La conception des sondes ultrasonores pour l’imagerie médicale est traditionnellement basée sur l’utilisation de matériaux piézoélectriques. Depuis quelques années, est apparue la technologie des CMUTs, (Capacitive Micromachined Ultrasonic Transducers). Ces microsystèmes électromécaniques se présentent comme une alternative attractive à la piézoélectricité, offrant la possibilité d’explorer de nouveaux designs de sonde, et d’expérimenter de nouveaux modes d’imagerie. Ce travail s’inscrit dans une dynamique de développement et d’évaluation des sondes CMUTs, de la modélisation à la démonstration par l’image. Des transducteurs multi-éléments CMUTs ont ainsi été conçus, et des prototypes de sondes d’échographie finalisés ont pu être réalisés, ce en adaptant les développements à la transduction capacitive et aux systèmes d’imagerie conventionnels. Leurs comportements électroacoustiques et acoustiques ont été étudiés et comparés à des sondes standards. Finalement, des démonstrations par l’image ont été apportées, et les points forts de cette technologie pour l’imagerie médicale ont pu être établis. / Fabrication of ultrasound probes for medical imaging conventionally exploits piezoelectric based materials. CMUTs technology (Capacitive Micromachined Ultrasonic Transducers) has emerged about a decade ago. These electromechanical micro-systems are presented as an alternative transduction mode, and gives new opportunities for probe design and novel imaging techniques. This dissertation aims to develop and review CMUTs probes for ultrasound imaging, from modeling to imaging demonstration. Multi-elements transducers with CMUT technology have been thus developed, and ultrasound probes were successfully achieved. Developments have been carried out, taking care of both capacitive transduction and standard ultrasound systems. Electro-acoustic and acoustic behavior were evaluated and compared to the state of the art piezoelectric probes. Finally, quantitative imaging assessments have been performed and have pointed out the strengths of CMUT technology for ultrasound imaging

abstract: Ultrasound imaging is one of the major medical imaging modalities. It is cheap, non-invasive and has low power consumption. Doppler processing is an important part of many ultrasound imaging systems. It is used to provide blood velocity information and is built on top of B-mode systems. We investigate the performance of two velocity estimation schemes used in Doppler processing systems, namely, directional velocity estimation (DVE) and conventional velocity estimation (CVE). We find that DVE provides better estimation performance and is the only functioning method when the beam to flow angle is large. Unfortunately, DVE is computationally expensive and also requires divisions and square root operations that are hard to implement. We propose two approximation techniques to replace these computations. The simulation results on cyst images show that the proposed approximations do not affect the estimation performance. We also study backend processing which includes envelope detection, log compression and scan conversion. Three different envelope detection methods are compared. Among them, FIR based Hilbert Transform is considered the best choice when phase information is not needed, while quadrature demodulation is a better choice if phase information is necessary. Bilinear and Gaussian interpolation are considered for scan conversion. Through simulations of a cyst image, we show that bilinear interpolation provides comparable contrast-to-noise ratio (CNR) performance with Gaussian interpolation and has lower computational complexity. Thus, bilinear interpolation is chosen for our system. / Dissertation/Thesis / M.S. Electrical Engineering 2013

Ultrafast plane-wave ultrasound imaging offers very high frame rates (exceeding thousands of frames per second) but entails large volumes of backscattered data collected by a sensor array over multiple plane-wave emissions at different angles. We propose a simple method for reducing the total amount of sampled data. First, we acquire the zero-angle data in full, and then we perform deterministic subsampling of the remaining nonzero-angle data. Our subsampling patterns are angle-specific and derived based on the zero-angle data using a Fourier-domain migration technique. We use two experimental datasets to evaluate the benefits and drawbacks of our proposed method in terms of spatial resolution and contrast-to-noise ratio, observed in the resulting B-mode images. / Graduate

Breast cancer is the second leading cause of death of women worldwide. Accurate lesion boundary detection is important for breast cancer diagnosis. Since many crucial features for discriminating benign and malignant lesions are based on the contour, shape, and texture of the lesion, an accurate segmentation method is essential for a successful diagnosis. Ultrasound is an effective screening tool and primarily useful for differentiating benign and malignant lesions. However, due to inherent speckle noise and low contrast of breast ultrasound imaging, automatic lesion segmentation is still a challenging task. This research focuses on developing a novel, effective, and fully automatic lesion segmentation method for breast ultrasound images. By incorporating empirical domain knowledge of breast structure, a region of interest is generated. Then, a novel enhancement algorithm (using a novel phase feature) and a newly developed neutrosophic clustering method are developed to detect the precise lesion boundary. Neutrosophy is a recently introduced branch of philosophy that deals with paradoxes, contradictions, antitheses, and antinomies. When neutrosophy is used to segment images with vague boundaries, its unique ability to deal with uncertainty is brought to bear. In this work, we apply neutrosophy to breast ultrasound image segmentation and propose a new clustering method named neutrosophic l-means. We compare the proposed method with traditional fuzzy c-means clustering and three other well-developed segmentation methods for breast ultrasound images, using the same database. Both accuracy and time complexity are analyzed. The proposed method achieves the best accuracy (TP rate is 94.36%, FP rate is 8.08%, and similarity rate is 87.39%) with a fairly rapid processing speed (about 20 seconds). Sensitivity analysis shows the robustness of the proposed method as well. Cases with multiple-lesions and severe shadowing effect (shadow areas having similar intensity values of the lesion and tightly connected with the lesion) are not included in this study.

