Дисертації з теми "CEST imaging"

Fluorescent probes are useful tools for studying chemical biology, available in a wide variety of colours and applicable to different biochemical processes. One of their hallmarks is the ability to tune their chemistry and allow them to selectively “turn on” in response to different biomolecular targets of interest. However, fluorescence is largely limited by shallow tissue depth of penetration. Magnetic resonance imaging (MRI) can overcome the depth of penetration limitations to better map these biochemical processes and mechanisms with contrast agents. Chemical exchange saturation transfer (CEST) MRI is an alternative method to generating contrast in MR imaging that, like fluorescence, can provide multiplexed imaging by varying the chemical shift of the exchangeable proton on the contrast agent. Previously, a paramagnetic CEST agent containing two tetramethylpiperidinyloxyl (TEMPO) moieties was shown to reduce the CEST signal of a lanthanide complex due to T1 shortening effects on bulk water. Herein, we present a probe design strategy capable of suppressing the diamagnetic CEST (diaCEST) signal with the use of an N-hydroxy piperidine moiety. This discovery that N-hydroxy piperidine is capable of suppressing the diaCEST signal was applied to the study the activity of fibroblast activation protein-α (FAP). FAP is an enzyme involved in maintaining the tumour environment and its interactions can help understand tumour development, invasion and metastasis.

The in vivo detection of enzyme activity is a significant biomarker in tumorigenesis. Assessment of enzyme activity relative to enzyme concentration can serve as quite an accurate measurement of several disease states. Chemical Exchange Saturation Transfer (CEST) MRI is a non-invasive imaging technique that can be used to evaluate enzyme activity. Compared to other contrast agents CEST MRI agents have a slower chemical exchange rate and thus have greater specificity for detecting the intended biomarker. Chapter 1 provides an overview of the advances made in the field of molecular imaging for detection of cancer biomarkers. The molecular mechanism of each technique is explained with specific examples and advantages as well as disadvantages of each technique. Chapter 2 investigates the specific example of detection of an enzyme, γ-glutamyl transferase (GGT) in ovarian cancer tumor models using a catalyCEST MRI contrast agent. This chapter discusses the step-by step evaluation of the non-metallic contrast agent, from synthesis to evaluation of its catalytic efficiency with Michaelis Menten kinetics studies and finally in vivo GGT detection in ovarian tumor models of OVCAR-8 and OVCAR-3. Chapter 3 investigates the enzyme, Kallikrein-6 and its detection in HCT116 colon cancer tumor model. In addition to enzyme detection, enzyme inhibition using Antithrombin III inhibitor has also been explored within in vitro media and in vivo HCT116 tumor model. Chapter 4 introduces the catalyCEST agent for detection of sulfatase enzyme. This chapter discusses the synthesis of this agent and its ability to detect sulfatase in bacterial cell suspension and mammalian cell suspension. These examples portray catalyCEST MRI as a platform technology for enzyme activity detection. Finally in Chapter 5 future ideas have been proposed to improve the in vivo detection and broaden the applications of catalyCEST MRI in the field of enzyme studies.

Tumor acidosis is an important biomarker in cancer. We have developed a noninvasive imaging method, termed acidosis Chemical Exchange Saturation Transfer (acidoCEST) MRI to measure extracellular pH (pHe) in the tumor microenvironment. Chapter 1 introduces the importance of measuring tumor acidosis and presents various imaging modalities and their shortcoming to measure pHe. Chapter 2 describes the optimization of acidoCEST MRI for in vivo pHe measurement. The acidoCEST MRI protocol consists of a CEST-FISP acquisition and Lorentzian line shape fittings. We determined the optimal saturation time, saturation power and bandwidth, 5 sec, 2.8 µT and 90 Hz respectively. We also tried various routes of administration to increase contrast agent uptake in the tumor. We decided upon 200 µL bolus followed by 150 µL/hr infusion. The optimized acidoCEST MRI protocol was tested on a mammary carcinoma mouse model of MDA- MB-231. Our method can detect an increase in pHe in the bladder and tumor of the mice treated with bicarbonate. We used this optimized acidoCEST MRI method to measure pHe in lymphoma tumor model of Raji, Ramos and Granta 519 as described in Chapter 3. Pixel-wise pHe maps showed tumor heterogeneity. The pHe of Raji, Ramos and Granta 519 were determined to be mildly acidic with no significant difference. Chapter 4 describes the evolution of pixel-wise analysis in more detail. Besides the pHe map and spatial heterogeneity, we were able to determine the % contrast agent uptake. We monitored these biomarkers in two different mammary carcinoma mouse models, MDA- MB-231 and MCF-7 longitudinally and made comparisons between the different tumor models: MCF-7 were more acidic, more heterogeneous and faster growing than MDA- MB-231.

