Die vorliegende medizinische Dissertation untersucht nicht-invasive bildgebende Verfahren wie die konventionelle Sonographie, die Acoustic radiation force impulse (ARFI)-Elastographie sowie die Transiente Elastographie (TE) zur Detektion von Komplikationen in der Frühphase nach allogener Stammzelltransplantation. Dem kurativen Therapieansatz der Stammzelltransplantation steht ein hohes Komplikationspotential gegenüber. Besonders hepatobiliär treten Graft-versus-host Erkrankungen (GvHD) sowie Gefäßkomplikationen (VOD) auf. Der bisherige diagnostische Goldstandard, die Leberbiopsie, ist als invasives Verfahren mit einer hohen Intra- und Inter-Untersucher-Variabilität sowie der geringen Repräsentativität als Screeningmethode ungeeignet. Die Elastographieverfahren ARFI und TE als nicht-invasive Alternativen ermitteln die Lebergewebesteifigkeit als Surrogatparameter fibrotischer Veränderungen und wurden bereits in zahlreichen Studien als geeignete Diagnoseverfahren für Leberfibrose und -zirrhose unterschiedlicher Ätiologie definiert. Ziel dieser prospektiven Pilotstudie war die Evaluation der genannten Methoden zur Detektion von Frühkomplikationen nach allogener Stammzelltransplantation. Die Ergebnisse der Studie zeigen, dass sowohl die konventionelle Sonographie als auch die Transiente Elastographie pathologische Organveränderungen vor allem des hepatobiliären Systems detektieren können. Allerdings erscheinen diese Veränderungen unspezifisch. Es bestehen keine signifikanten Unterschiede zwischen Patienten mit und ohne Komplikationen. Anders bei der ARFI-Elastographie. Hier zeigten die Messwerte im linken Leberlappen signifikant höhere Werte bei Patienten mit Komplikationen. Zusammenfassend ist die ARFI-Elastographie zur Prädiktion möglicher Komplikationen nach allogener Stammzelltransplantation geeignet, sollte allerdings mit anderen diagnostischen Verfahren ergänzt werden.:III. Inhaltsverzeichnis I. Vorbemerkungen 2 II. Bibliographische Beschreibung 3 III. Inhaltsverzeichnis 4 IV. Abkürzungsverzeichnis 5 1. Einleitung 1.1. Hämatopoetische Stammzelltransplantation 6 2. Komplikationen nach allogener Stammzelltransplantation und deren Diagnostik 2.1. Akute Komplikationen 8 2.2. Akute und chronische Graft-versus-host Erkrankung 9 2.3. Hepatobiliäre Komplikationen 12 2.3.1. Veno-occlusive disease 12 2.3.2. Drug-induced liver injury 14 2.3.3. Problematik der Diagnostik 16 3. Risikostratifizierung bei Stammzelltransplantation 16 3.1. Karnovsky Index und Eastern Cooperative Oncology Group Index 16 3.2. Hematopoietic cell transplantation comorbidity index 17 3.3. Leberspezifisches Risikoassessment 18 4. Nicht-invasive Leberdiagnostik 19 4.1. Konventionelle Sonographie 19 4.2. Elastographie 20 4.2.1. Transiente Elastographie 21 4.2.2. Acoustic radiation force impulse imaging 22 5. Prospektive Studie: Sonographische Evaluation von Komplikationen in der Frühphase nach allogener Stammzelltransplantation 23 5.1. Methodik 24 5.2. Eigener Arbeitsanteil 24 6. Publikationsmanuskript 25 7. Zusammenfassung 32 8. Literaturverzeichnis 36 9. Selbständigkeitserklärung 44 10. Lebenslauf 45 11. Danksagung 46

Abstract not available. / by Wong Lai-hung, Grace. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 218-252). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.

