Academic literature on the topic 'RMN à champ cyclé'
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Journal articles on the topic "RMN à champ cyclé"
Canet, D. "Les gradients de champ radio-fréquence (gradients B1) en RMN." Journal de Chimie Physique 92 (1995): 1893–904. http://dx.doi.org/10.1051/jcp/1995921893.
Full textTshiamala, Kabula, Joël Vebrel, and Bernard Laude. "Utilisation de la spectroscopie RMN 1H à haut champ pour la détermination de la configuration et de la conformation des cycloadduits obtenus par action de diphenylnitrilimine sur divers dihydro-1,2 naphtalenes substitués en 1." Spectrochimica Acta Part A: Molecular Spectroscopy 41, no. 3 (1985): 499–503. http://dx.doi.org/10.1016/0584-8539(85)80158-6.
Full textDissertations / Theses on the topic "RMN à champ cyclé"
Ducroix, Alice. "Multi-scale dynamics of water inside boehmite : a NMR approach." Electronic Thesis or Diss., Sorbonne université, 2023. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2023SORUS575.pdf.
Full textFor several domains of chemistry, catalyst take up a significant place since they ensure a quicker reaction, a better selectivity and reduce the use of raw material. Industry has recently turned to heterogeneous catalyst whose recovery is easier. These catalysts consist of a porous support and active sites distributed on the surface through the support porosity. To fully optimized the support, recent studies have tackled the issue of accessibility of molecules to the reaction sites. This one includes the comprehension of solvent mobility and molecular traffic in the porous medium. The heterogeneous catalytic support par excellence is γ-alumina, obtained by a topotactic calcination of boehmite. Texture and porous properties are then mostly inherited from boehmite, especially from the organization of agglomerates and aggregates. This organization is mostly obtained during the kneading, (peptization) and the extrusion steps of the boehmite-to-alumina process. Transport and multi-scale dynamics inside boehmite will then be investigated during these two steps particularly how solvent molecules (here water) move inside this material and what mechanisms drive the dynamics . To study this dynamics, boehmite suspensions with different initial textures will be obtained through dialysis and osmotic stress and extrudates from the traditional industrial route. Transport around the interface of aggregates and pore walls (nanometric scale) will be studied by Field Cycling Nuclear Magnetic Resonance on a ns-µs time scale. Diffusion was followed at the surface of such objects and was found to be governed by a strong interaction with the surface and especially the surface curvature. A consequent residence time (≈ 8µs) of water molecules at the surface and a rather slow surface diffusion coefficient (< 3. 10-10 m2/s) was exhibited. At the micron scale, dynamics is investigated by Pulsed Field Gradient NMR on a millisecond to second time scale. Diffusion seems to be driven by the topological structure imposed by the complex organization of aggregates and agglomerates (connected pore, anisotropy, etc.)
Chanet, Nicolas. "Imagerie par résonance magnétique à champ cyclé in vivo." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS574/document.
Full textFast Field Cycling Magnetic Resonance Imaging (FFC-MRI) has the ability to separate two key processes that both depends on the main field intensity B0. On one hand, signal acquisition and localization and on the other hand NMR relaxation, basis of MRI contrast. The equipment thus combines a standard MR scanner with a secondary system to rapidly switch the magnetic field B0 as compared to relaxation times. FFC enables to measure the evolution of NMR relaxation as a function of magnetic field B0, namely the NMR dispersion (NMRD) profile. Combining it with MRI the NMRD profile can be localized in vivo, together with the usual characterization at fixed B0. The NMRD profile of water carries information on molecular mobility in the surrounding biological tissues, and is thus another source of contrast. The objective of this PhD project was to further develop and evaluate the potential of FFC-MRI between 1 T and 2 T in a cancer model. This work required original instrumental and methodological developments to integrate FFC in MRI. First a precise measurement of magnetic field time profile was developed, as well as the compensation of eddy currents and of irreproducible transients in the secondary system. Moreover acquisition sequences with better signal to noise efficiency and applicable for longitudinal as well as transverse relaxation were implemented. Finally a kidney tumor mouse model was explored with FFC MRI
Assemat, Gaëtan. "RMN haut champ et bas champ pour l'analyse de produits de santé." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30268/document.
