Tesis por compendio / [ES] La focalización de ultrasonidos tiene muchas aplicaciones en una gran variedad de áreas tanto científicas como industriales. Los ultrasonidos focalizados son una de las herramientas principales usada por médicos en todo el mundo para obtener imágenes biomédicas de diferentes tipos de tejidos y órganos de manera no invasiva. En las últimas décadas, el uso de ultrasonidos focalizados de alta intensidad (HIFU, por sus siglas en inglés) ha surgido como una de las técnicas principales para el tratamiento de cáncer mediante la ablación térmica de tumores de manera no invasiva. Además, los ultrasonidos focalizados están emergiendo en los últimos años como uno de los métodos más prometedores para el tratamiento de las enfermedades cerebrales, con la aparición de nuevas técnicas disruptivas como la apertura reversible de la barrera hematoencefálica o la neuromodulación. En entornos industriales, los ultrasonidos son ampliamente utilizados como uno de los métodos principales para la evaluación no destructiva de materiales y estructuras, debido a que las ondas acústicas pueden penetrar en los objetos a distancias donde la luz no puede debido a la elevada absorción y dispersión. En este sentido, diseñar estructuras capaces de focalizar ultrasonidos es de una gran relevancia tanto para la comunidad científica como para los sectores médicos e industriales. Esta tesis presenta nuevos diseños de lentes acústicas capaces de controlar los parámetros principales del haz de ultrasonidos focalizados, proporcionando diferentes tipos de perfiles de focalización adecuados para una gran variedad de aplicaciones y escenarios. En particular, se han diseñado y adaptado al campo de los ultrasonidos las lentes de Fresnel (Fresnel Zone Plates, FZPs), ampliamente utilizadas en el campo de la óptica. Se ha presentado una nueva técnica de modulación espacio-temporal capaz de controlar la posición del foco de ultrasonidos tanto en espacio como en tiempo, aumentando así la versatilidad de este tipo de dispositivos. También se ha demostrado el funcionamiento en el campo de la acústica de nuevos diseños basados en aplicar secuencias binarias a una lente de Fresnel convencional, como las secuencias fractales de Cantor o las secuencias de M-bonacci generalizadas, capaces de modificar las propiedades de focalización de las lentes, incluyendo el número, posición y forma de los focos acústicos. Además, se introduce un nuevo diseño de lentes esféricas rellenas de líquido capaces de generar jets ultrasónicos, con mucho potencial en aplicaciones de imagen de alta resolución en campo cercano. Se ha demostrado que, cambiando el líquido interno de la lente o ajustando el ratio de mezcla entre dos líquidos, se pueden controlar los parámetros principales del jet. Los diseños propuestos en la tesis han sido validados tanto empleando simulaciones numéricas como realizando medidas experimentales, allanando el camino para el uso de este tipo de estructuras en aplicaciones de focalización de ultrasonidos. / [CA] La focalització d'ultrasons té moltes aplicacions en moltes àrees científiques i industrials. Els ultrasons focalitzats són una de les eines principals utilitzada per metges a tot el món per obtenir imatges biomèdiques de diferents tipus de teixits i òrgans de manera no invasiva. En les últimes dècades, els ultrasons focalitzats d'alta intensitat (HIFU, per les seues sigles en anglès) han aparegut com una de les tècniques principals per al tractament de càncer mitjançant l'ablació de tumors de manera no invasiva. A més, els ultrasons focalitzats estan emergint en els últims anys com un dels mètodes més prometedors per al tractament de les malalties cerebrals, amb l'aparició de noves tècniques disruptives com l'obertura reversible de la barrera hematoencefàlica o la neuromodulació. En entorns industrials, els ultrasons són àmpliament utilitzats com un dels mètodes principals per a l'avaluació no destructiva de materials i estructures, pel fet que les ones acústiques poden penetrar en els objectes a distàncies on la llum no pot a causa de l'elevada absorció i dispersió. En