WO2009040208A1 - Arrangement for detecting mrt signals with a preamplifier in a shielded region - Google Patents

Arrangement for detecting mrt signals with a preamplifier in a shielded region Download PDF

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Publication number
WO2009040208A1
WO2009040208A1 PCT/EP2008/061283 EP2008061283W WO2009040208A1 WO 2009040208 A1 WO2009040208 A1 WO 2009040208A1 EP 2008061283 W EP2008061283 W EP 2008061283W WO 2009040208 A1 WO2009040208 A1 WO 2009040208A1
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Prior art keywords
receiving coil
arrangement according
preamplifier
signals
mrt
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PCT/EP2008/061283
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German (de)
French (fr)
Inventor
Ralph Oppelt
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Siemens Aktiengesellschaft
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Publication of WO2009040208A1 publication Critical patent/WO2009040208A1/en

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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
    • 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
    • G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
    • 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
    • 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
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3621—NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation
    • 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
    • G01R33/42—Screening
    • G01R33/422—Screening of the radio frequency field

Definitions

  • MRI magnetic resonance imaging
  • the receiver coil is connected to a preamplifier that amplifies the received MRI signal for further processing.
  • the preamplifier is to be arranged as close as possible to the receiving coil, since the wired connection between coil and amplifier has a noticeable, finite attenuation, so that the inherently weak MRI signal is more or less attenuated depending on the line length.
  • the length of the cable connection therefore reduces the signal-to-noise ratio.
  • SNR Ratio
  • the preamplifier since the preamplifier has a finite metallic extension, it distorts the homogeneity or magnetic field of the receiving coil.
  • the homogeneity of the receiving coil describes the location-dependent sensitivity of the coil to MRT signals in the space enclosed by the coil, which optimally should be the same throughout the entire sensitivity range.
  • the consequence of distortions in the case of imaging are image artifacts in the form of light and dark zones in the image, ie lack of homogeneity. This effect is exacerbated when two or even several receiver coils overlap, since their intrinsic decoupling then deteriorates.
  • preamplifiers are either located remotely from the receiver coil, with the poor SNR taken into account, or the preamplifier is placed in close proximity to the coil, typically with line lengths of a few cm, bringing with it the homogeneity consequences described above.
  • the aim of the invention is therefore to provide an arrangement which allows detection of MRT signals with a high signal-to-noise ratio and the greatest possible homogeneity.
  • the arrangement according to the invention uses the so-called skin effect, according to which a high-frequency current such as that induced in the receiving coil in an MRT measurement always flows on the outside of a conductor and the interior of a closed metallic sheath remains field-free or current-free , This is also true for the most part when the sheath is used at some small areas, e.g. is broken for the passage of a cable.
  • the preamplifier according to the invention is positioned directly on the receiving coil under a metallic cover which is electrically connected to the outside of the conductor, the cover takes over the function of Leiterau- outside, so that the area under the cover remains field-free. Accordingly, neither the homogeneity of the receiver coil is disturbed, nor is the preamplifier influenced by external fields.
  • Preamplifier positioned on the receiver coil such that the input of the preamplifier is in the immediate vicinity of the point at which the induced MRT in the receiver coil Signal is tapped. This is usually done on a shortening capacitor. This ensures that the length of the cable connection is minimized and thus the SNR is maximized.
  • the preamplifier can also be housed within the waveguide with appropriate miniaturization, so that it is no longer visible to the external magnetic field. Also in this case, the preamplifier is placed in the immediate vicinity of the location where the MRI signal is tapped.
  • FIG. 1 shows a schematic plan view of a first exemplary embodiment of the invention with a preamplifier integrated in the receiving coil
  • Figure Ib is a schematic side view of the first embodiment
  • Figure 2 is a schematic side view of a second embodiment of the invention with a placed on the receiving coil preamplifier.
  • FIG. 1 a shows a first exemplary embodiment of the invention in plan view, in which a miniaturized preamplifier 10 is arranged within a receiving coil 20.
  • the receiving coil 20 has the form of an interrupted torus, for example realized by a copper tube, and consists of two halves 21, 22 which are connected to each other via shortening capacitors 30, 31.
