Dissertations / Theses on the topic 'SWIR imaging'

Photos captured in the shortwave infrared (SWIR) spectrum are interesting in military applications because they are independent of what time of day the pic- ture is captured because the sun, moon, stars and night glow illuminate the earth with short-wave infrared radiation constantly. A major problem with today’s SWIR cameras is that they are very expensive to produce and hence not broadly available either within the military or to civilians. Using a relatively new tech- nology called compressive sensing (CS), enables a new type of camera with only a single pixel sensor in the sensor (a SPC). This new type of camera only needs a fraction of measurements relative to the number of pixels to be reconstructed and reduces the cost of a short-wave infrared camera with a factor of 20. The camera uses a micromirror array (DMD) to select which mirrors (pixels) to be measured in the scene, thus creating an underdetermined linear equation system that can be solved using the techniques described in CS to reconstruct the im- age. Given the new technology, it is in the Swedish Defence Research Agency (FOI) interest to evaluate the potential of a single pixel camera. With a SPC ar- chitecture developed by FOI, the goal of this thesis was to develop methods for sampling, reconstructing images and evaluating their quality. This thesis shows that structured random matrices and fast transforms have to be used to enable high resolution images and speed up the process of reconstructing images signifi- cantly. The evaluation of the images could be done with standard measurements associated with camera evaluation and showed that the camera can reproduce high resolution images with relative high image quality in daylight.

Thesis (M.S. in Combat Systems Sciences and Technology)--Naval Postgraduate School, December 2007.
Thesis Advisor(s): Haegel, Nancy ; Karunasiri, Gamani. "December 2007." Description based on title screen as viewed on January 18, 2008. Includes bibliographical references (p. 65-67). Also available in print.

A Single pixel camera is just that, a camera that uses only a single pixel to take images. Though, it is a bit more to it than just a pixel. It requires several components which will be explained in the thesis. For it to be viable it also needs the sampling technology Compressive sensing which compresses the data in the sampling stage, thus reducing the amount of data required to be sampled in order to reconstruct an image. This thesis will present the method of building an SPC with the required hardware and software. Different types of experiments, such as detection of small changes in a scene and different wavelength bands, has been conducted in order to test the performance and application areas for the SPC. The resulting system is able to produce images of resolutions up to 512x512 pixels. Disturbances such as movement in the scene or the camera itself being shaken became less of a problem with the addition of a second pixel. This thesis proves that an SPC is a viable technology with many different areas of application and it is a relatively cheap way of making a camera for the infrared spectrum.

