A Lagrangian formalism presented by Hay, Ilinskii, Zabolotskaya, and Hamilton [J. Acoust. Soc. Am. 132, 124--137 (2012)] to calculate the pulsation of a spherical bubble, immersed in liquid and near one or two viscoelastic layers, is extended here to include bubble translation. The method presented here is simplified from that given by Hay et al. in that only a single interface between a liquid and a viscoelastic half-space is considered. In the present approach the force on the bubble due to the presence of the liquid-solid interface is calculated using a Green's function that takes into account elastic waves and viscosity in the layer, and the viscous boundary layer within the liquid near the interface. Previous models and experiments have shown that the direction of bubble translation near a viscoelastic layer is correlated with the direction of a liquid jet often produced by the bubble during collapse. In this dissertation an attempt is made to model the pulsation and translation of a spherical bubble near a liquid-solid interface to infer the direction of bubble translation in reference to material parameters of the liquid and viscoelastic medium, and the standoff distance of the bubble from the interface. The analysis is simplified by demonstrating that the direction of bubble translation can be inferred from the phase of the component of the Green's function associated with the reverberant pressure gradient. For linear bubble pulsation it is shown that the domain of material properties of the viscoelastic medium which generally corresponds to bubble translation away from the interface occurs when the effective stiffness of the viscoelastic medium is greater than the effective damping for both itself and the liquid. The analysis is performed assuming the viscoelastic medium is similar to soft tissue, and its dynamics are described by a Voigt, Kelvin, or Maxwell model. The simulations are compared with existing experimental data. Effects of high-amplitude bubble pulsation are explored in terms of how the simulations differ as the pulsation amplitude increases. At higher pulsation amplitudes, it is shown that bubble translation is still described qualitatively by analyzing the phase of the reverberant pressure gradient. / text

A new class of polymer coated lanthanide fluoride nanoparticle aggregates (NPAs) was developed as potential MRI contrast agents. The NPA synthesis has been perfected to control the size distribution and optimize relaxivities. Polyacrylic acid was used as a stabilizing polymer, and was conjugated to folic acid to improve targeting to SK-BR-3 breast cancer cells. Terbium was incorporated in the synthesis to study the passive and active targeting properties of NPAs. Through a series of microscopy experiments, a significant difference in uptake between NPAs with and without targeting moieties occurs after 48 hours of incubation. The relaxivity of the optimized nanoparticles was measured to be 56 s-1(mg/ml)-1 using a 1.5 T scanner, which may be compared to that of the commercially available Gd3+-DTPA [R1 = 7 s-1(mg/ml)-1]. Abdominal perfusion studies in rats also demonstrated that the NPAs provide better contrast of the vasculature than Gd3+-DTPA does at the same mass concentration.

Microbubble contrast agents for ultrasound are widely used in numerous medical applications, both diagnostic and therapeutic. Due to their size, similar to that of red blood cells, microbubbles are able to traverse the entire vascular bed, enabling their utilization for applications such as tumour diagnosis. Vaporizable submicron droplets of liquid perfluoro- carbon potentially represent a new generation of extravascular contrast agents for ultrasound. Droplets of a few hundred nanometers in diameter have the ability to extravasate selectively in regions of tumour growth while staying intravascular in healthy tissues. Upon extravasation, these droplets may be vaporized with ultrasound and converted into gas bubbles. In this thesis we argue that vaporized submicron perfluorocarbon droplets possess the necessary stability and acoustic characteristics to be potentially applicable as a new gener- ation of extravascular ultrasound contrast agents. We examine, separately, the ultrasound conditions necessary for vaporization of the droplets into microbubbles, the size and stability of these bubbles following vaporization, on timescales ranging from nanoseconds to minutes, and the bubbles’ acoustic response to incident diagnostic ultrasound. We show that submicron droplets may be vaporized into bubbles of a few microns in diameter using single ultrasound pulse within the diagnostic range. The efficiency of conversion is shown to be on the order of at least 10% of the exposed droplets converting into stable microbubbles. The bubbles are shown to be stabilized by the original coating material encapsulating the droplet precursors, and be stable for at least minutes following vaporization. Finally, vaporized droplets are shown to be echogenic, with acoustic characteristics comparable to these of the commercially available ultrasound contrast agents. The results presented here show that vaporized droplets possess the necessary stability properties and echogenicity required for successful application as contrast agents, suggesting potential for their future translation into clinical practice.