  • the gap width between the halves 21, 22 is typically 1-5 mm, for example, adapted to the mechanical size of the shortening capacitors 30, 31.
  • the shortening capacitors 30, 31 cause the receiving coil 20 is tuned to resonance, although its circumference or halves are significantly shorter than the wavelength of the received MRI signals.
  • the receiver coil typically has a diameter of 10-30cm.
  • a toroidal receiving coil 20 has a round or elliptical cross-section with a diameter of approximately 10-15 mm, which is sufficient for receiving the preamplifier 10.
  • a rectangular cross section would also be conceivable.
  • a tubular construction of the receiving coil 20 with a round cross-section is HF technically preferable because of lower losses, while planar
  • the preamplifier 10 is placed in the receiving coil 20 in the immediate vicinity of the shortening capacitor 31 at one end of the receiving coil half 22.
  • the MRT signal present at the opposite ends of the receiving coil halves 21, 22 is tapped off via the capacitor 31 and is fed via the shortest possible leads 41, e.g. 5-20mm length given to the preamplifier 10.
  • the attenuation of the leads 41 leading from the coil 20 to the preamplifier 10 is minimized and thus the SNR is maximized.
  • the alternating currents induced in the receiving coil 20 essentially flow on the surface of the conductor, while the interior of the coil 20 or of the tous remains field and current-free. Due to the positioning of the preamplifier 10 within the receiving coil 20, it can therefore be ruled out that an interaction with the magnetic field of the coil 20 or a disturbance of the homogeneity of the receiving coil 20 takes place.
  • the preamplifier output signal is passed to the outside via a very thin coaxial line 40, which leaves the interior of the torus through an opening 50, for further signal processing.
  • the diameter of the coaxial line 40 is about 1 mm.
  • the line length plays a minor role on the output side of the preamplifier 10, since the line attenuation due to the pre-amplification is no longer significant.
  • the homogeneity of the receiving coil 20 is practically not disturbed by the line 40 because of the very small diameter.
  • the coaxial line 40 can also supply the power to the preamplifier 10 in a known manner.
  • any repercussions from the output line 40 to the receiving coil 20 can be reduced by a standing wave barrier integrated in the preamplifier 10.
  • FIG. 1 b schematically shows a side view of the first exemplary embodiment, from which it becomes clear that the preamplifier 10 is arranged in the field-free interior of the receiver coil 20 or of the copper tube mentioned above by way of example.
  • FIG. 2 shows a second embodiment of the arrangement according to the invention, in which the receiving coil 120 is designed as an annular, flat and double-sided copper-coated printed circuit board 160, wherein the printed circuit board 160 consists of dielectric material.
  • an epoxy resin bonded glass fiber fabric (FR4) is preferably used.
  • the preamplifier 110 represented in FIG. 2 by a plurality of individual components, is placed on the receiving coil 120 below a metallic cover 170.
  • the cover 170 is soldered all around to the receiving coil 120 or to its copper coating 180 (not shown), so that the induced alternating currents flowing on the surface of the receiving coil 120 due to the skin effect are forced onto the cover 170.
  • the printed circuit board 160 is also copper-coated on its front sides, at least in the region of the preamplifier 110, so that the receiving coil corresponds to a metallic tube with a rectangular cross-section filled with a dielectric.
  • the MRT signals of the receiving coil 120 are tapped off via a shortening capacitor 130 and transmitted by the MRT signals to the preamplifier 110 over the shortest possible lines 141.
  • the preamplifier 110 is therefore again placed as close as possible to the capacitor 130.
  • the lines 141 to the preamplifier input can be formed as a thin strip conductors or in the form of cable connections.
  • the capacitor 130 is arranged in the copper coating 180 of the printed circuit board via a gap 190, which, in analogy to the first exemplary embodiment, realizes the separation between two receiving coil halves.
  • the preamplifier output signal is passed out through a very thin coaxial line 140 through the opening 151 for further signal processing to the outside, similar to the first embodiment.
  • the shortening capacitors 130, 131 and / or the components of the preamplifier 110 are SMD components (surface mounted devices), while the receiver coil 120 is a planar, double-sided copper-clad GFRP circuit board 160, such as FIG It is used, for example, for the production of printed circuit boards.
  • the dielectric used for the printed circuit board 160 is FR4.
  • the receiving coil can also be equipped with more or less than two shortening capacitors. Basically, it would be sufficient to provide only a gap with only one shortening capacitor in the receiver coil. At higher frequencies, advantageously, three or more shortening capacitors can also be accommodated in the receiving coil for better reduction of unwanted electric fields.
  • a ring of three or more sections results which are advantageous, but not necessary, of the same size and which are connected via three or more shortening capacitors.
  • the preamplifier is positioned at which of the shortening capacitors the preamplifier is positioned.

