1,721,064 research outputs found
"In vivo Very Low Frequency EPR Spectroscopy: Pharmacokinetics of Pyrrolidine Nitroxide Free Radicals on Whole Rat"
No full textPlatelet aggregation profiles in cluster headache: evidence of abnormal responses to ADP and PAF
No full textMagnetostatic Simulation and Design of Novel Radiofrequency Coils Based on Transverse Field Current Elements for Magnetic Resonance Applications
Full text linkRadiofrequency (RF) coils are key components in Magnetic Resonance (MR) systems and can be categorized into volume and surface coils according to their shapes. Volume RF coils can generate a uniform field in a large central sample’s region, while surface RF coils, usually smaller than volume coils, typically have a higher Signal-to-Noise Ratio (SNR) in a reduced Region Of Interest (ROI) close to the coil plane but a relatively poorer field homogeneity. Circular and square loops are the simplest and most used design for developing axial field surface RF coils. However, for specific MR applications, the use of dedicated transverse field RF coils can be necessary or advantageous. Building on a previously developed and validated RF coil simulator, based on the magnetostatic approach, here we explore the potential applications of novel multiple axial field and transverse field surface RF coils in non-standard configurations. We demonstrate via numerical simulations that simple volume RF coils, matching a Helmholtz-like design, can be built with two identical transverse field RF coils separated by a given distance. Following well-known principles, the SNR of such novel configurations can be improved by a factor of up to √2 by combining two 90° rotated coils, producing, inside a central ROI, a circularly polarized B1 field
Biot–Savart-Based Design and Workbench Validation at 100 MHz of Transverse Field Surface RF Coils
Full text linkRadiofrequency (RF) surface coils are extensively used as receivers in magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) systems thanks to their high signal-to-noise ratio (SNR). For specific magnetic resonance applications, the design of dedicated RF surface coils with a transverse (to the coil’s plane) RF magnetic field pattern can be necessary. Such transverse-field RF coils are constituted by several central linear (parallel or crossing) conductor elements connected by return current paths. Typically, the outer shape of such RF coils is circular or squared, although other geometries can be used. This paper describes the implementation and validation of a transverse-field RF surface coil simulator based on magnetostatic analysis, which permits the design and optimization of square butterfly and figure-of-eight RF coils with adjustable size and mutual distance between the central linear current elements. The simulation results, compared with the ones provided by a standard square loop RF coil, were validated with 100 MHz workbench measurements performed on three home-built prototypes. Finally, two novel quadrature RF coil structures designed by overlapping two orthogonal square butterfly and figure-of-eight RF coils were simulated and theoretically characterized. The RF coils described here should be suitable for a wide range of MRI/MRS preclinical/clinical applications, mainly at fields below 3 T
Your Attack Is Too DUMB: Formalizing Attacker Scenarios for Adversarial Transferability
Full text linkEvasion attacks are a threat to machine learning models, where adversaries attempt to affect classifiers by injecting malicious samples. An alarming side-effect of evasion attacks is their ability to transfer among different models: this property is called transferability. Therefore, an attacker can produce adversarial samples on a custom model (surrogate) to conduct the attack on a victim’s organization later. Although literature widely discusses how adversaries can transfer their attacks, their experimental settings are limited and far from reality. For instance, many experiments consider both attacker and defender sharing the same dataset, balance level (i.e., how the ground truth is distributed), and model architecture. In this work, we propose the DUMB attacker model. This framework allows analyzing if evasion attacks fail to transfer when the training conditions of surrogate and victim models differ. DUMB considers the following conditions: Dataset soUrces, Model architecture, an..
Harnessing Surface Plasmons for Magnetic Resonance Imaging Applications
No full textHighly localized electromagnetic waves appearing in subwavelength structures, such as surface plasmons lying on a metal surface, are fundamental ingredients in nanophotonics since they offer novel routes for advanced subwavelength light control. Negative-magnetic-permeability metamaterials, already proposed for nuclear magnetic resonance imaging (MRI) applications, can also support magnetic-surface-plasmon excitations. Here we propose to exploit this phenomenon to increase MRI efficiency. We show that a negative-magnetic-permeability metamaterial slab, coupled to a standard radio-frequency surface coil, supports highly localized magnetic surface plasmons, allowing us to boost and to spatially manipulate the radio-frequency electromagnetic field. Our predictions indicate that the configuration considered holds great potential to enhance the MRI signal-to-noise ratio with respect to standard setups
Magnetic Localized Surface Plasmons For Magnetic Resonance Imaging Applications
No full textRecently, a great deal of research efforts has been focused on subwavelength photonics devices for magnetic resonance imaging (MRI), one of the cornerstone diagnostic techniques in life science. We show that the excitations of magnetic localized surface plasmons (MLSPs), surface waves hosted by a subwavelength negative magnetic permeability sphere, can yield a strong enhancement of the MRI scanner performances. In addition, we demonstrate that MLSPs can be mimicked by substituting the negative permeability metamaterial (MM) sphere with a homogeneous high-permittivity one of the same radius. Our approach overcomes several limits of the standard MM approaches (generally, based on effective medium theories) avoiding complex 3D fabrication procedures and removing the local spatial MM inhomogeneities whose presence is detrimental in subwavelength photonics applications
Platelet serotonin pathway in menstrual migraine
No full textIn order to understand the possible 5-hydroxytryptamine (5HT) anomalies in migraine, particularly in the period before the headache attack, we compared the levels of 5HT, its stable metabolite 5-hydroxyindoleacetic acid (5HIAA) and platelet monoaminoxidase (MAO) activity in patients with menstrual migraine with those of healthy female controls. In every subject, blood samples were drawn during both follicular and late luteal phases of the menstrual cycle. In controls, platelet 5HT levels remained stable, whereas 5HIAA levels and MAO activity were higher in the luteal than in the follicular phase, suggesting an increased catabolism of 5HT which occurs physiologically just before menses. In menstrual migraine 5HIAA levels and MAO activity showed similar changes with higher values in the luteal than in the follicular phase. The luteal phase values were significantly higher than those of controls. Also, and in contrast to controls, 5HT levels decreased in the luteal phase. These data suggest that 5HT availability is reduced in menstrual migraine, possibly due to an increased catabolism and/or to a reduced synthesis, and hence predisposes patients to migraine attacks
Dual-Channel Transverse Fields Radiofrequency Coils for 1.5 T Magnetic Resonance Imaging
Full text linkThis theoretical study presents the design and analytical/numerical optimization of novel dual-channel transverse fields radiofrequency (RF) surface coils for 1.5 T Magnetic Resonance Imaging (MRI). The research explores a planar setup with two channels on a row with aligned spatial orientation of the RF coils, aiming to solve a common design drawback of single-channel transverse field RF coils: the reduced Field Of View (FOV) along the direction of the RF field. A significant challenge in this design is the efficient decoupling of two sets of transverse field RF coils to prevent mutual interference. Our modeling approach integrates thin wire theoretical modeling, magnetostatic computation for strip conductor coils, and their full-wave electromagnetic simulation. Key findings at 64 MHz demonstrate that strategic geometric placement among the two-channel RF coil and the introduction of geometrical asymmetry in the design of the individual RF coils does minimize the mutual inductance, paving the way for effective dual-channel MRI applications. This decoupling approach allows to enhance the FOV, providing a theoretical framework for the development of optimized dual-channel transverse field RF coil configurations. The current design was validated with full-wave numerical study at 64 MHz (1H, 1.5 T), has the potential to be extended at lower or higher frequencies, and the presence of lossy samples needs to be considered in the latter case
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