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17

Pao, Tsang-Long. "Ultrasonic tapered phased arrays for three-dimensional imaging." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13541.

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Cannon, Cormac. "Motion-compensation for complementary-coded medical ultrasonic imaging." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/3768.

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Ultrasound is a well-established tool for medical imaging. It is non-invasive and relatively inexpensive, but the severe attenuation caused by propagation through tissue limits its effectiveness for deep imaging. In recent years, the ready availability of fast, inexpensive computer hardware has facilitated the adoption of signal coding and compression techniques to counteract the effects of attenuation. Despite widespread investigation of the topic, published opinions vary as to the relative suitability of discrete-phase-modulated and frequency-modulated (or continuous-phase-modulated) signals for ultrasonic imaging applications. This thesis compares the performance of discrete binary-phase coded pulses to that of frequency-modulated pulses at the higher imaging frequencies at which the effects of attenuation are most severe. The performance of linear and non-linear frequency modulated pulses with optimal side-lobe characteristics is compared to that of complementary binary-phase coded pulses by simulation and experiment. Binary-phase coded pulses are shown to be more robust to the affects of attenuation and non-ideal transducers. The comparatively poor performance of frequency-modulated pulses is explained in terms of the spectral characteristics of the signals and filters required to reduce side-lobes to levels acceptable for imaging purposes. In theory, complementary code sets like bi-phase Golay pairs offer optimum side-lobe performance at the expense of a reduction in frame rate. In practice, misalignment caused by motion in the medium can have a severe impact on imaging performance. A novel motioncompensated imaging algorithm designed to reduce the occurrence of motion artefacts and eliminate the reduction in frame-rate associated with complementary-coding is presented. This is initially applied to conventional sequential-scan B-mode imaging then adapted for use in synthetic aperture B-mode imaging. Simulation results are presented comparing the performance of the motion-compensated sequential-scan and synthetic aperture systems with that of simulated systems using uncoded and frequency-modulated excitation pulses.

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Mireault, Alfred Norman. "Mechanical design of an ultrasonic tomographic imaging system." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105689.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 42-44).
The paper presents the design and fabrication of a prototype for limb imaging aimed at tackling several of the issues. The design of the a US probe positioning system is intended to augment a system for motion measurement as well as a framework for the integration of motion and US data. The design of the imaging system below represents early steps towards a full-volume imaging technique for use in computer-aided prosthetic socket design.
by Alfred Norman Mireault.
S.B.

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Guérendel, Philippe. "Ultrasonic modeling--application to deep-water multiples imaging." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/52920.

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Smyth, Katherine Marie. "Piezoelectric micro-machined ultrasonic transducers for medical imaging." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108938.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 175-184).
Next generation medical imaging technology hinges on the development of cost effective and array compatible transducers making piezoelectric micro-machined ultrasonic transducers (pMUTs) an attractive alternative to the current bulk piezoelectric technology. This thesis aims to realize pMUT potential starting with the development of an effective single cell model that is further scaled to optimize multi-cell elements in a 1D array. In the first half of this work, a transverse mode, lead zirconate titanate (PZT) pMUT plate cell is fabricated using common micro-fabrication techniques and a PZT sol-gel deposition process. Through derivation using a novel Greens function solution technique, an equivalent circuit model with explicitly defined lumped parameters is presented and validated through electrical impedance measurements of fabricated devices and finite element modeling. The equivalent circuit is a crucial design tool as transducer performance metrics, including experimentally validated acoustic domain values, are shown to be defined directly from the lumped parameters. In the second half, figures of merit are identified from these performance metrics and an expanded multi-cell model is employed to strategically target improvements in both bandwidth and coupling while maintaining high pressure output. The resulting, optimized multicell elements in a 1D array are fabricated via a commercially viable, wafer-scale manufacturing process including a novel PZT dry etch. A top-down fabrication approach facilitates achievement of the largest active area of a multi-cell pMUT to date consisting of over 1000 cells in a 200pm x 4mm element footprint, and more substantially, results in the highest electromechanical coupling recorded for a pMUT to date measured at 9 ± 1.4% per element.
by Katherine Marie Smyth.
Ph. D.