Gas filled microbubbles (MBs) stabilized by a shell (e.g. lipids) are commonly used as ultrasound (US) contrast agents. Attaching biomolecules to the surface of MBs allows for molecular US imaging of various diseases. With the increased interest in targeted US imaging, new platforms to prepare disease-targeted MBs are necessary. Furthermore, attaching signaling agents to MBs creates multi-modal imaging opportunities, enhancing visualization and quantification of disease biomarkers. In this thesis, MBs labeled with 99mTc and/or rhodamine dye by taking advantage of the strong interaction between biotin and streptavidin are reported. Radiolabeling of MBs was achieved in good radiochemical yield (~ 30%). 99mTc-labeled MBs were targeted to vascular endothelial growth factor receptor 2 (VEGFR2) using an anti-VEGFR2 antibody and to prostate specific membrane antigen (PSMA) using small-molecule based PSMA inhibitors. In vitro evaluations showed successful binding of MBs to the target while in vivo targeting assessments were unsuccessful. New strategies to target MBs to the site of interest were then developed through the use of the bioorthogonal reaction between tetrazine (Tz) and trans-cyclooctene (TCO). A biotinylated derivative of Tz was loaded on streptavidin coated MBs to create a Tz-derivatized MB (MBTz). Targeting MBTz to extracellular markers of cancer such as VEGFR2, PSMA and urokinase plasminogen activator receptor (uPAR) in vitro was achieved using TCO-conjugated antibodies. In vivo targeting was successful for VEGFR2 and PSMA, but not uPAR. Translating the new strategy to other US contrast agents was then investigated. Gas vesicles (GVs) produced in halobacteria were conjugated with TCO using amide-coupling chemistry. A 99mTc-labeled derivative of Tz was loaded on TCO-GVs (RCY= 59%) and their distribution assessed by SPECT/CT imaging and ex vivo tissue counting. Having established a convenient platform to conjugate molecules to GVs and MBs, future work focuses on developing a new generation of human compatible molecular US imaging probes. / Dissertation / Doctor of Philosophy (PhD)

Evolution of vulnerable carotid plaques are crucial reason for cerebral ischemic strokes and identifying them in the early stage can become very important in avoiding the risk of stroke. In order to improve the identification and quantification accuracy of infancy plaques better visualization techniques are needed. Improving the visualization and quantification of neovascularization in carotid plaque using contrast enhanced ultrasound imaging still remains a challenging task. In this thesis work, three optimization techniques are proposed, which showed an improvement in the sensitivity of contrast agents when compared to the conventional clinical settings and insonation strategies. They are as follows:1) Insonation at harmonic specific (2nd harmonic) resonance frequency instead of resonance frequency based on maximum energy absorption provides enhanced nonlinear contribution.2) At high frequency ultrasound imaging, shorter pulse length will provide improved harmonic signal content when compared to longer pulse lengths. Applying this concept to multi- pulse sequencing (Pulse Inversion and Cadence contrast pulse sequencing) resulted in increased magnitude of the remaining harmonic signal after pulse summations.3) Peak negative pressure optimization of Pulse Inversion and Cadence contrast pulse sequencing was showed to further enhance the nonlinear content of the backscattered signal from contrast microbubbles without increasing the safety limits, defined by the mechanical index.The results presented in this thesis are based on computational modeling (Bubblesim software) and as a future continuation we plan to verify the simulation results with vitro studies.