aquest sentit, dissenyar estructures capaces de focalitzar ultrasons és d'una gran rellevància tant per a la comunitat científica com per als sectors mèdics i industrials. Aquesta tesi presenta nous dissenys de lents acústiques capaços de controlar els paràmetres principals del feix d'ultrasons focalitzats, proporcionant diferents tipus de perfils de focalització adequats per a una gran varietat d'aplicacions i escenaris. En particular, s'han dissenyat i adaptat al camp dels ultrasons les lents de Fresnel (Fresnel Zone Plates, FZPs), àmpliament utilitzades en el camp de l'òptica. S'ha presentat una nova tècnica de modulació espai-temporal capaç de controlar la posició del focus d'ultrasons tant en espai com en temps, augmentant així la versatilitat d'aquest tipus de dispositius. També s'ha demostrat el funcionament en el camp de l'acústica de nous dissenys basats en aplicar seqüències binàries a una lent de Fresnel convencional, com les seqüències fractals de Cantor o les seqüències de M-bonacci generalitzades, capaces de modificar les propietats de focalització de les lents, incloent el nombre, posició i forma dels focus acústics. A més, s'introdueix un nou disseny de lents esfèriques plenes de líquid capaces de generar jets ultrasònics, amb molt potencial en aplicacions d'imatge d'alta resolució en camp proper. S'ha demostrat que, canviant el líquid intern de la lent o ajustant la ràtio de barreja entre dos líquids, es poden controlar els paràmetres principals del jet. Els dissenys proposats en la tesi han estat validats tant emprant simulacions numèriques com realitzant mesures experimentals, aplanant el camí per a l'ús d'aquest tipus d'estructures en aplicacions de focalització d'ultrasons. / [EN] Ultrasound focusing has many applications in a wide range of fields. Focused ultrasound is one of the main tools used by doctors all over the world to obtain biomedical images of different kind of tissues non-invasively. In the past decades, high intensity focused ultrasound (HIFU) appeared as one of the fundamental techniques for cancer treatment through non-invasive thermal tumor ablation. In addition, focused ultrasonic waves are recently emerging as one of the main tools to treat brain diseases, with novel disruptive techniques such as blood-brain barrier opening or neuromodulation. In industrial environments, ultrasonic waves are widely employed as one of the primary methods for the non-destructive evaluation (NDE) of materials and structures, as acoustic waves are able to penetrate deep into objects otherwise opaque using optical techniques. In this sense, designing structures capable of focusing ultrasonic waves is of great interest and relevance for the scientific, the industrial, and the biomedical sectors. This thesis devises new designs of acoustic lenses capable of controlling the main parameters of the focused ultrasound beam, achieving different kinds of focusing profiles suitable for a wide variety of scenarios. In particular, Fresnel Zone Plates (FZPs), commonly used in optics, are designed and adapted to the ultrasound domain. A novel spatio-temporal modulation technique capable of controlling the ultrasound focus location in both time and space is presented, increasing the versatility of this kind of devices. New design techniques based on applying a binary sequence to FZPs are also demonstrated, such as Cantor fractal sequences or generalized M-bonacci sequences, which modify the focusing properties of the lens, including the number, location, and shape of the different acoustic foci. In addition, acoustic jets generated by liquid-filled spherical lenses are devised for near-field high resolution imaging, demonstrating their applicability in the ultrasound domain. It is demonstrated that, by changing the inner liquid of the spherical lens or by tuning the mixing ratio between two liquids, the main focal parameters of the ultrasonic jet can be accurately controlled. The proposed designs are validated using both numerical simulations and experimental measurements, paving the way for the use of these kind of structures in focused ultrasound applications. / This work would not have been possible without the following funding sources: PAID-01-18 personal FPI grant from Universitat Politècnica de València; Spanish government MINECO TEC2015-70939-R project; Spanish government MICINN RTI2018-100792-B-I00 project; Generalitat Valenciana AICO/2020/139 project. / Pérez López, S. (2021). Design of Acoustic Lenses for Ultrasound Focusing Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/179907 / Compendio