Abstract

The invention relates to an arrangement for detecting and further processing MRT signals, in which the signal-to-noise ratio of the MRT signals which are forwarded to downstream amplifiers is optimized by arranging the preamplifier in the immediate vicinity of the signal tap. In addition, placing the preamplifier in a region which is shielded from external magnetic fields (Faraday cage) means that a disruption in the homogeneity of the receiving coil can be virtually precluded by the preamplifier.

Description

Beschreibungdescription
ANORDNUNG ZUR DETEKTION VON MRT-SIGNALEN MIT VORVERSTÄRKER IN EINEM ABGESCHIRMTEN BEREICHARRANGEMENT FOR DETECTING MRI SIGNALS WITH PREAMPLIFIER IN A SHIELDED AREA
Die Messgröße der Magnetresonanztomographie (MRT) ist die Magnetisierung eines zu untersuchenden Volumens in einem äußeren konstanten Magnetfeld. Durch spezielle elektromagnetische Anregungsimpulse wird eine Komponente der Magnetisierung erzeugt, die in einer Empfangsspule das in einem MRT-The measurement of magnetic resonance imaging (MRI) is the magnetization of a volume to be examined in an external constant magnetic field. By special electromagnetic excitation pulses, a component of the magnetization is generated, which in a receiving coil that in an MRI
Experiment zu messende Signal erzeugt. Die Empfangsspule ist mit einem Vorverstärker verbunden, der das empfangene MRT- Signal zur Weiterverarbeitung verstärkt.Experiment generated signal to be measured. The receiver coil is connected to a preamplifier that amplifies the received MRI signal for further processing.
Dabei ist der Vorverstärker möglichst nah bei der Empfangsspule anzuordnen, da die kabelgebundene Verbindung zwischen Spule und Verstärker eine merkliche, endliche Dämpfung aufweist, so dass das naturgemäß schwache MRT-Signal je nach Leitungslänge mehr oder weniger gedämpft wird. Mit der Länge der Kabelverbindung sinkt daher das Signal-zu-Rausch-In this case, the preamplifier is to be arranged as close as possible to the receiving coil, since the wired connection between coil and amplifier has a noticeable, finite attenuation, so that the inherently weak MRI signal is more or less attenuated depending on the line length. The length of the cable connection therefore reduces the signal-to-noise ratio.
Verhältnis (SNR) . Eine Anordnung des Vorverstärkers in unmittelbarer Nähe der Empfangsspule wäre demnach hinsichtlich des SNR optimal.Ratio (SNR). An arrangement of the preamplifier in the immediate vicinity of the receiving coil would therefore be optimal in terms of SNR.
Da der Vorverstärker jedoch eine endliche metallische Ausdehnung aufweist, verzerrt er die Homogenität bzw. das Magnetfeld der Empfangsspule. Hierbei beschreibt die Homogenität der Empfangsspule die ortsabhängige Empfindlichkeit der Spule auf MRT-Signale im von der Spule umschlossenen Raum, welche optimalerweise im gesamten Empfindlichkeitsbereich gleich sein sollte. Die Folge der Verzerrungen sind im Falle der Bildgebung Bildartefakte in Form von hellen und dunklen Zonen im Bild, d.h. mangelnde Homogenität. Dieser Effekt verschärft sich, wenn sich zwei oder auch mehrere Empfangsspulen überla- gern, da sich dann deren intrinsische Entkopplung verschlechtert. Bisher werden Vorverstärker entweder entfernt von der Empfangsspule angeordnet, wobei das schlechte SNR in Kauf genommen wird, oder der Vorverstärker wird in unmittelbarer Nähe der Spule untergebracht, typischerweise mit Leitungslängen von einigen wenigen cm, was die oben beschriebenen Folgen für die Homogenität mit sich bringt.However, since the preamplifier has a finite metallic extension, it distorts the homogeneity or magnetic field of the receiving coil. In this case, the homogeneity of the receiving coil describes the location-dependent sensitivity of the coil to MRT signals in the space enclosed by the coil, which optimally should be the same throughout the entire sensitivity range. The consequence of distortions in the case of imaging are image artifacts in the form of light and dark zones in the image, ie lack of homogeneity. This effect is exacerbated when two or even several receiver coils overlap, since their intrinsic decoupling then deteriorates. Heretofore, preamplifiers are either located remotely from the receiver coil, with the poor SNR taken into account, or the preamplifier is placed in close proximity to the coil, typically with line lengths of a few cm, bringing with it the homogeneity consequences described above.
Ziel der Erfindung ist es daher, eine Anordnung anzugeben, die eine Detektion von MRT-Signalen mit hohem Signal-zu- Rausch-Verhältnis und möglichst großer Homogenität ermöglicht.The aim of the invention is therefore to provide an arrangement which allows detection of MRT signals with a high signal-to-noise ratio and the greatest possible homogeneity.
