Добірка наукової літератури з теми "Short te spectroscopy"

Arterial Spin Labeling (ASL) is a noninvasive MRI-based method to measure cerebral blood flow (CBF). Recently, the study of ASL as a functional tool has emerged once CBF fluctuation comes from capillaries in brain tissue, giving a more spatially specific response when compared to the standard functional MRI method, based on the blood oxygenation level-dependent (BOLD) contrast. Although the BOLD effect could be desirable to study brain function, if one aims to quantify CBF, such effect is considered contamination that can be more attenuated if short TE value is used in the image acquisition. An approach that provides both CBF and function information in a simultaneous acquisition is the use of a dual-echo ASL (DE-ASL) readout. Our purpose was to evaluate the information provided by DE-ASL regarding CBF quantification and functional connectivity with a motor task. Pseudocontinuous ASL of twenty healthy subjects (age: 32.4 ± 10.2 years, 13 male) was acquired at a 3T scanner. We analyzed the influence of TE on CBF values and brain connectivity provided by CBF and concurrent BOLD (cc-BOLD) time series. Brain networks were obtained by the general linear model and independent component analysis. Connectivity matrices were generated using a bivariate correlation (Fisher Z values). No effect of the sequence readout, but significant effect of the TE value, was observed on gray matter CBF values. Motor networks with reduced extension and more connections with important regions for brain integration were observed for CBF data acquired with short TE, proving its higher spatial specificity. Therefore, it was possible to use a dual-echo readout provided by a standard commercial ASL pulse sequence to obtain reliable quantitative CBF values and functional information simultaneously.

Thermoelectric (TE) devices have short service lives. These materials undergo thermal degradation at elevated temperatures by processes such as oxidation or sublimation. Our substrates were skutterudite-based TE materials. We covered their surfaces with a liquid high-temperature polymer (HTP)—crosslinked after the deposition, what converted those surfaces into solid coatings. Sintering was performed at 250 °C for times of up to 48 h on both uncoated (control) and HTP-coated samples. The changes caused by thermal degradation were evaluated by thermogravimetric analysis, electrical resistivity, and energy-dispersive X-ray spectroscopy, and observed by scanning electron microscopy. Significant mitigation of oxidation and sublimation of our TE materials was achieved.

In this article, we put forward a simple method for the synthesis of thermoelectric (TE) composite materials. Both n- and p-type composites were obtained by ball-milling the insoluble and infusible metal coordination polymers with other polymer solutions. The particle size, film morphology and composition were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The TE properties of the drop-cast composite film were measured at different temperatures. An inkjet-printed flexible device was fabricated and the output voltage and short-circuit current at various hot-side temperatures ( T hot ) and temperature gradients (Δ T ) were tested. The composite material not only highly maintained the TE properties of the pristine material but also greatly improved its processability. This method can be extended to other insoluble and infusible TE materials for solution-processed flexible TE devices.

L’imagerie spectroscopique (IS) par résonance magnétique nucléaire du cerveau permet d’identifier les biomarqueurs du métabolisme cérébral sain ou pathologique. À court TE, les métabolites ayant des couplages J forts et des temps de relaxation T2 courts peuvent être détectées. Le rapport signal sur bruit et la résolution spectrale croît avec l’intensité du champ B0. Cependant, l’hétérogénéité des champs B0 et B1 ainsi que les erreurs associées au déplacement chimique augmentent avec B0. De bons profils de sélection sont obtenus avec le module de sélection du volume d’intérêt de type semi-LASER comparés à ceux obtenus avec des impulsions conventionnelles. De plus, cette séquence est moins sensible aux hétérogénéités du champ B1 et les erreurs liées au déplacement chimique sont moins importantes. La limitation la plus contraignante de la technique d’imagerie spectroscopique conventionnelle est probablement sa longue durée d’acquisition qui dépend de la résolution spatiale. L’imagerie spectroscopique spatiale (ISS) en encodant simultanément l’information spatiale et spectrale réduit considérablement le temps d’acquisition minimum. Il devient ainsi possible d’acquérir des données supplémentaires telles qu’une dimension spatiale et/ou une deuxième dimension spectrale. Nous avons mis en place une technique d’imagerie spectroscopique spirale pour l’étude du cerveau humain. Le TE est de 17 ms dans le cas de sélection du volume d’intérêt avec le module PRESS utilisant des impulsions RF conventionnelles et de 32 ms dans le cas de semi-LASER. Ces modules de sélection ont été combinés avec des modules de saturation des signaux de l’eau et du volume externe adaptés. Nous avons développé les programmes de calcul de la trajectoire mesurée et de la reconstruction des données à deux dimensions spatiales et une dimension spectrale. Nous avons obtenu une bonne saturation des lipides extra crâniens. Nous avons obtenu de meilleurs profils et une nette réduction des erreurs associées au déplacement chimique avec le module semi-LASER comparé avec ceux obtenus avec le module PRESS. L’application de la trajectoire mesurée à la reconstruction des données réduit les artefacts associés aux imperfections du système de gradients. Sur les spectres acquis à un TE de 17 ms (PRESS) et de 32 ms (semi-LASER) nous avons quantifié significativement le NAA, la choline, la créatine et le myo-inositol. Nous avons démontré la faisabilité de l’acquisition de données d’imagerie spectroscopique spirale volumétrique à TE court chez l’homme à 3T en une durée compatible avec celle des examens cliniques. D’autres travaux doivent être réalisés afin d’optimiser la séquence semi-LASER pour la détection de métabolites fortement couplés, comme le glutamate et la glutamine
Proton magnetic resonance chemical shift imaging (CSI) at short time (TE) in vivo allows characterization of the spatial distribution of strongly J-coupled and short T2 biomarkers relevant to healthy or pathologic metabolism. We have developed a volumetric CSI technique for human brain studies at 3 Tesla in an experiment time compatible with patient examination. Pulse sequence modules for selection of the volume of interest (PRESS and semi-LASER), and for suppression of water and outer volume signals were implemented and optimized. The use of spiral K-space trajectories allowed acquisition speed-up by simultaneous encoding of spatial and spectral dimensions. Techniques of calibration and optimisation of the effective trajectory were developed, as well as an algorithm for reconstruction of 2 or 3 D spatial – 1 D spectral data sets. The method was validated in vivo on human brain with TEs of 17 ms (PRESS) or 32 ms (semi-LASER), on healthy subjects. Good saturation of subcutaneous lipids was obtained. Semi-LASER, by its use of adiabatic RF pulses, brought both sharper spatial selection profiles less sensitive to B1 inhomogeneity, and reduced chemical shift displacement errors. Using the measured trajectory for data reconstruction reduced artefacts associated with gradient hardware imperfections. NAA, Creatine, Choline, myo-Inositol and Glutamate/Glutamine were significantly quantified both with PRESS and semi-LASER. Clinical application of short TE volumetric spiral CSI at 3T can be considered