This thesis consists of 3 studies: 1. Determination of the minimal important difference (MID) of the visual analogue scale for dyspnoea (VASD): Determining the MID of the VASD is essential to interpret the results of trials in patients with malignant pleural effusions (MPEs). Patients undergoing a pleural procedure assessed the change in their VASD and the degree of change in their symptoms on a Likert scale. The mean VASD in patients experiencing a ‘small but just worthwhile’ decrease in their symptoms is the MID for the VASD and was found to be 22mm (95% CI 16 - 27mm). 2. Development of a thoracic ultrasound septation score (TUSS): A TUSS is important for objectively assessing the degree of septation within a pleural effusion. An iterative process was used to demonstrate that degree of septation predicts clinical outcome, to identify candidate factors for inclusion in a TUSS and to determine which factors predicted the degree of septation. The final TUSS consisted of an assessment of the degree of homogeneity of septation distribution and number of septations at the most septated area. 3. Effect of an indwelling pleural catheter (IPC) versus standard care for relieving dyspnoea in patients with MPEs: the TIME2 randomised controlled trial (RCT). The objective of this unblinded RCT was to determine whether IPCs are more effective than chest drains and talc pleurodesis at relieving dyspnoea in patients with MPEs. 106 patients were randomised to either IPC or standard care in a 1:1 ratio. The primary outcome was daily VASD over 42 days post intervention. Dyspnoea improved in both groups with no significant difference in mean dyspnoea in the first 42 days (mean score: IPC 25mm (95% CI 19 – 30), standard care 24mm (95% CI 19 – 29)).

Rotator cuff tendinopathy accounts for the majority of cases of shoulder pain, however, the aetiology and pathophysiology of the condition is poorly understood and treatment interventions for the condition have been introduced on an empirical basis, guided only by unproven theories of biological and structural changes in and around the affected tissue. This thesis explores changes in the provision of surgical interventions for rotator cuff tendinopathy, showing a rapid, sustained increase over the last decade. Investigation into the use of ultrasound as a clinical and research tool led to the development of an independent learning method for surgeons using the modality for shoulder imaging and highlighted the technological limitations of contrast enhanced ultrasound in assessing the microvascularity of the supraspinatus tendon. Development of a novel biopsy method for sampling the supraspinatus tendon permitted collection of tissue samples from several cohorts of individuals with rotator cuff tendinopathy. These studies, for the first time, described tissue changes across the whole spectrum of pathology suggesting the possibility of an early inflammatory phase of the condition followed by tissue senescence and reduced viability as pathology progressed. Paired samples taken before and after treatment identified reduced tissue activity in response to glucocorticoid therapy and a potential healing response from the supraspinatus tendon following surgical repair. Significant deterioration in tissue activity and viability was shown as age increased in a large cohort of individuals, highlighting the major impact of ageing as a factor in the onset and progression of rotator cuff tendinopathy. The techniques introduced provide standardised, reproducible methods for further evaluation of rotator cuff tendinopathy and the development of novel therapeutic interventions.