<p>Ultrasound can be used for a variety of therapeutic purposes. High-intensity focused ultrasound (HIFU) has progressed over the past decade to become a viable therapeutic method and is valuable as a non-invasive alternative to many surgical procedures. Ultrasonic thermal therapies can also be used to release thermally sensitive liposomes encapsulating chemotherapeutic drugs. In the brain, the permeability of the blood-brain barrier to drugs, antibodies, and gene transfer can be increased with a mechanical mechanism using ultrasound and contrast agent.</p><p>The work presented in this dissertation tests the hypothesis that a diagnostic system can be used for combined imaging and therapeutic applications. In order to evaluate the effectiveness of a diagnostic system for use in therapeutic applications, a set of non-destructive tests is developed that can predict the potential for high acoustic output. A rigorous, nondestructive testing regimen for standard, diagnostic transducers to evaluate their potential for therapeutic use is formulated. Based on this work, transducer heating is identified as the largest challenge. The design and evaluation of several custom diagnostic transducers with various modifications to reduce internal heating are described. These transducers are compared with diagnostic controls using image contrast, face heating, hydrophone, and ARFI displacement measurements. From these results, we conclude that the most promising design is a passively and actively cooled, PZT-4 multilayer composite transducer, while the acoustically lossless lens and capactive micro-machined transducers evaluated herein are determined to be ineffective.</p><p>Three therapeutic applications are evaluated for the combined system. Image-guided spot ablations, such as in the treatment of early stage liver cancers, could not be successfully performed; however, the additional acoustic output requirements are determined to be on the order of 2.4 times those that can be currently produced without transducer damage in a clinically relevant amount of time (10-20 seconds per spot). The potential of a diagnostic system for a hyperthermia application is shown by producing temperatures for the duration necessary to release chemotherapeutic agents from thermally-activated liposomes without damage to the transducer. Finally, a mechanically-based therapeutic method for opening the BBB with ultrasonic contrast agent and specialized sonication regimes under ultrasonic B-mode guidance is demonstrated.</p><p>These studies indicate that a diagnostic system is capable of both moderate thermal and mechanical therapeutic applications under co-registered image-guidance.</p> / Dissertation

Particle separation is of great interest to many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In addition, current gold standard active separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. In this dissertation, a sheathless acoustic-based microfluidic platform using surface acoustic wave for not only size-dependent but also density-dependent particle separation has been investigated. In this platform, two different functions were incorporated within a single microfluidic channel with varying the number of pressure node and position. The first function was to align particles on the center of the microfluidic channel without adding any external sheath flow. The second function was to separate particles according to their size or density. Two different size-pairs of polystyrene particles with different diameters (3 µm and 10 µm for general size-resolution, 3 µm and 5 µm for higher size-resolution) were successfully separated. Also, the separation of two 10 µm diameter, different-density particle streams (polystyrene: 1.05 g/cm3, melamine: 1.71 g/cm3) was successfully demonstrated. The effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. A range of high separation efficiencies with 94.8-100 % for size-based separation and 87.2 - 98.9 % for density-based separation were accomplished. In this dissertation, an acoustic-based microfluidic platform using dual acoustic streaming for active mixing has also been investigated. The rapid and high efficiency mixing of a fluorescent dye solution and deionized water in a microfluidic channel was demonstrated with single acoustic excitation by one interdigital transducer (IDT) as well as dual excitation by two IDTs. The mixing efficiencies were investigated as a function of applied voltage and flow rates. The results indicate that with the same operation parameters, the mixing efficiency with dual-IDT design increased to 96.7 % from 69.8 % achievable with the traditional single-IDT design. The effect of aperture length of the IDT on mixing efficiency was also investigated. Additionally, the effects of the polydimethylsiloxane (PDMS) channel wall thickness on the insertion loss and the particle migration to the pressure node due to acoustic radiation forces induced by SAW have been investigated. The results indicate that as the PDMS channel wall thickness decreased, the SAW insertion loss is reduced as well as the velocity of the particle migration due to acoustic forces increased significantly. As an example, reducing the side wall thickness of the PDMS channel from 8 mm to 2 mm in the design results in 31.2 % decrease in the insertion loss at the resonant frequency of 13.3 MHz and 186 % increase the particle migration velocity at the resonant frequency of 13.3 MHz with input power of 27 dBm. Lastly, a novel acoustic-based method of manipulating the particles using phase-shift has been proposed and demonstrated. The location of the pressure node was adjusted simply by modulating the relative phase difference (phase-shift) between two IDTs. As a result, polystyrene particles of 5 µm diameter trapped in the pressure node were manipulated laterally across the microfluidic channel. The lateral displacements of the particles from -72.5 µm to 73.1 µm along the x-direction were accomplished by varying the phase-shift with a range of -180° to 180°. The relationship between the particle displacement and the phase-shift of SAW was obtained experimentally and shown to agree with theoretical prediction of the particle position.