La bio-imagerie d’environnements biologiques, complexes et hétérogènes utilisant des nanoparticules est uniquement pertinente si leurs propriétés intrinsèques et de surface sont contrôlées pour favoriser une diffusion en profondeur. En effet, la forme (rapports de forme, nanotubes, nanosphères), les dimensions (quelques nanomètres à quelques dizaines de nanomètres), les charges de surface et les interactions de surface avec le milieu environnant sont des paramètres décisifs. Ils régulent par exemple la mobilité et le devenir des nanoparticules à l’intérieur des milieux biologiques, dont par exemple les microenvironnements tumoraux. Dans cette thèse, nous nous sommes principalement concentrés sur les nanotubes de carbone, semi-conducteurs et à mono-parois dans le but d’adapter leur diffusion dans des environnements biologiques en contrôlant leurs propriétés de surface. Ce choix a été motivé car ces nanotubes présentent des atouts majeurs pour des applications en bio-imagerie. Leur longueur d’onde d’émission se trouve dans l’infrarouge court (SWIR), ce qui correspond à la deuxième fenêtre de transparence biologique. Ils sont également photostables et il a été prouvé qu’ils présentent une pénétration importante dans le tissu de par leur morphologie 1D. Pour étudier la mobilité des nanotubes dans des environnements complexes, nous avons suivi leurs trajectoires à l’échelle de la particule unique et appliqué les approches de microscopie de fluorescence à super-résolution. Nous avons tout d’abord détecté des modifications morphologiques associées à une fibrose à un stade précoce sur des tranches de foie de souris. Pour cela nous avons employé une stratégie de microscopie corrélative pour identifier l’environnement biologique in situ (noyaux et membranes des cellules) autour des nanotubes en plus de l’étude de leurs mobilités. Ce premier projet nous a motivé à explorer une deuxième stratégie pour disperser des nanotubes en augmentant leur brillance tout en conservant leur furtivité. Nous avons étudié de quelle manière le changement du coating autour du nanotubes (taille moléculaire du PEG ou présence d’une insaturation) impactait leur brillance et leur diffusivité. Cette diffusion a été testée sur différents modèles avec une hétérogénéité croissante allant du gel d’agarose à des extraits de matrice extracellulaire. Nous avons distingué deux tailles moléculaires de PEG découlant sur des dispersions compatibles à nos études. Enfin, dans le but d’étendre la bibliothèque de nanoparticules émettant dans le SWIR pour des applications de bio-imagerie, nous avons étudié un autre type de nanoobjets luminescents : des clusters d’or et des nanoparticules polymères chargées avec des clusters. L’analyse de leur luminescence ainsi que leur potentiel pour des études de suivi de particules uniques ont été évalués. L’analyse de clusters d’or uniques a été réalisée montrant une excellente brillance, mais uniquement dans un environnement sec. Par ailleurs, nous avons prouvé que les nanoparticules polymériques étaient détectables au niveau de la particule unique lorsqu’elles diffusaient dans un environnement aqueux ce qui fait d’elles d’excellentes candidates pour des applications de bio-imagerie
Bioimaging of complex and heterogeneous biological environments using nanoparticles is only relevant if one controls their intrinsic and surface properties to promote their diffusion in depth. Indeed, the shape (i.e. aspect ratios, nanotubes, nanospheres), the dimension (from a few nanometers up to a few tens of nanometers), the surface charges and the surface interactions with the surrounding environment are key parameters. They regulate for instance the mobility and the future of nanoparticles inside the biological milieu, such as tumoral microenvironments. In this PhD thesis, we mainly focused on semiconducting single-walled carbon nanotubes with the aim to tailor and apply their diffusion in bio-environments by controlling their surface properties. This choice was motivated by their exceptional advantages for bio-imaging applications. Their emission wavelength is in the short-wave infrared region (SWIR), which corresponds to the second window of biological transparency. In addition, they are photostable and it has been proved that they show a high tissue penetration ability due to their nanoscale 1D morphology. To study the mobility of nanotubes in complex environments, we tracked their trajectories at the single particle level and applied super-resolution fluorescence microscopy approaches. We first detected morphological modifications associated with early-stage fibrosis on murine liver slices. To that end, we employed a correlative microscopy strategy to identify the in situ biological environment (cell membranes and nuclei) surrounding the nanotubes in addition to the study of their mobilities. This first work motivated us to explore a second strategy to suspend the nanotubes to enhance their brightness while maintaining their stealth behaviours. We investigated how changing the coating around the nanotubes (PEG molecular size or presence of an insaturation) impacted their brightness and diffusivity. Diffusion has been tested within various models with growing complexity from an agarose gel to extracts of the extracellular matrix. We distinguished two molecular sizes of PEG rising to suspensions of nanotubes suitable for our studies. Finally, with the aim of expanding the library of SWIR-emitting nanoparticles for biological imaging, we investigated another type of luminescent nanoobjects: gold nanoclusters and polymeric nanoparticles loaded with such clusters. The analysis of their luminescence as well as their potential for single particle tracking were evaluated. Single gold cluster analysis has been conducted showing excellent brightness, but only in a dried environment. In addition, the polymeric nanoparticles were shown to be detectable at the single particle level diffusing within an aqueous media constituting promising candidates for bioimaging applications

This thesis focuses on the concept of Single Well Imaging (SWI) in which a seismic source and receivers are deployed in a borehole to investigate the surrounding geology. The Uniwell project (1997-1999) was the first attempt to develop the SWI method; it used a fluid-coupled downhole source, which unfortunately generated high amplitude guided waves in the borehole which obscured all other useful information. Initial research work detailed in this thesis focused on removing the high amplitude guided waves, known as tube waves. Two-step source signature deconvolution using first the recorded source signature, and then the tube-wave reflected from the bottom of the well, succeeded in compressing the tube wave. The results were not consistent across all receivers, but there is enough correlation to identify a P-wave. Further work concentrates on using a new technique called Empirical Mode Decomposition to separate the tube-wave mode from the data. This identifies three dominant modes and a possible body wave arrival, but the results are ambiguous due to the inability of the decomposition to focus on the narrow bandwidth of interest. The source signature deconvolution technique can also be used to process real-time vertical seismic profiling (VSP) data down-hole, during pauses in drilling, in what is referred to as a Seismic-While-Drilling (SWD) setup. Results show that the technique is versatile and robust, giving 1 ms precision on first-break picking even in very noisy data. I also apply the technique to normal VSP data to improve both the resolution and the signal-to-noise ratio. A major effort in this thesis is to consider the effect of a clamped downhole source to overcome the tube-wave problem, using a magnetostrictive source. Earlier work established that the use of a reaction mass tended to excite resonances in the tool which caused the transducer to break. A new design for the source was developed in cooperation with colleagues which utilises a hydraulic amplifier design and a low power coded waveform driving method exploiting the time-bandwidth product to extract the signal from the noise. My results show that as the run time increases the resolution improves. With a run length of 80s it is possible to resolve the signal transmitted 50 cm through a granite formation. This analysis led to a revised design of the source to improve its efficiency. I have used finite difference modelling, with a variable grid technique, to compare an ideal explosive source with an ideal clamped source. The fluid-coupled source emits high amplitude tube waves which virtually obscure the body wave, whereas the clamped source emits a clearly identifiable P-wave along with lower amplitude tube waves. This clearly illustrates the advantage of an ideal clamped source. To model the source more accurately the idealwavelet is replaced by the respective recorded source signatures, and the data is then processed by cross correlation with the appropriate signature. The results show that the coded waveform approaches the resolution of the ideal wavelet very well, with all major events being visible. However, the fluid-coupled source performs very poorly with only the highest amplitude tube-wave visible. This work illustrates that by replacing a fluid-coupled source by a clamped source driven by a coded waveform, and by processing the data using cross correlation or signature deconvolution, it is possible to minimise or eliminate tube-wave noise from a SWI survey. It is hoped that the results outlined here will provide the basis for a new SWI method than can be used to prolong the supply of North Sea oil.