Enzymes are important biomarkers for determining tumor growth and progression. We have developed two molecules to image enzyme response by catalyCEST MRI. This technology allows for non-invasive detection of enzymes. A background of importance of measuring enzyme activity and MRI agents developed for this purpose have been covered in Chapter 1. We have synthesized a responsive paramagnetic Chemical Exchange Saturation Transfer (CEST) agent, called Tm-DO3A-cadaverine. This contrast agents has been successfully cross-linked to the protein albumin by the enzyme transglutaminase leading to the appearance of CEST at -9.2 ppm. The enzyme catalysis has been validated by measuring chemical exchange rates. We have shown that the position of the CEST peak is influenced by the conformation of the molecule depending on the neighboring amino acids to glutamine. This is the first example to show the appearance of CEST due to formation of a covalent bond. We have also synthesized a diamagnetic CEST agent with a large chemical shift dispersion to detect cathespin B activity. Upon enzyme mediated cleavage of PheArgSal, the aryl amide CEST peak at 5.3 ppm disappears. Taking a ratio of the CEST effects from salicylic acid at 9.5 ppm and aryl amide at 5.3 ppm we can detect enzyme activity. The salicylic acid moiety also undergoes some slow response due to enzyme action, as evident by the disappearance of CEST at 9.5 ppm. However, this proof of concept study is the first example of a DIACEST agent designed to measure enzyme activity using a ratio of two CEST effects from the same substrate. The last chapter highlights suggests improvements to the catalyCEST research. The appendix shows the use of bulk magnetic susceptibility measurements by NMR to determine bio-distribution of lanthanides in ex-vivo tissue.

MRI is a powerful imaging method that offers several advantages including non-ionizing radiation, significant depth of penetration, and great spatial resolution. Current demand for precision medicine and the movement toward personalized medicine have encouraged researchers in the field of medical imaging to develop MRI-based techniques. Various techniques are now available for molecular imaging by MRI. MRI started by utilizing T1 relaxation properties of molecules but soon after other relaxation mechanisms such as T2 and recently Chemical Exchange Saturation Transfer (CEST) were developed. Each of those MRI techniques offers advantages and disadvantages such as differences in experimental procedures, complexity of the method, selectivity and specificity of signals, and translation into clinical applications. We have been developing MRI techniques and responsive contrast agents for CEST MRI in the Pagel laboratory (Contrast Agent and Molecular Imaging Laboratory, also called CAMEL) for the past decade. We have mainly utilized MRI techniques and responsive contrast agents to detect and measure cancer biomarkers. Detection of the activity of enzymes and measurement of pH have been our main focus, and we have developed catalyCEST MRI probes and techniques for the detection of the activity of enzymes and acidoCEST for the measurement of pH. My research started with investigation on paramagnetic agents as potential CEST MRI probes (paraCEST) and continued with an investigation on diamagnetic agents (diaCEST). I completed several projects in which I prepared and evaluated paraCEST and diaCEST contrast agents for the detection of DT-diaphorase, and alkaline phosphatase enzymes, respectively. Although CEST MRI was my main activity in CAMEL, I started a new direction in CAMEL after encountering a series of observations that were unexplainable with CEST MRI. Through my research, I introduced a new class of responsive contrast agents based on the T2-Exchange (T2-Ex) relaxation mechanism. I employed the T2-Ex mechanism to evaluate responsive contrast agents for the detection of nitric oxide biomolecule and nitroreductase enzyme. My research activities in the CAMEL group resulted in one review paper, one book chapter, two published research articles, and two submitted research manuscripts at the time of preparing my PhD dissertation. In addition to my projects, I was involved in another project that focused on nanocapsule drug delivery, which resulted in a second author publication.

Chemical exchange saturation transfer (CEST) MRI has the ability to noninvasively measure endogenous biomarkers and exogenous agents relevant to various diseases and medical conditions. My work has focused on the development of MRI pulse sequences and data analysis methods to more accurately estimate endogenous and exogenous CEST contrast measurements at 7 T and 3 T magnetic field strengths. Chapter 1 discusses the various sources of signal that have been measured with CEST MRI in the clinic, the acquisition methods used to acquire these signals, and the data analysis methods used to quantify the CEST effects from these signals. Appendix A describes the development of a respiration gated CEST pulse sequence that was ultimately used with a lung fibrosis mouse model to measure extracellular pH (pHe) of the fibrotic lesions. Appendix B describes the development of a data processing algorithm that used the Bloch equations modified for chemical exchange to generate more accurate and precise pHe estimates both at 7 T and 3 T magnetic field strengths relative to a previous data processing algorithm. Appendix C describes the development of a retrospective gating technique for the lung that generates more accurate and precise endogenous CEST contrast measurements.