Current research within the field of ultrasound contrast agents (UCAs) aims at developing capsules which are not only acoustically active, but also have a chemically modifiable surface. This enables use in new areas, including targeted drug delivery and theranostics. For such purposes, air-filled microbubbles (MBs) with a polyvinyl alcohol (PVA) shell are being studied. Ultrasound imaging velocimetry (UIV) is a technique used to evaluate various types of liquid flows by tracking patterns caused by UCAs across ultrasound images, and has shown great potential for flow measurements in terms of accuracy. The aim of this thesis was to implement a basic UIV program in Matlab to investigate the flow behavior of air-filled PVA MBs being pumped through a phantom, mimicking a blood vessel. The images were acquired using the programmable Verasonics research system by plane wave imaging with coherent compounding, and UIV was implemented as a post-processing technique. Three parameters were varied to study how the UIV performance and flow behavior of the MBs were affected: the concentration of MBs, the flow velocity, and the transducer voltage. The resulting velocity vector fields showed that it is possible to track PVA MBs using the implemented UIV program, and that the concentration 5·106 MBs/ml gave the best results out of the five concentrations tested. The generated velocity vector fields indicated a turbulent and pulsatile flow behavior, which was in line with the predicted flow behavior, although there was a disparity between the measured average flow velocity of the MBs and the predicted flow velocity. It was also observed that the MBs were increasingly pushed in the axial direction with increasing voltage, as according to theory. Even though a more advanced UIV algorithm could improve the accuracy of the velocity measurements, the results show possible use of air-filled PVA MBs in combination with UIV. / Nuvarande forskning inom ultraljudskontrastmedel syftar till att utveckla kapslar som inte bara är akustiskt aktiva, utan som även har en kemiskt modifierbar yta. Detta möjliggör användning inom nya områden, så som målinriktade läkemedel och theanostics. För detta syfte studeras luftfyllda mikrobubblor med ett skal av polyvinylalkohol (PVA). Ultrasound imaging velocimetry (UIV) är en teknik som används för att analysera olika typer av vätskeflöden genom att spåra mönster orsakade av ultraljudskontrastmedel över ett antal ultraljudsbilder. Metoden har visats ha stor potential för flödesmätningar, och hög noggrannhet har uppnåtts. Detta projekt syftade till att implementera ett grundläggande UIV-program i Matlab för att undersöka flödesbeteenden hos luftfyllda PVA-mikrobubblor som pumpas genom en modell av ett blodkärl. Ultraljudsbilderna togs med hjälp av det programmerbara forskningssystemet Verasonics, genom att använda planvågsavbildning och coherent compounding, och UIV implementerades som ett efterbearbetningsprogram. Tre parametrar varierades för att studera hur prestandan av UIV-programmet och flödesbeteendet hos mikrobubblorna påverkades: koncentrationen av mikrobubblor, flödeshastigheten, och spänningsamplituden hos ultraljudsproben. De resulterande hastighetsvektorfälten visade det möjligt att evaluera flödesbeteenden hos PVA-mikrobubblor med hjälp av det implementerade UIV-programmet. Bäst resultat erhölls genom att använda koncentrationen 5·106 mikrobubblor/ml, av de fem testade koncentrationerna. De genererade hastighetsvektorfälten indikerade ett turbulent och pulserande flöde, vilket överensstämde med teorin, trots att det fanns skillnader mellan genomsnittliga uppmätta flödeshastigheter och den beräknade flödeshastigheten. Det kunde också observeras att mikrobubblorna trycktes i den axiella riktningen när spänningsamplituden ökade, vilket överensstämde med teorin. Trots att metodens noggrannhet skulle kunna ökas genom att använda ett mer avancerat UIV-program, visade resultaten på möjligheten att använda luftfyllda PVA-mikrobubblor i kombination med UIV.

The primary purpose of this work was to evaluate the capability of nanoparticles to transform electromagnetic energy at microwave frequencies into therapeutic heating. Targeted nanoparticles, in conjunction with microwave irradiation, can increase the temperatures of the targeted area over the peripheral region. Therefore, to become clinically viable, microwave absorbing nanoparticles must first be identified, and a system to monitor the treatment must be developed. In this study, ultrasound temperature imaging was used to monitor the temperature of deep lying structures. First, a material-dependent quantity to correlate the temperature induced changes in ultrasound images (i.e. apparent time shifts) to differential temperatures was gathered for a tissue-mimicking phantom, porcine longissimus dorsi muscle, and porcine fat. Then microwave nanoabsorbers were identified using an infrared radiometer. The determined nanoabsorbers were then injected into ex-vivo porcine longissimus dorsi muscle tissue. Ultrasound imaging frames were gathered during microwave treatment of the inoculated tissue. Finally, the ultrasound frames were analyzed using the correlation between temperature and apparent shifts in ultrasound for porcine muscle tissue. The outcome was depth-resolved temperature profiles of the ex-vivo porcine muscle during treatment. The results of this study show that magnetite is a microwave nanoabsorber that increases the targeted temperature of microwave hyperthermia treatments. Overall, there is clinical potential to use microwave nanoabsorbers to increase the efficiency of microwave hyperthermia treatments. / text