This thesis explores the effects of operating parameters on the location and shape of lifted flames in a Low Swirl Burner (LSB). In addition, it details the development and analysis of a CH PLIF imaging system for visualizing flames in lean combustion systems. The LSB is studied at atmospheric pressure using LDV and CH PLIF. CH* chemiluminescence is used for high pressure flame imaging. A four-level model of the fluorescing CH system is developed to predict the signal intensity in hydrocarbon flames. Results from imaging an atmospheric pressure laminar flame are used to validate the behavior of the signal intensity as predicted by the model. The results show that the fluorescence signal is greatly reduced at high pressure due to the decreased number of CH molecules and the increased collisional quenching rate. This restricts the use of this technique to increasingly narrow equivalence ratio ranges at high pressures. The limitation is somewhat alleviated by increasing the preheat temperature of the reactant mixture. The signal levels from high hydrogen-content syngas mixtures doped with methane are found to be high enough to make CH PLIF a feasible diagnostic to study such flames. Finally, the model predicts that signal levels are unlikely to be significantly affected by the presence of strain in the flow field, as long as the flames are not close to extinction. The results from the LSB flame investigation reveal that combustor provides reasonably robust flame stabilization at low and moderate values of combustor pressure and reference velocities. However, at very high velocities and pressures, the balance between the reactant velocity and the turbulent flame speed shifts in favor of the former resulting in the flame moving downstream. The extent of this movement is small, but indicates a tendency towards blow off at higher pressures and velocities that may be encountered in real world gas turbine applications. There is an increased tendency of relatively fuel-rich flames to behave like attached flames at high pressure. These results raise interesting questions about turbulent combustion at high pressure as well as provide usable data to gas turbine combustor designers by highlighting potential problems.

Die Magnetresonanztomographie stellt für die Detektion von zerebralen und spinalen Läsionen bei der Multiplen Sklerose die sensitivste bildgebende Methode dar und ist ein Instrument, die räumliche und zeitliche Dissemination der Erkrankung abbilden zu können. Die Spezifität des Verfahrens ist aber gering und die Applikation von MR-Kontrastmittel bei der Diagnostik zwingend notwendig. Bei der suszeptibilitätsgewichteten Magnetresonanzbildgebung (SWI) handelt sich um ein MR-Verfahren, das Schwankungen der magnetischen Suszeptibilität in der Gradientenechosequenz nutzt, um einen Bildkontrast zu erzeugen. Dadurch ist es möglich, hochaufgelöst und sensitiv Magnetfeldinhomogenitäten zu detektieren. In der vorliegenden prospektiven Studie wurden im Zeitraum von 2010 bis 2013 MRT-Untersuchungen unter Einschluss der suszeptibilitätsgewichteten Bildgebung in einem Kollektiv von 41 Patienten (33 weiblich, 8 männlich;; Durchschnittsalter 40 Jahre) mit gesicherter Multipler Sklerose und einem Vergleichskollektiv von 43 Patienten (28 weiblich, 15 männlich;; Durchschnittsalter 45 Jahre), bei denen weder bildgebend noch klinisch Hinweise auf eine Multiple Sklerose vorlagen, durchgeführt. Die Untersuchung wurde mit einem 1,5-Tesla-Magnetresonanz- tomographen realisiert. Das besondere wissenschaftliche Interesse galt dabei der „normal erscheinenden weißen Substanz“ (NAWM) und den zerebralen Läsionen. In der FLAIR-Sequenz wurden die MS-Läsionen und ROIs detektiert und markiert. Anschließend erfolgte die Übertragung in gleicher Schichthöhe auf die SWI-, T1w- und ADC-Sequenz. Zur Differenzierung von akuten und chronischen Läsionen erfolgte im Untersuchungsablauf die intravenöse Gabe von Gadolinium-DTPA- Kontrastmittel. Schon längere Zeit werden im wissenschaftlichen Diskurs krankheitsspezifische Veränderungen in der NAWM vor Auftreten der MS-Läsionen vermutet. Die Sensitivität der FLAIR-Sequenz ist aber scheinbar unzureichend. Mit der SWI- Bildgebung konnten statistisch signifikante SI-Unterschiede zwischen Referenz- und MS-Gruppe in der NAWM herausgearbeitet werden. Nach Kontrastmittelgabe wurden dabei keine Veränderungen der Signalintensität der NAWM in den beiden Gruppen festgestellt, was gegen die Hypothese einer primären Schrankenstörung in der Pathogenese der Erkrankung spricht. Insgesamt wurden 669 Läsionen identifiziert. Es folgte eine Differenzierung in 11 KM-aufnehmende (ACM-) Läsionen, 546 nicht KM-aufnehmende (NACM-) Läsionen und 112 „black holes“ (BLH). Eine gezielte Auswertung der Phasen- und Magnitudenbilder wurde nicht durchgeführt. Besonders in den KM-anreichernden Läsionen (ACM) sind bereits vor der KM-Gabe statistisch erhöhte Signalintensitäten in der SWI-Sequenz nachweisbar. Dies könnte theoretisch für den Nachweis akuter Läsionen, ohne dass eine KM-Gabe notwendig ist, genutzt werden. Doch ist die Anzahl dieser Läsionen in der Untersuchung zu gering, um verlässliche Aussagen diesbezüglich machen zu können. Dafür sind weitere Studien notwendig. Zusammenfassend betrachtet handelt es sich bei der SWI um ein hoch sensitives bildgebendes Verfahren, welches eine ausgezeichnete Differenzierung von ZNS- Läsionen ermöglicht und Veränderungen der NAWM bei der Enzephalomyelitis disseminata nachweisen kann. Es stellt somit eine sinnvolle Ergänzung zur konventionellen MS-Diagnostik dar und ist ein innovatives bildgebendes In-vivo- Verfahren zur weiteren Erforschung der Multiplen Sklerose.

