A doença de Alzheimer (DA) é uma patologia neurodegenerativa progressiva e a forma de demência mais prevalente no mundo. As alterações fisiopatológicas da DA têm sido associadas a dois marcadores neuropatológicos clássicos: a deposição de placas de β- amilóide e a formação de emaranhados neurofibrilares da proteína tau hiperfosforilada. Porém, devido a complexidade da DA, outros mecanismos têm sido propostos como coadjuvantes no processo neurodegenerativo, entre eles eventos neuroinflamatórios, a quebra da homeostasia de sistemas de neurotransmissão e disfunção sináptica. Esta pletora de eventos patológicos parece preceder a fase de demência por um longo período onde a doença age de forma silenciosa, ou seja, onde não existem evidências sintomatológicas. Na presente tese, avançamos no entendimento de vias de sinalização associadas com a hipersforforilação da proteína tau envolvendo a disfunção da proteína fosfatase 2A e neurotoxicidade do sistema glutamatérgico. Além disso, avaliamos os radiofármacos de tomografia de emissão de pósitrons (PET) disponíveis para visualização in vivo e não invasiva da fisiopatologia da DA. Finalmente, avaliamos um novo biomarcador de PET, o [11C]ABP688, para visualizar flutuações no sistema glutamatérgico e avançamos no entendimento do impacto das células gliais no sinal do PET [18F]FDG, o radiofármaco mais utilizado na clínica atualmente para visualizar metabolismo de glicose cerebral. O [11C]ABP688 pode ser diretamente incluído em estudos clínicos e a reconceptualização do [18F]FDG proposta nesta tese pode alterar a maneira atual como vemos o metabolismo de glicose na DA e em outras doenças neurodegenerativas. Finalmente, nesta tese, avançamos em termos de mecanismos, e no contexto da busca por um diagnóstico precoce e acurado da DA. / Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most prevalent cause of dementia worldwide. The AD pathophysiological features have been associated to two main classic neuropathological markers: depositon of β-amyloid plaques and formation of neurofibrillary tangles of hyperphosphorylated tau. Due to AD complexity, however, additional mechanisms have been proposed as contributors to the neurodegenerative process, such as neuroinflammatory changes, altered neurotransmission, and synaptic dysfunction. These pathological events seem to precede the dementia phase by many years, resulting in a long silent period, i.e., a preclinical phase. In this thesis, we advanced in the understanding of signaling pathways associated with tau hyperphosphorylation, which includes dysfunction of protein phosphatase 2A (PP2A) and glutamatergic neurotoxicity. Furthermore, we underscored radiopharmaceuticals currently available for imaging AD pathophysiology in vivo and non-invasively with positron emission tomography (PET). Finally, we evaluated a new PET biomarker, [11C]ABP688, for visualizing glutamatergic fluctuations and advanced in the understating of how glial cells contribute to the [18F]FDG signal, the widely used radiopharmaceutical in clinical settings for visualizing cerebral glucose metabolism. Our findings have high translational value and direct impact in clinical settings, which can potentially alter the way we interpret glucose metabolism in AD and other neurodegenerative disorders. In summary, in this thesis, we have advanced in terms of molecular mechanisms, and in the use of PET biomarkers toward an early and accurate diagnosis of AD.

L’hadronthérapie est une technique de traitement des cancers basée sur l’utilisation de faisceaux d’ions (principalement des protons et des ions 12 C). L’intérêt des ions repose sur deux propriétés fondamentales. La première est d’ordre balistique. Le mode d’interaction des ions avec la matière, caractérisé par le phénomène de pic de Bragg, se traduit par une faible dispersion spatiale de l’énergie déposée dans les tissus. Ceci permet un très bon niveau de conformation au volume tumoral. La seconde est d’ordre biologique, notamment pour les ions 12 C qui présentent une cytotoxicité élevée, utile pour le traitement de tumeurs radiorésistantes. Pour pouvoir utiliser toutes les possibilités offertes par les faisceaux d’ions, de nouveaux outils de contrôle qualité doivent être mis au point. L’utilisation des particules secondaires générées lors de l’irradiation est la voie choisie pour vérifier la conformité des traitements d’hadronthérapie. Certaines de ces particules secondaires présentent une distribution d’activité fortement corrélée au dépôt de dose. C’est le cas des noyaux émetteurs β + dont la détection est basée sur le principe de la tomographie par émission de positons (TEP). La mesure de la distribution en radionucléides émetteurs β + produits par fragmentation du projectile et/ou de la cible permet de détecter des erreurs sur le parcours des ions. Nous présentons ici les travaux de construction d’un démonstrateur appelé DPGA et la mise au point des outils qui lui sont associés pour réaliser la vérification du parcours des ions à partir de la mesure de l’activité β + induite lors des traitements d’hadronthérapie. Le but du DPGA est de pouvoir évaluer certains choix matériels et logiciels avec comme objectif de pouvoir, à terme, effectuer la mesure du parcours des ions en ligne pendant l’irradiation. / Hadrontherapy is a radiation therapy for cancer based on ion beams (mainly protons or carbon ions). This type of treatment offers two advantages compared with conventional x-ray therapy. First the ions penetrate the tissues with little diffusion and the energy transfer is maximum just before stopping (Bragg peak). Then the ions offer a superior dose conformity with tumor volume. Moreover carbon ions offer a higher biological effectiveness useful for radioresistant tumors treatments. To fully exploit the ion beams properties, new quality assurance procedures have to be defined. These controls can be achieved by measuring the β + activation which is induced during the treatments by means of Positon Emission Tomography (PET). PET can be applied for ion range verification because of the correlation between the dose distribution and the spatial distribution of secondary β + activity. We present in this thesis the building of a demonstrator called DPGA and the design of several of its tools dedicated for ion range verification. The aim of the DPGA is to trial hardware and software solutions for an on-line measurement during irradiation.

