WO2021223977A1

WO2021223977A1 - Double tuned reception coil for a magnetic resonance tomography system

Info

Publication number: WO2021223977A1
Application number: PCT/EP2021/059877
Authority: WO
Inventors: Chang-Hoon Choi; Jörg FELDER; Suk Min Hong; Michael SCHWERTER; Nadim Joni Shah
Original assignee: Forschungszentrum Jülich GmbH
Priority date: 2020-05-05
Filing date: 2021-04-16
Publication date: 2021-11-11
Also published as: DE102020205632A1; EP4147064A1

Abstract

The invention relates to a reception coil for a magnetic resonance tomography and/or spectroscopy system, to a method for tuning a reception coil, to a reception coil arrangement for a magnetic resonance tomography and/or spectroscopy system, to a magnetic tomography and/or spectroscopy system and to a use of a PIN diode. A reception coil (1) for a magnetic resonance tomography and/or spectroscopy system can be tuned to receive two different frequencies (10). The reception coil (1) comprises: a coil body (2) which is intended for detecting nuclear magnetic resonance signals and has a capacitor (3) located in or on the coil body (2); and a tuning circuit (9) which is in operative connection with the coil body (2) and is intended for tuning the reception coil (1). The tuning circuit (9) has a PIN diode (8) and an inductor (7). The PIN diode (8) is connected in series with the inductor (7) and in parallel with the capacitor (3).

Description

Double tuned receiving coil for a magnetic resonance tomography

system

description

The invention relates to a receiving coil for a magnetic resonance tomography and / or spectroscopy system, a method for tuning a receiving coil, a receiving coil arrangement for a magnetic resonance tomography and / or spectroscopy system, a magnetic resonance tomography and / or spectroscopy system and a Use of a PIN diode.

Magnetic resonance tomography (MRT) is a non-invasive imaging method for examining body parts, with which high-resolution sectional images of the body can be generated for medical diagnostics. It is based on the resonant excitation of certain atomic nuclei contained in the body or supplied to the body by means of strong magnetic fields and alternating magnetic fields in the radio frequency range (nuclear magnetic resonance), which induces an electrical signal in a receiving coil. In this way, high-resolution images can be generated.

To carry out the MRT, high-frequency antennas - referred to as coils in MRI - are used, which are arranged on or around the body to be examined. An arrangement particularly close to the body is advantageous for high signal-to-noise ratios and thus for high-quality images. Often, separate transmitter and receiver coils are used to excite the atomic nuclei and to receive the nuclear magnetic resonance signals. The publication "A transmit-only / receive-only (TORO) RF System for high-field MRI / MRS applications" by Barberi et al., Published in "Magnetic Resonance in Medicine", describes the use of a bird cage coil. birdcage ”) as a transmitter coil and a surface coil arranged inside the birdcage coil as a receiver coil.

In addition to protons, other atomic nuclei are also used to carry out further investigations. This became possible some time ago due to the increased magnetic flux density of MRT devices, since a comparatively high signal-to-noise ratio can be achieved with these systems despite the lower occurrence of these non-proton nuclei and their lower sensitivity. It MRT machines exist that allow the investigation of protons as well as non-proton nuclei. The publication “Whole brain ³¹ P MRSI at 7T with a dual-tuned receive array” by Rowland et al. , published in "Magnetic Resonance in Medicine", describes a double-tuned receiving coil arrangement for ¹ H and ³¹ P, in which double tuning was achieved by an LC trap circuit with a coil and a capacitor, which splits the resonance of a connected magnetic resonance coil . The use of conventional, lossy LC trap circuits leads to a deterioration in the coil quality in the case of proton nuclei and non-proton nuclei, which is particularly undesirable in the case of non-proton nuclei.

The publication "Three-layered radio frequency coil arrangement for sodium MRI of the human brain at 9.4 tesla" by Shajan et al., Published in "Magnetic Resonance in Medicine", describes the transmission using a four-channel coil arrangement for the purpose of exciting the atomic nuclei and the reception of nuclear magnetic resonance signals with a 29-channel RF receiver coil for the ²³ Na signal and a four-channel dipole antenna for the ¹ H signal. The publication “An 8-channel receive array for improved ³¹ P MRSI of the whole brain at 3T” by van Uden et al., Published in “Magnetic Resonance in Medicine”, describes the integration of a developed eight-channel receiving coil for ³¹ P into a commercially available double-tuned transmitter and receiver coil for ¹ H and ³¹ P to increase the sensitivity. However, the coil arrangements described lead to an impairment of the ¹ H performance compared to an arrangement of simply tuned proton multi-channel receiving coils. The design of the required transmitter coil assigned to the receiver coil is also complicated here, since a large number of blocking circuits is necessary in order to avoid coupling and interference from non-proton frequencies.