Gliomas are a common type of brain tumour and for the treatment of a patient it is important to determine the tumour’s grade of malignancy. This is done today by a biopsy, a histopathological analysis of the tumourous tissue, that is classified by the World Health Organization on a malignancy scale from I to IV. Recent studies have shown that the local image variance (LIV) and the intratumoural susceptibility signal (ITSS) in susceptibility-weighted MR images correlate to the tumour grade. This thesis project aims to develop a software program as aid for the radiologists when grading a glioma. The software should by image analysis be able to separate the gliomas into low grade (I-II) and high grade (III-IV). The result is a graphical user interface written in Python 3.4.3. The user chooses an image, draws a region of interest and starts the analysis. The analyses implemented in the program are LIV and ITSS mentioned above, and the code can be extended to contain other types of analyses as research progresses. To validate the image analysis, 16 patients with glioma grades confirmed by biopsy are included in the study. Their susceptibility-weighted MR images were analysed with respect to LIV and ITSS, and the outcome of those image analyses was tested versus the known grades of the patients. No statistically significant difference could be seen between the high and the low grade group, in the case of LIV. This was probably due to hemorrhage and calcification, characteristic for some tumours and interpreted as blood vessels. Concerning ITSS a statistically significant difference could be seen between the high and the low grade group (p < 0.02). The sensitivity and specificity was 80% and 100% respec- tively. Among these 16 gliomas, 11 were astrocytic tumours and between low and high grade astrocytomas a statistically significant difference was shown. The degree of LIV was significantly different between the two groups (p < 0.03) and the sensitivity and specificity were 86% and 100% respectively. The degree of ITSS was significantly different between the two groups (p < 0.04) and the sensitivity and specificity were 86% and 100% respectively. Spearman correlation showed a correlation between LIV and tumour grade (for all gliomas r = 0.53 and p < 0.04, for astrocytomas r = 0.84 and p < 0.01). A correlation was also found between ITSS and tumour grade (for all gliomas r = 0.69 and p < 0.01, for astrocytomas r = 0.63 and p < 0.04). The results indicate that SWI is useful for distinguishing between high and low grade astrocytoma with 1.5T imaging within this cohort. It also seems possible to distinguish between high and low grade glioma with ITSS.

A new sampling theory, called compressive sensing (CS), has recently emerged and its fundamental idea can be distilled as: it is possible to obtain near complete recovery of a signal/image from a small set of mixed measurements of it if the signal/image possesses properties akin to sparseness. Based on this theory, we have developed a unique hardware platform for imaging and spectroscopy applications which incorporates a spatial modulator and a single pixel detector. Random projections of the signal/image are applied to the light modulator and the modulated light is focused on the single detector generating a series of photovoltage values which are later used in the image reconstruction. For wavelengths outside the visible spectrum, where it is especially expensive to produce the large detector arrays, this scheme provides a far better solution using a single detector element.

碩士
國立交通大學
理學院應用科技學程
100
ABSTRACT Shortwave infrared (Short Wave InfraRed, SWIR), its wavelength is 0.9 ~ 1.7um,the spectrum of this band in nature for the human eye can not seen, the heat sensor developed by the majority on the early military purposes in this range. Since the detection of the thermal sensor is not subjected to the limitations of weather conditions,we can get the accurate identification,rather the sensitivity of the sensor itself the target, The development of the thermal sensor technology becomes more sophisticated, and the cost is substantially reduced, so the product life has gradually diversified, in addition to military applications covered the manufacturing industry, food, medical and measurement, monitoring, development, etc.everywhere, the heat sensor on the circuit design and improved image quality requirements is also increasingly subject to considerable attention. In this thesis, One dimensional line sensing system with two-dimensional array sensor system studied by the methods of measurement of the thermal sensor and the target under test, analysis and resolution of the optical lens and a sense of temperature on thermal radiation measurement capability, individual analysis and assessment of the performance difference of the thermal sensor system.