A doença de Alzheimer (DA) é uma patologia neurodegenerativa progressiva e a forma de demência mais prevalente no mundo. As alterações fisiopatológicas da DA têm sido associadas a dois marcadores neuropatológicos clássicos: a deposição de placas de β- amilóide e a formação de emaranhados neurofibrilares da proteína tau hiperfosforilada. Porém, devido a complexidade da DA, outros mecanismos têm sido propostos como coadjuvantes no processo neurodegenerativo, entre eles eventos neuroinflamatórios, a quebra da homeostasia de sistemas de neurotransmissão e disfunção sináptica. Esta pletora de eventos patológicos parece preceder a fase de demência por um longo período onde a doença age de forma silenciosa, ou seja, onde não existem evidências sintomatológicas. Na presente tese, avançamos no entendimento de vias de sinalização associadas com a hipersforforilação da proteína tau envolvendo a disfunção da proteína fosfatase 2A e neurotoxicidade do sistema glutamatérgico. Além disso, avaliamos os radiofármacos de tomografia de emissão de pósitrons (PET) disponíveis para visualização in vivo e não invasiva da fisiopatologia da DA. Finalmente, avaliamos um novo biomarcador de PET, o [11C]ABP688, para visualizar flutuações no sistema glutamatérgico e avançamos no entendimento do impacto das células gliais no sinal do PET [18F]FDG, o radiofármaco mais utilizado na clínica atualmente para visualizar metabolismo de glicose cerebral. O [11C]ABP688 pode ser diretamente incluído em estudos clínicos e a reconceptualização do [18F]FDG proposta nesta tese pode alterar a maneira atual como vemos o metabolismo de glicose na DA e em outras doenças neurodegenerativas. Finalmente, nesta tese, avançamos em termos de mecanismos, e no contexto da busca por um diagnóstico precoce e acurado da DA. / Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most prevalent cause of dementia worldwide. The AD pathophysiological features have been associated to two main classic neuropathological markers: depositon of β-amyloid plaques and formation of neurofibrillary tangles of hyperphosphorylated tau. Due to AD complexity, however, additional mechanisms have been proposed as contributors to the neurodegenerative process, such as neuroinflammatory changes, altered neurotransmission, and synaptic dysfunction. These pathological events seem to precede the dementia phase by many years, resulting in a long silent period, i.e., a preclinical phase. In this thesis, we advanced in the understanding of signaling pathways associated with tau hyperphosphorylation, which includes dysfunction of protein phosphatase 2A (PP2A) and glutamatergic neurotoxicity. Furthermore, we underscored radiopharmaceuticals currently available for imaging AD pathophysiology in vivo and non-invasively with positron emission tomography (PET). Finally, we evaluated a new PET biomarker, [11C]ABP688, for visualizing glutamatergic fluctuations and advanced in the understating of how glial cells contribute to the [18F]FDG signal, the widely used radiopharmaceutical in clinical settings for visualizing cerebral glucose metabolism. Our findings have high translational value and direct impact in clinical settings, which can potentially alter the way we interpret glucose metabolism in AD and other neurodegenerative disorders. In summary, in this thesis, we have advanced in terms of molecular mechanisms, and in the use of PET biomarkers toward an early and accurate diagnosis of AD.