La maladie de Huntington (MH) est une maladie neurodégénérative héréditaire qui affecte le cerveau. Cette maladie est caractérisée par des signes cliniques tels que la dépression, la démence ainsi que des troubles moteurs s’aggravant au fil du temps. Ces déficiences sont dues à une augmentation anormale de la taille des répétitions CAG dans le gène codant la protéine huntingtine. Celle-ci s’accumule dans les cellules cérébrales et entraine leur mort. Des études antérieures ont démontré que le profil métabolique mesuré en spectroscopie RMN ¹H pouvait être altéré chez les patients atteints de cette maladie ainsi que des atrophies majeures de certaines structures du cerveau. Des hypothèses impliquant des défauts du métabolisme énergétique ont été avancées pour expliquer en partie la physiopathologie de la maladie. Les acteurs du métabolisme pourraient ainsi constituer des biomarqueurs d’intérêt. A l'aide d'une modalité d'IRM prometteuse appelée CEST (Chemical Exchange Saturation Transfer : Transfert de Saturation par Echange Chimique) il est possible de détecter des protons labiles faiblement concentrés qui sont classiquement indétectables en IRM. Il devient ainsi possible de cartographier in vivo la distribution de métabolites comme le glutamate (qui est un neurotransmetteur) ou le glucose (qui est le carburant des cellules) qui sont potentiellement impliqués dans les maladies neurodégénératives. Les développements méthodologiques effectués lors de cette thèse ont ensuite été appliqués à des modèles de rongeurs de la maladie de Huntington (souris KI140, souris R6/1, rats BACHD) afin d'identifier les biomarqueurs potentiels de la pathologie et d'évaluer la pertinence de ces méthodes IRM innovantes. L’ensemble de ces résultats et des méthodes mises en place durant cette thèse montrent le potentiel de l’imagerie CEST pour l’étude des maladies neurodégénératives
Huntington's disease (HD) is a inherited neurodegenerative disease affecting the brain. This disease is characterized by clinical symptoms such as psychiatric, cognitive and motor disorders worsening over time. These deficiencies are due to an abnormal increase in the size of the CAG repeats in the gene encoding the huntingtin protein. Thisaccumulates in the brain cells and causes their death. Previous studies have shown that the metabolic profile measured in ¹H NMR spectroscopy can be altered in patients with this disease as well as major atrophy of certain structures of the brain. Hypotheses involving defects in energy metabolism have been advanced to explain partially the pathophysiology of the disease. The metabolic actors could thus be biomarkers of interest. Using a promising MRI modality called Chemical Exchange Saturation Transfer (CEST), it is possible to detect low-concentrated labile protons that are classically undetectable in MRI. It thus becomes possible to map in vivo the distribution of metabolites such as glutamate (which is a neurotransmitter) or glucose (which is the fuel of cells) which are potentially involved in neurodegenerative diseases. The methodological developments carried out during this thesis were then applied to rodent models of Huntington's disease (KI140 mice, R6/1 mice, BACHD rats) in order to identify potential biomarkers of the pathology and to evaluate the relevance of these innovative MRI methods. All of these results and methods implemented during this thesis show the potential of CEST imaging for the study of neurodegenerative diseases

Detection of enzyme activity has gained popularity in molecular imaging because increased activity of enzymes such as urokinase plasminogen activator (uPA) can serve as biomarkers and assist in cancer diagnosis. Chemical exchange saturation transfer (CEST) Magnetic Resonance Imaging (MRI) is a non-invasive technique that can be utilized to detect enzyme activity; however, CEST MRI is not the only technique that can assess enzyme activity. Chapter 1 provides an overview of various imaging modalities that have been used to detect enzyme activity in vivo. Advances made in probe-design are discussed, in addition to advantages and disadvantages of each technique. Chapter 2 focuses on detection of uPA activity in a pancreatic cancer tumor model using a catalyCEST MRI contrast agent. Chapter 2 also discusses the importance of uPA in tumor biology, addresses the synthesis of the contrast agent, and evaluates the results of in vivo detection and ex vivo validation of uPA activity in response to therapy of pancreatic tumor models of Capan-2. The in vivo and ex vivo results showed no significant difference in uPA activity between chemotherapy-treated and non-treated mice. Additionally, no significant difference was observed between before and after chemotherapy-treated groups. Chapter 3 addresses some of the limitations of the study detailed in Chapter 2 and proposes improvements.

Předkládaná Diplomová práce se zabývá analýzou a tvorbou modelů dýchacích cest předčasně narozených dětí. Nejprve je položen teoretický základ v oblasti vývoje dýchacího ústrojí a tvorby modelů dýchacích cest. Poté jsou představeny využité zobrazovací modality a popsány metody pro práci s obrazovými daty. Praktická část práce se zabývá vytvořením modelů dýchacích cest tří novorozenců. Všechny tyto modely jsou vytvořeny na základě klinických CT a MRI dat novorozenců narozených ve 30. týdnu gestačního věku. U těchto vytvořených modelů jsou dále analyzovány vybrané parametry související s anatomickou strukturou dýchacích cest. Na základě analýzy těchto parametrů byl následně navrhnut reprezentativní model, odpovídající dýchacím cestám novorozence daného gestačního věku.