Diese Aufgabe wird durch das im Hauptanspruch angegebene Verfahren gelöst. Vorteilhafte Ausgestaltungen ergeben sich aus den abhängigen Ansprüchen.This object is achieved by the method specified in the main claim. Advantageous embodiments emerge from the dependent claims.
Die erfindungsgemäße Anordnung nutzt den sog. Skin-Effekt, wonach ein hochfrequenter Strom wie derjenige, der bei einer MRT-Messung in der Empfangsspule induziert wird, immer auf der Außenseite eines Leiters fließt und das Innere einer geschlossenen metallischen Hülle feld- bzw. stromfrei bleibt. Dies gilt auch größtenteils dann, wenn die Hülle an einigen kleinflächigen Stellen z.B. zur Durchführung eines Kabels durchbrochen ist.The arrangement according to the invention uses the so-called skin effect, according to which a high-frequency current such as that induced in the receiving coil in an MRT measurement always flows on the outside of a conductor and the interior of a closed metallic sheath remains field-free or current-free , This is also true for the most part when the sheath is used at some small areas, e.g. is broken for the passage of a cable.
Wenn also der Vorverstärker erfindungsgemäß direkt auf der Empfangsspule unter einer metallischen Abdeckung positioniert wird, die elektrisch leitend mit der Leiteraußenseite verbunden ist, übernimmt die Abdeckung die Funktion der Leiterau- ßenseite, so dass der Bereich unter der Abdeckung feldfrei bleibt. Es wird demnach weder die Homogenität der Empfangsspule gestört noch wird der Vorverstärker durch äußere Felder beeinflusst .Thus, if the preamplifier according to the invention is positioned directly on the receiving coil under a metallic cover which is electrically connected to the outside of the conductor, the cover takes over the function of Leiterau- outside, so that the area under the cover remains field-free. Accordingly, neither the homogeneity of the receiver coil is disturbed, nor is the preamplifier influenced by external fields.
Vorteilhafterweise werden die metallische Abdeckung und derAdvantageously, the metallic cover and the
Vorverstärker derart auf der Empfangsspule positioniert, dass der Eingang des Vorverstärkers in unmittelbarer Nähe der Stelle liegt, an der das in der Empfangsspule induzierte MRT- Signal abgegriffen wird. Üblicherweise geschieht dies an einem Verkürzungskondensator. Hiermit ist gewährleistet, dass die Länge der Kabelverbindung minimiert und damit das SNR ma- ximiert wird.Preamplifier positioned on the receiver coil such that the input of the preamplifier is in the immediate vicinity of the point at which the induced MRT in the receiver coil Signal is tapped. This is usually done on a shortening capacitor. This ensures that the length of the cable connection is minimized and thus the SNR is maximized.
Für den Fall, dass die Empfangsspule als z.B. rohrförmiger Hohlleiter ausgebildet ist, kann der Vorverstärker bei entsprechender Miniaturisierung auch innerhalb des Hohlleiters untergebracht werden, so dass er für das äußere Magnetfeld nicht mehr sichtbar ist. Auch in diesen Fall wird der Vorverstärker in unmittelbarer Nähe der Stelle platziert, an der das MRT-Signal abgegriffen wird.In the event that the receiving coil is used as e.g. tubular waveguide is formed, the preamplifier can also be housed within the waveguide with appropriate miniaturization, so that it is no longer visible to the external magnetic field. Also in this case, the preamplifier is placed in the immediate vicinity of the location where the MRI signal is tapped.
Weitere Vorteile, Merkmale und Einzelheiten der Erfindung er- geben sich aus den im Folgenden beschriebenen Ausführungsbeispielen sowie anhand der Zeichnungen.Further advantages, features and details of the invention will become apparent from the embodiments described below and from the drawings.
Dabei zeigt:Showing:
Figur 1 schematische Draufsicht auf ein erstes Ausführungsbeispiel der Erfindung mit einem in die Empfangsspule integrierten Vorverstärker,FIG. 1 shows a schematic plan view of a first exemplary embodiment of the invention with a preamplifier integrated in the receiving coil,
Figur Ib eine schematische Seitenansicht des ersten Ausführungsbeispiels, Figur 2 eine schematische Seitenansicht eines zweiten Ausführungsbeispiels der Erfindung mit einem auf der Empfangsspule platzierten Vorverstärker.Figure Ib is a schematic side view of the first embodiment, Figure 2 is a schematic side view of a second embodiment of the invention with a placed on the receiving coil preamplifier.