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22

Keshmiri, Esfandabadi Yasamin <1988&gt. "Compressive Sensing and Imaging of Guided Ultrasonic Wavefields." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9410/1/COMPRESSIVE%20SENSING%20AND%20IMAGING%20OF%20GUIDED%20ULTRASONIC%20WAVEFIELDS.pdf.

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Structural health monitoring (SHM) and Nondestructive Evaluation (NDE) technologies can be used to predict the structural remaining useful life through appropriate diagnosis and prognosis methodologies. The main goal is the detection and characterization of defects that may compromise the integrity and the operability of a structure. The use of Lamb waves, which are ultrasonic guided waves (GW), have shown potential for detecting damage in specimens as a part of SHM or NDT systems. These methods can play a significant role in monitoring and tracking the integrity of structures by estimating the presence, location, severity, and type of damage. One of the advantages of GW is their capacity to propagate over large areas with excellent sensitivity to a variety of damage types while guaranteeing a short wavelength, such that the detectability of large structural damages is guaranteed. The Guided ultrasonic wavefield imaging (GWI) is an advanced technique for Damage localization and identification on a structure. GWI is generally referred to as the analysis of a series of images representing the time evolution of propagating waves and, possibly, their interaction with defects. This technique can provide useful insights into the structural conditions. Nowadays, high-resolution wavefield imaging has been widely studied and applied in damage identification. However, full wavefield imaging techniques have some limitations, including slow data acquisition and lack of accuracy. The objectives of this dissertation are to develop novel and high resolution Guided Wavefield Imaging techniques able to detect defects in metals and composite materials while reducing the acquisition time without losing in detection accuracy.

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Li, Bo. "Detection of particles and estimation of size distribution in process fluids /." Online version of thesis, 1992. http://hdl.handle.net/1850/11258.

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Eljaaidi, Abdalla Agila. "2D & 3D ultrasound systems in development of medical imaging technology." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2193.

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Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016.
Ultrasound is widely used in most medical clinics, especially obstetrical clinics. It is a way of imaging methods that has important diagnostic value. Although useful in many different applications, diagnostic ultrasound is especially useful in antenatal (before delivery) diagnosis. The use of two-dimensional ultrasound (2DUS) in obstetrics has been established. However, there are many disadvantages of 2DUS imaging. Several researchers have published information on the significance of patients being shown the ultrasound screen during examination, especially during three- and four-dimensional (3D/4D) scanning. In addition, a form of ultrasound, called keepsake or entertainment ultrasound, has boomed, particularly in the United States. However, long-term epidemiological studies have failed to show the adverse effects of ultrasound in human tissues. Until now, there is no proof that diagnostic ultrasound causes harm in a human body or the developing foetus when used correctly. While ultrasound is supposed to be absolutely safe, it is a form of energy and, as such, has effects on tissues it traverses (bio-effects). The two most important mechanisms for effects are thermal and non-thermal. These two mechanisms are indicated on the screen of ultrasound devices by two indices: The thermal index (TI) and the mechanical index (MI). These are the purposes of this thesis: • evaluate end-users’ knowledge regarding the safety of ultrasound; • evaluate and make a comparison between acoustic output indices (AOI) in B-mode (2D) and three-dimensional (3D) ultrasound – those measured by thermal (TI) and mechanical (MI) indices; • assess the acoustic output indices (AOI) to benchmark current practice with a survey conducted by the British Medical Ultrasound Society (BMUS); and • review how to design 2D and 3D arrays for medical ultrasound imaging

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廖威賢 and Wai-yin Liu. "Ultrasonic reflection tomography over circular aperture." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31210910.

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Sebastian, Dalys. "Development of a field-deployable voice-controlled ultrasound scanner system." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0625104-170951/.

