ES2344391B1 - DEVICE FOR IMPROVING THE SENSITIVITY OF THE RECEIVING COILS MEDICAL IMAGES BY MAGNETIC RESONANCE. - Google Patents
DEVICE FOR IMPROVING THE SENSITIVITY OF THE RECEIVING COILS MEDICAL IMAGES BY MAGNETIC RESONANCE. Download PDFInfo
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- 230000005291 magnetic effect Effects 0.000 title claims abstract description 21
- 230000035945 sensitivity Effects 0.000 title claims abstract description 14
- 238000002595 magnetic resonance imaging Methods 0.000 claims abstract description 12
- 239000003990 capacitor Substances 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 5
- 230000008878 coupling Effects 0.000 claims description 2
- 238000010168 coupling process Methods 0.000 claims description 2
- 238000005859 coupling reaction Methods 0.000 claims description 2
- 238000005259 measurement Methods 0.000 abstract description 8
- 230000006978 adaptation Effects 0.000 description 9
- 238000013461 design Methods 0.000 description 5
- 238000003384 imaging method Methods 0.000 description 5
- 230000035699 permeability Effects 0.000 description 5
- 230000005672 electromagnetic field Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 230000008685 targeting Effects 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 230000003187 abdominal effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
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- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000005293 ferrimagnetic effect Effects 0.000 description 1
- 239000002902 ferrimagnetic material Substances 0.000 description 1
- 238000002847 impedance measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 239000002887 superconductor Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 210000001835 viscera Anatomy 0.000 description 1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/341—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils
- G01R33/3415—Constructional details, e.g. resonators, specially adapted to MR comprising surface coils comprising arrays of sub-coils, i.e. phased-array coils with flexible receiver channels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
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Abstract
Dispositivo para mejorar la sensibilidad de las bobinas receptoras en imágenes médicas por resonancia magnética.Device to improve the sensitivity of Receiving coils in medical magnetic resonance imaging.
La presente invención tiene por objeto un dispositivo para mejorar la sensibilidad de las bobinas de superficie que se usan en la obtención de imágenes mediante resonancia magnética (RM) para aplicaciones médicas. Dicho dispositivo consta de un elemento focalizador del campo magnético, una bobina receptora y un circuito electrónico de adaptación al sistema de medida, con el que se consigue aumentar la capacidad de obtener imágenes profundas mediante dichas bobinas de superficie, o asimismo aumentar la calidad de las imágenes que se obtendrían habitualmente a partir de dichas bobinas, o asimismo disminuir el tiempo de adquisición de las mismas.The present invention aims at a device to improve the sensitivity of the coils of surface used to obtain images by magnetic resonance imaging (MRI) for medical applications. Saying device consists of a magnetic field focusing element, a receiver coil and an electronic circuit adapted to the measurement system, with which it is possible to increase the capacity of obtain deep images by means of said surface coils, or also increase the quality of the images that would be obtained usually from said coils, or also decrease the acquisition time of them.
Description
Dispositivo para mejorar la sensibilidad de las bobinas receptoras en imágenes médicas por resonancia magnética.Device to improve the sensitivity of Receiving coils in medical magnetic resonance imaging.
La presente invención tiene por objeto un dispositivo para mejorar la sensibilidad de las bobinas de superficie que se usan en la obtención de imágenes mediante resonancia magnética (RM) para aplicaciones médicas. Dicho dispositivo consta de un elemento focalizador del campo magnético, una bobina receptora y un circuito electrónico de adaptación al sistema de medida, con el que se consigue aumentar la capacidad de obtener imágenes profundas mediante dichas bobinas de superficie, o asimismo aumentar la calidad de las imágenes que se obtendrían habitualmente a partir de dichas bobinas, o asimismo disminuir el tiempo de adquisición de las mismas.The present invention aims at a device to improve the sensitivity of the coils of surface used to obtain images by magnetic resonance imaging (MRI) for medical applications. Saying device consists of a magnetic field focusing element, a receiver coil and an electronic circuit adapted to the measurement system, with which it is possible to increase the capacity of obtain deep images by means of said surface coils, or also increase the quality of the images that would be obtained usually from said coils, or also decrease the acquisition time of them.