Die Figur Ia zeigt ein erstes Ausführungsbeispiel der Erfin- düng in Draufsicht, bei dem ein miniaturisierter Vorverstärker 10 innerhalb einer Empfangsspule 20 angeordnet ist. Die Empfangsspule 20 hat die Form eines unterbrochenen Torus, beispielsweise realisiert durch ein Kupferrohr, und besteht aus zwei Hälften 21, 22, die über Verkürzungskondensatoren 30, 31 miteinander verbunden sind. Die Spaltbreite zwischen den Hälften 21, 22 beträgt typischerweise l-5mm, bspw. ange- passt an die mechanische Größe der Verkürzugskondensatoren 30, 31. Die Verkürzungskondensatoren 30, 31 bewirken, dass die Empfangsspule 20 auf Resonanz abgestimmt ist, obwohl ihr Umfang bzw. ihre Umfanghälften deutlich kürzer als die Wellenlänge der empfangenen MRT-Signale sind. Die Empfangsspule hat typischerweise einen Durchmesser von 10-30cm. Eine torus- förmige Empfangspule 20 hat einen runden bzw. ellipsenförmi- gen Querschnitt mit einem für die Aufnahme des Vorverstärkers 10 ausreichenden Durchmesser von etwa 10-15mm. Denkbar wäre auch ein rechteckiger Querschnitt. Eine rohrförmige Bauweise der Empfangsspule 20 mit rundem Querschnitt ist wegen gerin- gerer Verluste HF-technisch vorzuziehen, während planareFIG. 1 a shows a first exemplary embodiment of the invention in plan view, in which a miniaturized preamplifier 10 is arranged within a receiving coil 20. The receiving coil 20 has the form of an interrupted torus, for example realized by a copper tube, and consists of two halves 21, 22 which are connected to each other via shortening capacitors 30, 31. The gap width between the halves 21, 22 is typically 1-5 mm, for example, adapted to the mechanical size of the shortening capacitors 30, 31. The shortening capacitors 30, 31 cause the receiving coil 20 is tuned to resonance, although its circumference or halves are significantly shorter than the wavelength of the received MRI signals. The receiver coil typically has a diameter of 10-30cm. A toroidal receiving coil 20 has a round or elliptical cross-section with a diameter of approximately 10-15 mm, which is sufficient for receiving the preamplifier 10. A rectangular cross section would also be conceivable. A tubular construction of the receiving coil 20 with a round cross-section is HF technically preferable because of lower losses, while planar
Strukturen, d.h. Empfangsspulen mit rechteckigem Querschnitt, fertigungstechnisch vorteilhaft sind.Structures, i. Reception coils with rectangular cross-section, manufacturing technology are advantageous.
Der Vorverstärker 10 wird in der Empfangsspule 20 in unmit- telbarer Nähe des Verkürzungskondensators 31 an einem Ende der Empfangsspulenhälfte 22 platziert. Das an den sich gegenüberliegenden Enden der Empfangsspulenhälften 21, 22 anliegende MRT-Signal wird über dem Kondensator 31 abgegriffen und über möglichst kurze Leitungen 41 von z.B. 5-20mm Länge auf den Vorverstärker 10 gegeben. Somit ist garantiert, dass die Dämpfung der von der Spule 20 zum Vorverstärker 10 führenden Leitungen 41 minimiert und damit das SNR maximiert ist.The preamplifier 10 is placed in the receiving coil 20 in the immediate vicinity of the shortening capacitor 31 at one end of the receiving coil half 22. The MRT signal present at the opposite ends of the receiving coil halves 21, 22 is tapped off via the capacitor 31 and is fed via the shortest possible leads 41, e.g. 5-20mm length given to the preamplifier 10. Thus, it is guaranteed that the attenuation of the leads 41 leading from the coil 20 to the preamplifier 10 is minimized and thus the SNR is maximized.
Aufgrund des Skin-Effektes fließen die in der Empfangsspule 20 induzierten Wechselströme im Wesentlichen an der Oberfläche des Leiters, während das Innere der Spule 20 bzw. des To- rus feld- und stromfrei bleibt. Durch die Positionierung des Vorverstärkers 10 innerhalb der Empfangsspule 20 kann daher ausgeschlossen werden, dass eine Wechselwirkung mit dem Mag- netfeld der Spule 20 bzw. eine Störung der Homogenität der Empfangsspule 20 stattfindet.Due to the skin effect, the alternating currents induced in the receiving coil 20 essentially flow on the surface of the conductor, while the interior of the coil 20 or of the tous remains field and current-free. Due to the positioning of the preamplifier 10 within the receiving coil 20, it can therefore be ruled out that an interaction with the magnetic field of the coil 20 or a disturbance of the homogeneity of the receiving coil 20 takes place.