Dentre as técnicas diagnósticas por imagem, em Medicina Nuclear, têm-se destacado a Tomografia por Emissão de Pósitrons (PET). O PET fornece imagens funcionais da região ou órgão de interesse, possibilitanto o diagnóstico de várias doenças e, também, um mapeamento da evolução ou regressão das mesmas. Os atuais sistemas PET apresentam blocos de cristais arranjados em geometria circular, mas a busca por novos arranjos, em geometrias diferenciadas, é pertinente, pois pode possibilitar um melhor desempenho destes tomógrafos. O objetivo deste estudo é avaliar o desempenho de um sistema PET constituído por blocos de cristais em arranjo elipsoidal. Para tal estudo, fez-se uso do GATE, ambiente de simulação para tomografia por emissão que apresentou resultados satisfatórios comparados à aparelhos utilizados na rotina clínica. Desta forma, elaborou-se dois sistemas PET, o primeiro com 46 blocos de cristais arranjados em geometria circular, no qual, os detectores opostos foram separados a uma distância de 816,4 mm na direção transaxial. No segundo caso, utilizou-se 36 blocos de cristais, arranjados em geometria elíptica, onde os detectores foram separados a uma distância de 500 mm na direção vertical e 816,4 mm na direção horizontal. Uma vez realizadas as simulações, fez-se os testes de validação para Sensibilidade, Fração de Espalhamento, NEC (Noise Equivalente Count Rate) e Resolução Espacial, para então, avaliar e comparar o desempenho do sistema PET para ambas as geometrias propostas. Estes testes foram feitos de acordo com as especificações da norma NEMA NU 2-2007. Para o teste de sensibilidade, com o phantom localizado no centro do FOV transaxial do tomógrafo, obteve-se um ganho no sistema PET, com geometria elíptica, de 28,7% em relação ao sistema convencional, de geometria circular. Para o phantom deslocado à 10 cm do centro do FOV transaxial, a sensibilidade do sistema PET elíptico foi 26,2% superior em relação ao circular. O tempo de aquisição para cada simulação neste teste foi de 400 s. Para os testes de Fração de Espalhamento e NEC foram realizadas 33 simulações, para cada geometria, variando o tempo de aquisição e a atividade. A fração de espalhamento na geometria elíptica foi de 35,5% e na circular 34,6%. Na geometria circular, a curva NEC atinge o pico máximo em 259,3 kcps a uma concentração de atividade de 34,1 kBq ml-1 , já para geometria elíptica, o pico máximo é atingido em 239,1 kcps a uma concentração de atividade de 24,8 kBq ml-1 . As medidas foram adquiridas em três posições transaxiais (x,y) no centro do FOV e, posteriormente, deslocadas em ¼ do centro do FOV, totalizando 6 medidas para cada geometria. Para cada uma destas 6 medidas, encontrou-se a FWHM (largura a meia altura) e a FWTM (largura a 10% do máximo) nos 3 eixos de coordenadas (x,y,z), assim, para cada geometria proposta obteve-se 18 valores de FWHM e 18 valores de FWTM. A geometria elíptica apresentou melhoras na resolução espacial em FWHM em 4 dos 18 valores de resolução. Já para FWTM, a geometria elíptica apresentou melhora em 8 dos 18 valores de resolução. Em relação a FWHM, onde houve melhora na resolução espacial, teve-se um ganho médio de 18,7%. Já as perdas, em resolução espacial foi em média 43,26%. Para FWTM, a melhora em resolução espacial foi em média 12,09%, mas a perda de resolução, neste caso, foi em média 45,59%. Pode-se concluir que a geometria proposta apresenta algumas vantagens em relação a geometria convencional. Na geometria elíptica há uma redução de 10 blocos de cristais em relação a geometria circular, o que possivelmente gera uma redução no custo de fabricação do tomógrafo. Em relação a sensibilidade, há uma melhora significativa para nova geometria, bem como uma redução da concentração da atividade na qual o tomógrafo alcança seu melhor desempenho, embora ocorra uma ligeira diminuição na taxa de contagens no sistema elíptico. Essa redução na concentração de atividade pode ocasionar uma redução no tempo de exame e utilização de menos material radioativo, reduzindo o risco ao paciente e o custo do exame, bem como possibilitando a realização de um maior número de exames num mesmo intervalo de tempo. A fração de espalhamento do sistema elíptico é ligeiramente maior em relação ao sistema circular. A principal perda do sistema PET elíptico está na resolução espacial, onde não houve melhoras para maior parte das medidas realizadas, necessitando de alguns ajustes que pode se dar, entre outras coisas, no arranjo dos blocos de cristais. Acredita-se que ajustes na angulação dos detectores e na formação das coincidências seja possível melhorias nas resoluções, e NEC. / Among the diagnostic imaging techniques, in Nuclear Medicine, have been prominent in Positron Emission Tomography (PET). PET provides functional images of the region or organ of interest, allowing diagnostic of various diseases and also a mapping of the development or regression of the same. Current PET systems feature blocks arranged in circular geometry crystals, but the search for new arrangements, in different geometries, is relevant because it can provide a better performance of these scanners. The objective of this study is to evaluate the performance of a PET system consisting of blocks of crystals ellipsoidal arrangement. For this study, we used the GATE simulation environment for emission tomography that presented satisfactory results compared to the devices used in the clinical routine. This way we prepared two PET systems, the first one containing 46 blocks of crystals arranged in a circular geometry, where the opposite detectors were separated by a distance of 816.4 mm in the transaxial direction. In the second case, we used 36 blocks of crystals arranged in an elliptical geometry, where the detectors are separated a distance of 500 mm in the vertical direction and 816.4 mm in the horizontal direction. After the simulations were performed, the validation tests for sensitivity, scatter fraction, NEC (Noise Equivalent Count Rate) and Spatial Resolution were made, to finally evaluate and compare the performance of the PET system for both proposed geometries. The tests were made accordingly to specified NEMA NU 2-2007 standard. For the sensitivity test, with the phantom located in the center of FOV transaxial of the tomography, we obtained a gain in PET system with elliptical geometry of 28.7% compared to the conventional system, the circular geometry. For the phantom shifted to 10 cm from the center of the transaxial FOV, the sensitivity of PET elliptical system was 26.2% higher than in the circular. The acquisition time for each simulation in this test was 400 s. For