In some applications, combined transmit and receive coils are also used. The publication "Design and construction of a novel ¹ H / ¹⁹ F double-tuned coil system using PIN diode switches at 9.4 T" by Choi et al., Published in the "Journal of Magnetic Resonance", describes the switching of double-tuned transmission and receiving coils between two frequencies. The publication “32-channel 3 tesla receive-only phased-array head coil with soccer-ball element geometry” by Wiggins et al., Published in “Magnetic Resonance in Medicine”, describes a receiving coil for imaging the human brain. This is designed as a helmet-shaped coil arrangement with 32 channels, which hugs the head closely and comprises individual pentagonal and hexagonal coils arranged in the shape of a soccer ball. Similar circuits were used in both papers, but Choi et al. used them to double-tune the transmit and receive coils, while Wiggins et al. they used to detune the ¹ H receiving coil arrangement.

The patients and the sensitive receiving devices including the receiving coil itself are often protected by detuning or decoupling the receiving coil during transmission. US 8 013 609 B2 describes an MRT system with a transmission phase and a reception phase, which has a transmission coil, a reception coil and a detuning circuit for detuning the reception coil during the transmission phase for the above-mentioned purpose. US 10 120 045 B2 discloses a high-frequency coil for an MRT system which, for the above-mentioned purpose, comprises a decoupling circuit with fast-switching PIN diodes for passive or active decoupling of the high-frequency coil from one or more other high-frequency coils.

US2018 / 0252783 A1 describes a dual frequency system for transmitting and receiving two frequencies in an MRT system. The dual frequency system includes a doubly tuned receiver coil for receiving two different frequencies. Here, too, decoupling is provided, namely by means of active and passive decoupling. The tuning to the respective frequency takes place by means of a PIN diode and a capacitor, which are connected in series, so that the resonance frequency is shifted to the non-proton frequency when the PIN diode conducts, and the resonance frequency is shifted back to the proton frequency when the PIN diode blocks. As a result of the PIN diode resistance or the injection of shot noise, the quality of the arrangement deteriorates when the PIN diodes are conducted, that is, when tuned to the non-proton frequency.

The object of the invention is to provide a further developed receiving coil, a further developed method for tuning a receiving coil, a further developed receiving coil arrangement, a further developed magnetic resonance tomography and / or spectroscopy system as well as a further developed use of a PIN diode. The object is achieved by the receiving coil according to claim 1 and the method for tuning a receiving coil, the receiving coil arrangement, the magnetic resonance tomography and / or spectroscopy system and the use of a PIN diode according to the independent claims. Refinements are given in the subclaims.

A receiver coil for a magnetic resonance tomography and / or spectroscopy system, which can be tuned to receive two different frequencies, is used to achieve the object. This comprises a coil body for the detection of nuclear magnetic resonance signals as well as a tuning circuit, which is operatively connected to the coil body, for tuning the receiving coil. The receiving coil has a capacitance arranged in or on the coil body and the tuning circuit has a PIN diode and an inductance. The PIN diode is connected in series with the inductance and in parallel with the capacitance.

This enables coordination to two different resonance frequencies or Larmor frequencies, in particular for examining different atomic nuclei or for examining different magnetic flux densities of the static magnetic field. In particular, the coordination takes place for the purpose of examining different atomic nuclei. The receiving coil is also referred to as a doubly tuned or doubly tunable receiving coil. The invention makes it possible to maintain the sensitivity for non-proton nuclei, which is accordingly as good as that of an individually tuned coil, in the development of doubly tuned multi-channel receiving coils and receiving coil arrangements.