Das Vorverstärkerausgangsignal wird über eine sehr dünne Koaxialleitung 40, die das Innere des Torus durch eine Öffnung 50 verlässt, zur weiteren Signalverarbeitung nach außen geleitet. Typischerweise beträgt der Durchmesser der Koaxialleitung 40 etwa lmm. Die Leitungslänge spielt ausgangsseitig des Vorverstärkers 10 eine untergeordnete Rolle, da die Lei- tungsdämpfung wegen der Vorverstärkung nicht mehr wesentlich ins Gewicht fällt. Die Homogenität der Empfangsspule 20 wird durch die Leitung 40 wegen des sehr geringen Durchmessers praktisch nicht gestört. Über die Koaxialleitung 40 kann ne- ben der Übermittlung der vorverstärkten MRT-Signale an die nachgeordnete Elektronik auch die Energiezufuhr des Vorverstärkers 10 in bekannter Weise erfolgen. Außerdem können durch eine in dem Vorverstärker 10 integrierte Mantelwellensperre eventuelle Rückwirkungen von der Ausgangsleitung 40 auf die Empfangsspule 20 verringert werden.The preamplifier output signal is passed to the outside via a very thin coaxial line 40, which leaves the interior of the torus through an opening 50, for further signal processing. Typically, the diameter of the coaxial line 40 is about 1 mm. The line length plays a minor role on the output side of the preamplifier 10, since the line attenuation due to the pre-amplification is no longer significant. The homogeneity of the receiving coil 20 is practically not disturbed by the line 40 because of the very small diameter. In addition to the transmission of the preamplified MRT signals to the downstream electronics, the coaxial line 40 can also supply the power to the preamplifier 10 in a known manner. In addition, any repercussions from the output line 40 to the receiving coil 20 can be reduced by a standing wave barrier integrated in the preamplifier 10.
Die Figur Ib zeigt schematisch eine Seitenansicht des ersten Ausführungsbeispiels, aus der deutlich wird, dass der Vorverstärker 10 im feldfreien Inneren der Empfangsspule 20 bzw. des oben beispielhaft genannten Kupferrohres angeordnet ist.FIG. 1 b schematically shows a side view of the first exemplary embodiment, from which it becomes clear that the preamplifier 10 is arranged in the field-free interior of the receiver coil 20 or of the copper tube mentioned above by way of example.
Die Figur 2 zeigt eine zweite Ausführungsform der erfindungsgemäßen Anordnung, bei der die Empfangsspule 120 als ringförmige, flächige und doppelseitig kupferbeschichtete Leiter- platte 160 ausgestaltet ist, wobei die Leiterplatte 160 aus dielektrischem Material besteht. Hierbei kommt vorzugsweise ein mit Epoxydharz gebundenes Glasfasergewebe (FR4) zum Einsatz. Der Vorverstärker 110, in der Figur 2 dargestellt durch mehrere Einzelkomponenten, ist auf der Empfangsspule 120 un- terhalb einer metallischen Abdeckung 170 platziert. Die Abdeckung 170 ist rundum mit der Empfangsspule 120 bzw. mit deren Kupferbeschichtung 180 verlötet (nicht dargestellt) , so dass die wegen des Skin-Effektes an der Oberfläche der Empfangsspule 120 fließenden induzierten Wechselströme auf die Abde- ckung 170 gedrängt werden. Der Raum zwischen der AbdeckungFIG. 2 shows a second embodiment of the arrangement according to the invention, in which the receiving coil 120 is designed as an annular, flat and double-sided copper-coated printed circuit board 160, wherein the printed circuit board 160 consists of dielectric material. In this case, an epoxy resin bonded glass fiber fabric (FR4) is preferably used. The preamplifier 110, represented in FIG. 2 by a plurality of individual components, is placed on the receiving coil 120 below a metallic cover 170. The cover 170 is soldered all around to the receiving coil 120 or to its copper coating 180 (not shown), so that the induced alternating currents flowing on the surface of the receiving coil 120 due to the skin effect are forced onto the cover 170. The space between the cover
170 und der Oberfläche der Empfangsspule 120, in dem der Vorverstärker 110 untergebracht ist, bleibt demnach nahezu feld- und stromfrei. Umgekehrt stört der Vorverstärker 110 die Homogenität der Empfangsspule 120 nicht. Die Leiterplatte 160 ist zumindest im Bereich des Vorverstärkers 110 auch an ihren Stirnseiten kupferbeschichtet, so dass die Empfangsspule einem mit einem Dielektrikum ausgefüllten metallischen Rohr mit rechteckigem Querschnitt entspricht. Für die Verbindung des Vorverstärkers 110 nach außen sind in der Verlötung zwischen Abdeckung 170 und der Oberfläche der Empfangsspule 120 minimale Öffnungen 150, 151 zur Durchfüh- rung der Eingangs- 141 und Ausgangsleitungen 140 des Vorverstärkers 110 vorhanden. Solange die Öffnungen 150, 151 hinreichend klein bleiben, kann davon ausgegangen werden, dass sie den Skin-Effekt nicht merklich beeinflussen.170 and the surface of the receiving coil 120, in which the preamplifier 110 is housed, thus remains almost field and current-free. Conversely, the preamplifier 110 does not disturb the homogeneity of the receiving coil 120. The printed circuit board 160 is also copper-coated on its front sides, at least in the region of the preamplifier 110, so that the receiving coil corresponds to a metallic tube with a rectangular cross-section filled with a dielectric. For the connection of the preamplifier 110 to the outside in the soldering between the cover 170 and the surface of the receiving coil 120 minimum openings 150, 151 for passing through the input 141 and output lines 140 of the preamplifier 110 is present. As long as the openings 150, 151 remain sufficiently small, it can be assumed that they do not significantly affect the skin effect.