Microbubble contrast agents for ultrasound are widely used in numerous medical applications, both diagnostic and therapeutic. Due to their size, similar to that of red blood cells, microbubbles are able to traverse the entire vascular bed, enabling their utilization for applications such as tumour diagnosis. Vaporizable submicron droplets of liquid perfluoro- carbon potentially represent a new generation of extravascular contrast agents for ultrasound. Droplets of a few hundred nanometers in diameter have the ability to extravasate selectively in regions of tumour growth while staying intravascular in healthy tissues. Upon extravasation, these droplets may be vaporized with ultrasound and converted into gas bubbles. In this thesis we argue that vaporized submicron perfluorocarbon droplets possess the necessary stability and acoustic characteristics to be potentially applicable as a new gener- ation of extravascular ultrasound contrast agents. We examine, separately, the ultrasound conditions necessary for vaporization of the droplets into microbubbles, the size and stability of these bubbles following vaporization, on timescales ranging from nanoseconds to minutes, and the bubbles’ acoustic response to incident diagnostic ultrasound. We show that submicron droplets may be vaporized into bubbles of a few microns in diameter using single ultrasound pulse within the diagnostic range. The efficiency of conversion is shown to be on the order of at least 10% of the exposed droplets converting into stable microbubbles. The bubbles are shown to be stabilized by the original coating material encapsulating the droplet precursors, and be stable for at least minutes following vaporization. Finally, vaporized droplets are shown to be echogenic, with acoustic characteristics comparable to these of the commercially available ultrasound contrast agents. The results presented here show that vaporized droplets possess the necessary stability properties and echogenicity required for successful application as contrast agents, suggesting potential for their future translation into clinical practice.

A new class of polymer coated lanthanide fluoride nanoparticle aggregates (NPAs) was developed as potential MRI contrast agents. The NPA synthesis has been perfected to control the size distribution and optimize relaxivities. Polyacrylic acid was used as a stabilizing polymer, and was conjugated to folic acid to improve targeting to SK-BR-3 breast cancer cells. Terbium was incorporated in the synthesis to study the passive and active targeting properties of NPAs. Through a series of microscopy experiments, a significant difference in uptake between NPAs with and without targeting moieties occurs after 48 hours of incubation. The relaxivity of the optimized nanoparticles was measured to be 56 s-1(mg/ml)-1 using a 1.5 T scanner, which may be compared to that of the commercially available Gd3+-DTPA [R1 = 7 s-1(mg/ml)-1]. Abdominal perfusion studies in rats also demonstrated that the NPAs provide better contrast of the vasculature than Gd3+-DTPA does at the same mass concentration.

The utility of microbubble agents in a variety of diagnostic and therapeutic ultrasound techniques has been widely demonstrated, most notably in Contrast Enhanced Ultrasound (CEUS) imaging. Unfortunately, the underlying mechanisms of their response to ultrasound excitation are poorly understood, restricting the development of promising techniques, such as quantitative perfusion imaging. A significant reason for this is that current microbubble characterisation techniques suffer from one or more of the following limitations: i) large experimental uncertainties, ii) physical restrictions on microbubble response and iii) failure to provide large data sets suitable for statistical analysis. This thesis presents a new technique to overcome these limitations. A co-axial microfluidic device is used to hydrodynamically confine microbubbles through the focal region of a laser and ultrasound field. The magnitude of light scattered by isolated microbubbles during ultrasound excitation is converted to radius using Mie Scattering theory. This technique is capable of obtaining large samples (>10³/min) of microbubbles to be efficiently characterised. The response of a commercial contrast agent, SonoVue®, is first investigated for a range of ultrasound exposure parameters; frequency (2 MHz - 4.5 MHz), peak negative pressure (6 kPa - 400 kPa) and pulse length (3 cycles - 8 cycles). Second the device is used to investigate the effect of composition and fabrication on microbubble response to similar ultrasound conditions. The results demonstrate a very large variability in microbubble response independent of initial size, indicating a significant lack of uniformity of coating properties. This is further supported by quantitative fluorescence imaging and quasi-static pressure chamber measurements. The implications of the findings for CEUS imaging and the development of microbubble contrast agents are discussed, as well as the limitations and suggested improvements of the characterisation technique.