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La obtención de imágenes médicas por RM es una técnica muy extendida en la actualidad. Se basa en la aplicación sucesiva de pulsos de radiofrecuencia sobre un tejido ya magnetizado por un campo magnético estático de gran intensidad. La aplicación de dichos campos permite, mediante un adecuado procesado de la señal, identificar la localización espacial de los espines nucleares y, de ese modo, obtener una imagen del objeto de estudio.Obtaining medical imaging by MRI is a Very widespread technique today. It is based on the application successive radiofrequency pulses on an already magnetized tissue by a static magnetic field of great intensity. The application of These fields allow, through proper signal processing, identify the spatial location of nuclear spins and, of That way, get a picture of the object of study.
Cuando se está interesado en obtener imágenes de una zona corporal específica del paciente, resulta útil recurrir a bobinas de superficie [M.R. Bendall, "Surface Coil Technology". in Magnetic Resonance Imaging, ed. by C.L. Partain, R.R. Price, J.A. Patton, M.V. Kulkarni, A.E. James, Saunders, Philadelphia, 1988] cuya capacidad para captar imágenes profundas depende típicamente de su tamaño: a mayor tamaño mayor sensibilidad. Ello es debido a que las líneas del campo magnético producido por la bobina de superficie tienden a dispersarse a medida que se alejan de la bobina, con lo que disminuye la sensibilidad de ésta, así como su capacidad de localización espacial.When you are interested in obtaining images of a specific body area of the patient, it is useful to use surface coils [MR Bendall, "Surface Coil Technology". in Magnetic Resonance Imaging , ed. by CL Partain, RR Price, JA Patton, MV Kulkarni, AE James, Saunders, Philadelphia, 1988] whose ability to capture deep images typically depends on their size: the larger the size, the greater the sensitivity. This is because the magnetic field lines produced by the surface coil tend to disperse as they move away from the coil, thereby decreasing the sensitivity of the coil, as well as its spatial location capacity.
Una forma de evitar la dispersión espacial de dichas líneas de campo es intercalar entre la bobina y el cuerpo del paciente un dispositivo capaz de focalizar dichas líneas de campo. En una reciente publicación [R. Marqués et al "Theory of three dimensional sub-diffraction imaging" Appl Phys. Lett., vol. 89, 21113 (2006)] se ha demostrado que es posible focalizar las líneas del campo electromagnético mediante dispositivos artificiales, obteniéndose un haz focalizado. De acuerdo con el Teorema de Reciprocidad de Lorentz, el incremento de la sensibilidad de una bobina de superficie a la que se le ha acoplado uno de estos dispositivos es igual a la capacidad de focalización de dicho dispositivo.One way to avoid spatial dispersion of said field lines is to insert a device capable of focusing said field lines between the coil and the patient's body. In a recent publication [R. Marqués et al "Theory of three dimensional sub-diffraction imaging" Appl Phys. Lett ., Vol. 89, 21113 (2006)] it has been shown that it is possible to focus the lines of the electromagnetic field by artificial devices, obtaining a focused beam. According to the Lorentz Reciprocity Theorem, the increase in the sensitivity of a surface coil to which one of these devices has been coupled is equal to the focusing capacity of said device.
Existen diversos dispositivos capaces teóricamente de producir esta focalización del campo magnético. En 2000, J. Pendry [J. Pendry "Negative refraction makes perfect lens", Phys. Rev. Lett., vol. 85, 3967-3970 (2000)] demostró que una lámina de espesor d de un hipotético medio con permitividad relativa \varepsilon_{r}=-1 y permeabilidad relativa \mu_{r}=-1 era capaz de focalizar el campo electromagnético de modo que cualquier distribución de campo se reproducía a una distancia 2d al otro lado de la lámina.There are several devices theoretically capable of producing this focusing of the magnetic field. In 2000, J. Pendry [J. Pendry "Negative refraction makes perfect lens", Phys. Rev. Lett., Vol. 85, 3967-3970 (2000)] showed that a sheet of thickness d of a hypothetical medium with relative permittivity ε r = −1 and relative permeability mu r = = 1 was able to focus the electromagnetic field of so that any field distribution was reproduced at a distance 2d on the other side of the sheet.