Wie im ersten Ausführungsbeispiel werden die MRT-Signale der Empfangsspule 120 über einem Verkürzungskondensator 130 abgegriffen und von diesem über möglichst kurze Leitungen 141 an den Vorverstärker 110 übertragen. Der Vorverstärker 110 ist daher wieder so dicht wie möglich am Kondensator 130 plat- ziert. Dadurch wird auch im zweiten Ausführungsbeispiel sichergestellt, dass die Leitungsverluste aufgrund der Dämpfung minimal bleiben. Die Leitungen 141 zum Vorverstärkereingang können als dünne Leiterbahnen oder aber in Form von Kabelverbindungen ausgebildet sein. Der Kondensator 130 ist über ei- nem Spalt 190, der in Analogie zum ersten Ausführungsbeispiel die Trennung zwischen zwei Empfangsspulenhälften realisiert, in der Kupferbeschichtung 180 der Leiterplatte angeordnet.As in the first exemplary embodiment, the MRT signals of the receiving coil 120 are tapped off via a shortening capacitor 130 and transmitted by the MRT signals to the preamplifier 110 over the shortest possible lines 141. The preamplifier 110 is therefore again placed as close as possible to the capacitor 130. As a result, it is also ensured in the second embodiment that the line losses due to the damping remain minimal. The lines 141 to the preamplifier input can be formed as a thin strip conductors or in the form of cable connections. The capacitor 130 is arranged in the copper coating 180 of the printed circuit board via a gap 190, which, in analogy to the first exemplary embodiment, realizes the separation between two receiving coil halves.
Das Vorverstärkerausgangsignal wird ähnlich wie im ersten Ausführungsbeispiel über eine sehr dünne Koaxialleitung 140 durch die Öffnung 151 zur weiteren Signalverarbeitung nach außen geleitet.The preamplifier output signal is passed out through a very thin coaxial line 140 through the opening 151 for further signal processing to the outside, similar to the first embodiment.
Speziell im zweiten Ausführungsbeispiel sind die Verkürzungs- kondensatoren 130, 131 und/oder die Bauteile des Vorverstärkers 110 SMD-Bauteile (surface mounted devices, oberflächen- montierbare Bauteile), während die Empfangsspule 120 eine flächige, doppelseitig kupferbeschichtete GFK-Leiterplatte 160 ist, wie sie bspw. für die Herstellung von Platinen ver- wendet wird. Insbesondere ist das für die Leiterplatte 160 verwendete Dielektrikum FR4. Weiterhin kann die Empfangsspule auch mit mehr oder weniger als zwei Verkürzungskondensatoren ausgestattet werden. Grundsätzlich würde es genügen, in der Empfangsspule nur einen Spalt mit nur einem Verkürzungskondensator vorzusehen. Bei höheren Frequenzen können zur besseren Reduktion von unerwünschten elektrischen Feldern vorteilhafterweise auch drei oder mehr Verkürzungskondensatoren in der Empfangsspule untergebracht werden. Dementsprechend ergibt sich ein Ring aus drei oder mehr Teilstücken, die vorteilhaft, aber nicht not- wendig, gleich groß sind und die über drei oder mehr Verkürzungskondensatoren verbunden sind. Aus Symmetriegründen spielt es hierbei keine Rolle, an welchem der Verkürzungskondensatoren der Vorverstärker positioniert wird. Specifically, in the second embodiment, the shortening capacitors 130, 131 and / or the components of the preamplifier 110 are SMD components (surface mounted devices), while the receiver coil 120 is a planar, double-sided copper-clad GFRP circuit board 160, such as FIG It is used, for example, for the production of printed circuit boards. In particular, the dielectric used for the printed circuit board 160 is FR4. Furthermore, the receiving coil can also be equipped with more or less than two shortening capacitors. Basically, it would be sufficient to provide only a gap with only one shortening capacitor in the receiver coil. At higher frequencies, advantageously, three or more shortening capacitors can also be accommodated in the receiving coil for better reduction of unwanted electric fields. Correspondingly, a ring of three or more sections results which are advantageous, but not necessary, of the same size and which are connected via three or more shortening capacitors. For reasons of symmetry, it does not matter at which of the shortening capacitors the preamplifier is positioned.