Scatter Fraction test and NEC, were made 33 simulations for each geometry, varying the time of acquisition and activity. The scatter fraction in the elliptical geometry was 35,5% and 34,6% in the circular geometry. In the circular geometry, NEC curve reaches its peak in 259.3 kcps at an activity concentration of 34.1 kBq ml-1, for the elliptical geometry, the maximum peak is reached at 239.1 kcps at an activity concentration of 24.8 kBq ml-1. For the spatial resolution test we used a point source containing 18F with 4 MBq activity and acquisition time of 200 s. The measurements were acquired in three transaxials positions (x,y) in the center of FOV and, shifted in ¼ of the center of the FOV, summarizing 6 measurements for each geometry. For each one of these 6 measurements, we found the FWHM (Full width at half-maximum amplitude) and the FWTM (Full width at tenth-maximum amplitude) in the three axis (x,y,z), in this way, for each proposed geometry, we obtained 18 values of FWHM and 18 values of FWTM. The elliptical geometry showed improvement in the spatial resolution in FWHM in 4 of the 18 resolution values. For the FWTM, the elliptical geometry showed improvement in 8 of 18 resolution values. Regarding the FWHM, where there was an improvement in spatial resolution, we obtained the average gain of 18,7%. For the losses, in spatial resolution was an average of 43,26%. For the FWTM, the improvement in spatial resolution was an average percentage of 12,09%, while the loss of resolution had the average percentage of 45,59%. It can be concluded that the proposed geometry showed some advantages regarding the traditional geometry. In the elliptical geometry there is one reduction of 10 blocks of crystals in relation to the circular geometry, which possibly can cut fabrication costs of the tomography. Regarding to sensibility, there is a significant improvement for the new geometry, as well as one reduction of the activity concentration in which the tomography reaches the best performance, although the occurrence of a slight fall in the counts in the elliptical system. This reduction in the activity concentration can help to reduce the test time and the use less radioactive material, reducing the risk for the patients and the test costs, as well as improving the number of tests in the same period of time. The scattering fraction in the elliptical system is slight higher to the circular system. The major loss in the elliptical PET system is the spatial resolution, where there was not improvement for the great fraction of the obtained measurements, requiring some modifications that can be made, in special, in the crystal blocks arrangement. It is believed that some modifications to the angle of the detectors and in the formation of the coincidences can improve the resolutions and NEC.

Radio emission from pulsars is believed to originate from charged particles streaming along the open magnetic field lines, radiating within a narrow cone at each of the two magnetic poles. In each rotation of the star, the emission beam sweeping across the observer’s line of sight, is seen as a pulse of radio emission. Average pulse profiles integrated over several hundreds of individual pulses, along with polarization information, reveal the viewing geometry and various emission properties(e.g., emission in multiple cones, frequency dependence of the emission altitude, notches in the average profiles, etc.), and provide some clues about the possible emission mechanisms. The sequence of individual pulses generally exhibit richer details, e.g., pulse-nulling, variety of subpulse drifting, polarization mode-changing, micro-structure and giant pulse emission, etc., and seem to be more crucial and promising in probing the underlying physical processes. The physical understanding of many of the above properties and phenomena is still far from complete. In first two parts of this thesis, we address a few of these aspects, and probe related details by mapping the pulsar polar emission patterns, while in the last part, we present our searches for dispersed signals(periodic as well as transient) at very low frequencies. More specifically, Part-I makes use of the present understanding of drifting subpulses phenomenon to reconstruct the emission patterns in nearly complete polar cap region of the pulsar B1237+25, and addresses the origin of emission in multiple cones using these reconstructed emission maps. In Part-II, we discuss a need for new instrumentation primarily motivated by the need for tomographic studies of pulsar polar emission regions. We report the consequent design and development of a novel, self-contained multi-band receiver (MBR)system, intended for use with a single large aperture to facilitate sensitive and high time-resolution observations simultaneously in 10 discrete frequency bands sampling a wide spectral span(100–1500MHz) in a nearly log-periodic fashion. Part-III presents our deep searches designed to detect radio transient as well as periodic signals from the (so far) “radio-quiet” gamma-ray pulsars — a population of radio silent pulsars recently discovered using the Large Area Telescope on the Fermi-satellite. Brief descriptions of the issues addressed in the three parts of the thesis, along with a summary of respective results, is as follows. 1. Origin of Radio Emission in Multiple Cones Many pulsars exhibit systematic variations in position and intensity of their subpulses, a phenomenon now well known as “subpulse drifting”. Ruderman & Sutherland(1975) suggested this regular modulation to be a manifestation of a carousel of “spark” discharges in the acceleration zone of the star, circulating around the magnetic axis because of the E×B drift. In the qualitative framework of the above carousel model, the coherent modulation in a subpulse sequence can be mapped back to the underlying pattern of sub-beams/emission-columns (see, for example, Deshpande & Rankin, 1999). However, the completeness with which the underlying configuration of sub-beams can be sampled depends on how close our line of sight approaches the magnetic axis. The bright pulsar B1237+25 has a special viewing geometry where the sightline traverses almost through the magnetic axis, thus providing an excellent opportunity to map and study the underlying patterns across the full transverse slice of its polar emission region. However, the rich variety in pulse-to-pulse fluctuations in this pulsar makes this task challenging. In Chapter 2, we present our analysis of a number of pulse-sequences from this star observed with the Arecibo telescope, wherein we search for, and use, coherent modulation in sub-sequences, to map the underlying emission patterns. The reconstructed maps provide a convenient way to study the details in multiple emission cones, and any inter-relationship between them. More specifically, we have utilized these maps to explore whether the multiple cones of this pulsar originate from a common seed pattern or not. A summary of results The results obtained from our study of B1237+25 are summarized below: 1 The underlying carousel of sparks for this pulsar appears to lack stability over long durations. The circulation period, deduced using smaller length sub-sequences, appears to vary over a large range(about18 to34 times the rotation period). 