Lo scopo del lavoro di ricerca è stato lo sviluppo di applicazioni per il recupero e il riciclo dei materiali, partendo da approcci classici di separazione e caratterizzazione fino all’utilizzo di strumenti innovativi per il riconoscimento e il monitoraggio dei materiali attraverso applicazioni di imaging iperspettrale. Uno degli obiettivi della ricerca, è stato quello di utilizzare sistemi di acquisizione HyperSpectral Imaging (HSI) per ottenere informazioni utili per l’esplorazione dei dati, applicando metodi di analisi multivariata in modalità supervisionata; pertanto l’applicazione di un approccio ingegneristico trasversale ha permesso di sviluppare dei sistemi online per il recupero e il riciclo di scarti eterogenei, che possono trovare ampio spazio in future soluzioni di tipo industriale. La prima parte di questo studio ha riguardato la caratterizzazione e la valorizzazione di uno scarto proveniente da un impianto di smistamento di rifiuti plastici indifferenziati urbani, dividendo il processo in fasi principali, come l’identificazione dei polimeri attraverso la classica spettroscopia FT-IR, il riconoscimento dei polimeri attraverso l’analisi HSI, lo sviluppo di un processo di separazione sperimentale e la certificazione del campione in Combustibile Solido Secondario (CSS) di qualità. È stato utilizzato un approccio di tipo analitico, basato sull’analisi HSI, per eseguire una caratterizzazione dei rifiuti plastici post-imballaggio, finalizzato all’identificazione dei polimeri plastici che costituiva il campione rappresentativo; l’applicazione di questa tecnica è particolarmente adatta ad applicazioni di tipo online, con la possibilità di valutare qualitativamente e quantitativamente la presenza dei diversi polimeri che costituiscono il rifiuto. La successiva parte del lavoro, ha visto l'approfondimento della ricerca e lo sviluppo di una metodologia innovativa per il recupero e il riciclo dei rifiuti elettronici a fine vita. I rifiuti elettronici hanno una composizione molto eterogenea, per cui alcuni elementi e componenti sono difficili da individuare e riconoscere, anche per via dello sviluppo sempre crescente di nuove tecnologie e la crescente miniaturizzazione dei componenti che vengono utilizzati. Al fine di migliorare il recupero di materie prime e aumentare il livello di tutela ambientale, una corretta caratterizzazione di questi rifiuti rappresenta il primo e necessario passo per il recupero di metalli preziosi e terre rare.

