Probe efficiency improvement with remote and transmission line tuning and matching

In certain nuclear magnetic resonance (NMR) applications in which accessibility to the gantry is limited, performing optimal tuning and matching represents a major problem. Here, we discuss a method of tuning NMR probe circuits and matching their impedances which uses cables with different impedance values. This simple but efficien method may be advantageous compared with much more difficul perfect tuning and matching.Spanish Comision Interministerial de Ciencia y Tecnologıa (CICYT) for funding (BIO97– 0543).Publicad

MRI visualization of small structures using improved surface coils

In this paper we present the spatial resolution enhancement and noise reduction level achieved with an optimized inductively coupled surface coil specificall designed for our experiments. The technique of designing and implementing customized coils for magnetic resonance imaging of very small structures is described. We have designed a low cost prototype of an inductively coupled circular surface coil, tuned for 1H magnetic resonance imaging at 200 MHz. The coil is mounted on a customized teflo support. The inductive coupling used in this coil improves the signal-to-noise ratio by reducing various loss mechanisms (specially the dielectric losses). Test images have been acquired to determine the evolution of induced articular lesions in a rabbit animal model, as well as brain tumors in rats. The images show high spatial resolution, excellent B1 fiel homogeneity and no ‘‘hot spots’’. Comparing these images with those acquired with conventional coils, one find better spatial resolution and signal-to-noise ratio, as well as larger fiel of view with less intense illumination artifact. The methodology can be used in any application that requires high quality imaging of small structures.Publicad

Optimal design for MRI surface coils

Objetivo: Demostrar la posibilidad de diseñar y construir sondas de superficie o antenas específicas para la visualización de cada tejido en particular; haciendo uso de la técnica IRM, de modo que los resultados obtenidos sean muy superiores a los que se Consiguen mediante una sonda de superficie de propósito general. Material y métodos: El estudio ha sido realizado por el Grupo de Bioingeniería y Telemedicina de la Universidad Politécnica de Madrid y se ha llevado a cabo en el Instiluto Pluridisciplinar en la Universidad Complutense de Madrid, que cuenta con un equipo de resonancia BIOSPEC BMT-47/40 de Bruker: Se han diseñado sondas de superficie construidas a la medida de la región que se desea estudiar; optimizadas de modo que la homogeneidad del campo excitador de la muestra fuera lo más elevada posible, reduciendo además el artefacto de iluminación. Inicialmente se obtuvieron imágenes de un fantoma esférico de 50 mm de diámetro lleno de agua para luego adquirir imágenes de ratas y conejos de laboratorio. Resultados: Las imágenes adquiridas han permitido la comparación de los resultados obtenidos con la sonda comercial proporcionada por el fabricante del equipo y las sondas diseñadas; con estas últimas se consiguen imágenes de mayor calidad, pues además de poder visualizar tejidos más profundos en la muestra disminuye el artefacto de iluminación. Conclusiones: La construcción de sondas de superficie específicas para visualizar un determinado tejido o región anatómica permite mejorar la calidad de las imágenes. La extensión natural de este proyecto actualmente en curso consiste en traspasar estos resultados a equipos destinados a imagen para humanos.Objective: To demonstrate the possibilily of designing and comlmctillg specific slllfaee coils or antellllae for MRI viell'ing of each particular lisslle, producillg beller results Ihall those provided b), a general pll/pose su rface coi l. Material and methods: The slud)' lI'as pe/formed b), the Bioellgilleering alld Telemedicille Group of Madrid Pol)'teehllical Ulliversil)' and Ivas carried out al Ihe Pluridisciplillary IlIslitute of Ihe Ulliversidad Complutellse ill Madrid, usillg a BMT-47/40 BIOSPEC resonance ullit from Bruka SII/face coils Ivere custom-designed al/{I eOllstmctedforeach regioll to be studied, (md optimized to IllOke the specimell excitation field as homogelleous as jJossible, ill additioll lo reducing Ihe brightlless artijact. First, images lI'ere obtailled of a ro//Ild, lI'ater phalllommeasurillg 50 mm ill diamelel; afta lI'hich images of labomtOl)' rals al/{I rabbils lI'ere obtailled. Results: The images thus acqllired lI'ere campa red lI'ith the resulls obtailled Ivilh the coi! provided b), the manufactura of the eqllipment, alld ¡vere foulld to be of beller qualil)', alloll'illg the vielVing of deeper tissue fa the specimell as lI'ell as reducillg the brigllllless arl/facI. Conclusions: The cOllstructioll of sll/face coilsfor viell'illg specific tissues or anatomical regions improves image qualit)'. The lIexl Slep ill this ollgoing ¡J/vjeet lI'ill be the applicatioll of these cOllcepls to II/lits desiglIed for use ill IlIImalls.Publicad

High resolution in vivo imaging at high frequences with improved surface coils

Proceedings of: 18th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Amsterdam, 31 Oct. - 03 Nov. 1996.The enhancement of the spatial resolution with an optimised surface coil design for MR imaging of small structures at high frequencies is presented. Surface coils provide high signal-to-noise ratios (SNR) which allow to improve the spatial resolution. However, their sensitivity is limited to the region adjacent to the coil where the B1 field distribution is more homogeneous. The authors present an inductively coupled series-tuned circular coil prototype, optimised for 1H MR imaging at 200 MHz. The inductively coupled scheme provides a good SNR by reducing the different losses mechanisms. Preliminary images, acquired on a Bruker BIOSPEC-BMT 47/40 working at 4.7 T, have been realised over a rabbit knee. Images depict a high spatial resolution, an excellent B1 field homogeneity and no `hot spots'Publicad