2. The emission patterns corresponding to the outer and the inner cones are found to be significantly correlated with each other, implying that the emission in the two cones share a common seed pattern of sparks. This main result is consistent with the same radio frequency emission in the two cones, originating from a common seed pattern of sparks at two different altitudes. 3 The emission patterns corresponding to the outer and the inner cones are found to be offset from each other, consistently across various sub-sequences, by about 10◦ in magnetic azimuth. This large offset indicates certainly a twist in the emission columns, and most likely in the magnetic field geometry, between the two different emission altitudes. 4. The core component also seems to share its origin with the conal counterparts. Presence of a compact, diffuse and further-in carousel of sub-beams is consistent with the observed modulation in the core component of this pulsar. The featureless spectrum observed for many core-single pulsars can be explained readily when the diffuse pattern approaches uniformity. 2.Tomography of the Pulsar Magnetosphere: Development of a Multi-band Receiver Although drifting subpulses are now routinely interpreted in the qualitative framework of the carousel model, estimation of circulation time associated with the system of emission columns has been possible so far in only a handful of pulsars, and the important details determining such configurations, their evolution across the magnetosphere, and the pattern circulation are yet to be understood. Radius-to-frequency mapping in pulsars suggests that the lower frequency emission originates farther away from the surface of the star than the higher frequency emission. Hence, the sub-beam configuration mapped at a particular frequency provides a view of a single slice of the polar emission region at the corresponding emission altitude. Mapping of the underlying emission patterns simultaneously at a number of frequencies would amount to viewing a “tomograph” of the pulsar magnetosphere. Such tomographic studies would reveal not only the evolution of sub-beams across the magnetosphere but can also provide much needed clues about the generation of the sub-beam patterns, and their possible connection with the profile/polarization mode changes observed in various pulsars. Simultaneous multi-frequency observations, which are required for many other interesting astronomical studies as well, are usually carried out by using several telescope, each observing at different frequency. Such an approach has inherent complexity in coordinating various telescopes, in addition to numerous other difficulties which limit the desired advantages of such observations. Some of these difficulties, which we faced in our attempt of carrying out simultaneous multi-frequency observations using five different telescopes, are discussed in Chapter 3. We suggest an optimum approach to carry out simultaneous multi-frequency observations, using a single large aperture. In Chapter 4, we present the design of a novel, “self-contained” multi-band receiver(MBR) system developed for this purpose. The MBR system includes a suitable feed, broadband front-end, parallel analog and digital receiver pipelines, along with appropriate monitoring, synchronization and data recording systems. When used with a large aperture, the MBR facilitates high time-resolution observations simultaneouslyin10discretefrequencybandssampling a wide spectral span(100–1500MHz) in a nearly log-periodic fashion. The raw voltage time sequences corresponding to each of the two linear polarization channels for each of the 10 spectral bands are simultaneously recorded, each sampling a bandwidth of 16 MHz at the Nyquist rate. The dual-polarization multi-band feed, a key component of the MBR, is designed to have good responses only overthe10discretebandspre-selected as relatively RFI-free, and hence provides preliminary immunity against RFI. The MBR also offers significant tunability of the center frequencies of each of the 16-MHz sub-bands separately, within the spectral spans of respective bands. Similarity of the 10 sub-band receiver chains provides desired compatibility, in addition to an easy inter-changeability of these units, if required, and an overall modularity to the system. The MBR was used with the 110 meter Green Bank Telescope to conduct test observations on a few bright continuum sources, and about 20 hours of observations on a number of bright pulsars. Using these observations, we have constructed a preliminary tomograph of the polar emission region of B0809+74, and studied the spectral evolution of emission altitudes and flux density ofB0329+54(Chapter5). Although the MBR system design is optimized for tomographic studies of pulsar polar emission regions, the simultaneous multi-frequency observations with such a system offer particular advantages in fast transient searches. The MBR is also suitable for several other astronomical investigations, e.g., studying the spectral evolution of average properties of pulsars and propagation effects, single-dish continuum studies and surveys/studies of recombination lines. 