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Basoglu, Chris. "A generalized programmable system and efficient algorithms for ultrasound backend processing /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/5978.

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Parsons, Adrian. "Seismic exploration techniques applied to ultrasonic imaging within concrete." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368818.

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Coila, Pacompia Andres Leonel. "Regularized spectral log difference technique for ultrasonic attenuation imaging." Master's thesis, Pontificia Universidad Católica del Perú, 2017. http://tesis.pucp.edu.pe/repositorio/handle/123456789/8991.

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The attenuation coefficient slope (ACS) has the potential to be used for tissue characterization and as a diagnostic ultrasound tool, hence complementing B-mode images. The ACS can be valuable for estimation of other ultrasound parameters such as the backscatter coefficient. There is a well-known tradeoff between the precision of the estimated ACS values and the data block size used in spectral-based techniques such as the spectral log difference (SLD). This trade-off limits the practical usefulness of spectral-based attenuation imaging techniques. In this thesis work, the regularized spectral log difference (RSLD) technique is presented in detail and evaluated with simulations and experiments with physical phantoms, ex vivo and in vivo. The ACS values obtained when using the RSLD technique were compared to the ones obtained when using the SLD technique, as well as the ground truth ACS values obtained with insertion loss techniques. The results showed that the RSLD technique allowed significantly decreasing estimation variance when using small data block sizes (i.e., standard deviation of percentage error reduced by more than an order of magnitude in all cases when using 10 x 10 data blocks) without sacrificing estimation accuracy. Therefore, the RSLD allows for the reconstruction of attenuation coefficient images with an improved trade-off between spatial resolution and estimation precision.
Tesis

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Gunarathne, Gunti P. P. "A new real-time high speed ultrasonic imaging system." Thesis, Loughborough University, 1986. https://dspace.lboro.ac.uk/2134/32232.

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An ultrasonic imaging technique was to be developed for sizing and characterization of defects in thick sections of steel. The problems generally found with the existing techniques in such applications are low speed, inadequate image quality, large size and high cost.

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Krishna, Aditya. "Topological Imaging of Tubular Structures using Ultrasonic guided waves." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0111.