L'imagerie par résonance magnétique du transfert de saturation par échange chimique (IRM CEST) représente un outil puissant pour l'étude du métabolisme, offrant une résolution temporelle et spatiale supérieure ainsi qu'une sensibilité accrue par rapport à la spectroscopie par résonance magnétique. L'IRM CEST permet la détection indirecte de certains métabolites grâce à l'interaction entre leurs protons et ceux de l'eau. Le CEST peut cartographier le glucose, le glutamate et la créatine, qui sont des métabolites importants impliqués dans les cancers et les maladies neurodégénératives et musculosquelettiques, ce qui en fait un outil de bio-imagerie prometteur. Le développement rapide de l'IRM à haut champ magnétique (≥7 T) au cours des dernières décennies a grandement bénéficié au CEST, ouvrant la voie à de nouvelles applications et suscitant ainsi un intérêt croissant.L'objectif de cette thèse est de développer l'IRM CEST dans un contexte clinique, en tirant pleinement parti des champs magnétiques élevés pour augmenter la robustesse et la vitesse des acquisitions CEST. Pour ce faire, nous nous concentrons sur deux objectifs principaux. Le premier est de développer la méthode d'imagerie CEST dans un environnement clinique, en surmontant les limitations pratiques associées aux scanners IRM cliniques à haut champ, notamment les contraintes strictes du débit d'absorption spécifique (DAS) et des hétérogénéités de champ (B1) des RadioFréquences (RF).Pour atteindre ce premier objectif, une séquence CEST en transmission parallèle a été mise au point. La transmission parallèle utilise une antenne d'émission RF multicanal, qui peut être contrôlée indépendamment pour réduire l'hétérogénéité B1. En utilisant la transmission parallèle, nous avons mis en œuvre une stratégie d'acquisition qui nous a permis de produire des images CEST avec trois fois moins d'hétérogénéité B1, et deux fois plus rapidement que l'état de l'art de la littérature.Le deuxième objectif est d'évaluer la performance du CEST, pondérée en glucose et glutamate, dans la détection et la caractérisation du vieillissement normal et pathologique. Une étude clinique a été réalisée, impliquant des volontaires sains jeunes et âgés ainsi que des patients atteints de la maladie d'Alzheimer. Les résultats ont montré que le CEST peut détecter les variations globales de glutamate et de glucose dans le cerveau associées au vieillissement. L'acquisition et l'exploitation de données provenant de patients atteints de la maladie d'Alzheimer sont, eux, toujours en cours.En conclusion, cette thèse a permis de développer des méthodes CEST à haut champ et d'évaluer leurs performances dans l'étude du vieillissement. Ces résultats ouvrent des perspectives encourageantes pour l'utilisation du CEST comme biomarqueur de la maladie d'Alzheimer et d'autres maladies neurodégénératives
Chemical Exchange Saturation Transfer Magnetic Resonance Imaging (CEST MRI) represents a powerful tool for the study of metabolism, offering superior temporal and spatial resolution as well as increased sensitivity compared to Magnetic Resonance Spectroscopy (MRS). CEST MRI enables the indirect detection of certain metabolites through the interaction between their labile protons and those of bulk water. CEST can map glucose, glutamate, creatine, which are important metabolites involved in cancers, and neurodegenerative and musculoskeletal diseases, representing therefore a promising bioimaging tool. The rapid development of high magnetic field MRI ((≥7 T) in recent decades greatly benefits CEST, opening up new applications and generating growing interest.The aim of this thesis is to develop CEST MRI in a clinical context, taking full advantage of high magnetic fields to increase the robustness and speed of CEST acquisitions. To this end, we focus on two main objectives. The first is to develop the CEST imaging method in a clinical environment, overcoming the practical limitations associated with high-field clinical MRI scanners, notably the strict constraints of Specific Absorption Rate (SAR) and RadioFrequency (RF) field heterogeneities (B1).To achieve this first objective, a parallel transmission CEST sequence was developed. Parallel transmission uses a multi-channel RF transmit antenna, which can be controlled independently to reduce B1 heterogeneity. Moreover, parallel transmission also allows optimized energy management using virtual observation points (a strategy developed in the laboratory) By making use of parallel transmission we have implemented an acquisition strategy which allowed us to produce CEST images with three times less B1 heterogeneity, and two times faster than compared to the state of the art literature reports.The second objective is to evaluate the performance of CEST, glucose, and glutamate weighted, in detecting and characterizing normal and pathological aging. A clinical study was carried out, involving young and elderly healthy volunteers as well as Alzheimer’s disease (AD) patients. The results showed that CEST can detect global variations in glutamate and glucose in the brain associated with aging. The acquisition and exploitation of data from AD patients is still in progress.In conclusion, this thesis has enabled the development of high-field CEST methods and the evaluation of their performance in the study of aging. These results open up encouraging prospects for the use of CEST as a biomarker of AD and other neurodegenerative diseases

