Earlier work on RF metasurfaces for preclinical MRI has targeted applications such as whole‐body imaging and dual‐frequency coils. In these studies, a nonresonant loop was used to induce currents into a metasurface that was operated as a passive inductively powered resonator. However, as we show in this study, the strategy of using a resonant metasurface reduces the impact of the loop on the global performance of the assembled coil. To mitigate this deficiency, we developed a new approach that relies on the combination of a commercial surface coil and a coupled‐wire structure operated away from its resonance. This strategy enables the extension of the sensitive volume of the surface coil while maintaining its local high sensitivity without any hardware modification. A wireless coil based on a two parallel coupled‐wire structure was designed and electromagnetic field simulations were carried out with different levels of matching and coupling between both components of the coil. For experimental characterization, a prototype was built and tested at two frequencies, 300 MHz for 1H and 282.6 MHz for 19F at 7 T. Phantom and in vivo MRI experiments were conducted in different configurations to study signal and noise figures of the structure. The results showed that the proposed strategy improves the overall sensitive volume while simultaneously maintaining a high signal‐to‐noise ratio (SNR). Metasurfaces based on coupled wires are therefore shown here as promising and versatile elements in the MRI RF chain, as they allow customized adjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adapted to different Larmor frequencies without loss of performance.
Magnetic resonance imaging (MRI), a non-invasive and safe imaging method, is largely used for the assessment of multiple organs including knee. Due to the complexity of the knee joint, better images quality are required. Over the last decades, a variety of coil solutions has been proposed to improve MR image quality. Interestingly, dielectric or metamaterial structures have been used as additional devices for their ability to tailor electromagnetic field at a given scale. However, the use of these devices is often limited by their complexity and bulkiness. The present study aimed at improving the B1 transmit field for knee imaging at 3T through the design and manufacturing of a convenient and comfortable passive metasurface. A cylindrical array of conductive stripes was used to redistribute by inductive coupling the radiofrequency field generated by the body coil of the MRI scanner. This design takes no more space than a thin sheet placed around the leg of the patient. We have shown in simulation and experimentally the accuracy of this solution. For a given flip angle during signal acquisition, the improved transmit field allowed a reduction of the necessary input power. In addition to that, the structure had a negligible influence on the electric field inside the tissue and so did not significantly increase the specific absorption rate (SAR).
Due to the reduction of wavelengths inside the human tissues at ultra-high field magnetic resonance imaging (MRI), head coils usually present B 1 + magnetic field inhomogeneities located at the temporal lobes of the brain. This problem has been effectively targeted by different approaches, with the downside that they can either decrease the B 1 + field in other important areas or be uncomfortable to the patient. Here, we present a new approach based on Hilbert fractal inspired dipoles. Our structures are able to improve simultaneously the B 1 + field in each temporal lobe without diminishing the patients' comfort or the B 1 + field in other parts of the brain.
El establecimiento del Espacio Europeo de Educación Superior y el incremento de convenios de intercambio de estudiantes Erasmus ha conducido a un aumento en la oferta de asignaturas en inglés. Todo ello ha repercutido en un aumento en la participación de estudiantes extranjeros en programas de grado y postgrado. Existe además una creciente demanda por parte del alumnado general en el aprendizaje de nuevas materias en inglés con el objetivo de incrementar su empleabilidad internacional futura. La utilización de un segundo idioma requiere un diseño adecuado del material didáctico específico sin perjuicio del proceso realización-interpretación-aprendizaje. En este contexto, las TICs se han revelado como una nueva estrategia para minimizar las desventajas enumeradas anteriormente. El objetivo de este trabajo es el desarrollo de material docente bilingüe español-inglés con el objetivo de facilitar el estudio y guiar al alumno en el aprendizaje y autoevaluación de asignaturas de experimentación en Química. Con este fin, se emplearon las nuevas tecnologías tales como presentaciones en PowerPoint para desarrollar un cuaderno interactivo de laboratorio que se implementó en la plataforma Moodle. Un segundo objetivo consistió en la evaluación del material desarrollado por parte de estudiantes internacionales Erasmus de grados en Química y Biología.
Passive inductive metamaterials have been explored as alternative radio frequency (RF) coils for magnetic resonance imaging (MRI) with the aim to control and optimize the imaged volume and the sensitivity independently. Nevertheless, such structures result in a low signal-to-noise ratio (SNR) since the contribution of the loop in the global performance of the coil is reduced. Therefore, the purpose of this work is to explore a new strategy by combining off-resonance metamaterials with a resonant surface coil and observe the advantages that can be obtained. An elementary structure consisting of two parallel off-resonance wires coupled with a resonant surface coil was numerically analyzed. For experimental characterization, a prototype was built and tested in a 7 T MRI scanner for proton ( 1 H) and fluorine ( 19 F) using a phantom. In addition, other coil setups were tested for reference and comparison in terms of B1 + magnetic field homogeneity, signal and noise. The resultsshow that with this new strategy a conventional surface coil can be optimized in terms of sensitive volume while maintaining its high SNR. Metamaterials permit a customized adjustment of volume and sensitivity in addition to the simple adaptation to other nuclei, making them beneficial elements in the design of RF coils.
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