abstract: Modern medical conditions, including cancer, traumatic brain injury, and cardiovascular disease, have elicited the need for cell therapies. The ability to non-invasively track cells in vivo in order to evaluate these therapies and explore cell dynamics is necessary. Magnetic Resonance Imaging provides a platform to track cells as a non-invasive modality with superior resolution and soft tissue contrast. A new methodology for cellular labeling and imaging uses Nile Red doped hexamethyldisiloxane (HMDSO) nanoemulsions as dual modality (Magnetic Resonance Imaging/Fluorescence), dual-functional (oximetry/ detection) nanoprobes. While Gadolinium chelates and super paramagnetic iron oxide-based particles have historically provided contrast enhancement in MRI, newer agents offer additional advantages. A technique using 1H MRI in conjunction with an oxygen reporter molecule is one tool capable of providing these benefits, and can be used in neural progenitor cell and cancer cell studies. Proton Imaging of Siloxanes to Map Tissue Oxygenation Levels (PISTOL) provides the ability to track the polydimethylsiloxane (PDMS) labeled cells utilizing the duality of the nanoemulsions. 1H MRI based labeling of neural stem cells and cancer cells was successfully demonstrated. Additionally, fluorescence labeling of the nanoprobes provided validation of the MRI data and could prove useful for quick in vivo verification and ex vivo validation for future studies. / Dissertation/Thesis / Masters Thesis Bioengineering 2014

Made available in DSpace on 2018-06-27T18:56:28Z (GMT). No. of bitstreams: 3 Valnir de Paula.pdf: 2329033 bytes, checksum: 989bd5d1109793d5b0ba4e36a71ad934 (MD5) Valnir de Paula.pdf.txt: 111221 bytes, checksum: e193938f84364f16942c08f8c27a80b8 (MD5) Valnir de Paula.pdf.jpg: 3313 bytes, checksum: b9abaf2a3f9be69ba98dca42617b7fef (MD5) Previous issue date: 2011-12-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The use of nanoscale products in several areas, including medicine, is a growing reality. The magnetic nanoparticles (MNPs) for being able to present a significant effect of magnetization when exposed to an external magnetic field, have been the focus of several studies, and among their applications is their use as contrast agent in magnetic resonance images. This technique provides images based on the nuclear behavior of the atoms of anatomical structures, which can be best highlighted by the use of contrast agents, usually paramagnetic. The MNPs represent an alternative to the current class of paramagnetic contrast agents for nuclear magnetic resonance, used for a long time, with advantages from a physical point of view, because they highlight even more the magnetic behavior of protons in different tissues, especially liver, spleen and lymphatic system, whose defense cells endocyte these MNPs, making healthy parenchyma dark (hyposignal), so that any injuries stand out in the images, facilitating their identification. This study has aimed to assess the contrast degree of the organs of the phagocyte system, injecting NPMs doses ranging from 0.46 to 7.2 mg/kg in rats, by caudal intravenous flow and subjecting them to nuclear magnetic resonance imaging. The MNPs was divided into two groups, both with a core of magnetite, varying the coating, which has been dextran in group 1, and oleic acid in group 2. The expected effect was that the organs of the phagocyte system would have some degree of signal loss in the images, indicating that the NPMs were internalized by the cells of these organs. With the usual contrast agent, paramagnetic, which does not enter cells, the effect is the hypersignal in the vascular system and in hypervascularized organs. We have compared the images obtained from T1 TSE and T2 TSE sequences with the control obtained before injection. The results have shown that both dextran coated MNPs and the ones coated with oleic acid have caused the hyposignal effect in the images, ranging from weak to strong, depending on the administered dose, especially in T2 TSE sequences. The dextran coated MNPs have shown higher efficiency, considering that the hyposignal effects have occurred with lowers doses, compared to the effects caused by NPMs coated with oleic acid. It can be concluded, given the evident hyposignal effect presented by the organs of the phagocyte system, the potential application of MNPs as a contrast agent in magnetic resonance studies. / A utilização de produtos de escala nanométrica nas mais diversas áreas, inclusive na medicina, é uma realidade crescente. As nanopartículas magnéticas (NPMs), por serem capazes de apresentar efeito expressivo de magnetização quando expostas a um campo magnético externo, têm sido foco de vários estudos e, entre as suas aplicações está o uso como agente de contraste em imagens de ressonância magnética nuclear. Esta técnica fornece imagens baseadas no comportamento nuclear dos átomos das estruturas anatômicas, as quais podem ser melhor destacadas pelo uso de agentes de contraste. As NPMs representam uma classe alternativa aos atuais agentes de contraste, paramagnéticos, com vantagens do ponto de vista físico, pois destacam ainda mais o comportamento magnético dos prótons de diferentes tecidos. Isto é mais evidente no fígado, baço e sistema linfático, cujas células de defesa endocitam estas NPMs, tornando o parênquima sadio escuro (hipossinal), de forma que eventuais lesões se sobressaeam nas imagens, facilitando a sua identificação. O objetivo deste trabalho foi avaliar o grau de contrastação dos órgãos do sistema fagocitário, injetando-se doses de NPMs que variaram de 0,46 a 7,2 mg/Kg em ratos, por via endovenosa caudal e submetendo-os a imageamento por ressonância magnética nuclear. As NPMs foram divididas em 2 grupos, ambos com núcleo de magnetita, variando-se o revestimento, que no grupo 1 foi de dextrana e o do grupo 2, de ácido oléico. O efeito desejado foi que os órgãos do sistema fagocitário apresentassem algum grau de perda de sinal nas imagens, indicando que as NPMs foram internalizadas pelas células desses órgãos. Com o agente de contraste usual, paramagnético, que não entra nas células, o efeito é de hiperssinal no sistema vascular e em órgãos hipervascularizados. Comparou-se as imagens obtidas de sequências T1 TSE e T2 TSE com as de controle, obtidas antes da injeção. Os resultados obtidos evidenciaram que, tanto as NPMs revestidas com dextrana, quanto às revestidas com ácido oléico causaram efeito de hipossinal nas imagens, que variaram de fraco a acentuado, dependendo da dose administrada, principalmente em sequências T2 TSE. As NPMs revestidas com dextrana apresentaram maior eficiência, considerando que os efeitos de hipossinal ocorreram com doses menores do que as revestidas com ácido oléico. Pode-se concluir, considerando o evidente efeito de hipossinal apresentado pelos órgãos do sistema fagocitário, que há potencial de aplicação destas NPMs como agente de contraste em estudos de ressonância magnética.