L’effet des composés paramagnétiques sur le déplacement chimique des protons, c’est-à-dire sur leur fréquence de résonance propre, beaucoup utilisé en RMN conventionnelle, peut également être un outil de contraste en Imagerie par Résonance Magnétique (IRM) pour réaliser des images encodées en fréquence et donc sélectives selon la nature ou l’environnement de l’entité que l’on cherche à révéler. Cette approche fait intervenir le transfert d’aimantation par échange chimique de protons mobiles, en anglais « Chemical Exchange Saturation Transfer » (CEST). Le principe consiste à saturer sélectivement un signal donné de protons labiles appartenant à la structure-même de l’agent de contraste ou aux molécules d’eau qui lui sont transitoirement liées, à l’aide d’une impulsion radiofréquence bien choisie. L’image résulte alors de l’altération du signal des protons échangés. Le fonctionnement de la méthode repose sur l’existence effective de deux ensembles ou réservoirs de protons, celui correspondant aux protons associés à l’agent de contraste et celui représenté par le milieu environnant, autrement dit l’eau des tissus, ces deux réservoirs présentant une fréquence de résonance bien distincte. Les systèmes LipoCEST, liposomes encapsulant un complexe paramagnétique de lanthanide, permettent une telle différenciation de deux réservoirs de protons constitutifs d’une part de l’eau contenue dans la cavité interne des liposomes (dont la fréquence de résonance est modifiée par l’agent paramagnétique) et d’autre part de l’eau présente à l’extérieur de la structure. La sensibilité de tels systèmes est principalement due au grand nombre de protons contenus dans le réservoir interne. La nature de l’agent paramagnétique joue un rôle déterminant dans la sélectivité de l’effet CEST et la nature de la membrane des liposomes dont la perméabilité permet un échange plus ou moins rapide entre les deux réservoirs d’eau doit être sélectionnée de manière à conduire à une réponse CEST efficace.Les travaux réalisés au cours de cette thèse portent sur une telle mise au point avec pour objectif l’optimisation de systèmes destinés à une IRM-CEST après administration par voie intraveineuse. De ce fait, le diamètre des liposomes a été fixé inférieur à 200 nm et leur surface recouverte de chaînes de poly(éthylène glycol) pour assurer leur future stabilité dans le compartiment sanguin. Le choix des agents de déplacement chimique à centre lanthanide, principalement des complexes de thulium, a été fixé à partir de leurs propriétés structurales et magnétiques. La méthodologie spécialement développée pour encapsuler ces entités au sein de liposomes de compositions lipidiques induisant des perméabilités membranaires distinctes a permis la mise au point d’un nouvel agent de contraste LipoCEST
The effect of paramagnetic compounds in the chemical shift of endogenous protons, i.e., their resonance frequency, widely used in conventional NMR, can also be a tool to modulate the contrast in magnetic resonance imaging (MRI) by achieving frequency-encoded images depending on the nature or the environment of the entity or tissue to be revealed. This approach involves the transfer of magnetization by chemical exchange of protons also referred to as "Chemical Exchange Saturation Transfer" (CEST). The principle consists in selectively saturate by applying a radio frequency pulse, the signal of labile protons transiently belonging to the structure of the contrast agent or to the water molecules which are associated transiently to it. The image then results from the alteration of the signal of the exchanged protons. The method is based on the actual existence of two sets of protons or pools with two distinct resonance frequencies, one corresponding to the protons associated with the contrast agent and the other represented by the surrounding bulk water.LipoCEST systems, liposomes encapsulating a paramagnetic lanthanide complex, allows such a differentiation of two proton pools constituted on one hand by the water molecules contained in the inner cavity of the liposomes (with a resonance frequency changed by the paramagnetic agent ) and on the other hand by the water present outside the vesicle structure. The sensitivity of such systems is mainly due to the large number of protons in the inner pool. The nature of the paramagnetic agent plays a role in the selectivity of the CEST effect while the nature of the liposome membrane and related permeability behavior controls the proton exchange kinetics between the two water pools. These two parameters must be selected and adjusted to provide effective CEST contrast.The work in this thesis aimed at such a development by optimizing liposome systems for MRI-CEST after intravenous administration. Therefore, the diameter of the liposomes was set below 200 nm and their surface covered by chains of poly (ethylene glycol) to ensure stability in the blood compartment. The choice of chemical shift agents based on lanthanide complexes, mainly thulium-based derivatives, was established from their structural and magnetic properties. The methodology specially developed to encapsulate these entities into vesicles of different membrane composition and permeability to water allowed to generate a new LipoCEST contrast agent

Stroke is one of the leading causes of death and adult disability worldwide. The major therapeutic intervention for acute ischemic stroke is the administration of recombinant tissue plasminogen activator (rtPA) to help to restore blood flow to the brain. This has been shown to increase the survival rate and to reduce the disability of ischemic stroke patients. However, rtPA is associated with intracranial haemorrhage and thus its administration is currently limited to only about 5% of ischemic stroke patients. More advanced imaging techniques can be used to better stratify patients for rtPA treatment. One new imaging technique, chemical exchange saturation transfer (CEST) magnetic resonance imaging, can potentially image intracellular pH and since tissue acidification happens prior to cerebral infarction, CEST has the potential to predict ischemic injury and hence to improve patient selection. Despite this potential, most studies have generated pH-weighted rather than quantitative pH maps; the most widely used metric to quantify the CEST effect is only able to generate qualitative contrast measurements and suffers from many confounds. The greatest clinical benefit of CEST imaging lies in its ability to non-invasively measure quantitative pH values which may be useful to identify salvageable tissue. The quantitative techniques and work presented in this thesis thus provide the necessary analysis to determine whether a threshold for the quantified CEST effect or for pH exists to help to define tissue outcome following stroke; to investigate the potential of CEST for clinical stroke imaging; and subsequently to facilitate clinical translation of CEST for acute stroke management.

In ischaemic stroke a disruption of cerebral blood flow leads to impaired metabolism and the formation of an ischaemic penumbra in which tissue at risk of infarction is sought for clinical intervention. In stroke trials, therapeutic intervention has largely been based on perfusion-weighted measures, but these have not been shown to be good predictors of tissue outcome. The aim of this thesis was to develop analysis techniques for magnetic resonance imaging (MRI) of chemical exchange saturation transfer (CEST) in order to quantify metabolic signals associated with tissue fate in patients with acute ischaemic stroke. This included addressing robustness for clinical application, and developing quantitative tools that allow exploration of the in-vivo complexity. Tissue-level analyses were performed on a dataset of 12 patients who had been admitted to the John Radcliffe Hospital in Oxford with acute ischaemic stroke and recruited into a clinical imaging study. Further characterisation of signals was performed on stroke models and tissue phantoms. A comparative study of CEST analysis techniques established a model-based approach, Bloch-McConnell model analysis, as the most robust for measuring pH-weighted signals in a clinical setting. Repeatability was improved by isolating non-CEST effects which attenuate signals of interest. The Bloch-McConnell model was developed further to explore whether more biologically-precise quantification of CEST effects was both possible and necessary. The additional model complexity, whilst more reflective of tissue biology, diminished contrast that distinguishes tissue fate, implying the biology is more complex than pH alone. The same model complexity could be used reveal signal patterns associated with tissue outcome that were otherwise obscured by competing CEST processes when observed through simpler models. Improved quantification techniques were demonstrated which were sufficiently robust to be used on clinical data, but also provided insight into the different biological processes at work in ischaemic tissue in the early stages of the disease. The complex array of competing processes in pathological tissue has underscored a need for analysis tools adequate for investigating these effects in the context of human imaging. The trends herein identified at the tissue level support the use of quantitative CEST MRI analysis as a clinical metabolic imaging tool in the investigation of ischaemic stroke.