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Les structures tubulaires sont largement utilisées dans diverses industries telles que l’aérospatiale, le pétrole et le gaz, le nucléaire, etc. Le Contrôle Non Destructive (CND) de ces structures joue un rôle crucial au cours de leur cycle de vie. Afin de tester de grandes structures avec une accessibilité limitée, la méthode de CND utilisant des ondes guidées a été développée comme une solution viable. En raison de la nature de ces ondes, elles sont capables de se propager sur de grandes distances sans perdre une grande partie de leur énergie. Cependant, elles sont complexes puisque leur vitesse dépend de la fréquence, c'est-à-dire qu'elles sont dispersives. Classiquement, l’étude de ce type d’ondes nécessite des simulations par éléments finis coûteuses. Cette thèse propose une alternative à de telles simulations avec une méthode rapide et robuste pour simuler la propagation d'ondes guidées dans des structures tubulaires.Partant de ces calculs, pour localiser des défauts, l'objectif de ce travail est d'obtenir des images topologiques 3D de structures tubulaires isotropes multicouches par propagation de ces ondes guidées ultrasonores. Un modèle mathématique est proposé où l'équation d'onde est convertie en une équation différentielle ordinaire par rapport au rayon «r» en utilisant les transformées de Fourier et de Laplace pour les variables spatiales et temporelles respectivement. La solution en ondes partielles, exprimée comme une combinaison des fonctions de Bessel, permet la création d'un algorithme semi-analytique rapide et robuste pour calculer la fonction de Green de structures tubulaires. Un modèle approché en présence de défauts numériques est ensuite développé. La réponse des défauts est considérée comme la réponse cumulative des sources secondaires, visant à annuler le champ de contraintes incident et diffracté présent en son sein. Ensuite, le modèle numérique est validé par des mesures expérimentales.Enfin, la technique de l'imagerie topologique est introduite. Cette méthode d'imagerie est basée sur la corrélation entre les champs ultrasonores sans et avec défaut. La polyvalence et la flexibilité de l'outil numérique en conjonction avec cette méthode d'imagerie sont ensuite démontrées avec succès en localisant et imageant une multitude de défauts numériques et expérimentaux avec des dimensions aussi faibles que 1/40e de la longueur d'onde
Tubular structures are widely used in a variety of industries such as Aerospace, Oil and Gas, Nuclear, etc. Non Destructive Evaluation (NDE) of these structures plays a crucial role during it’s life cycle. In order to test large structures with limited accessibility, guided wave testing was developed as a viable solution. Due to the nature of these waves, they are able to propagate over large distances without losing much of their energy. However, they are also complex in that their velocity is frequency dependent i.e. they are dispersive. Conventionally, guided wave testing require costly finite element simulations. This thesis offers an alternative to such simulations with a quick and robust method to simulate guided wave propagation in tubular structures.Based on these calculations, the aim of this work is to obtain the 3d topological image of multilayered isotropic tubular structures using ultrasonic guided waves to locate defects. A mathematical model has been proposed where the wave equation is converted to an ordinary differential equation with respect to radius 'r' using the Fourier and Laplace transforms for the spatial and temporal variables respectively. The partial wave solution, expressed as a combination of Bessel’s functions, allows for the creation of a fast robust semi-analytical algorithm to compute the Green function in tubular structures. A model to approximate numerical defects is then developed. The defect response is considered as the cumulative response of secondary sources, aiming to negate the incident and diffracted stress field present within it. Next, the numerical model is validated with experimental measurements.Finally, the technique of Topological Imaging is introduced. This method of imaging is based on the idea of performing a correlation between two wave fields for defect localization. The versatility and flexibility of the numerical tool in conjunction with the method of imaging is then successfully demonstrated by localising and imaging a multitude of numerical and experimental defects with dimensions as low as 1=40th of the wavelength

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Benane, Mehdi Yanis. "Ultrafast, broadband and multi-pulse transmissions for ultrasonic imaging." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1268/document.

