225 research outputs found
Photoacoustics for Cardiovascular Applications
Get PDFIn the thesis entitled Photoacoustic imaging for Cardiovascular Applications, two cardiovascular diseases were tackled, namely atrial fibrillation and coronary atherosclerosis. An imaging algorithm was also devised to enhance imaging target super-localization. Photoacoustic imaging is an imaging modality which provides molecular information, based on optical absorption and subsequent thermoelastic expansion resulting in detectable pressure waves with common ultrasonic detectors. Capability of imaging tissue molecular changes was shown relevant to enable real-time monitoring of lesion formation in catheter-based ablation for atrial fibrillation as well as to assess lipid content of atherosclerotic plaques in an animal model in vivo. This thesis describes the development and design of the photoacoustic imaging system from instrumentation to realization in clinically translatable setups
Design and Experimental Validation of Intracardiac Photoacoustic Catheter: English
No full textAtrial fibrillation is a cardiac arrhythmia resulting from abnormal electrical conduction and impulse formation within the atria. To address this condition, a minimally invasive procedure called cardiac ablation is performed. Real-time visual feedback during this procedure plays a critical role in determining its success.Photoacoustic imaging is a technique capable of providing real-time visual feedback. Integrating photoacoustic capabilities into existing Radiofrequency ablation catheters poses a significant challenge, which this thesis addresses. The proposed integrated solution employs optical fibers for light delivery and an ultrasound transducer for signal reception.This work investigates the design of two light delivery systems for integrated photoacoustic-guided surgery. Monte Carlo simulations are employed to study three-dimensional light propagation in tissue, informing the catheter design specifications. Optimal fiber distances and orientations within the catheter are determined based on normalized fluence values and illumination spot size—critical parameters for assessing the amount of delivered light, its area of coverage, and depth of penetration. The methodology presented applies to various photoacoustic applications.The simulation study was able to successfully inform design specifications and it was able to establish a relation between design variables and the evaluation criteria such that it can be referred to for future designs. The comparative study yielded a better-performing design configuration and its optimal specifications were found out. This proves the use of a simulation-based evaluation to design a photoacoustic intracardiac catheter. In the final phase of this research, an experiment is set up to validate the light delivery of the design, which provides a clear outlook for the future of these designs into fabricated products.Mechanical Engineering | High-Tech Engineerin
Depth-resolved dynamics in turbid media via frequency-modulated scattering holography
No full textInterferometric diffuse optics (iDO) enables non-invasive measurement of deep tissue blood flow without requiring photon-counting detectors. Due to hardware constraints, achieving both optical properties and depth-dependent dynamics within a single modality remains a challenge for iDO. We present a simple method based on frequency-modulated light scattering that overcomes this limitation. © 2025 The Author(s
Improving Access to Laparoscopic Bilateral Tubal Ligation in LMICs: A Novel Lifting Device with an Integrated Imaging System
No full textBackground: Bilateral tubal ligation (BTL) is the most common method of contraception worldwide because it is safe and effective. However, its accessibility remains unequal among women in rural India, in part due to a lack of laparoscopic equipment. Rural hospitals therefore resort to gas insufflation-less laparoscopic surgery (GILLS) because it requires less complex equipment. The pneumoperitoneum is replaced by an abdominal wall lift (AWL) device, but these devices suffer from limitations concerning visibility and working space.Methods: Initiated by the identified medical needs in rural India, a novel AWL device with an integrated imaging system is designed based on methods from literature and input from local end-users. It is a stainless steel hollow circular hook housing an LED lighting system and a 5 MP camera module. It can be connected to any laptop with a USB-A port. The device substitutes for both the traditional AWL device and currently used laparoscopes. The design is exemplified by a fully functional aluminium prototype used for verification and validation.Results: The selected camera module is the key technology of this design because it provides state-of-the-art imaging at an unmatched price point. The lighting system used for the prototype does not provide enough light, has an asymmetric illumination distribution, and generates too much heat. A structural strength test showed that the strength of the prototype exceeds the material-adjusted design load by 30%. Furthermore, the prototype is cost-effective, lightweight, compatible with current AWL systems, and has limited waterproofness. User tests with an expert rural surgeon confirmed that this design has the potential to improve surgical outcomes of BTL and other procedures, and can increase access to specialized medical care in rural India.Conclusions: It is strongly recommended to continue the development of this AWL device. The focus points should be the shape and size of the loop (and related cost-effective production techniques), a new lighting system, and the waterproofness of the device. Collaboration with rural surgeons and local biomedical engineers is crucial for context-driven development and implementation.Mechanical Engineerin
Structured Illumination Imaging and Improvements in Scattering Medium