Un des défis majeurs en traitement radar consiste à identifier une cible cachée dans un environnement bruité. Pour ce faire, il est nécessaire de caractériser finement les propriétés statistiques du bruit, en particulier sa matrice de covariance. Sous l'hypothèse gaussienne, cette dernière est estimée par la matrice de covariance empirique (SCM) dont le comportement est parfaitement connu. Cependant, dans de nombreuses applications actuelles, tels les systèmes radar modernes à haute résolution par exemple, les données collectées sont de nature hétérogène, et ne peuvent être proprement décrites par un processus gaussien. Pour pallier ce problème, les distributions symétriques elliptiques complexes, caractérisant mieux ces phénomènes physiques complexes, ont été proposées. Dans ce cas, les performances de la SCM sont très médiocres et les M-estimateurs apparaissent comme une bonne alternative, principalement en raison de leur flexibilité par rapport au modèle statistique et de leur robustesse aux données aberrantes et/ou aux données manquantes. Cependant, le comportement de tels estimateurs reste encore mal compris. Dans ce contexte, les contributions de cette thèse sont multiples.D'abord, une approche originale pour analyser les propriétés statistiques des M-estimateurs est proposée, révélant que les propriétés statistiques des M-estimateurs peuvent être bien approximées par une distribution de Wishart. Grâce à ces résultats, nous analysons la décomposition de la matrice de covariance en éléments propres. Selon l'application, la matrice de covariance peut posséder une structure particulière impliquant valeurs propres multiples contenant les informations d'intérêt. Nous abordons ainsi divers scénarios rencontrés dans la pratique et proposons des procédures robustes basées sur des M-estimateurs. De plus, nous étudions le problème de la détection robuste du signal. Les propriétés statistiques de diverses statistiques de détection adaptative construites avec des M-estimateurs sont analysées. Enfin, la dernière partie de ces travaux est consacrée au traitement des images radar à synthèse d'ouverture polarimétriques (PolSAR). En imagerie PolSAR, un effet particulier appelé speckle dégrade considérablement la qualité de l'image. Dans cette thèse, nous montrons comment les nouvelles propriétés statistiques des M-estimateurs peuvent être exploitées afin de construire de nouvelles techniques pour la réduction du speckle
One of the main challenges in radar processing is to identify a target hidden in a disturbance environment. To this end, the noise statistical properties, especially the ones of the disturbance covariance matrix, need to be determined. Under the Gaussian assumption, the latter is estimated by the sample covariance matrix (SCM) whose behavior is perfectly known. However, in many applications, such as, for instance, the modern high resolution radar systems, collected data exhibit a heterogeneous nature that cannot be adequately described by a Gaussian process. To overcome this problem, Complex Elliptically Symmetric distributions have been proposed since they can correctly model these data behavior. In this case, the SCM performs very poorly and M-estimators appear as a good alternative, mainly due to their flexibility to the statistical model and their robustness to outliers and/or missing data. However, the behavior of such estimators still remains unclear and not well understood. In this context, the contributions of this thesis are multiple.First, an original approach to analyze the statistical properties of M-estimators is proposed, revealing that the statistical properties of M-estimators can be approximately well-described by a Wishart distribution. Thanks to these results, we go further and analyze the eigendecomposition of the covariance matrix. Depending on the application, the covariance matrix can exhibit a particular structure involving multiple eigenvalues containing the information of interest. We thus address various scenarios met in practice and propose robust procedures based on M-estimators. Furthermore, we study the robust signal detection problem. The statistical properties of various adaptive detection statistics built with M-estimators are analyzed. Finally, the last part deals with polarimetric synthetic aperture radar (PolSAR) image processing. In PolSAR imaging, a particular effect called speckle significantly degrades the image quality. In this thesis, we demonstrate how the new statistical properties of M-estimators can be exploited in order to build new despeckling techniques

La finesse de la résolution spectrale et spatiale des images hyperspectrales en font des données de très grande dimension. C'est également le cas d'autres types de données, où leur taille tend à augmenter pour de plus en plus d'applications. La complexité des données provenant de l'hétérogénéité spectrale et spatiale, de la non gaussianité du bruit et des processus physiques sous-jacents, renforcent la richesse des informations présentes sur une image hyperspectrale. Exploiter ces informations demande alors des outils statistiques adaptés aux grandes données mais aussi à leur nature non gaussienne. Des méthodes reposant sur la théorie des matrices aléatoires, théorie adaptée aux données de grande dimension, et reposant sur la robustesse, adaptée aux données non gaussiennes, sont ainsi proposées dans cette thèse, pour des applications à l'imagerie hyperspectrale. Cette thèse propose d'améliorer deux aspects du traitement des images hyperspectrales : l'estimation du nombre d'endmembers ou de l'ordre du modèle et le problème du démélange spectral. En ce qui concerne l'estimation du nombre d'endmembers, trois nouveaux algorithmes adaptés au modèle choisi sont proposés, le dernier présentant de meilleures performances que les deux autres, en raison de sa plus grande robustesse.Une application au domaine de la finance est également proposée. Pour le démélange spectral, trois méthodes sont proposées, qui tiennent comptent des diff érentes particularités possibles des images hyperspectrales. Cette thèse a permis de montrer que la théorie des matrices aléatoires présente un grand intérêt pour le traitement des images hyperspectrales. Les méthodes développées peuvent également s'appliquer à d'autres domaines nécessitant le traitement de données de grandes dimensions
Hyperspectral imaging generates large data due to the spectral and spatial high resolution, as it is the case for more and more other kinds of applications. For hyperspectral imaging, the data complexity comes from the spectral and spatial heterogeneity, the non-gaussianity of the noise and other physical processes. Nevertheless, this complexity enhances the wealth of collected informations, that need to be processed with adapted methods. Random matrix theory and robust processes are here suggested for hyperspectral imaging application: the random matrix theory is adapted to large data and the robustness enables to better take into account the non-gaussianity of the data. This thesis aims to enhance the model order selection on a hyperspectral image and the unmixing problem. As the model order selection is concerned, three new algorithms are developped, and the last one, more robust, gives better performances. One financial application is also presented. As for the unmixing problem, three methods that take into account the peculierities of hyperspectral imaging are suggested. The random matrix theory is of great interest for hyperspectral image processing, as demonstrated in this thesis. Differents methods developped here can be applied to other field of signal processing requiring the processing of large data