Un medio artificial con \varepsilon_{r} y \mu_{r} simultáneamente negativos (y, eventualmente, con \varepsilon_{r}=-1 y \mu_{r}=-1) fue patentado por D. Smith et al. [Int. App. Number: PCT/US01/08563] y publicado también en el año 2000 [D. Smith et al. "Composite Médium with Simultaneously Negative Permeability and Permittivity", Phys. Rev. Lett., vol. 84, 4184-4188 (2000)]. No obstante, las frecuencias normalmente usadas en la adquisición de imágenes médicas por RM posibilitan tratar independientemente el campo eléctrico y el campo magnético, de modo que para este propósito sólo sería necesaria una lámina con \mu_{r}=-1. Esta posibilidad fue demostrada usando láminas de ferrita, que poseen una zona de permeabilidad negativa cerca de la frecuencia de resonancia ferrimagnética, en [Marqués et al. "Near-field enhanced imaging by a magnetized ferrite slab", Appl. Phys. Lett. Vol. 86, 023505 (2005)]. No obstante, en RM no es posible usar materiales ferrimagnéticos, por lo que esta realización resulta del todo inapropiada para la aplicación deseada.An artificial medium with \ varepsilon_ {r} and \ mu_ {r} simultaneously negative (and, eventually, with \ varepsilon_ {r} = -1 and \ mu_ {r} = -1) was patented by D. Smith et al. [Int. App. Number: PCT / US01 / 08563] and also published in the year 2000 [D. Smith et al. "Composite Medium with Simultaneously Negative Permeability and Permittivity", Phys. Rev. Lett. , vol. 84, 4184-4188 (2000)]. However, the frequencies normally used in the acquisition of medical images by MRI make it possible to independently treat the electric field and the magnetic field, so that for this purpose only a sheet with \ mu_ {r} = - 1 would be necessary. This possibility was demonstrated using ferrite sheets, which have a negative permeability zone near the ferrimagnetic resonance frequency, in [Marqués et al. "Near-field enhanced imaging by a magnetized ferrite slab", Appl. Phys. Lett. Vol. 86, 023505 (2005)]. However, in RM it is not possible to use ferrimagnetic materials, so this embodiment is completely inappropriate for the desired application.
Recientemente, se ha reportado un dispositivo basado en un principio físico diferente, capaz también de producir la focalización del campo magnético bajo ciertas circunstancias [M. Freiré et al. "Planar magnetoinductive lens for three-dimensional subwavelength imaging", Apl. Phys. Lett., vol. 86, 182505 (2005)]. Dicho dispositivo, llamado "lente magnetoinductiva", tiene un comportamiento similar al de la mencionada lámina de \mu_{r}=-1, aunque su diseño sólo involucra dos láminas paralelas de resonadores magnéticos.Recently, a device based on a different physical principle has been reported, also capable of producing the magnetic field focusing under certain circumstances [M. Freiré et al . "Planar magnetoinductive lens for three-dimensional subwavelength imaging", Apl. Phys. Lett. , vol. 86, 182505 (2005)]. Said device, called "magnetoinductive lens", has a behavior similar to that of the aforementioned sheet of µm = {1}, although its design only involves two parallel sheets of magnetic resonators.
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En la Fig. 1 se representa un esquema del dispositivo. En éste aparece el dispositivo focalizador (1), la bobina receptora (2) y el circuito de adaptación (3).A schematic of the device. This shows the focusing device (1), the receiver coil (2) and the adaptation circuit (3).
En la Figura 2 se representa un esquema de la realización preferida del dispositivo focalizador, constituido por un arreglo tridimensional (en red cúbica simple) de resonadores con forma de espira circular (el elemento capacitivo se representa por un corte en la espira).A schematic of the preferred embodiment of the focusing device, consisting of a three-dimensional array (in simple cubic network) of resonators with circular spiral shape (the capacitive element is represented by a cut in the loop).
En la Figura 3, de modo meramente descriptivo y sin ánimo de ser exhaustivos, se representan algunos de los resonadores que podrían utilizarse para realizar el dispositivo focalizador de la Fig. 2. Se trata de una espira con un condensador conectado en serie (4), de un par de tiras metálicas en forma de anillo, cortadas y apiladas de modo conveniente (5) y de una modificación del diseño anterior en la que ambas tiras se conectan para formar una hélice (6), de manera que el acoplo capacitivo entre los anillos (4) y (5) proporcionan una capacidad distribuida que sustituye al condensador.In Figure 3, purely descriptive and without being exhaustive, some of the resonators that could be used to make the device focuser of Fig. 2. It is a turn with a condenser connected in series (4), of a pair of metal strips in the form of ring, cut and stacked conveniently (5) and one modification of the previous design in which both strips are connected to form a propeller (6), so that the capacitive coupling between the rings (4) and (5) provide a distributed capacity that It replaces the condenser.