An analysis of the Leap-Frog Discontinuous Galerkin method for Maxwell equations

In this paper, we explore the accuracy limits of a Finite-Element Time-Domain method applied to the Maxwell equations, based on a Discontinuous Galerkin scheme in space, and a Leap-Frog temporal integration. The dispersion and dissipation properties of the method are investigated, as well as the anisotropy of the errors. The results of this novel analysis are represented in a practical and comprehensible manner, useful for the application of the method, and for the understanding of the behavior of the errors in Discontinuous Gelerkin Time-Domain methods. A comparison with the Finite-Difference Time-Domain method, in terms of computational cost, is also includedThe work described in this paper and the research leading to these results has received funding from the European Community’s Seventh Framework Programme FP7/2007-2013, under grant agreement no 205294 (HIRF SE project), and from the Spanish National Projects TEC2010-20841-C04-04, CSD2008-00068, and the Junta de Andalucia Project P09-TIC-

Automatic tuning and matching of a small multifrequency saddle coil at 4.7 T

A new circuit design for automatically tuning and matching a saddle coil for small animal imaging is presented. This design allows working at 1H, 19F, and 3He resonance frequencies in a 4.7 T spectrometer. It is based on a balanced circuit with commercial variable capacity diodes controlled by a computer using digital potentiometers. The change between two different frequencies can be accurately performed in a few seconds. System Q is compared, between 140–210 MHz, to the same coil tuned and matched with high Q variable capacitors. Differences lower than 5% were found with a loaded coil. The proposed design has initially been evaluated in 19F and 1H NMR images acquired with a five-tube phantom. An application is also shown for the acquisition of 3He, 19F, and 1H lung images in a control ratPublicad

Multidimensional nos supervised analysis (textural and spacial) in MRI tomography for watercore detection

4 Pags., 2 figs.This work has been carried out in the frame of the European project InsideFood (Integrated sensing and imaging devices for designing, monitoring and controlling microstructure of foods). The aim of this project is to provide technological solutions for exploring the microstructure of foods, by the combination and application of different non-destructive techniques such as X-ray CT, OCT, MRI, NMR, TRS and SRS, aimed at online sensing of food microstructure, water status, texture and optical properties. Magnetic Resonance Imaging (MRI) has been used in order to detect watercore disorder in three different varieties of apples, which are non commercialized due to their watercore development problems. These three varieties are: Ascara2, Rebellón and Tempera, which were grown under favourable conditions for the development of such disorder. At first step, MRI has been used for screening the apples population in order to detect those ones which had watercore problems. Then, an image analysis has been done in all these apples, in order to check the evidences of such disorder. Several methods have been used: Texture analysis, Principal Components Analysis (PCA) and Cluster AnalysisPeer reviewe

A Subcell Finite-Difference Time-Domain Implementation for Narrow Slots on Conductive Panels

Funded by the European Union under GA no 101101961-HECATE. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or Clean Aviation Joint Undertaking. Neither the European Union nor the granting authority can be held responsible for them. The project is supported by the Clean Aviation Joint Undertaking and its Members and, by Spanish Ministry of Science and Innovation (MICINN) under projects eSAFE-UAV PID2019-106120RB-C32; PID2019-106120RB-C33.Efficiently modeling thin features using the finite-difference time-domain (FDTD) method involves a considerable reduction in the spatial mesh size. However, in real-world scenarios, such reductions can lead to unaffordable memory and CPU requirements. In this manuscript, we present two stable and efficient techniques in FDTD to handle narrow apertures on conductive thin panels. One technique employs conformal methods, while the other utilizes subgridding methods. We validate their performance compared to the classical Gilbert-Holland model and present experimental results in reverberation environments to shed light on these models' actual confidence margins in real electromagnetic compatibility (EMC) scenarios.European Union (EU) 101101961HECATEClean Aviation Joint UndertakinSpanish Government eSAFE-UAV PID2019-106120RB-C32, PID2019-106120RB-C3

A New efficient and stable 3D Conformal FDTD

A novel conformal technique for the FDTD method, here referred to as Conformal Relaxed Dey-Mittra method, is proposed and assessed in this letter. This technique helps avoid local time-step restrictions caused by irregular cells, thereby im- proving the global stability criterion of the original Dey-Mittra method. The approach retains a second-order spatial convergence. A numerical experiment based on the NASA almond has been chosen to show the improvement in accuracy and computational performance of the proposed method.The work described in this letter and the research leading to these results has received support from the Projects TEC2013- 48414-C3-01 and TEC2015-68766-REDC (MINECO, Spain), P12-TIC-1442 (Junta de Andalucia, Spain), Alhambra-UGRFDTD (AIRBUS DS), and by the CSIRC alhambra.ugr.es supercomputing center

Electric characterization of a Bioinspired Gripper

This work focuses on a normally open bioinspired microgripper, which corresponds to the Microelectromechanical Systems (MEMS) field, as well as on its scaling and fabrication process in aluminum 6053 for performance testing. The design was inspired by the mandibles of ants. Its structure is composed of a flexible M-type amplifier and a Z-shaped chevron actuator. The design and simulation were performed using ANSYSTM. The aluminum resistivity and the equivalent resistance of the gripper were calculated, and experimental tests were carried out with an inductor (L), capacitor (C) and resistor (R) electrical property meter, LCR. Experimental characterization of the gripper was carried out, applying a sweep of electric current from 5 up to 60 A to the actuator. The temperature values were registered using a thermographic camera; the displacement was determined using a microscope. The average error between numerical and experimental results of the actuator shaft temperature is lower than 13%