Non-invasive measurement of pH provides multiple potential benefits in oncology such as better identifying the type of drug that can be more effective in chemotherapy, potentially identifying tumors that are more likely to metastasize and also better assessing the treatment effects. Chemical Exchange Saturation Transfer (CEST) Magnetic Resonance Imaging (MRI) is a versatile non-invasive technique for molecular imaging. AcidoCEST MRI techniques have been developed over the recent years to perform tumor pH measurements by utilizing a contrast agent for which chemical exchange saturation transfer effects depend on the pH of the microenvironment. Quantitative description of CEST MRI signals are generally done via modeling Bloch-McConnell equations by incorporating pH as a parameter or by fitting Lorentzian line shapes to observed z-spectra and then computing a log ratio of the CEST effects from multiple labile protons of the same molecule (ratiometric method). Modeling using Bloch-McConnell equations is complicated and requires careful inclusion of many scan parameters to infer pH. The ratiometric method requires contrast agents that have multiple labile protons, thus making it unsuitable to use for molecules with a single labile proton. Furthermore, depending on the pH, sometimes it might not be possible to numerically compute the ratio due to the inability of detecting signal peaks for certain labile protons. Our aim here is to develop a machine learning based method that learns the CEST signal patterns from observed z-spectra on temperature and concentration-controlled contrast agent phantoms independent of the type of the contrast agent. Our results indicate that the machine learning method provides more general and accurate prediction of pH in comparison to the ratiometric method based on the phantom CEST dataset. Our method is more general in the sense that it does not require explicit modeling of signal peaks that are dependent on the type of contrast agent. We also describe a state of the art variational autoencoder based algorithm extending our machine learning method to measure tumor pH in vivo using AcidoCEST MRI on mouse tumor models.

For a thorough investigation of metabolic changes in cases of increased activity or disease, a high-resolution imaging modality would be of high-value. Conventional MR-based metabolite mapping techniques suffer from low spatial resolution and poor sensitivity to low concentrated metabolites. In this work, a novel optimization approach for high-resolution metabolic imaging by means of chemical exchange saturation transfer (CEST) and nuclear Overhauser effect (NOE) will be introduced. The general term of saturation transfer comprises CEST, NOE and magnetization transfer (MT). It describes the transfer of saturated magnetization from low concentrated solute metabolites to bulk water, after frequency selective RF irradiation was applied. The strong enhancement of attenuation effects—observed in a Z-spectrum—can be used to detect changes in metabolite concentrations. The vast complexity of in vivo tissue heavily distorts the baseline in Z-spectra. With a background spin system, modeled from a scout acquisition, saturation pulse amplitudes for each frequency offset were modulated, such that a specific target signal intensity was achieved. Further, a framework for a retrospective look-up correction of magnetic field inhomogeneities and background spin system deviations was developed. The approach of a prospective baseline enhancement (PROBE) was investigated by means of sensitivity and specificity in vitro. It was subsequently translated into a clinical setting at 3 T. A high-resolution mapping of elevated lactate in ischemic regions of acute stroke patients became feasible.

of the thesis Considerable research attention has been paid to the neural regulation of the lower urinary tract (LUT) in past three decades. The aim of this work is mapping of a brain activity by functional magnetic resonance imaging (fMRI) using refined scanning protocol with synchronously performed urodynamics. We aimed to detect neural activity associated with pelvic floor muscle (PF) contractions, filling of urinary bladder and miction. In addition we evaluated using fMRI brain activity associated with urinary bladder filling in patients with a complete spinal cord injury (SCI). We hypothesized activation of brainstem and forebrain areas in receiving information from the vagal nerves. Adjustments of urodynamic system enabled successful implementation of synchronous filling cystometry with fMRI evaluation of cortical activity. We concluded that synchronous urodynamic examination is a novel feasible method that facilitates and enhance interpretation of fMRI data acquired. The main clusters of brain activation during PF contractions were observed in the medial surface of the frontal lobe (primary motor area) and supplementary motor area (SMA). We detected neural activity associated with filling of urinary bladder and miction in middle and inferior frontal gyrus, angular gyrus, posterior and...