En la Figura 4 se representa un esquema de la bobina receptora de la realización preferida, formada por una simple espira circular.A schematic of the receiver coil of the preferred embodiment, formed by a simple circular loop
En la Figura 5 y sin ánimo de ser exhaustivo se representa el esquema de un posible circuito de adaptación.In Figure 5 and with no intention of being exhaustive, It represents the scheme of a possible adaptation circuit.
Finalmente, en la figura 6 se representa una simulación electromagnética de la sensibilidad de una espira circular con y sin el elemento focalizador que, a efectos de la simulación, se supone un medio efectivo de permeabilidad relativa \mu_{r}=-1. La sensibilidad es directamente proporcional al valor del campo magnético creado por una corriente de módulo unidad sobre la espira. Así, el eje vertical de coordenadas en las figuras corresponde al cálculo del campo magnético axial normalizado producido por una bobina de 3 pulgadas de diámetro, con y sin el elemento localizador, cuando una corriente de módulo unidad fluye por la bobina. El eje horizontal corresponde a la distancia en centímetros medida a lo largo del diámetro de la bobina con el origen de coordenadas en el centro de la bobina. La bobina se halla situada a 4 centímetros de un plano de referencia que podría representar la piel del paciente en un experimento de resonancia magnética. En las figuras se muestra el valor del campo para distintas distancias en centímetros a este plano de referencia. Puede observarse como la presencia del elemento focalizador aumenta la intensidad del campo magnético y, por tanto, la sensibilidad de la espira, en el interior del cuerpo del paciente.Finally, in figure 6 a electromagnetic simulation of the sensitivity of a spiral circulate with and without the focusing element that, for the purpose of simulation, an effective means of relative permeability is assumed \ mu_ {r} = - 1. Sensitivity is directly proportional to value of the magnetic field created by a unit module current On the turn. Thus, the vertical axis of coordinates in the figures corresponds to the calculation of the normalized axial magnetic field produced by a coil of 3 inches in diameter, with and without the locator element, when a unit module current flows by the coil. The horizontal axis corresponds to the distance in centimeters measured along the diameter of the coil with the coordinate origin in the center of the coil. The coil is located 4 centimeters from a reference plane that could represent the patient's skin in a resonance experiment magnetic The figures show the value of the field for different distances in centimeters to this reference plane. It can be seen how the presence of the focusing element increases the intensity of the magnetic field and therefore the sensitivity of the spire, inside the patient's body.
La invención consta de:The invention consists of:
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- El dispositivo de focalizaciónHe targeting device
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- Una bobina receptora de superficie, cuyo objeto es recibir la señal de radiofrecuencia procedente de los espines nuclearesA surface receiving coil, whose purpose is to receive the signal from radiofrequency from nuclear spins
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- El circuito de adaptación entre la bobina y el aparato de medida.He adaptation circuit between the coil and the measure.
Todos esto elementos se disponen en orden directo a partir del cuerpo del paciente, de modo que la bobina sea el elemento mas externo, y se conecta a una máquina y a un sistema de medida de RM convencionales.All these elements are arranged in order. direct from the patient's body, so that the coil is the outermost element, and connects to a machine and a system of conventional MRI measurement.
Pasemos en primer lugar a considerar las diversas posibilidades para realizar el dispositivo de focalización. En primer lugar consideraremos la posibilidad de realizar un medio con \mu_{r}=-1 apropiado para la aplicación que se considera. Es importante señalar que es preciso obtener las propiedades magnéticas que se desean a partir de elementos no magnéticos que no interfieran con los fuertes campos magnéticos estáticos que se utilizan en RM. En principio cualquier colección de resonadores que proporcionen bucles cerrados corriente podrían ser útiles para nuestro propósito. Sin embargo, a las frecuencias de operación en RM para aplicaciones médicas, la longitud de onda electromagnética es de varios metros, mientras que las bobinas de superficie no pueden tener un tamaño superior a unas decenas de centímetros. Por tanto, el dispositivo que se pretende obtener ha de tener una escala de detalle no superior a algunos centímetros. Ello obliga a que el tamaño eléctrico de los elementos del medio artificial deba ser del orden de 1/100 o aún menor, lo que constituye una restricción bastante fuerte para el diseño de dichos elementos. Una buena solución es usar anillos metálicos con un condensador conectado en serie. Dichos elementos fueron ya propuestos por Shelkunoff and Friis en 1952 [S. A. Schelkunoff