3. Searches for Decameter-wavelength Counterparts of Radio-quiet Gamma-ray Pulsars Before the launch of the Fermi gamma-ray space telescope, the “radio-quiet” gamma-ray pulsar population consisted of only one pulsar ,i.e., Geminga (for example, see Bignami& Caraveo,1996; Abdo etal.,2009). High sensitivity of the Large Area Telescope(LAT) on the Fermi-satellite made it possible, for the first time, to perform blind searches for pulsars in γ-rays. Since the Fermi-operation started, the number of pulsars known to emit in γ-rays has seen an extraordinary increase — from less than 10 to 117 pulsars. About one-third of these pulsars have been discovered in blind searches of the LAT data. Despite deep radio searches, only 4 of these LAT-discovered pulsars could be detected, suggesting the rest of these to be “radio-quiet” gamma-ray pulsars. One of the possible explanations for the apparent absence of radio emission from these pulsars is that their narrow radio beams miss the line of sight towards earth (Brazier & Johnston, 1999), and hence appear as “radio-quiet”. The radius-to-frequency mapping in radio pulsars suggests that the emission beam becomes wider at low frequencies, increasing the probability of our line of sight passing through the beam. However, all of the deep searches mentioned above were carried out at higher radio frequencies(∼1GHz and above, and some at300MHz,Ray etal.,2011;Pletsch etal.,2012),and the lower frequency domain(<≈100 MHz) has remained relatively unexplored. Given the expected widening of emission beam, follow-up searches of the radio-quiet pulsars at low radiofrequencies could also be revealing. With this view, we searched the archival data of the pulsar/transient survey at 34.5 MHz, carried out using the Gauribidanur telescope during 2002-2006,for any periodic or transient dispersed signal along the direction of many of the LAT-discovered pulsars. Motivated by an intriguing possible detection of the pulsar J1732−3131 from the above search, we carried out further extensive follow-up observations and deep searches for pulsed(periodic as well as transient) radio emission from a selected sample of radio-quiet pulsars. Chapters 6 and 7 present details of our observations, detection strategies and methodologies, and interesting results obtained in a few of the target directions. The results obtained from these searches include: 1 A possible detection of periodic radio pulses from J1732−3131 was made, using the archival data, at a dispersion measure(DM) of15.44 ±0.32 pc/cc. We also detected 10 individual bright pulses in the same observing session, although marginally above the detection threshold, at a DM consistent with that associated with the periodic signal. The apparent brightness of these single pulses, and similarity of their apparent distribution in pulse-longitude with that of giant pulses in J0218+4232, suggest that these might be giant pulses. Our DM-based distance estimate, using Cordes & Lazio electron density model(2002),matches well with earlier estimates based on gamma-ray emission efficiency. 2 In our follow-up deep searches, we could not detect any readily apparent pulsed radio signal(neither periodic nor single pulses) from J1732−3131, i.e., above a detection threshold of 8σ. However, when we time-aligned and co-added data from observing sessions at 21different epochs, and dedispersed using the DM estimated from the candidate detection, the average profile shape is found to be completely consistent with that from the candidate detection. Finding the same profile shape after 10 years of the original detection suggests that the signal is unlikely to be due to RFI or a mere manifestation of random noise. 3.In a couple of the observing sessions towards the telescope pointing direction of RA=06:34:30, DEC=10◦ , we detected a few ultra-bright pulses at two different DMs of about2pc/cc and3.3 pc/cc, respectively. However, when dedispersed at the DMs suggested by the bright single pulses, no significant signal was found at the expected periodicities of our targetpulsarsJ0633+0632 andJ0633+1746,which would be in the telescope beam centered at above coordinates. Energies of these strong pulses in the two observing sessions are comparable to typical energies of giant pulses from the Crab pulsar at decameter wavelengths. 4. No significant pulsed signal(periodic or transient), above a detection threshold of 8σ,was found towards the directions of other selected radio-quiet gamma-ray pulsars. Time-aligning and combining of observations at different epochs allowed us to carry out deep searches for signals at the expected periodicities of these pulsars. Despite the large background sky-temperature at decameter wavelengths, the minimum detectable flux density in our deep searches are comparable with those from previous searches at higher frequencies, when scaled using a spectral index of −2.0 and assuming no turn-over in the spectrum.

Mechanical ventilation in itself can harm the lung and cause ventilator-induced lung injury (VILI), which can induce or aggravate acute respiratory distress syndrome (ARDS). Much debate remains over pivotal concepts regarding the pathophysiology of VILI, especially about the precise contribution, kinetics, and primary role of potential VILI mechanisms. Consequently, it remains largely unknown how best to design a well-timed and full-bodied mechanical ventilation strategy. Little is known also about small airways dysfunction in ARDS. Dynamic positron emission tomography (PET) with [18F]fluoro-2-deoxy-D-glucose (18F-FDG) can be used to image cellular metabolism, which during lung inflammation mainly reflects neutrophil activity, allowing the study of regional lung inflammation in vivo. We studied the regional evolution of inflammation using dynamic PET/CT imaging of 18F-FDG in VILI and during different lung-protective mechanical ventilation strategies. By dynamic CT we investigated also the location and magnitude of peripheral airway closure and alveolar collapse under high and low distending pressures and high and low inspiratory oxygen fraction. Piglets were submitted to an experimental model of early ARDS combining repeated lung lavages and injurious mechanical ventilation. The animals were subsequently studied during sustained VILI, or submitted to distinct approaches of lung-protective mechanical ventilation: the one recommended by the ARDS Network (ARDSNet), or to one defined as open lung approach (OLA). The normally and poorly aerated regions - corresponding to intermediate gravitational zones - were the primary targets of the inflammatory process accompanying early VILI, which may be attributed to the small volume of the aerated lung that receives most of ventilation. The ARDSNet strategy did not attenuate global pulmonary inflammation during 27h and led to a concentration of inflammatory activity in the upper and poorly aerated lung regions. The OLA, in comparison with the ARDSNet approach, resulted in sustained and better gas exchange and lung mechanics. Moreover, the OLA strategy resulted in less global and regional inflammation. Dynamic CT data suggested that a significant amount of airway closure and related reabsorption atelectasis occurs in acute lung injury. Whether potential distal bronchioles injury (“bronchiolotrauma”) is a critical and decisive element in ventilator-associated lung injury is a matter for future studies.