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L'échographie est un outil de diagnostic largement utilisé grâce à des vertus telles que l'acquisition / traitement de données en temps réel, la facilité d'utilisation et la sécurité pour le patient / praticien pendant l'examen. Cependant, comparée à d'autres méthodes d'imagerie telles que la tomographie à rayons X et l'imagerie par résonance magnétique, l'échographie présente l'inconvénient de fournir une qualité d'image relativement basse. Dans cette thèse, nous étudions une méthode capable d'augmenter la qualité d'image, permettant ainsi de meilleurs diagnostics échographiques. Afin d'augmenter le rapport signal / bruit des signaux reçus, nous proposons d'utiliser des signaux modulés en fréquence (chirps). Pour éviter l'effet négatif de la bande passante limitée de la sonde, nous modulons en amplitude les signaux d'excitations afin d'augmenter l'énergie du signal dans les bandes de fréquences où la sonde est moins efficace. Pour compresser l'énergie des échos, nous utilisons des filtres de Wiener afin d'obtenir un bon compromis résolution spatiale / stabilité du bruit. Nous combinons cette méthode appelée REC (Resolution Enhancement Technique) avec l’imagerie ultrarapide. Nous montrons des résultats simulés et expérimentaux (in-vitro, ex-vivo et in-vivo) prometteurs. De plus, nous adaptons REC afin de compenser l'effet d'atténuation tissulaire. Cette amélioration est validée expérimentalement sur des phantoms. Nous adaptons également REC à la propagation non linéaire des ondes ultrasonores, en proposant une technique d'inversion d'impulsions qui utilise REC pour fournir une meilleure résolution et un meilleur rapport contraste / bruit. Ensuite, nous appliquons REC à différents schémas d’acquisition tels que les ondes divergentes et la transmission multi-lignes (MLT). Nous montrons également que la qualité d’image peut être augmentée davantage en tenant compte de la réponse impulsionnelle spatiale de la sonde lorsque REC et MLT sont combinés
Ultrasound imaging is a diagnostic tool widely used thanks to such virtues as real-time data acquisition / processing, ease of use and safety for the patient / practitioner during examination. However, when compared to other imaging methods such as X-ray tomography and Magnetic Resonance Imaging, the echography has the disadvantage to provide relatively low image quality. In this thesis, we study a method that is able to increase the ultrasound image quality, thus paving the way towards improved diagnostics based on echography and novel ultrasound applications. In order to increase the echo signal to noise ratio of the received signals, we propose to use linear frequency modulated signals, also called chirps. To avoid the negative effect of the bandlimited acquisition probe, we apply a pre-enhancement step on the probe excitation signals in order to boost the signal energy in the frequency bands where the probe is less efficient. To compress the echo energy in reception, we use Wiener filters that allow obtaining a good trade-off between the spatial resolution and noise stability. We apply the previously detailed pipeline, also called REC (Resolution Enhancement Technique) on ultrafast imaging schemes. We show promising results in simulation and in-vitro, ex-vivo, in-vivo acquisitions. Furthermore, we adapt REC in such way that the frequency dependent tissue attenuation effect is compensated for. This improvement is validated in simulation and phantom experiments. We also adapt REC to the nonlinear propagation of ultrasound waves, by proposing a pulse inversion technique that uses REC to provide a better image resolution and contrast to noise ratio. Then, we demonstrate the generality of the REC method by applying it to different acquisition schemes such as diverging wave compounding and Multi Line Transmit (MLT). We also show that the image quality can be increased more by taking into account the spatial impulse response of the ultrasound probe when REC and MLT are combined

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Majhi, Subhra. "Ultrasonic Wave based Monitoring and Imaging of Civil Infrastructure." Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/78313.

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Australian infrastructure which is predominantly close to the coast are at risk of corrosion. The prevalent visual monitoring of infrastructure warrant alleviation. Ultrasonic waves rely on interaction of waves with the substrate structure. In reinforced concrete infrastructure, they can travel through embedded rebar or surrounding concrete. Processing these wave have revealed their traits. Representative images coalescing these waves are developed. A synergistic wave based monitoring scheme through rebar and concrete is presented to disseminate corrosion.

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Liu, Wai-yin. "Ultrasonic reflection tomography over circular aperture /." [Hong Kong] : University of Hong Kong, 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13440019.

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Hu, Rui, and 胡瑞. "Applications of non-invasive vascular imaging techniques in cardiovascular risk assessment and management." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36923242.

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Neethling-Du, Toit Merle. "Ultrasound features of the deep infrapatellar Bursa." Thesis, Cape Peninsula University of Technology, 2006. http://hdl.handle.net/20.500.11838/2584.

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Thesis (MTech (Radiography))--Cape Peninsula University of Technology, 2006.
The knee is one of the most complicated joints in the body. The deep infrapatellar bursa being only a small water-pocket and forming a small part of the knee. The deep infrapatellar bursa can get inflamed and cause great discomfort, especially to professional sportsmen and -women. If such a inflammation is present, a common treament option are to inject a cortisone solution into the bursa for quick relieve and healing. This study was performed to investigate the specific ultrasound features of a normal deep infrapatellar bursa. Thus enableing more specific and accurate diagnosis of deep infrapatellar bursitis or not, which in turn leads to quicker recovery of the patients.

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Lefley, Paul W. "A sensing system for two dimensional acoustical imaging." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328408.

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Lai, Di. "Independent component analysis (ICA) applied to ultrasound image processing and tissue characterization /." Online version of thesis, 2009. http://hdl.handle.net/1850/11367.

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Munro, W. S. H. "Ultrasonic phased arrays for use in imaging and automatic vehicle guidance." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334215.