and T. H. Friis Antennas. Theory and practice, Wyley, New York, 1952] para obtener medios artificiales con una elevada respuesta magnética. En nuestro caso, la capacidad y la autoinducción del elemento deben sintonizarse de modo que la frecuencia de resonancia del mismo quede algo por debajo de la frecuencia de operación de la RM. De ese modo puede conseguirse, mediante un cuidadoso proceso de sintonía, que el medio artificial presente una permeabilidad efectiva \mu_{r}=-1 a la frecuencia de obtención de las imágenes de RM. El mismo tipo de elementos puede aplicarse al diseño de las "lentes magnetoinductivas" mencionadas mas arriba.Let us first of all consider the various possibilities to realize the targeting device. First we will consider the possibility of making a medium with \ mu_ {r} = - 1 appropriate for the application under consideration. It is important to note that it is necessary to obtain the desired magnetic properties from non-magnetic elements that do not interfere with the strong static magnetic fields that are used in MRI. In principle any collection of resonators that provide current closed loops could be useful for our purpose. However, at the operating frequencies in RM for medical applications, the electromagnetic wavelength is several meters, while the surface coils cannot be larger than a few tens of centimeters. Therefore, the device to be obtained must have a scale of detail not exceeding a few centimeters. This requires that the electrical size of the elements of the artificial environment must be of the order of 1/100 or even smaller, which constitutes a rather strong restriction for the design of said elements. A good solution is to use metal rings with a capacitor connected in series. These elements were already proposed by Shelkunoff and Friis in 1952 [SA Schelkunoff and TH Friis Antennas. Theory and practice , Wyley, New York, 1952] to obtain artificial means with a high magnetic response. In our case, the capacity and the self-induction of the element must be tuned so that the resonance frequency of the element is somewhat below the operating frequency of the MRI. In this way it can be achieved, through a careful tuning process, that the artificial medium has an effective permeability mu r = = 1 at the frequency of obtaining the MR images. The same type of elements can be applied to the design of the "magnetoinductive lenses" mentioned above.
El uso de condensadores se traduce inevitablemente en un cierto nivel de pérdidas. Para evitar esto cuando se requieran altas ratios señal - ruido, es posible recurrir a un resonador compuesto por dos anillos conductores o superconductores cortados y apilados, según el diseño propuesto por Black en 1994 [R. D. Black et al. "Electronics for a High Temperature Superconducting system for Magnetic Resonance Microimaging" IEEE Transactions on Biomedical Engineering. vol. 41, 195-197 (1994)]. U otra topología de parecidas prestaciones, capaz de ofrecer tamaños eléctricos en la resonancia tan pequeños como los referidos mas arriba.The use of capacitors inevitably results in a certain level of losses. To avoid this when high signal-to-noise ratios are required, it is possible to resort to a resonator consisting of two conductor rings or superconductors cut and stacked, according to the design proposed by Black in 1994 [RD Black et al . "Electronics for a High Temperature Superconducting system for Magnetic Resonance Microimaging" IEEE Transactions on Biomedical Engineering. vol. 41, 195-197 (1994)]. Or another topology of similar performance, capable of offering electric resonance sizes as small as those referred to above.
La bobina receptora es una simple espira, o colección de espiras, de bajas pérdidas (opcionalmente súper-conductoras) adaptada a la impedancia de entrada del sistema de medida, que puede ser un sistema de RM convencional. Para ello debe contar con un circuito de adaptación de impedancias, que lo adapte a la impedancia de entrada del sistema de medida, que normalmente será de 50 \Omega.The receiving coil is a simple turn, or collection of turns, low losses (optionally super-conductive) adapted to the impedance of measurement system input, which can be an RM system conventional. To do this you must have an adaptation circuit of impedances, which adapt it to the input impedance of the system measurement, which will normally be 50 \ Omega.
Finalmente debe mencionarse que el dispositivo focalizador puede combinarse con varias bobinas de recepción como la descrita en el marco de un sistema de adquisición de imágenes en paralelo (parallel imaging) [R. M. Heideman et al. "A brief Review of parallel magnetic resonance imaging" Eur. Radiology, vol. 13, 2323-2337 (2003)] resultando en un incremento en la resolución espacial y/o la sensibilidad de dichas bobinas.Finally, it should be mentioned that the focusing device can be combined with several receiving coils as described in the framework of a parallel imaging system [RM Heideman et al. "A brief Review of parallel magnetic resonance imaging" Eur. Radiology , vol. 13, 2323-2337 (2003)] resulting in an increase in spatial resolution and / or sensitivity of said coils.