Gemcitabine is a highly potent chemotherapeutic nucleoside agent used in the treatment of several cancers and solid tumors. However, it is therapeutically limitated because of toxicity to normal cells and its rapid intracellular deamination by cytidine deaminase into the inactive uracil derivative. Modification at the 4-(N) position of gemcitabine's exocyclic amine to an -amide functionality is a well reported prodrug strategy which has been that confers a resistance to intracellular deamination while also altering pharmacokinetics of the parent drug. Coupling of gemcitabine to carboxylic acids with varying terminal moieties afforded the 4-N-alkanoylgemcitabines whereas reaction of 4-N-tosylgemcitabine with the corresponding alkyl amines gave the 4-N-alkylgemcitabines. The 4-N-alkanoyl and 4-N-alkyl gemcitabine analogues with a terminal hydroxyl group on the 4-N-alkanoyl or 4-N-alkyl chain were efficiently fluorinated either with diethylaminosulfur trifluoride or under conditions that are compatible with the synthetic protocols for 18F labeling, such as displacement of the corresponding mesylate with KF/Kryptofix 2.2.2. The 4-N-alkanoylgemcitabine analogues displayed potent cytostatic activities against murine and human tumor cell lines with 50% inhibitory concentration (IC50) values in the range of low nM, whereas cytotoxicity of the 4-N-alkylgemcitabine derivatives were in the low to modest µM range. The cytostatic activity of the 4-N-alkanoylgemcitabines was reduced by several orders of magnitude in the 2'-deoxycytidine kinase (dCK)-deficient CEM/dCK- cell line while the 4-N-alkylgemcitabines were only lowered by 2-5 times. None of the 4-N-modified gemcitabines were found to be substrates for cytosolic dCK, however all were found to inhibit DNA synthesis. As such, the 4-N-alkanoyl gemcitabine derivatives likely need to be converted to gemcitabine prior to achieving their significant cytostatic potential, whereas the 4-N-alkylgemcitabines reach their modest activity without "measurable" conversion to gemcitabine. Thus, the 4-N-alkylgemcitabines provide valuable insight on the metabolism of 4-N-modified gemcitabine prodrugs.

No description available.

Introduction and Objectives Calcific aortic valve disease (CAVD) is the most common valvular disease, accounting for 50% of all valve disorders and is the third most common cardiovascular disease following coronary disease and hypertension.[1,2] Currently, there is no pharmacological agent capable of reversing or slowing down the progression of CAVD and treatment of severe cases consists of surgical repair or valve replacement[2]. Hence, there is a crucial need for earlier detection using predictive biomarkers that will allow for preventative intervention as opposed to post-symptomatic disease treatment or management. Namely, one target of particular interest is the expression of matrix metalloproteinases (MMPs) (specifically MMP-1, -2, and -9) which are upregulated in CAVD prior to calcification events and have been previously shown to serve as an attractive molecular imaging target.1–3 The primary objective of this study is to assess the feasibility of detecting biomarkers of CAVD by various in vivo imaging modalities, such as PET and echocardiography. In addition, this study assesses disease progression in various mouse strains to qualify an appropriate CAVD animal model. Methods In vivo and ex vivo imaging of C57Bl/6 and ApoE-/- (n = 8 per strain cohort) mouse models are used to link unique features of matrix remodelling with CAVD progression. At baseline and longitudinal follow-up (4, 8, and 12 months), in vivo hemodynamic impairment is assessed through echocardiography, and calcification and MMP activity are measured using PET with a series of radiotracers: [18F]NaF for calcification, [18F]BR351 for the molecular targets of MMP-2 and -9, and [18F]FMBP with molecular target specificity for MMP-13. Following imaging, aortic valve (AV) tissue is harvested, sectioned, and analyzed for calcification, inflammatory markers, collagen types, and MMP activity in AV leaflets. Tracer autoradiography, immunofluorescence, and in situ zymography are used to confirm in vivo imaging results with improved resolution and quantification in valves. Histological sample preparation, experimentation, and analyses are then repeated in human AV tissue samples for relative comparison of biomarker expression in animal models. Results Echocardiography suggests positive signs of disease progression in experimental animal models. In comparison to WT, ApoE-/- mice show: increased peak velocity (p<0.0001), decreased aortic valve area (p<0.001), and irregular valve dynamics. [18F]NaF PET imaging shows expected bone uptake and low calcium-burden in young and WT animals. [18F]FMBP shows increased uptake in the valve area of diseased models at later timepoints, 1.530 compared to <0.001 %ID/g (p<0.005), in disease vs control animals respectively. Furthermore, confirmation of sought-after biomarkers has also been assessed by analysis of various histological sample preparations including the presence of leaflet calcification, upregulation of MMP-2, -9, and -13, matrix remodelling, lipids, inflammatory markers, and activated MMP expression. Conclusion Findings from this study suggest that molecular imaging techniques using target-specific radiotracers, as well as echocardiography for assessment of hemodynamic impairment, are feasible solutions in predicting disease onset in CAVD specific animal models.