<p>Tissue stiffness can be an indicator of various types of ailments. However, no standard diagnostic imaging modality has the capability to depict the stiffness of tissue. To overcome this deficiency, various elasticity imaging methods have been proposed over the past 20 years. A promising technique for elasticity imaging is acoustic radiation force impulse (ARFI) based shear wave imaging. Spatially localized acoustic radiation force excitation is applied impulsively to generate shear waves in tissue and its stiffness is quantified by measuring the shear wave speed (SWS).</p><p>The aim of this thesis is to contribute to both the clinical application of ARFI shear wave imaging and its technical development using the latest advancements in ultrasound imaging capabilities.</p><p>To achieve the first of these two goals, a pilot imaging study was conducted to evaluate the suitability of ARFI shear wave imaging for the assessment of liver fibrosis using a rodent model of the disease. The stiffness of severely fibrotic rat livers were found to be significantly higher than healthy livers. In addition, liver stiffness was correlated with fibrosis as quantified using collagen content.</p><p>Based on these findings, an imaging study was conducted on patients undergoing liver biopsy at the Duke University Medical Center. A robust SWS estimation algorithm was implemented to deal with noisy patient shear wave data using the random sample consensus (RANSAC) approach. RANSAC estimated liver stiffness was found to be higher in severely fibrotic and cirrhotic livers, suggesting that ARFI shear wave imaging may potentially be useful for the staging of severe</p><p>fibrosis in humans.</p><p>To achieve the second aim of this thesis, a system capable of monitoring ARFI induced shear wave propagation in 3D was implemented using a 2D matrix array transducer. This capability was previously unavailable with conventional 1D arrays. This system was used to study the precision of time-of-flight (TOF) based SWS estimation. It was found that by placing tracking beam locations at the edges of the SWS measurement region of interest using the 2D matrix array, TOF SWS precision could be improved in a homogeneous medium.</p><p>The 3D shear wave imaging system was also used to measure the SWS in muscle, which does not conform to the isotropic mechanical behavior usually assumed for tissue, due to the parallel arrangement of muscle fibers. It is shown that the SWS along and across the fibers, as well as the 3D fiber orientation can be estimated from a single 3D shear wave data-set. In addition, these measurements can be made independent of the probe orientation relative to the fibers. This suggests that 3D shear wave imaging can be useful for characterizing anisotropic mechanical properties of tissue.</p> / Dissertation

<p>The rupture of arterial plaques is the most common cause of ischemic complications including stroke, the fourth leading cause of death and number one cause of long term disability in the United States. Unfortunately, because conventional diagnostic tools fail to identify plaques that confer the highest risk, often a disabling stroke and/or sudden death is the first sign of disease. A diagnostic method capable of characterizing plaque vulnerability would likely enhance the predictive ability and ultimately the treatment of stroke before the onset of clinical events.</p><p>This dissertation evaluates the hypothesis that Acoustic Radiation Force Impulse (ARFI) imaging can noninvasively identify lipid regions, that have been shown to increase a plaque's propensity to rupture, within carotid artery plaques <italic>in vivo</italic>. The work detailed herein describes development efforts and results from simulations and experiments that were performed to evaluate this hypothesis.</p><p>To first demonstrate feasibility and evaluate potential safety concerns, finite-element method simulations are used to model the response of carotid artery plaques to an acoustic radiation force excitation. Lipid pool visualization is shown to vary as a function of lipid pool geometry and stiffness. A comparison of the resulting Von Mises stresses indicates that stresses induced by an ARFI excitation are three orders of magnitude lower than those induced by blood pressure. This thesis also presents the development of a novel pulse inversion harmonic tracking method to reduce clutter-imposed errors in ultrasound-based tissue displacement estimates. This method is validated in phantoms and was found to reduce bias and jitter displacement errors for a marked improvement in image quality <italic>in vivo</italic>. Lastly, this dissertation presents results from a preliminary <italic>in vivo</italic> study that compares ARFI imaging derived plaque stiffness with spatially registered composition determined by a Magnetic Resonance Imaging (MRI) gold standard in human carotid artery plaques. It is shown in this capstone experiment that lipid filled regions in MRI correspond to areas of increased displacement in ARFI imaging while calcium and loose matrix components in MRI correspond to uniformly low displacements in ARFI imaging.</p><p>This dissertation provides evidence to support that ARFI imaging may provide important prognostic and diagnostic information regarding stroke risk via measurements of plaque stiffness. More generally, the results have important implications for all acoustic radiation force based imaging methods used clinically.</p> / Dissertation