La realización preferida sigue el esquema de la Figura 1. Los elementos del dispositivo focalizador son resonadores formados por anillos metálicos impresos, con un condensador conectado en serie (4). Dichos elementos se disponen de acuerdo con una red cúbica, tal y como se muestra en la Figura 2. Para la realización de las medidas el dispositivo focalizador se coloca directamente sobre el paciente, sobre la zona de su cuerpo que se quiere estudiar, aplicándose entonces una secuencia convencional de campos magnéticos de radiofrecuencia.The preferred embodiment follows the scheme of the Figure 1. The elements of the focusing device are resonators formed by printed metal rings, with a condenser connected in series (4). These elements are arranged in accordance with a cubic network, as shown in Figure 2. For the carrying out the measurements the focusing device is placed directly on the patient, on the area of his body that wants to study, then applying a conventional sequence of radio frequency magnetic fields.
La bobina de recepción, cuyo esquema se muestra en la Figura 4, se ha de colocar sobre el dispositivo focalizador y conectarse a la salida con el circuito de adaptación. El circuito de adaptación puede consistir en esencia en un condensador variable conectado en paralelo con la bobina para sintonizar ésta a una frecuencia de resonancia que coincida con la frecuencia de emisión de los espines nucleares y un condensador en serie para adaptar el circuito global a la impedancia característica del sistema de medida y garantizar así la máxima transferencia de potencia [R. R. Edelman et al, "Surface coil MR imaging of abdominal viscera", Mag. Res., vol. 157, 425, (1985)]. Si se desea poner la bobina muy próxima al dispositivo focalizador, es posible modificar este circuito simple de acuerdo con el circuito de la realización preferida (Fig. 5), en el cual la adecuada sintonía de los condensadores C_{1} y C_{2} permite seleccionar tanto la impedancia de la bobina vista desde el sistema de medida, como la impedancia vista desde la espira, de modo que se mejore la adaptación entre la espira, el dispositivo focalizador y el sistema de medida. Otros circuitos de adaptación pueden ser diseñados de acuerdo con este u otros propósitos. Finalmente, puede ser también deseable modular los elementos del dispositivo focalizador (y/o sintonizar externamente sus características) para mejorar la adaptación entre éste y el sistema de medida.The receiving coil, whose scheme is shown in Figure 4, must be placed on the focusing device and connected to the output with the adaptation circuit. The adaptation circuit can essentially consist of a variable capacitor connected in parallel with the coil to tune it to a resonance frequency that coincides with the emission frequency of the nuclear spins and a series capacitor to adapt the global circuit to the impedance measurement system characteristic and thus guarantee maximum power transfer [RR Edelman et al , "Surface coil MR imaging of abdominal viscera", Mag. Res., vol. 157, 425, (1985)]. If it is desired to place the coil very close to the focusing device, it is possible to modify this simple circuit according to the circuit of the preferred embodiment (Fig. 5), in which the suitable tuning of the capacitors C 1 and C 2 } allows you to select both the impedance of the coil seen from the measurement system, and the impedance seen from the coil, so that the adaptation between the coil, the focusing device and the measuring system is improved. Other adaptation circuits can be designed according to this or other purposes. Finally, it may also be desirable to modulate the elements of the focusing device (and / or externally tune its characteristics) to improve the adaptation between it and the measurement system.
Claims (2)
- a)to)
- un elemento focalizador del campo magnético colocado directamente sobre el paciente que consta de una colección de resonadores, preferentemente formados por anillos metálicos impresos con un condensador conectado en serie, dispuestos de acuerdo con una red cúbica.a focusing element of the magnetic field placed directly on the patient that consists of a collection of resonators, preferably formed by metal rings printed with a capacitor connected in series, arranged in accordance with a network cubic
- b)b)
- una ó más bobinas receptoras de superficie colocadas sobre el elemento focalizador, preferentemente formadas por una simple espira circular ó colección de espiras de bajas pérdidas adaptadas a la impedancia del aparato de medida.one or more surface receiving coils placed on the element focalizer, preferably formed by a simple circular loop or collection of low loss turns adapted to impedance of the measuring device.
- c)C)
- un circuito de adaptación de impedancias entre la bobina y el aparato de medida.a impedance matching circuit between the coil and the device of measure.
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| PCT/ES2009/000183 WO2010018247A1 (en) | 2008-08-05 | 2009-04-02 | Device for improving the sensitivity of receiver coils in medical magnetic resonance imaging |
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