Tese de mestrado em Engenharia Biomédica e Biofísica, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013
Com o crescente aumento das intensidades de campo magnético e performance dos gradientes em ressonância magnética (RM), novas técnicas de imagiologia médica têm surgido que apresentam novos contrastes entre diferentes tecidos. No entanto, este tipo de imagens são desenvolvidas e optimizadas para o cérebro adulto que se sabe ter tempos de relaxação diferentes daqueles presentes no cérebro de um recém-nascido. Esta diferença é inerente ao alto teor em água presente no cérebro de um recém-nascido. O principal objectivo deste projecto é então proceder à otimização de técnicas avançadas de RM como susceptibilidade magnética (SWI) e de quantificação dos tempo de relaxação (DESPOT1 e DESPOT2) para o cérebro de recém-nascidos. O sinal de RM é medido sob a forma de um número complexo caracterizado por uma intensidade e uma fase. Normalmente em RM, o sinal de fase é ignorado e apenas a intensidade do sinal é utilizada para proceder à reconstrução das imagens. No entanto, a fase do sinal complexo è extremamente rica em informação relativa às diferenças de susceptibilidade entre tecidos diferentes, sendo por isso bastante útil para realçar este tipo de contraste. Uma das questões que dificulta a utilização das imagens de fase é o facto de apenas poderem registar valores no intervalo de [-π; π) o que resulta no mapeamento de valores que caiam fora desse intervalo para o seu interior. Uma vez que a informação de interesse nas imagens de fase corresponde a estruturas de pequena dimensão, caracterizadas por frequências elevadas no espaço de Fourier, SWI consiste na utilização de imagens de fase sujeitas a um filtro passa-alto simples (janela rectangular. Tal permite extraír a informação de interesse, que posteriormente é utilizada para realçar contraste de susceptibilidade em imagens de intensidade. Este mapeamento da informação de susceptibilidade na imagem de intensidade é realizado através da multiplicação da mesma por uma máscara extraída da imagem de fase filtrada para as baixas frequências. Isto tem um particular interesse para a visualização do sistema vascular venoso uma vez que diferenças de susceptibilidade entre sangue venoso e os tecidos envolventes permitem identificar estruturas venosas mesmo em vasos com dimensões inferiores à resolução de aquisição. Isto é possível graças às propriedades paramagnéticas da deoxiihemoglobina presente no sangue venoso. Neste trabalho o protocolo normalmente utilizado para SWI foi adaptado e implementado à realidade dos recém-nascidos. Ao mesmo tempo foi também desenvolvida uma interface gráfica de modo a facilitar o processamento e construção de imagens ponderadas em susceptibilidade. Este processamento foi desenvolvido integrando a FSL-FMRIB Software Library 5.0 juntamente com MatLab2012a. A interface gráfica foi desenvolvida em ambiente de programação MatLab2012a com o auxílio da ferramenta guide. Uma pequena discussão sobre o efeito da dimensão do voxel de aquisição também é incluída neste trabalho. É pratica comum os voxeis das imagens de SWI serem adquiridos com um quociente entre a resolução do plano de visualização e a espessura dos cortes (AR, do inglês voxel aspect ratio) apresentar valores entre 2 e 4. No entanto, este tipo de aquisição induz uma excelente visualização apenas para um dos (normalmente o plano transversal) e uma muito má visualização nos restantes planos. Com isto em mente, resolveu-se também neste projecto, propor a utilização de um voxel de aquisição isotrópico em detrimento do que é prática comum na literatura. Espera-se que este tipo de aquisição isotrópica reduza um pouco o contraste de susceptibilidade obtido, no entanto após inspeção visual de algumas imagens obtidas em voluntários decidimos que o ganho em informação nos dois restantes planos de visualização ortogonais justificaria essa pequena perda de contraste. Este facto não foi no entanto devidamente avaliado e mais estudos seriam necessários para uma correcta avaliação desta característica. Na segunda parte do projecto apresentado nesta tese, foi implementada uma técnica de quantificação em RM conhecida por \Driven Equilibrium Single Pulse Observation of T1 and T2 - DESPOT1 e DESPOT2". Esta técnica (neste trabalho referida como DESPOT) permite de forma bastante rápida estimar T1 e T2. Mais uma vez, devido ao facto de o cérebro de recém-nascidos ter um conteúdo superior em água relativamente ao cérebro adulto, uma adaptação deve ser feita de modo a garantir a qualidade das imagens obtidas. Esta técnica consiste na utilização de sequências de RM conhecidas como Steady-State Free Precession (SSFP) e Spoiled Gradient Echo (SPGR) para obter imagens mantendo todos os parâmetros constantes, ao mesmo tempo que se variam os Flip Angles (FA). Isto permite ajustar um modelo matemático que melhor explique as medições realizadas de modo a estimar os tempos de relaxação T1 e T2. Para garantir a precisão da estimação dos parâmetros T1 e T2, simulações de Monte Carlo foram criadas onde se verificou que, usando a ferramenta de MatLab2012a fminsearch, como algoritmo de otimização é possível obter uma precisão de estimação (quociente entre variância de estimação e o quadrado do valor correcto) de aproximadamente 5% relativamente ao valor correcto. Uma avaliação da capacidade de estimar T1 e T2 foi realizada com modelos matemáticos de um e dois compartimentos que procuram explicar o sinal de RM medido em DESPOT. O modelo de dois compartimentos foi publicado por Deoni et al. em 2008, onde foi sugerido que é possível estimar as fracções relativas de cada um dos compartimentos em cada voxel medido. No entanto, os resultados obtidos para o modelo de dois compartimentos não foram satisfatórios. Foi decidido que uma avaliação mais profunda e tentativa de resolução deste problema saía fora dos objectivos do projecto. O Crámer-Rao lower bound (CRLB) (em português limite inferior de Crámer-Rao), é uma ferramenta estatística que permite estimar qual a variância mínima alcançável aquando da estimação de parâmetros com base no ajuste de um modelo matemático a um conjunto de medições. De modo a finalizar o trabalho apresentado nesta tese, proposémo-nos a utilizar a minimização do CRLB para seleccionar o conjunto de FA que permite estimar T1 e T2 com melhor precisão. Em primeiro lugar mostramos que a variância prevista pelo CRLB se encontra em concordância com a variância obtida com as simulações de Monte Carlo. Isto permite confirmar a viabilidade da utilização do CRLB para optimizar o protocolo de estimação de T1 e T2. Para tal, foi desenvolvida uma função de custo utilizando o CRLB para optimizar o conjunto de FA que minimiza e garante a melhor precisão considerando de uma matriz de combinações de T1 e T2. A função de custo consiste em minimizar o maior valor de precisão (definida como o quociente entre a variância e o quadrado do valor correcto para o parâmetro) é calculada numa grelha de combinações de parâmetros T1 e T2, garantindo assim, que a cada iteração do processo de otimização o pior cenário era minimizado. Os resultados obtidos permitiram concluir que é possível optimizar o protocolo de DESPOT garantindo uma precisão mínima num grelha de combinações de diferentes T1 e T2. Foi também possível concluir que se pode reduzir significativamente o número de medições necessárias para a estimação sem aumentar significativamente a precisão desta. Este facto é de extrema importância para obter imagens de RM em recém-nascidos onde é necessário reduzir o tanto quanto possível os tempos de aquisição de modo evitar artefactos de movimento. Ambas as vertentes (SWI e DESPOT) deste projecto foram avaliadas pela equipa técnica e estão aptas a serem incorporadas em ambiente clínico permitindo o desenvolvimento de futuros projectos nestas áreas.
With recent increase of clinical MR field strength and gradient performance, advanced imaging techniques have been proposed that allow new types of contrast and tissue parameter quantification. However this advanced techniques are typically optimized to the adult brain which is known to have different relaxation times T1 and T2 relative to the neonatal brain because of its higher water content. The main purpose of this work is to optimize advanced imaging techniques such as susceptibility weighted imaging (SWI) and driven equilibrium single pulse observation of T1 and T2 (DESPOT1 and DESPOT2) in order to be applied to the neonatal brain. In this work, a neonatal SWI protocol was developed by adapting a gold standard adult protocol presented in the literature. Also a graphical user interface was developed in order to provide an easy tool to reconstruct susceptibility weighted images. Single compartment and multi-compartment DESPOT estimation precision was estimated from both a Monte Carlo (MC) and Cramer-Rao Lower Bound (CRLB) approaches. CRLB is a statistical tool that allows us to estimate the minimum possible variance that can be obtained when estimating parameters of a mathematical model given a set of independent noisy measurements. Furthermore, the CRLB was used as a tool to optimize the DESPOT protocol regarding both precision and acquisition time. In this work a neonatal SWI protocol is proposed. Also we show that the CRLB can be used to optimize the DESPOT1 and DESPOT2 acquisition scheme and that the number of measurements usually made can be reduced without significantly compromising parameter estimation.