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Ashraf, Muhammad. "A 3D ultrasonic camera for subsea applications." Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318304.

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Tang, Mei-yee. "Medical imaging : applications of functional magnetic resonance imaging and the development of a magnetic resonance compatible ultrasound system /." View the Table of Contents & Abstract, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36749710.

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Tang, Mei-yee, and 鄧美宜. "Medical imaging: applications of functional magnetic resonance imaging and the development of a magnetic resonancecompatible ultrasound system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37897688.

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Pomeroy, Simon. "Ultrasonic phased arrays for robotics modelling and experimental implementation." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254469.

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Satir, Sarp. "Modeling and optimization of capacitive micromachined ultrasonic transducers." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54303.

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The objective of this research is to develop large signal modeling and optimization methods for Capacitive Micromachined Ultrasonic Transducers (CMUTs), especially when they are used in an array configuration. General modeling and optimization methods that cover a large domain of CMUT designs are crucial, as many membrane and array geometry combinations are possible using existing microfabrication technologies. Currently, large signal modeling methods for CMUTs are not well established and nonlinear imaging techniques utilizing linear piezoelectric transducers are not applicable to CMUTs because of their strong nonlinearity. In this work, the nonlinear CMUT behavior is studied, and a feedback linearization method is proposed to reduce the CMUT nonlinearity. This method is shown to improve the CMUT performance for continuous wave applications, such as high-intensity focused ultrasound or harmonic imaging, where transducer linearity is crucial. In the second part of this dissertation, a large signal model is developed that is capable of transient modeling of CMUT arrays with arbitrary electrical terminations. The developed model is suitable for iterative design optimization of CMUTs and CMUT based imaging systems with arbitrary membrane and array geometries for a variety of applications. Finally, a novel multi-pulse method for nonlinear tissue and contrast agent imaging with CMUTs is presented. It is shown that the nonlinear content can be successfully extracted from echo signals in a CMUT based imaging system using a multiple pulse scheme. The proposed method is independent of the CMUT geometry and valid for large signal operation. Experimental results verifying the developed large signal CMUT array model, proposed gap feedback and multi-pulse techniques are also presented.

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Zhu, Hui. "Scatterer number density estimation for tissue characterization in ultrasound imaging /." Online version of thesis, 1990. http://hdl.handle.net/1850/10882.

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SAUTTO, MARCO. "ANALOG FRONT-END CIRCUITS FOR HIGHLY INTEGRATED ULTRASOUND IMAGING SYSTEMS." Doctoral thesis, Università degli studi di Pavia, 2017. http://hdl.handle.net/11571/1203280.

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Ultrasound imaging is a well-established medical diagnostic technique. Compared with other imaging modalities, such as for example X-ray, ultrasound is harmless to the patient and less expensive while providing real-time imaging capability with adequate resolution for most applications. Piezoelectric materials have dominated the ultrasound transducers technology for a long time but, thanks to the intense research activity in recent years, capacitive micromachined ultrasonic transducers (CMUT) are emerging as a competitive alternative for next generation imaging systems. The objective of the thesis is to analyze the ultrasound system, when a CMUT is used instead of a piezoelectric transducer, to identify and design the best integrated solution to optimize the front-end performance. After giving an overview of the ultrasound system and the Capacitive Micromachined Ultrasonic Transducer (CMUT) in Chapter 1, Chapter 2 presents a thorough comparison between RX amplifier alternatives. The impact on the pulse-echo frequency response and SNR is assessed. The study demonstrates that a capacitive-feedback stage provides a remarkable improvement in the noise-power performance compared to the very popular resistive-feedback amplifier, at the expense of a low-frequency shift of the pulse-echo response, making it suitable for integration of dense CMUT arrays for low and mid-frequency ultrasound imaging applications. Then, Chapter 3 proposes the design of a CMUT front-end circuits comprising a TX driver, T/R switch and RX amplifier. Realized in BCD8-SOI technology from STMicroelectronics, the TX delivers up to 100V pulses, while the RX shows 70dB dynamic range with very low noise at 1mW only power dissipation. Measurement results and imaging experiments are presented and discussed. In Chapter 4, the non-linear behavior of the CMUT is discussed and possible solution proposed. Experimental results demonstrate a significant reduction of the second-harmonic distortion, estimated to be lower than -30 dB, resulting in good linearization for typical nonlinear imaging operation. In addition, Chapter 5 shows a novel amplifier architecture exploiting the regeneration feature of the cross-coupled pair. It will be used as Programmable Gain Amplifier (PGA) in the ultrasound chain. A test-chip in 0.18 μm CMOS provides 15dB to 66dB gain over 50MHz bandwidth. With state-of-the-art noise and linearity performance, a record GBW up to 100GHz is demonstrated with only 420 μW power dissipation.