La Tomographie par Emission de Positons (TEP) au 2-[18]-Fluoro-2-désoxy-D-glucose (FDG) est une méthode d’imagerie fonctionnelle particulièrement utilisée en oncologie afin de quantifier le métabolisme glucidique des lésions tumorales. En routine clinique, l’analyse quantitative de ces images est réalisée à l’aide de la valeur de fixation normalisée, notée SUV. Des approches de quantification plus élaborées existent dans la littérature, mais elles requièrent généralement de multiples prélèvements sanguins et/ou l’acquisition d’un examen TEP d’au moins 50 minutes. De ce fait, elles sont difficilement applicables en routine clinique. Notre travail a porté sur le développement d’une approche non-invasive, nommée ParaPET, basée sur les travaux initiaux de [Barbolosi et al.2016], permettant la détermination d’une cartographie de biomarqueurs dynamiques et requérant une unique acquisition TEP de durée limitée. Notre approche intègre plusieurs améliorations, parmi lesquelles l’élaboration d’un nouveau modèle d’estimation de la concentration moyenne de FDG et de l’erreur de mesure associée, basé sur un protocole de reconstructions TEP multiples utilisant un rééchantillonnage temporel des données, la détermination de la concentration d’activité sanguine de FDG à l’aide des images TEP de l’aorte, et la caractérisation des lésions tumorales à l’échelle du voxel. Notre approche a été évaluée sur une base de données de 31 patients atteints d’un cancer bronchique non à petites cellules (CBNPC) que nous avons construite au préalable. Notre analyse a porté sur la détermination du biomarqueur Ki , représentant le débit net entrant de FDG. Nos résultats ne montrent pas de différence significative dans l’estimation de Ki entre notre approche et la méthode de référence, l’analyse graphique de Patlak [Patlak et al. 1983]. Nous avons également montré l’existence d’une forte corrélation (R2 ¸ 0,87) entre les images de Ki et de SUV. Cependant, ces images ne sont pas identiques, et peuvent apporter des informations supplémentaires, par exemple pour les régions nécrotiques. Enfin, nous avons étudié la variation relative de Ki (¢(K¤ i )) et de SUVmax (¢(SUVmax )) entre les examens pré- et per-thérapeutiques. Nous avons constaté une corrélation médiocre entre ¢(K¤ i ) et ¢(SUVmax ) (R2 = 0,60) sur l’ensemble de la plage de variation, mais une corrélation plus importante à partir des valeurs de ¢(SUVmax ) ¸ 40 %. Il conviendrait d’approfondir la signification et l’intérêt médical associé aux faibles variations de SUV et de Ki . Au final, l’approche ParaPET permet une détermination simplifiée des paramètres cinétiques de la fixation du FDG, qui enrichiront les caractéristiques tumorales pouvant présenter un intérêt pour la radiomique. / Positron Emission Tomography (PET) with 2-[18]-Fluoro-2-deoxy-D-glucose (FDG) is a functional imaging technique especially used in oncology to quantify glucose metabolism of tumour lesions. In clinical routine, quantitative analysis of these images is carried out using the standardized uptake value (SUV). More sophisticated quantification approaches have been proposed in the literature, but they requiremultiple blood samples and/or at least a 50 minutes PET acquisition. As a result, they are difficult to implement in clinical routine. Our work focused on the development of a non-invasive approach, named ParaPET, based on the initial work of [Barbolosi et al. 2016], allowing the determination of 3D maps of dynamic biomarkers and only requiring a PET scan of a limited duration. Our approach includes several improvements, including the development of a new model for the estimation of the FDG activity concentration and the associated measurement error, based on amultiple PET reconstruction protocol using temporal data resampling, the determination of the blood FDG activity concentration using PET aorta images, and the characterisation of tumour lesions at a voxel level. Our approach was evaluated on a database of 31 patients with non-small cell lung cancer (NSCLC) treated by chemo-radiation therapy, that we previously constructed. Our analysis focused on thedetermination of the biomarker Ki , the net influx of FDG in the lesion. Our results show no significant difference in the Ki estimate between our approach and the reference method, the Patlak graphical analysis [Patlak et al. 1983]. We also have shown the existence of a strong correlation between Ki and SUV images (R2 ¸ 0,87).However, these images are not identical, and may provide additional information, for example for necrotic regions. Finally, we studied the relative variation of Ki (¢(K¤ i )) and SUVmax (¢(SUVmax )) between pre- et per-therapeutic PET scans. We have found a poor correlation between ¢(K¤i ) et ¢(SUVmax ) (R2 = 0,60) over the entire range of variation, but a higher correlation from ¢(SUVmax ) values ¸ 40 %. The meaning and the medical interest associated with small variations of SUV and Ki should be further investigated. To conclude, our ParaPET approach allows a simplified determination of kinetic parameters of FDG uptake, which will enhance the tumour characteristics that may be of interest for radiomics.