Optical imaging methods incorporating observation of the mucosal surface of organs with narrowband filtered light are diagnostic tools with a significant development in recent years and have become an integral and inseparable part of the diagnostic process of benign and malignant pathologies of the mucosal surface of various anatomical systems of the human body. Malignant and premalignant lesions of the upper aero-digestive tract (UADT) are no exception. The present work demonstrates the benefits of evaluation of changes in microvascular architecture by narrowband imaging. Its major advantage is a more accurate diagnosis of premalignant and malignant mucosal pathologies in the head and neck region based on the identification of significant changes in superficial vascularity. There is a very strong correlation of these vascular changes with the final histopathological analysis. The present data have shown that videoendoscopic examination with narrowband imaging significantly improves the distinction between benign and malignant mucosal lesions even in the UADT pathologies with a similar tendency to neoangiogenesis (squamous cell papilloma vs. squamous cell carcinoma). It also refines the determination of surface extension of tumoral changes and helps to localize and accurately diagnose tumors of...

ABSTRACT This work is focused on the synthesis of a family of new macrocyclic ligands with exchangeable protons on coordinating groups that could potentially serve (after complexation with suitable paramagnetic lanthanide(III) ions) as responsive contrast agents (CAs) for magnetic resonance imaging (MRI). It is expected that measurement of extracellular pH should bring information for tumorous disease diagnoses and/or for suggesting the most efficient treatment. Therefore, our attention was focused on pH-dependent CAs based on a PARAmagnetic Chemical Exchange Saturation Transfer (PARACEST) mechanism capable of reporting pH changes in tissue. The PARACEST-related properties of a series of Ln(III) complexes with the CEST effect caused by amino groups coordinated to the central Ln(III) metal ions were investigated. Such a kind of PARACEST CA is new and has had no precedent in the literature. It was shown that these Ln(III) complexes produce a pH-sensitive PARACEST effect in the pH region relevant for living systems. The study brings proof-of-principle for utilization of complexes with a linear diamine pendant arm, i.e. complexes with two exchanging proton pools, for ratiometric pH determination by MRI independently on the probe concentration. In addition, to ensure a higher kinetic inertness of the...

Summaries in Spanish and English
Text in Spanish
The aim of this dissertation is to analyse those poems in which the image of the knife, el cuchillo, appears in the collection El rayo que no cesa, by Miguel Hernandez. The poet manifests his all-encompassing tragic view of life by means of this recurring negative symbol. The poetry of Miguel Hernandez is autobiographical: The universal themes of nature, love and death reveal a close link between the course of his life and the evolution of his poetry. El rayo que no cesa is central to the evolution of Hernandez's poetry: it is the product of the crisis of conscience that propelled the poet toward a radical change of world-view. The book reveals his frustration with love within the rigid norms of the society of his time. The poet expresses his bitterness by means of destructive images such as knife, sword, and ray/flash, images that project the tragic fate that threatened his entire existence.
Esta disertacion tiene por objeto analizar los poemas en que aparece la imagen del cuchillo en el libro El rayo que no cesa, de Miguel Hernandez, y demostrar que la insistencia de este simbolo negativo revela la cosmovisi6n tragic a que de 1a vida tenia el poeta. La poesia de Miguel Hernandez es poesia autobiogr&fica. La trayectoria de su vida esta intimamente ligada a la evolution de su obra en los temas universales de la naturaleza, el amor y la muerte. El rayo que no cesa es libro clave en su evolution pues es fruto de la crisis de conciencia que motiva en el poeta una metamorfosis ideol6gica. Este libro desvela su amor frustrado debido a las normas rigidas de la sotiedad de la epoca. Miguel Hernandez expresa su amargura con imageries destructivas como cuchillo, espada y rayo, imagenes que presagian la amenaza de un destino tragico que abarco toda su existencia.
Classics and Modern European Languages
M.A. (Spanish)

Summaries in Spanish and English
Text in Spanish
The aim of this dissertation is to analyse those poems in which the image of the knife, el cuchillo, appears in the collection El rayo que no cesa, by Miguel Hernandez. The poet manifests his all-encompassing tragic view of life by means of this recurring negative symbol. The poetry of Miguel Hernandez is autobiographical: The universal themes of nature, love and death reveal a close link between the course of his life and the evolution of his poetry. El rayo que no cesa is central to the evolution of Hernandez's poetry: it is the product of the crisis of conscience that propelled the poet toward a radical change of world-view. The book reveals his frustration with love within the rigid norms of the society of his time. The poet expresses his bitterness by means of destructive images such as knife, sword, and ray/flash, images that project the tragic fate that threatened his entire existence.
Esta disertacion tiene por objeto analizar los poemas en que aparece la imagen del cuchillo en el libro El rayo que no cesa, de Miguel Hernandez, y demostrar que la insistencia de este simbolo negativo revela la cosmovisi6n tragic a que de 1a vida tenia el poeta. La poesia de Miguel Hernandez es poesia autobiogr&fica. La trayectoria de su vida esta intimamente ligada a la evolution de su obra en los temas universales de la naturaleza, el amor y la muerte. El rayo que no cesa es libro clave en su evolution pues es fruto de la crisis de conciencia que motiva en el poeta una metamorfosis ideol6gica. Este libro desvela su amor frustrado debido a las normas rigidas de la sotiedad de la epoca. Miguel Hernandez expresa su amargura con imageries destructivas como cuchillo, espada y rayo, imagenes que presagian la amenaza de un destino tragico que abarco toda su existencia.
Classics & Modern European Languages
M.A. (Spanish)