Chronic liver diseases are the eighth leading cause of death in Brazil and a major public health problem in the world. Liver biopsy is the best available reference standard for evaluating and classifying stages of liver diseases, but it presents limitations and complications that are common in invasive methods. In recent years, elasticity imaging methods have been the focus of intense research activity with the ability to measure mechanical properties of soft tissues in a non-invasive way. Shear wave elastography is one of the most promising methods because it enables to quantitatively assess tissue elasticity. However, the current depth range of shear wave elastography impedes its application in obese patients, which have a great risk of developing liver disease. The aim of this study is to investigate the use of shear wave elastography in deeper tissues using a two-dimensional ultrasound transducer array. An efficient transducer array arrangement was simulated, fabricated and characterized. The results show that the proposed transducer configuration presents enhanced transmitting capabilities for generating tissue displacement in deeper tissues. In addition, numerical simulations were performed in order to track the tissue deformation and reconstruct its elastic properties. / Doenças crônicas do fígado são a oitava causa de morte no Brasil e um dos principais problemas de saúde pública do mundo. A biópsia do fígado é o melhor padrão de referência disponível para avaliação e classificação dos estágios das doenças hepáticas, mas apresenta limitações e complicações que são comuns nos métodos invasivos. Nos últimos anos, métodos de imagem por elasticidade têm sido o foco de intensa atividade de pesquisa, pois têm a capacidade de medir propriedades mecânicas dos tecidos moles de maneira não invasiva. A elastografia por ondas de cisalhamento é um dos métodos mais promissores, pois permite avaliar quantitativamente a elasticidade do tecido. No entanto, a atual faixa de profundidade da elastografia por ondas de cisalhamento impede sua aplicação em pacientes obesos, que apresentam grande risco de desenvolver doença hepática. O objetivo deste estudo é investigar o uso da elastografia por onda de cisalhamento em tecidos mais profundos usando um transdutor de ultrassom bidimensional. Uma configuração eficiente de transdutores matriciais foi simulada, fabricada e caracterizada. Os resultados mostram que o transdutor proposto possui capacidade de transmissão melhorada para gerar deslocamento em tecidos profundos. Além disso, simulações numéricas foram realizadas para monitorar a deformação do tecido e reconstruir suas propriedades elásticas.

Recent advances and interest in ultrasound particle manipulation calls for theoretical understanding of acoustic radiation force and torque exerted on a configuration of multiple particles. In this thesis we theoretically study the acoustic radiation force and torque exerted by an arbitrary acoustic beam on a cluster of spherical particles in an inviscid fluid. The method is based on the partial-wave expansion (PWE) and the translational addition theorem for spherical wave functions. The combination of (PWE) and addition theorem Method enable us to solve the associated multiple scattering problem by numerically computing the (PWE) coefficients in a system of linear equations. On the other hand, when we consider the radiation force and torque exerted on a single sphere, the addition theorem has the advantage to solve this problem in a closed form. After obtaining the PWE coefficients, the acoustic radiation force and torque is computed through the farfield series solution. To illustrate the method, the acoustic radiation force and torque exerted on a single or multiple spheres are analyzed. In the case of a single sphere, the force is generated by a spherically focused ultrasound beam, where as the torque is generated by a Bessel vortex beam. For the multiple spheres configuration, the radiation force is induced by a traveling and a standing plane wave. In a specific configuration of three olive oil droplets suspended in water, with radii of the order of the wavelength, we found that rescattering events produce an acoustic interaction force, which significantly changes the radiation force on each droplet depending on the inter-droplet distance. In addition, we have found for the first time that an acoustic interaction torque due to the nonsymmetric spatial distribution of the acoustic energy density to the droplets. Further more, our study does not have restrictions on the spheres size compared to the wave length, nor on their composition material, which includes rigid, void, compressional liquid, elastic and viscoelastic solids, and layered material. Finally, this study has direct applications on methods for noncontact object handling by acoustic waves such as acoustic levitation, acoustical tweezers, and acoustophoresis in lab-on-a-chip devices. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Recentes avanços e interesse em manipulação de partículas necessitam de uma maior compreensão teórica da força de radiação e torque acústico exercidos sobre uma configuração de múltiplas partículas. Nesta tese, nós estudamos teoricamente a força de radiação e torque acústico exercido por um feixe acústico arbitrário em um conjunto de partículas esféricas suspensas em um fluido não viscoso. O método baseia-se na expansão de ondas parciais (EOP) e no teorema translacional da adição para funções de onda esférica. A combinação do método de ondas parciais com o teorema da adição nos permitir resolver o problema de espalhamento mútiplo computando numericamente os coeficientes da expansão em um sistema de equações lineares. Por outro lado, quando consideramos a força e torque de radiação exercidos sobe uma única esfera, o teorema da adição tem a vantagem para resolver este problema exatamente. Após a obtenção dos coeficientes, a força e o torque de radiação são calculados usando um método em séries no campo distante. Para ilustrar o método, a força e o torque exercidos sobre uma ou multiplas esferas são analisados. Para o de uma única esfera, a força de radiação é gerada por um feixe de ultrassom focalizado. Para uma configuração de multiplas esferas, a força de radiação é induzida por ondas planas e estacionarias. Numa configuração específica de três gotas de azeite suspensas em água, com raios da ordem do comprimento de onda, verificou-se que as ondas reespalhadas produzem uma força de interação acústica, o que altera significativamente a força de radiação em cada gota em função da distância inter-gota. Além disso, verificou-se, pela primeira vez que um torque de interação acústico devido a uma distribuição espacial não simétrica da densidade de energia acústica para as gotas. Além disso, nosso estudo não tem restrições quanto ao tamanho esferas em comparação com o comprimento de onda, nem sobre a sua composição, que inclui rígida, líquida, elástica e sólidos viscoelásticos. Por fim, este estudo tem aplicações diretas sobre os métodos de manipulação de objetos sem contato por ondas acústicas, tais como a levitação acústica, pinças acústicas e acoustophoresis em dispositivos lab-on-a-chip.

The study of acoustic radiation force and torque phenomena has attracted an enormous interest of the scientific community, due to applications of these phenomena in noncontact particles manipulation. In this work, we perform a theoretical analysis of acoustic radiation force and torque exerted on a homogeneous visco elastic particle in the Rayleigh scattering limit (the particle radius is much smaller than the incident wavelength) by a wave with arbitrary geometry. Our study is based on the partial-wave expansion in spherical coordinates of the incident and scattered waves. In this context, the radiation force and torque are obtained analytically in terms of an infinite series which involves the scattering and incident expansion coefficients. We assume that the particle behaves as a linear viscoelastic solid, which obeys the fractional Kelvin-Voigt model. Analytical expressions for the radiation force and torque are obtained considering the low- and high-frequency approximation in the viscoelastic model. The developed theory is used to describe the interaction of acoustic waves (traveling and standing plane waves, and zero and first-order Bessel beams) with a low-and high-density polyethylene particle. Our results show that the axial acoustic radiation force might become negative (i.e. in opposition to the wave propagation direction) when a certain condition involving the physical parameters of the particle is satisfied. Negative acoustic radiation torque due a beam of first-order Bessel may also occur when the same condition of negative radiation force is met. Remarkably, this is the first time that negative radiation force is predicted on a homogeneous particle in the Rayleigh scattering regime. Further more, the stability of the transverse acoustic radiation force generated by a Bessel beam is also investigated. We show a full 3D tractor Bessel vortex beam acting on the high-density polyethylene (HDPE). In the analysis of acoustic radiation force generated on a viscoelastic particle by a standing plane wave, relevant deviations arose in comparison with the solid elastic model for the particles. The magnitude of the radiation force and torque on a HDPE described by the viscoelastic model behaves differently (negative radiation force) compared with other materials (solid elastic and compressible fluid particle) due to traveling plane wave and Bessel beams. Finally, we believe that this study may help further enhance the development of acoustic levitation, particle handling in acoustofluids, and acoustical tweezers devices. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo dos fenômenos de força e torque de radiação acústico tem atraído um enorme interesse da comunidade científica, devido a aplicações desses fenômenos em manipulação de partículas sem contato. Neste trabalho, realizamos uma análise teórica da força e torque de radiação acústico exercido sobre uma partícula visco elástica homogênea no limite do espalhamento de Rayleigh (o raio da partícula é muito menor que o comprimento de onda incidente) por uma onda com geometria arbitrária. Nosso estudo baseia-se na expansão de ondas parciais em coordenadas esféricas das ondas incidente e espalhada. Nesse contexto, a força e o torque de radiação são obtidos analiticamente em termos de uma série infinita que envolve os coeficientes de expansão das ondas espalhada e incidente. Assumimos que a partícula se comporta como um sólido viscoelástico linear, que obedece o modelo de Kelvin-Voigt fracionário. Fórmulas analíticas para a força e torque de radiação são obtidas considerando uma aproximação de baixa e de alta frequência no modelo viscoelástico. A teoria desenvolvida é usada para descrever a interação de ondas acústicas (onda plana progressiva, onda plana estacionária, feixes de Bessel de ordem zero e de primeira ordem) com partículas de polietileno de baixa e de alta densidade. Os nossos resultados mostram que a força de radiação acústica axial pode ser negativa (isto é, em oposição à direção de propagação da onda) quando uma determinada condição envolvendo os parâmetros físicos da partícula é satisfeita. Torque de radiação acústico negativo devido a um feixe de Bessel de primeira ordem também pode ocorrer quando a mesma condição da força de radiação negativa for atendida. Notavelmente, esta é a primeira vez que a força de radiação negativa é prevista sobre uma partícula homogênea no regime de espalhamento Rayleigh. Além disso, a estabilidade transversal da força de radiação acústica gerada pelo feixe de Bessel também é investigada. Mostramos que um feixe de Bessel trator 3D completo atua sobre uma partícula de polietileno de alta densidade (PEAD). Na análise da força de radiação acústica gerada sobre uma partícula viscoelástica por uma onda plana estacionária, desvios relevantes surgiram em comparação com partícula sólida elástica. A amplitude da força e torque de radiação sobre uma PEAD descrita pelo modelo viscoelástico apresenta um comportamento diferente (força de radiação negativa) comparados com os outros materiais (sólida elástica e fluida com absorção longitudinal) devido a onda plana progressiva e feixes de Bessel. Por fim, acreditamos que este estudo pode ajudar a melhorar ainda mais o desenvolvimento de dispositivos de levitação acústica, manipulação de partículas em acustofluídica e pinças acústicas.

Chronic liver diseases are the eighth leading cause of death in Brazil and a major public health problem in the world. Liver biopsy is the best available reference standard for evaluating and classifying stages of liver diseases, but it presents limitations and complications that are common in invasive methods. In recent years, elasticity imaging methods have been the focus of intense research activity with the ability to measure mechanical properties of soft tissues in a non-invasive way. Shear wave elastography is one of the most promising methods because it enables to quantitatively assess tissue elasticity. However, the current depth range of shear wave elastography impedes its application in obese patients, which have a great risk of developing liver disease. The aim of this study is to investigate the use of shear wave elastography in deeper tissues using a two-dimensional ultrasound transducer array. An efficient transducer array arrangement was simulated, fabricated and characterized. The results show that the proposed transducer configuration presents enhanced transmitting capabilities for generating tissue displacement in deeper tissues. In addition, numerical simulations were performed in order to track the tissue deformation and reconstruct its elastic properties. / Doenças crônicas do fígado são a oitava causa de morte no Brasil e um dos principais problemas de saúde pública do mundo. A biópsia do fígado é o melhor padrão de referência disponível para avaliação e classificação dos estágios das doenças hepáticas, mas apresenta limitações e complicações que são comuns nos métodos invasivos. Nos últimos anos, métodos de imagem por elasticidade têm sido o foco de intensa atividade de pesquisa, pois têm a capacidade de medir propriedades mecânicas dos tecidos moles de maneira não invasiva. A elastografia por ondas de cisalhamento é um dos métodos mais promissores, pois permite avaliar quantitativamente a elasticidade do tecido. No entanto, a atual faixa de profundidade da elastografia por ondas de cisalhamento impede sua aplicação em pacientes obesos, que apresentam grande risco de desenvolver doença hepática. O objetivo deste estudo é investigar o uso da elastografia por onda de cisalhamento em tecidos mais profundos usando um transdutor de ultrassom bidimensional. Uma configuração eficiente de transdutores matriciais foi simulada, fabricada e caracterizada. Os resultados mostram que o transdutor proposto possui capacidade de transmissão melhorada para gerar deslocamento em tecidos profundos. Além disso, simulações numéricas foram realizadas para monitorar a deformação do tecido e reconstruir suas propriedades elásticas.