No full textBio-imaging plays an essential role in life sciences and medicine. Recently, structured illumination has emerged as a promising super-resolution technique. However, in the case of thick scattering media, the benefits of structured illumination can be significantly reduced compared to conventional illumination methods, resulting in significant degradation of imaging quality. Therefore, the question of dealing with the challenges posed by structured illumination in scattering media has become a topic of considerable focus. In this thesis, an experimental setup aimed at achieving super-resolution imaging using structured illumination is developed. The factors influencing the imaging process are systematically analyzed. At the same time, machine learning methods for recovering structured illumination patterns propagated through scattering media are explored. Overall, this research tackles the challenge of improving super-resolution imaging through scattering medium thereby contributing to the development of biological and medical imaging technologies.Mechanical Engineerin
Time-of-flight measurements of single-layer tissue with a chip-based optical frequency comb
No full textCerebral oxygen saturation is an important indicator that reflects the oxygen metabolism of the brain tissues in such patients. The utilization of near-infrared spectroscopy (NIRS) enables the identification of the oxygen saturation levels in nearby tissues by analyzing the distinct oxygenation states of hemoglobin-oxyhemoglobin (HbO2) and the distinctive molecular spectrum of deoxygenated hemoglobin (Hb). It is helpful to realize the objective of noninvasive continuous detection on cerebral oxygen saturation because near-infrared radiation can directly penetrate the skull to obtain the characteristics of the average oxygen saturation of the brain tissues. This also allows a noninvasive way to monitor blood flow in the brain. A frequency comb is a pulsed laser in the time domain and a sequence of discrete, uniformly spaced frequency lines in the frequency domain. Applying the frequency comb to NIRS has the potential to develop a high-speed and fs-level time-of-flight resolution blood flow measurement system. The objective of this thesis is to utilize a chip-based optical frequency comb as an illuminating source in order to conduct time-of-flight measurements of a single target, employing a Michelson interference experiment. The establishment of the time of flight in the single-layer case and the investigation of the non-ambiguity range form the fundamental basis for future experiments multi-layer.Mechanical Engineering | Micro-optics and Optomechatronic
Les études in Ising field theory and related problems
No full textThe main subject of this thesis is the Ising field theory, the field theory describing the scaling limit of the two-dimensional Ising model near its critical point. We study the Ising field theory in low- and high-temperature regimes.
In the low-temperature regime we address questions related to the mass spectrum of the bound states that exist in the theory. The overall goal is to study analytic properties of the masses taken as functions of the scaling variable in the theory. At this stage, we are primarily interested in the asymptotic series in the coupling parameter. We describe methods used for developing expansions in the coupling parameter when this parameter is sufficiently small. This gives rise to the low-energy and semiclassical series. Methods developed are then applied to a different model, a model that has many things in common with the Ising field theory, the two-dimensional quantum chromodynamics with infinite number of colors, also known as the ‘t Hooft model.
In the second part of the thesis we turn to the Ising field theory in the high- temperature regime. Here we study the problem of scattering in a weak magnetic field. We compute the leading perturbative correction to the scattering amplitude for the 2 -> 2 process. This is done first by means of standard methods based on the direct intermediate-state decomposition and dispersion relations. Then we compute the large energy asymptotic of the amplitude for this process directly using a known relation between the Ising field theory at zero magnetic field and classical sinh-Gordon equation. We obtain consistent results that show the logarithmic growth of the amplitude with energy at this order in magnetic field. Going beyond the leading order we argue that at large energies for a sufficiently weak magnetic field the amplitude exhibits a power-like decay.Ph.D.Includes bibliographical referencesIncludes vitaby Iskander Ziyatdino
The goatibex constellation of Fazil Iskander: translation and commentary
No full textFazil Iskander (1929- ) é um dos mais representativos escritores soviéticos remanescentes da geração do degelo. Devido ao desconhecimento deste autor no Brasil, este trabalho consiste na tradução da novela que lhe deu notoriedade, precedida por uma apresentação e comentário: Sozvezdie Kozlotura, em português, A constelação do capriuro, de 1966. Apesar de pertencer à tradição satírica russa, junto a nomes como Nikolai Gógol e Mikhail Bulgákov, a prosa de Iskander carrega as singularidades da sua origem não-russa. A sua terra natal, a Abkházia, com a sua história e costumes, além de reverberarem na obra do autor, entrecruzam-se com a cultura russo-soviética numa relação complexa que dá às suas narrativas um caráter único. Neste trabalho, foram analisados os elementos que tornam a sátira de Iskander tão inovadora.Fazil Iskander (1929- ) is one of the most representative remaining writers of the Thaw Generation. Due to the lack of recognition of this author in Brazil, the present dissertation consists in the translation of the short-novel that has made him internationally renowned, preceded by a presentation and commentary: Sozvezdie Kozlotura from 1966, or A constelação do Capriuro in Portuguese. Though the prose of Iskander belongs to the Russian satire tradition, along with names like Nikolai Gogol and Mikhail Bulgakov, it carries the singularities of his non-Russian origin. His motherland, Abkhazia, with its proper history and customs, besides reverberating on his works, entwines itself with the Russian-soviet culture in a complex and tense relationship that gives these narratives their unique nature. In this research, it is analyzed the characteristics that make the satire of Iskander so innovative
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