Die Magnetresonanztomographie stellt für die Detektion von zerebralen und spinalen Läsionen bei der Multiplen Sklerose die sensitivste bildgebende Methode dar und ist ein Instrument, die räumliche und zeitliche Dissemination der Erkrankung abbilden zu können. Die Spezifität des Verfahrens ist aber gering und die Applikation von MR-Kontrastmittel bei der Diagnostik zwingend notwendig. Bei der suszeptibilitätsgewichteten Magnetresonanzbildgebung (SWI) handelt sich um ein MR-Verfahren, das Schwankungen der magnetischen Suszeptibilität in der Gradientenechosequenz nutzt, um einen Bildkontrast zu erzeugen. Dadurch ist es möglich, hochaufgelöst und sensitiv Magnetfeldinhomogenitäten zu detektieren. In der vorliegenden prospektiven Studie wurden im Zeitraum von 2010 bis 2013 MRT-Untersuchungen unter Einschluss der suszeptibilitätsgewichteten Bildgebung in einem Kollektiv von 41 Patienten (33 weiblich, 8 männlich;; Durchschnittsalter 40 Jahre) mit gesicherter Multipler Sklerose und einem Vergleichskollektiv von 43 Patienten (28 weiblich, 15 männlich;; Durchschnittsalter 45 Jahre), bei denen weder bildgebend noch klinisch Hinweise auf eine Multiple Sklerose vorlagen, durchgeführt. Die Untersuchung wurde mit einem 1,5-Tesla-Magnetresonanz- tomographen realisiert. Das besondere wissenschaftliche Interesse galt dabei der „normal erscheinenden weißen Substanz“ (NAWM) und den zerebralen Läsionen. In der FLAIR-Sequenz wurden die MS-Läsionen und ROIs detektiert und markiert. Anschließend erfolgte die Übertragung in gleicher Schichthöhe auf die SWI-, T1w- und ADC-Sequenz. Zur Differenzierung von akuten und chronischen Läsionen erfolgte im Untersuchungsablauf die intravenöse Gabe von Gadolinium-DTPA- Kontrastmittel. Schon längere Zeit werden im wissenschaftlichen Diskurs krankheitsspezifische Veränderungen in der NAWM vor Auftreten der MS-Läsionen vermutet. Die Sensitivität der FLAIR-Sequenz ist aber scheinbar unzureichend. Mit der SWI- Bildgebung konnten statistisch signifikante SI-Unterschiede zwischen Referenz- und MS-Gruppe in der NAWM herausgearbeitet werden. Nach Kontrastmittelgabe wurden dabei keine Veränderungen der Signalintensität der NAWM in den beiden Gruppen festgestellt, was gegen die Hypothese einer primären Schrankenstörung in der Pathogenese der Erkrankung spricht. Insgesamt wurden 669 Läsionen identifiziert. Es folgte eine Differenzierung in 11 KM-aufnehmende (ACM-) Läsionen, 546 nicht KM-aufnehmende (NACM-) Läsionen und 112 „black holes“ (BLH). Eine gezielte Auswertung der Phasen- und Magnitudenbilder wurde nicht durchgeführt. Besonders in den KM-anreichernden Läsionen (ACM) sind bereits vor der KM-Gabe statistisch erhöhte Signalintensitäten in der SWI-Sequenz nachweisbar. Dies könnte theoretisch für den Nachweis akuter Läsionen, ohne dass eine KM-Gabe notwendig ist, genutzt werden. Doch ist die Anzahl dieser Läsionen in der Untersuchung zu gering, um verlässliche Aussagen diesbezüglich machen zu können. Dafür sind weitere Studien notwendig. Zusammenfassend betrachtet handelt es sich bei der SWI um ein hoch sensitives bildgebendes Verfahren, welches eine ausgezeichnete Differenzierung von ZNS- Läsionen ermöglicht und Veränderungen der NAWM bei der Enzephalomyelitis disseminata nachweisen kann. Es stellt somit eine sinnvolle Ergänzung zur konventionellen MS-Diagnostik dar und ist ein innovatives bildgebendes In-vivo- Verfahren zur weiteren Erforschung der Multiplen Sklerose.