Microalgae synthesize and store large volumes of lipids (potentially over 25% of dry weight) which could provide a renewable source of biodiesel. Traditional extraction techniques often produce poor lipid yields particularly from microalgae with robust cell walls. This project investigated the role of power ultrasound as a cell disruption step in lipid extraction from four microalgal species. Nile Red staining was used to assess the time when ultrasound induced increased membrane permeability in each species and lipids were extracted using an ultrasound assisted Bligh and Dyer extraction method. A 20 kHz probe system (40% amplitude, 0.086 W/cm3) caused increased lipid recovery from dry biomass in all cases; D. salina (no cell wall) from 15 to 22.5% of dry biomass after 1 minute (26% when stressed with 35 g/L NaCl). C. concordia (thin cell wall) from 7.5 to 10.5% of dry biomass after 2 minutes (27% with 25% nitrogen reduction in growth media). N. oculata (thick cell wall) from 6.5 to 10% of dry biomass after 16 minutes (31.5% when stressed with 30 g/L NaCl). The stressed cultures yield could be improved to 35% when ultrasound was combined with S070 beating beads. Chlorella sp. (thick cell wall) from 6.3 to 8.7% of dry biomass, after 16 minutes (44% was achieved when harvested at day 9 instead of 15). A Dual Frequency Reactor (16 and 20 kHz, 0.01 W/cm3) flow system with S070 beads demonstrated that high lipid extraction yields could be achieved on a larger level with N. oculata. After 4:48 minutes sonication 24% lipid recovery was achieved. This system could theoretically increase daily microalgal oil production from 3.96 to 5.76 L per day when compared to conventional techniques, at an extra production cost of only 2.9 p/litre (1.5% increase). D. salina, N. oculata and C. concordia resumed normal growth following sonication at 20 kHz after 1-20 days (8 minutes treatment for D. salina, 60 minutes treatment for N. oculata and 16 minutes treatment for C. concordia). It was found that the supernatant of sonicated D. salina and C. concordia when added to established cultures were able to boost their growth.

Doppler ultrasound imaging modalities arguably represent one of the most complex task performed (usually in real time) by ultrasound scanners. At the heart of these techniques lies the ability to detect and estimate soft tissues or blood motion within the human body. As they have become an invaluable tool in a wide range of clinical applications, these techniques have fostered an intensive effort of research in the field of signal processing for more than thirty years, with a push towards more accurate velocity or displacement estimation. Coded excitation has recently received a growing interest in the medical ultrasound community. The use of these techniques, originally developed in the radar field, makes it possible to increase the depth of penetration in B-mode imaging, while complying with safety standards. These standards impose strict limits on the peak acoustic intensity which can be transmitted into the body. Similar solutions were proposed in the early developments of Doppler flow-meters to improve the resolution / sensitivity trade-off from which typical pulsed Doppler systems suffer. This work discusses the potential improvements in resolution, sensitivity and accuracy achievable in the context of modern Doppler ultrasound imaging modalities (taken in its broadest sense, that is, all the techniques involving the estimation of displacements, or velocities). A theoretical framework is provided for discussing this potential improvements, along with simulations for a more quantitative assessment. Colour Flow Imaging (CFI) modalities are taken as the main reference technique for discussion, due to their historical importance, and their relevance in many clinical applications. The potential achievable improvement in accuracy is studied in the context of modern velocity estimation strategies, which can be broadly classified into narrowband estimators (such as the “Kasai” estimator still widely used in CFI) and time shift based wideband strategies (normalised crosscorrelation estimator used, for instance, in applications like strain or strain rate estimation, elastography, etc.). Finally, simulations and theoretical results are compared to experimental data obtained with a simple custom-designed experimental set-up, using a single-element transducer.

Anxiety and depression are highly prevalent and often comorbid disorders that cause significant personal and economic burdens (Lépine, 2001). Because a significant number of people with depression do not respond to therapy (Fava, 2003), the development of alternative treatment methods may lessen the burden of such mental disorders. Recent research has focused on brain stimulation methods, many of which require invasive surgery or have limited precision in targeting specific areas. Transcranial ultrasound (TUS) is an alternative, noninvasive brain stimulation method that has greater spatial precision than existing methods (Tufail, 2011). TUS has been found to excite neurons in animal brains (Tufail et. al, 2010) and increase positive mood in humans (Sanguinetti et al, 2013). The present study examined TUS, for the first time, as a potential mood intervention. Twenty-four college students with mild to moderate depressive symptoms were randomly assigned to TUS stimulation or TUS sham (no power administered). Participants completed one TUS session each day for five days. Although depression scores did not change differentially for TUS/Sham, trait worry decreased in the stimulation but not the sham condition. Additionally, those in the stimulation condition rated themselves significantly less tense ten minutes after stimulation compared to those in the sham condition. TUS stimulation did not impact a brain electrical activity index associated with approach motivation, frontal asymmetry. These results have significant implications for the potential utility of TUS as an intervention for anxiety disorders or worry-related psychopathology, warranting future investigation of implicated brain electrical activity and mood changes.