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Hall, James Stroman. "Adaptive dispersion compensation and ultrasonic imaging for structural health monitoring." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41159.

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Ultrasonic guided wave imaging methods offer a cost-effective mechanism to perform in situ structural health monitoring (SHM) of large plate-like structures, such as commercial aircraft skins, ship hulls, storage tanks, and civil structures. However, current limits in imaging quality, environmental sensitivities, and implementation costs, among other things, are preventing widespread commercial adoption. The research presented here significantly advances state of the art guided wave imaging techniques using inexpensive, spatially distributed arrays of piezoelectric transducers. Novel adaptive imaging techniques are combined with in situ estimation and compensation of propagation parameters; e.g., dispersion curves and transducer transfer functions, to reduce sensitivity to unavoidable measurement inaccuracies and significantly improve resolution and reduce artifacts in guided wave images. The techniques can be used not only to detect and locate defects or damage, but also to characterize the type of damage. The improved ability to detect, locate, and now characterize defects or damage using a sparse array of ultrasonic transducers is intended to assist in the establishment of in situ guided wave imaging as a technically and economically viable tool for long-term monitoring of plate-like engineering structures.

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Qian, Yichen. "Design of high frequency ultrasonic array transducers for medical imaging." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/336225/.

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Ultrasonic transducers have been widely used in the medical applications. High frequency array transducers have recently attracted many research interests, since it provides not only the electronic beamforming but also the very fine image resolution. The transducers are usually either annular or linear arrays. This study concentrates on the design of both types of array in high frequency applications. The annular array is firstly investigated, and an optimized design of array geometry is developed including the kerfs influence which is usually neglected in the design of high frequency arrays. The improved imaging performance is found by this optimized design. More interestingly, the conventional annular array with element having the same surface area has a relatively large sidelobe closest to the main lobe. Two methods are applied to suppress the sidelobe. The method of using high-impedance single matching to enlarge the element bandwidth only shows very limited lobe suppression, however, a novel matching approach is found. Another method of changing the array geometry from equal area elements to equal width ones successfully suppressed the sidelobe. The imaging results suggest that the novel equal width array shows a good improvement. The linear array is then analyzed. The kerfs influence again is found to be significant for the array especially for high frequency. It is essential to use a high attenuated kerfs material in the linear array design. More importantly, the limitation of current fabrication techniques forces the linear array to concede a high grating lobe in the imaging field if it operates in a relatively high frequency. A novel linear array is developed to suppress the grating lobe without using advanced fabrication techniques. The imaging results show that the novel linear array has a general reduction of -6dB for the lobe suppression. The novel design made the linear array operate in a very high frequency without strong grating lobe, and the array can be fabricated by current techniques.

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Choi, Hongsoo. "Fabrication, characterization and modeling of K₃₁ piezoelectric micromachined ultrasonic transducers (pMUTs)." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/h_choi_091007.pdf.

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Huck, Todd E. "A study of in vitro phase aberration measurements in ultrasonic imaging /." Online version of thesis, 1994. http://hdl.handle.net/1850/12135.

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Dissertations / Theses on the topic 'Ultrasonic imaging'

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