Full textThe purpose of this research was to demonstrate the interest of Nuclear Magnetic Resonance (NMR) to deal with analytical issues in the field of health products. The studies focused on two main axes. The first one targeted adulterated dietary supplements and the studies were conducted with high-field NMR. Various mono and bidimensional experiments revealed the illegal presence in dietary supplements claimed as natural, of erectile drugs and/or their structural analogues. These active substances can induce, without the consumer's knowledge, significant risks to his health. Moreover, analyses conducted with 1H and 13C NMR, highlighted cases of adulteration of dietary supplements for exercise and athletic performance with doping substances. The second axis explored the potential of low-field NMR for drug analysis. This technique, which is less expensive and more suitable for routine analyses than high-field NMR, has proved very effective in detecting cases of falsified medicines by simple one-dimensional 1H NMR experiments. Two-dimensional diffusion experiments (DOSY: Diffusion Ordered Spectroscopy), which provide virtual separation of the constituents of a complex mixture, were developed and applied for the first time to the de-formulation of a drug
Le, Bec Gaël. "Détection et traitement de signaux RMN en champ inhomogène." Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00177759.
Full textSi le champ magnétique statique est inhomogène, l'excitation de l'échantillon et la réception du signal doivent être large bande. Plusieurs séquences d'excitation ont été étudiées, dans le cadre d'applications RMN portables. L'utilisation d'impulsions modulées en fréquence permet de minimiser la puissance instantanée émise par le système. Une modélisation des signaux d'échos de nutation permet d'évaluer l'effet des défauts de corrélation entre les champs statique et RF. A la réception, si la fréquence de résonance n'est pas stable (la polarisation des aimants varie avec la température), la représentation des signaux d'écho dans le plan temps-fréquence permet d'améliorer le rapport signal sur bruit.
Une solution permettant de générer deux champs magnétiques perpendiculaires et corrélés a été proposée. Cette solution, basée sur le théorème de rotation de l'aimantation, est valable pour des systèmes infiniment longs. L'influence des effets de bord et de plusieurs imperfections a été étudiée. Une sonde RMN portable a été construite ; cette sonde mesure 8x3x1.5 cm3. Des premiers signaux ont été obtenus avec cette sonde.
Enfin, un spectromètre RMN existant a été adapté à des application RMN portable. Des préamplificateurs ont été construits et un nouveau logiciel de commande, plus souple, a été développé. Ce spectromètre a permis d'obtenir des signaux RMN en champ magnétique inhomogène.
Maffei, Pablo Fabian. "Développements en microscopie RMN par gradients de champ radiofréquence." Nancy 1, 1993. http://www.theses.fr/1993NAN10017.
Full textDang, Phuc Hung. "Développement d’aimant bas champ pour RMN Portable : Conception et construction." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0007/document.
Full textThis thesis focuses on the development of a magnet system for NMR applications with high homogeneity while maintaining the static magnetic field B0 as high as possible (100 ppm, 0.12T). Due to the application goals, the magnet dimensions are predefined as well as those of the region of interest according to the size of the used permanent magnets. Such system is dedicated to biomedical and agroalimentary applications. The goal of this research has been firstly, the discussion of parameters of magnetic materials which are essential to the construction of portable NMR magnets, and then the choice of the permanent magnet material the “NdFeB” that was explained. A compromise between the portability, price and the sensitivity has led to the design of a prototype of portable NMR magnet with a simple system of arrangement of 24 permanent magnets. The magnetic field and the homogeneity of the system were calculated and simulated by using ANSYS software and these results were correlated to those obtained by the Radia software. A new shim method has been used to increase the homogeneity and correct the field B0 imperfection. Based on these results, a prototype was realized. The results of the magnetic field strength and homogeneity obtained by measurements are in good correlation with the results obtained by simulation. Sufficient accuracy was reached to take into account and correct errors due to manufacturing tolerances of the magnets. Another magnet system based on Mandhalas configuration (Magnet Arrangement for Novel Discrete Halbach Layout) was studied. The comparison between two configurations made from circle and square magnets was performed by 2D simulation (using three criteria: mass, homogeneity and the magnetic field strength). The Mandhalas made from circle magnets give better results (0.32 T, 178 ppm). The 3D simulation was carried out to evaluate the total system. From these results, a passive shim system was also used in this case and the homogeneity significantly increases
Halidi, El Mohamed. "Études RMN et IRM en champ proche : développements et applications." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20261/document.