The effect of power ultrasound on algae blooms (Microcystis aeruginosa) over a 30 minute period was assessed using 200 and 400 mL suspensions of optical density of 2.0 at 680 nm. The frequencies employed were 20, 40, 580 (40%, 80%, and maximum intensity), 864 (40%, 80% and maximum intensity) and 1146 kHz (40%, 80% and maximum intensity). Ultrasound can induce two different effects on algal cells; inactivation at high power (≥ 0.0022 Wcm-3) and de-agglomeration at low power (≤ 0.0042 Wcm-3). Ultrasonic effects were observed using haemocytometer, optical density, UV-visible spectrometer, fluorospectrometer and flow cytometry. Using a 40 kHz bath (0.0214 Wcm-3) led to de-agglomeration resulting in an overall increase in algae of -0.28% by haemocytometer and -4.20% by optical density. The highest inactivation achieved was 91.54% (haemocytometer) and 44.63% (optical density) using 1146 kHz (maximum intensity, 0.0248 Wcm-3) and 200 mL suspension. In terms of efficiency to achieve inactivation (i.e. inactivation % / power) the best result was observed at 864 kHz (40% power setting, 0.0042 Wcm-3) with 200 mL suspension giving 8226.19 by haemocytometer and 5011.90 by optical density. This initial part of the study allowed a comparison to be made of the ultrasonic parameters that would lead to optimum algae removal in terms of acoustic energy input. The haemocytometer results for cells number were generally higher than those indicated by optical density which is probably due to the fact that the former records only cell numbers remaining whereas the latter is an overall measure of algae concentration (ruptured cells will still register, because their contents remain in suspension). Studies on de-agglomeration and inactivation were also undertaken using small or medium-scale ultrasonic equipment that were models for industrial scale systems. The following volumes of algae suspension and equipment were employed: Sonolator (Sonic Corporation, 5L flow), 16 kHz and 20 kHz Dual Frequency Reactor (DFR, Advanced Sonics LLC, 1L static and 3.5 L flow), 20 kHz Vibrating Tray (Advanced Sonics LLC, 1.5L static) and 20 kHz ultrasonic probe (made at Southeast University, 4L static). The most effective inactivation effects were obtained with the DFR reactor in static mode and 60% power setting for 10 minutes which achieved reductions calculated at 79.25% using haemocytometry and 60.44% by optical density. The third part of this study was to gain a greater understanding of the basic mechanisms of the action of ultrasound on algae and to interpret this in terms of its potential for algal cell removal and control. Algal cell activity was assessed by three methods: using a UV-visible spectrometer (Shimazu, 2450PC), a fluorometer (Shimazu, RF5301) and a flow cytometer (BD FACS Calibur). Ultrasonic damage to Chlorophyll A was revealed through observation of the loss in UV-Vis spectrophotometer peaks around 600 nm together with the decrease in fluorometer results for peaks around 500 and 680 nm. Flow cytometer results were able to identify the number of both intact cells and damaged/ruptured cells thus giving greater insight into the mechanism of ultrasonic inactivation. The direct rupture of cells by power ultrasound was prevalent at low frequencies ≤ 40 kHz due to the mechanical effects of cavitation collapse and inactivation of algal cells by free radicals occurred at high frequencies ≥ 100 kHz and medium powers where mechanical effects are much reduced. In conclusion, this work has shown that power ultrasound can provide a suitable method to control algal growth in small and medium laboratory scales. Scale-up beyond this point is the subject of further research but the results herein clearly demonstrate the importance of choosing the correct ultrasonic parameters in terms of frequency, power and exposure time.