Claims

Patentansprüche / Patent Claims Claims / Patent Claims
1. Anordnung zur Detektion und Weiterverarbeitung von MRT- Signalen mit einer Empfangsspule (20, 120) zur Detektion der MRT-Signale und einer mit der Empfangsspule (20, 120) über Leitungen (41, 141) verbundenen Vorrichtung (10, 110) zur Weiterverarbeitung der durch die Empfangsspule (20, 120) de- tektierten Signale, dadurch gekennzeichnet, dass die Vorrichtung (10, 110) in einem von einem äußeren Magnetfeld abgeschirmten Bereich der Empfangsspule (20, 120), am Ort des Abgriffs der MRT-Signale von der Empfangsspule (20, 120) angeordnet ist.1. Arrangement for the detection and further processing of MRT signals with a receiving coil (20, 120) for detecting the MRT signals and with the receiving coil (20, 120) via lines (41, 141) connected to the device (10, 110) Further processing of the detected by the receiving coil (20, 120) detected signals, characterized in that the device (10, 110) in a shielded from an external magnetic field portion of the receiving coil (20, 120), at the location of the tapping of the MRI signals from the receiving coil (20, 120) is arranged.
2. Anordnung nach Anspruch 1, dadurch gekennzeichnet, dass die Vorrichtung (10, 110) auf der Oberfläche der Empfangsspule (20, 120) unterhalb einer metallischen Abdeckung (170) platziert ist.2. Arrangement according to claim 1, characterized in that the device (10, 110) on the surface of the receiving coil (20, 120) is placed below a metallic cover (170).
3. Anordnung nach Anspruch 2, dadurch gekennzeichnet, dass die Empfangsspule (120) ein metallbeschichtetes (160) Dielektrikum ist.3. Arrangement according to claim 2, characterized in that the receiving coil (120) is a metal-coated (160) dielectric.
4. Anordnung nach Anspruch 3, dadurch gekennzeichnet, dass die Empfangsspule (120) flächig und doppelseitig kupferbeschichtet und das Dielektrikum ein mit Epoxydharz gebundenes Glasfasergewebe (FR4) ist.4. Arrangement according to claim 3, characterized in that the receiving coil (120) surface copper-coated and double-sided and the dielectric is an epoxy resin-bonded glass fiber fabric (FR4).
5. Anordnung nach Anspruch 4, dadurch gekennzeichnet, dass die Empfangsspule (120) zumindest im Bereich der Vorrichtung5. Arrangement according to claim 4, characterized in that the receiving coil (120) at least in the region of the device
(110) auch an ihren Stirnseiten metallbeschichtet, insbesondere kupferbeschichtet ist.(110) is also metallized on its front sides, in particular copper-coated.
6. Anordnung nach einem der Ansprüche 2 bis 5, dadurch ge- kennzeichnet, dass die Abdeckung (170) rundum mit der Metall- beschichtung (160) der Empfangsspule (120) verlötet ist und die Verlötung Öffnungen (150, 151) für ein- und ausgehende Leitungen (140, 141) aufweist. 6. Arrangement according to one of claims 2 to 5, character- ized in that the cover (170) is soldered all around with the metal coating (160) of the receiving coil (120) and the soldering openings (150, 151) for a and outgoing lines (140, 141).
7. Anordnung nach Anspruch 1, dadurch gekennzeichnet, dass die Vorrichtung (10, 110) im Inneren einer als Hohlkörper ausgebildeten Empfangsspule (20, 120) angeordnet ist.7. Arrangement according to claim 1, characterized in that the device (10, 110) in the interior of a hollow body formed as a receiving coil (20, 120) is arranged.
8. Anordnung nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Vorrichtung (10, 110) ein Vorverstärker ist.8. Arrangement according to one of the preceding claims, characterized in that the device (10, 110) is a preamplifier.
9. Anordnung nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Empfangsspule (20, 120) aus zwei jeweils halbringförmig ausgebildeten Elementen (21, 22) besteht und dass zumindest ein Verkürzungskondensator (30, 31, 130, 131) die beiden durch einen Spalt getrennten und gegenüber- liegend angeordneten Elemente (20, 21) elektrisch koppelt.9. Arrangement according to one of the preceding claims, characterized in that the receiving coil (20, 120) consists of two semi-annular elements (21, 22) and that at least one shortening capacitor (30, 31, 130, 131), the two by a Gap separated and oppositely arranged elements (20, 21) electrically coupled.
10. Anordnung nach Anspruch 9, dadurch gekennzeichnet, dass die von der Empfangsspule (20, 120) detektierten MRT-Signale zur Weiterleitung an die Vorrichtung (10, 110) über einem der Verkürzungskondensatoren (31, 131) abgegriffen werden.10. Arrangement according to claim 9, characterized in that the of the receiving coil (20, 120) detected MRT signals for transmission to the device (10, 110) via one of the shortening capacitors (31, 131) are tapped.
11. Anordnung nach Anspruch 10, dadurch gekennzeichnet, dass die Vorrichtung (10, 110) in unmittelbarer Nähe eines Verkürzungskondensators (31, 131) angeordnet ist.11. Arrangement according to claim 10, characterized in that the device (10, 110) in the immediate vicinity of a shortening capacitor (31, 131) is arranged.
12. Anordnung nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass über eine dünne Koaxialleitung12. Arrangement according to one of the preceding claims, characterized in that via a thin coaxial line
(40, 140) ein Ausgangssignal der Vorrichtung (10, 110) geleitet und/oder die Vorrichtung (10, 110) mit Energie versorgt wird.(40, 140) an output signal of the device (10, 110) passed and / or the device (10, 110) is energized.
13. Anordnung nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass Leitungen (41, 141) an Eingänge der Vorrichtung (10, 110) als dünne Leiterbahnen ausgebildet ist. 13. Arrangement according to one of the preceding claims, characterized in that lines (41, 141) to inputs of the device (10, 110) is designed as a thin strip conductors.
PCT/EP2008/061283 2007-09-25 2008-08-28 Arrangement for detecting mrt signals with a preamplifier in a shielded region WO2009040208A1 (en)

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DE102008008502B4 (en) * 2008-02-11 2014-08-14 Siemens Aktiengesellschaft Arrangement for controlling an antenna arrangement in a magnetic resonance apparatus

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US5296813A (en) * 1992-03-05 1994-03-22 Picker International, Inc. Magnetic resonance scanner with improved packaging for circuitry within the magnetic field
WO2006000928A2 (en) * 2004-06-25 2006-01-05 Koninklijke Philips Electronics, N.V. Integrated power supply for surface coils
US20070188175A1 (en) * 2006-02-13 2007-08-16 Burdick William E Jr Self-shielded packaging for circuitry integrated with receiver coils in an imaging system

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Publication number Priority date Publication date Assignee Title
US5296813A (en) * 1992-03-05 1994-03-22 Picker International, Inc. Magnetic resonance scanner with improved packaging for circuitry within the magnetic field
WO2006000928A2 (en) * 2004-06-25 2006-01-05 Koninklijke Philips Electronics, N.V. Integrated power supply for surface coils
US20070188175A1 (en) * 2006-02-13 2007-08-16 Burdick William E Jr Self-shielded packaging for circuitry integrated with receiver coils in an imaging system

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Publication number Priority date Publication date Assignee Title
DE102008008502B4 (en) * 2008-02-11 2014-08-14 Siemens Aktiengesellschaft Arrangement for controlling an antenna arrangement in a magnetic resonance apparatus

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