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De récents résultats d’études cliniques ont démontré l’efficacité de l’immunothérapie chez des patients atteints de cancer. Ce type de thérapie consiste à traiter les cellules cancéreuses en stimulant les défenses immunitaires du patient. Le but de ce projet de thèse est de mettre au point un biomarqueur d’efficacité de cette thérapie, afin d’une part de mieux comprendre les mécanismes biologiques mis en jeu, et d’autre part d’avoir un indicateur précoce et non-invasif de réponse du patient à l’immunothérapie. Pour ce faire, deux techniques d’imagerie (IRM et TEP) ont été utilisées comme outils de suivi in vivo de la biodistribution de différentes populations de cellules immunitaires. La première étape de ce travail a été d’établir différents protocoles de marquage des cellules immunitaires. Pour l’approche TEP, les cellules immunitaires ont été marquées avec du Zirconium 89 ; quant à l’IRM, deux techniques de marquage ont été étudiées : la première utilise des nanoparticules de fer, l’autre des micelles chargées en Fluor 19. Après validation de leur non-toxicité, la sensibilité de chaque marquage a été évaluée in vitro dans un premier temps, puis in vivo dans un deuxième temps, permettant ainsi d’étudier la biodistribution des cellules immunitaires après différents types d’injections. Le marquage au Zirconium 89 a ensuite été testé sur différents modèles animaux d’immunothérapies (par exemple PD1/PDL1). Enfin, les marquages directs ne permettant pas un suivi optimal des cellules à long terme, une approche de marquage cellulaire utilisant des gènes rapporteurs a été envisagée. Il s’agissait de modifier le génome des cellules immunitaires afin qu’elles puissent exprimer une enzyme (par exemple la thymidine kinase virale HSV1-TK) ou un transporteur (tel que le transporteur d’iode NIS) permettant l’internalisation d’un traceur radioactif in vivo, et de pouvoir ainsi réaliser un marquage indirect des cellules. / Recent clinical trial results have demonstrated the efficacy of immunotherapy in cancer patients. This type of therapy involves treating cancer cells by stimulating the patient's immune defenses. The aim of this thesis project is to develop a biomarker of efficacy for this therapy, in order to better understand the biological mechanisms involved, and to have an early and non-invasive indicator of the patient’s response to immunotherapy. To do this, two imaging techniques (MRI and PET) were used as in vivo monitoring tools for the biodistribution of different populations of immune cells. The first step of this work was to establish different protocols for labeling immune cells. For the PET approach, the immune cells were labeled with Zirconium 89; and for MRI, two labeling techniques were studied: the first uses iron nanoparticles, and the other uses micelles loaded with Fluorine 19. After validation of their non-toxicity, the sensitivity of each labeling was evaluated in vitro, then in vivo in a second step, thus making it possible to study the biodistribution of the immune cells after different types of injections. The labeling with Zirconium 89 was then tested on different animal models of immunotherapies (PD1/PDL1 for example). Finally, since direct markings do not allow optimal cellular monitoring in the long term, a cell labeling approach using reporter genes has been considered. It involved modifying the genome of the immune cells so that they could express an enzyme (for example the viral thymidine kinase HSV1-TK) or a transporter (such as the NIS iodine transporter) allowing the internalization of a radioactive tracer in vivo, and thus be able to carry out indirect labeling of the cells.