Thesis (MMed (Obstetrics and Gynaecology))--University of Stellenbosch, 2010. / Please refer to full text for abstract.

Acousto-electric (AE) effect comes from an interaction between electrical current and acoustic pressure generated when acoustic waves travel through a conducting material. It currently has two main application areas, ultrasound current source density imaging (UCSDI) and AE hydrophone. UCSDI can detect the current direction by modulating the dipole field with ultrasound pulse, and it is now used to form 3D imaging of dipole changing in one period of treatment, such as arrhythmia in the heart and epilepsy in the brain. As ultrasound pulse passes through electrical field, it convolutes or correlates with the inner product of the electric fields formed by the dipole and detector. The polarity of UCSDI is not determined by Doppler effect that exists in pulse echo (PE) signal, but the gradient of lead field potentials created by dipole and recording electrode, making the base-banded AE voltage positive at the anode and negative at cathode. As convolution shifts spectrum lower, the base band frequency for polarity is different from the center frequency of AE signal. The simulation uses the principles of UCSDI, and helps to understand the phenomena in the experiment. 3-D Fast Fourier Transform accelerates the computing velocity to resolve the correlation in the simulation of AE signal. Most single element hydrophones depend on a piezoelectric material that converts pressure changes to electricity. These devices, however, can be expensive, susceptible to damage at high pressure, and/or have limited bandwidth and sensitivity. An AE hydrophone requires only a conductive material and can be constructed out of common laboratory supplies to generate images of an ultrasound beam pattern consistent with more expensive hydrophones. Its sensitivity is controlled by the injected bias current, hydrophone shape, thickness and width of sensitivity zone. The design of this device needs to be the tradeoff of these parameters. Simulations were made to optimize the design with experimental validation using specifically fabricated devices composed of a resistive element of indium tin oxide (ITO).

Therapeutic efficacy of drugs depends on their ability to reach the treatment target. Drugs that exert their effect within cells are constrained by an inability to cross the cell membrane. Methods are being developed to overcome this barrier including biochemical and biophysical strategies. The application of ultrasound with microbubbles increases the permeability of cell membranes allowing molecules, which otherwise would be excluded, to enter the intracellular space of cells; a phenomenon known as sonoporation. This thesis describes studies aimed at improving our understanding of the mechanism underpinning sonoporation and of the exposure parameters affecting sonoporation efficiency. Cancer cells (KHT-C) in suspension were exposed to ultrasound and microbubbles – total of 97 exposure conditions. The effects on cells were assessed through uptake of cell-impermeable molecules (10 kDa to 2 MDa FITC-dextran), cell viability and microscopic observations of the plasma membrane using flow cytometry, colony assay and electron microscopy techniques. Sonoporation was a result of the interaction of ultrasound and microbubbles with the cell membrane. Disruptions (30-100 nm) were generated on the cell membrane allowing cell impermeable molecules to cross the membrane. Molecules up to 2 MDa in size were delivered at high efficiency (~70% permeabilisation). Sonoporation was short lived; cells re-established their barrier function within one minute, which allowed compounds to remain inside the cell. Following uptake, cells remained viable; ~50% of sonoporated cells proliferated. Sonoporation efficiency depended on ultrasound and microbubble exposure conditions. Microbubble disruption was a necessary but insufficient indicator of ultrasound-induced permeabilisation. The exposure conditions can be tailored to achieve a desired effect; cell permeability of ~70% with ~25% cell death versus permeability of ~35% with ~2% cell death. In addition, sonoporation depended on position in the cell cycle. Cells in later stages were more prone to being permeabilised and killed by ultrasound and microbubbles. This study indicated that sonoporation can be controlled through exposure parameters and that molecular size may not be a limiting factor. However, the transient nature may necessitate that the drug be in close vicinity to target cells in sonoporation-mediated therapies. Future work will extend the investigation into in vivo models.