Full textThe principle of NMR is based on the detection of the magnetization originating from the spin of atomic nuclei such as 13C, 31P and 1H. The sample is placed in a static magnetic field, which polarizes the ensemble of spins and it is excited by radiofrequency pulses (wavelength about one meter), that tilt the axis of the magnetization. When the magnetization returns to equilibrium, it generates an electromagnetic field which is classically detected by a receiving antenna (coil with atuning/matching circuit) in inductive coupling.In this work, we propose the use of a micrometer-sized probe positioned in the vicinity of the object of interest, at a distance well shorter than the wavelength of the radiated NMR signal.Our microprobe presents innovative characteristics (i) a capacitive coupling (electric field component), (ii) reduced dimensions for an accurate positioning, which ensure the detection of NMR signal from the sample and (iii) it has a broadband, which allows use to detect any nuclei without being tuned to the Larmor frequency.To introduce you this new alternative, the tools necessary to the understanding of this work, in this case the principle of NMR/MRI and an introduction of the theory of the electric near field are given initially.We made also a state of the art of existing methods and techniques for measuring the NMR signal to identify the benefits that such a system (method : capacitive coupling and device : microprobe near field) can bring to the NMR technique.Then, we have characterized our microprobe to enhance its localized detection due to its small size (127 μm in diameter and 2mm in length). In this stage of characterization, we demonstrated that the NMR signal recovered by our antenna can be described by the electric near field expression :E(x, z) = A(Kz ) exp(i(z/L)) exp(−x/L) +Propagative TermFinally, we applied our system to make NMR studies such as spectroscopy, the relaxometry and NMR Imaging. We have outlined some potential projects to the continuity of this work
Stout, Jacques. "Spectroscopie et Imagerie RMN multi-noyaux à très haut champ magnétique." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS312/document.
Full textBipolar disorder is a chronic affective disorder affecting 1 to 3% of the adult population worldwide and has a high level of comorbidity with suicide rates, substance abuse and other harmful conditions. The disorder has possible ties to schizophrenia and has been observed to have a strong genetic component. The exact biological underpinnings have not been firmly established, however abnormalities in limbic subcortical and prefrontal areas have been observed.Ever since its discovery more than half a century ago, a daily intake of Lithium salts has arguably become the most reliable treatment of the disorder, despite us possessing little to no understanding of its biochemical action. In order to shed some light on the effect of Lithium in the brain, we have developed Lithium-7 MR imaging at 7 and 17 Tesla in order to assess its cerebral concentration and distribution. Specifically, I worked on developing and validating several acquisition, reconstruction and quantification methods dedicated to 7Li MRI and MRS. Those methods were first applied to study ex vivo the cerebral distribution of lithium in rats. These rats were pretreated for 28 days with Li2CO3, sacrificed and their head fixated with PFA. Using a home-made 1H/7Li radiofrequency surface coil and a 7Li Turbo Spin echo acquisition and a modified phantom replacement method for quantification, we were able to measure Li concentration maps. Regional Li concentration values were then compared with those obtained with mass spectrometry.After this preclinical proof-of-concept study, an in vivo 7Li MRI protocol was designed to map the cerebral Li concentration in euthymic bipolar subjects at 7T. These individuals all followed a regular lithium treatment. For this study, we chose to use an ultra-short echo-time Steady State Free Precession sequence with non-Cartesian k-space sampling. A quantification and analysis pipeline similar to the one used for our preclinical study was applied for this study, with the addition of a correction step for B0 inhomogeneities. After conducting a statistical analysis at the cohort level, it was assessed that the left hippocampus, a major part of the limbic system that has been associated with BD on multiple occasions, exhibited systematically a high level of lithium. Finally, I developed a quantification method accounting for the different relaxation times of 7Li in the CSF and in the brain parenchyma. This method was applied to image lithium at 7T in a subset of bipolar patients reducing drastically the differences initially observed between the SSFP and bSSFP sequences
Dillmann, Baudouin. "Analyse du champ électromagnétique dans les bobines des sondes de HR-MAS utilisées pour la RMN à haut-champ." Phd thesis, Université Louis Pasteur - Strasbourg I, 2007. http://tel.archives-ouvertes.fr/tel-00207457.
Full textNguyen, Valérie. "Système de création de champ magnétique homogène à aimants ferrites pour l’imagerie RMN." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0120.
Full textBook chapters on the topic "RMN à champ cyclé"
"6. Cyclage de phase versus gradients de champ pulsés." In RMN : la boîte à outils, 57–66. EDP Sciences, 2020. http://dx.doi.org/10.1051/978-2-7598-2425-0-009.
Full text"6. Cyclage de phase versus gradients de champ pulsés." In RMN : la boîte à outils, 57–66. EDP Sciences, 2020. http://dx.doi.org/10.1051/978-2-7598-2425-0.c009.
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