Thesis (Ph. D.)--University of Alberta, 2010.
Title from pdf file main screen (viewed on July 17, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, [Department of] Physics, University of Alberta. Includes bibliographical references.

The complex multiphase flow physics of spray-swirl interaction in both reacting and non-reacting environment is of fundamental and applied significance for a wide variety of applications ranging from gas turbine combustors to pharmaceutical drug nebulizers. Understanding the intricate dynamics between this two phase flow field is pivotal for enhancing mixing characteristics, reducing pollutant emissions and increasing the combustion efficiency in next generation combustors. The present work experimentally investigates the near and far-field break-up, dispersion and coalescence characteristics of a hollow cone spray in an unconfined, co¬annular isothermal swirling air jet environment. The experiments were conducted using an axial-flow hollow cone spray nozzle having a 0.5 mm orifice. Nozzle injection pressure (PN = 1 bar) corresponding to a Reynolds number at nozzle exit ReN = 7900 used as the test setting. At this setting, the operating Reynolds number of the co-annular swirling air stream number (Res) was varied in four distinct steps, i.e. Res = 1600, 3200, 4800 and 5600. Swirl was imparted to the co¬axial flow using a guided vane swirler with blade angle of Ф=45° (corresponding geometric swirl number SG = 0.8). Two types of laser diagnostic techniques were utilized: Particle / Droplet imaging analysis (PDIA) and shadowgraph to study the underlying physical mechanisms involved in the primary breakup, dispersion and coalescence dynamics of the spray. Measurements were made in the spray in both axial and radial directions and they indicate that Sauter Mean Diameter (SMD) in radial direction is highly reliant on the intensity of swirl imparted to the spray. The spray is subdivided into two zones as function of swirl in axial and radial direction: (1) near field of the nozzle (ligament regime) where variation in SMD arises predominantly due to primary breakup of liquid films (2) far-field of the nozzle where dispersion and collision induced coalescence of droplets is dominant. Each regime has been analyzed meticulously, by computing probability of primary break-up, probability of coalescence and spatio-temporal distribution of droplets which gives probabilistic estimate of aforementioned governing phenomena. In addition to this, spray global length scale parameters such as spray cone angle, break-up length, wavelength of liquid film has been characterized by varying Res while maintaining constant ReN.

The complex multiphase flow physics of spray-swirl interaction in both reacting and non-reacting environment is of fundamental and applied significance for a wide variety of applications ranging from gas turbine combustors to pharmaceutical drug nebulizers. Understanding the intricate dynamics between this two phase flow field is pivotal for enhancing mixing characteristics, reducing pollutant emissions and increasing the combustion efficiency in next generation combustors. The present work experimentally investigates the near and far-field break-up, dispersion and coalescence characteristics of a hollow cone spray in an unconfined, co¬annular isothermal swirling air jet environment. The experiments were conducted using an axial-flow hollow cone spray nozzle having a 0.5 mm orifice. Nozzle injection pressure (PN = 1 bar) corresponding to a Reynolds number at nozzle exit ReN = 7900 used as the test setting. At this setting, the operating Reynolds number of the co-annular swirling air stream number (Res) was varied in four distinct steps, i.e. Res = 1600, 3200, 4800 and 5600. Swirl was imparted to the co¬axial flow using a guided vane swirler with blade angle of Ф=45° (corresponding geometric swirl number SG = 0.8). Two types of laser diagnostic techniques were utilized: Particle / Droplet imaging analysis (PDIA) and shadowgraph to study the underlying physical mechanisms involved in the primary breakup, dispersion and coalescence dynamics of the spray. Measurements were made in the spray in both axial and radial directions and they indicate that Sauter Mean Diameter (SMD) in radial direction is highly reliant on the intensity of swirl imparted to the spray. The spray is subdivided into two zones as function of swirl in axial and radial direction: (1) near field of the nozzle (ligament regime) where variation in SMD arises predominantly due to primary breakup of liquid films (2) far-field of the nozzle where dispersion and collision induced coalescence of droplets is dominant. Each regime has been analyzed meticulously, by computing probability of primary break-up, probability of coalescence and spatio-temporal distribution of droplets which gives probabilistic estimate of aforementioned governing phenomena. In addition to this, spray global length scale parameters such as spray cone angle, break-up length, wavelength of liquid film has been characterized by varying Res while maintaining constant ReN.