<p>In this thesis, we develop methods for addressing the deficiencies of array processing with linear thinned arrays. Our methods are designed for array systems mounted on moving platforms and exploit synthetic aperture processing techniques. In particular, we use array motion to decrease the sidelobe levels and increase the degrees of freedom available from thinned array systems. In this work, we consider two application areas 1) passive SONAR and 2) ultrasound imaging. </p><p>Synthetic aperture processing is a methodology for exploiting array motion and has been successfully used in practice to increase array resolution. By spatially sampling along the path of the array virtual sensors can be realized and coherently fused to the existing array. The novel contribution of this work is our application of synthetic aperture processing. Here our goal is not to increase array resolution, instead we propose to use the synthetic aperture process to expand the spatial covariance and spatial frequency sensing capabilities of thinned array system.</p><p> </p><p>In the passive sensing case, we use a class of thinned arrays know as co-prime linear sensor arrays for source localization. The class of co-prime arrays provides roughly half the aperture worth of spatial covariances and with modest array motion can be extended to the full aperture of the array. The amount of motion required to produce a full set of spatial covariances is shown to be a function of the co-prime array parameters and is only a fraction of the total aperture of the array. The full set of spatial covariances can be used to form a spatial covariance matrix with dimension equal to that of a uniform array. With a spatial covariance matrix in hand one can perform signal processing tasks as if the array were fully populated. Three methods for spatial covariance matrix estimation are compared in different source localization scenarios. In the work presented here, we demonstrate the benefits of our approach for achieving reduced sidelobe levels and extending the source localization capabilities above the limits of the static co-prime array. </p><p>In the active sensing case, we develop a framework for incorporating motion using thinned arrays for ultrasound imaging. In this setting, array motion is used to augment the spatial frequency sensing capabilities of the thinned array system. Here we develop an augmentation strategy based on using quarter-wavelength array translations to fill-in missing spatial frequencies not measured by the static thinned array. The quarter-wavelength translation enables the thinned array system to sample missing spatial frequencies and increase the redundancy of other spatial frequencies sampled by the array. We compare the level of redundancy in sampling the spatial frequencies achieved by the thinned arrays post translation to different levels of sample redundancy derived from pruning the transmit/receive events of a uniform array. In this manner, we are able to examine how the level of spatial frequency redundancy afforded by different thinned arrays compare over the full redundancy range of the uniform array. While artificially pruning the uniform array does not necessarily create realizable arrays, it provides the means to compare image quality at different spatial frequency redundancy levels. In this work, we are able to conclude that images formed from thinned arrays using the translated synthetic aperture process are capable of approximating images formed from the corresponding uniform array. In particular, the systems considered in this work have approximately one-third of the active sensors when compared to the uniform array. </p><p>In both application areas, the use of thinned arrays offers a reduction in the cost to deploy and maintain a given array system. The feature that makes it possible to overcome the spatial sampling deficiencies of thinned array systems is motion and it is at the core of the performance gains in these applications.</p> / Dissertation

Em formação de imagens por ultrassom de objetos com superfícies curvas, em imersão, se as velocidades de propagação no ruído e no objeto forem muito diferentes os efeitos de refração precisam ser compensados. Nesse caso a posição e a forma da superfície precisam ser conhecidas. Neste trabalho a superfície é detectada pelo mesmo array linear que captura os sinais para a formação de imagem.Dois métodos rápidos de detecção de superfície foram propostos, um baseado em técnicas de formação de imagem e outro que utiliza informações de tempo de percurso de ecos extraídas diretamente dos sinais de ultrassom.Os dois métodos foram comparados,e o método baseado em imagem apresentou uma maior tolerância a erros nos sinais, enquanto o método baseado em tempo de percurso mostrou-se mais rápido.Com a superfície detectada, a imagem foi formada por combinação de imagens por abertura sintética, que apresentou uma boa resolução. O uso conjunto dos métodos de detecção de superfície propostos e da formação de imagem resultou em uma taxa de imagens que permite ensaios interativos,com processamento em uma CPU de uso geral. / In ultrasound imaging ofobjects with curved surface, in immersion, the refraction eects must be compensated for if the propagation speed in the uid is very dierent from the speed in the object. In this case the surface position and shape must be known. In this work the surface is detected by the same linear array that captures the signals for the image formation. Two fast methods for surface detection were proposed,one is based on image formation techniques and another utilizes the echotime-of-ight information directly from the ultra\\sound signals.The two methods were compared,and the image-based method was more tolerant of signal errors, while the time-of-ight-based method was faster. After the surface detection, the image was formed by combination of synthetic aperture images,with a good resulting resolution. The utilization of the proposed surface detection methods together with the image formation resulted in an image rate that allows interactive testing, with processing on a general-purpose CPU.