The receiving coil is a receiving device for a magnetic resonance tomography system and / or a magnetic resonance spectroscopy system. It is used to receive or detect magnetic resonance signals, in particular by detecting an electrical voltage induced in the receiving coil. The receiving coil is, in particular, a high-frequency coil. A high-frequency coil is a coil that operates at a frequency in the radio wave range or radio frequency range, in particular in the MHz range, or is designed for such a range. So you can detect a high frequency field. In particular, it is part of an RF system (radio frequency) and is also referred to as a radio frequency or RF coil. The coil body can be a conductor loop, for example a wire loop. It is also known as the main coil block. The coil body can be designed as a stripline or a microstripline. It can be produced using 3D printing. Production by chemical etching of a circuit board or the use of self-adhesive copper tape is also possible. The coil body can also be produced by a screen printing process. It can be flexible so that it can be worn on the body embedded in textile. A multi-part bobbin is a bobbin that has several parts between which a tuning unit can be placed. The parts can be sections of a conductor track or conductor loop.

The resonance frequency of a resonator is determined by its inductance and capacitance, both of which depend on the geometry and the materials used. The receiving coil comprises at least one capacitance arranged in or on the coil body, each capacitance in particular comprising at least one capacitor, and is thus a resonator or oscillating circuit. The size of the coil body influences the inductance and thus also the resonance frequency of the resonator. The bobbin is set up to receive nuclear magnetic resonance signals. The receiving coil is set up to receive nuclear magnetic resonance signals of two different frequencies. The coil body can also have one or more inductances for influencing the reception frequency or for tuning. In particular, the coil body is designed as a loop coil. It goes without saying that tuning to more than two frequencies is also possible. In this case, the coil former can have several pairs with a PIN diode and at least one inductance and / or several tuning circuits.

A tuning circuit is a circuit that is suitable for tuning the receiving coil to a specific desired frequency, in particular one of several different frequencies. This is realized through the operative connection with the receiving coil. In particular, the tuning circuit is set up for selective tuning of the receiving coil. The tuning to different frequencies means the suitability of the receiving coil to receive signals of these frequencies or the optimization of the receiving coil to these frequencies. It is thus possible, for example, to switch between two different Larmor frequencies. A pure detuning, as is possible in conventional devices for protecting the components designed for reception in a combined transmitting and receiving coil, is not a coordination within the meaning of the invention. The receiver coil is designed as a pure receiver coil, so an additional transmitter coil is required to carry out magnetic resonance tomography or spectroscopy. A combined transmitting and receiving coil is not a receiving coil in the sense of the invention.

In particular, the receiving coil has no switch for switching between transmit and receive functions, no power divider to divide the transmit power or to adapt the transmit phases such as a Wilkinson divider, no transmit current source or no power amplifier and / or no phase shifter to protect the preamplifier . The receiving coil according to the invention can thus be produced more cost-effectively and more simply than a combined transmitting and receiving coil with the same number of channels. It is of course not ruled out that a power splitter is used to combine the received signal from several preamplifiers, in particular in a receiver coil arrangement with several receiver coils.

The capacitance is arranged in particular between parts of the coil body and is used to influence a resonance frequency of the resonator, that is to say to influence the frequency or resonance frequency of the receiving coil. The receiving coil thus comprises a resonator which comprises the coil body and the capacitance arranged between the parts of the coil body or is formed from these. The capacitance is independent of the tuning circuit and thus influences both possible frequencies. In particular, the capacitance comprises at least one capacitor.

The inductance arranged in the tuning circuit determines the extent of the frequency shift when tuning the receiving coil. In other words, the inductance is used to shift the frequency.

A PIN diode has an intrinsically conductive, weakly doped or undoped layer located between the positively doped layer and the negatively doped layer. As a result, it is able to be switched between conductive and non-conductive operation depending on the positive or negative bias voltage, also referred to as forward or forward current and reverse voltage. This is also known as forward or reverse operation. For reverse operation, reverse bias is applied so that the PIN diode is turned off. When operating in the forward direction, a forward current flows so that the PIN diode is switched on. The PIN diode thus serves as an electronic switch to selectively activate or deactivate the voting circuit and in this way to implement the voting. This enables the resonance frequency of the coil to be switched quickly.

In this way, depending on the operation of the PIN diode in the reverse or forward direction, the receiving coil can be tuned to different frequencies by shifting the frequency. In other words, when the PIN diode is on, a parallel resonant circuit is generated or switched, which influences the resonance frequency of the receiving coil or the resonator.

In particular, the tuning circuit has no pair of PIN diodes and / or only a single PIN diode. Due to the design of the coil as a pure receiving coil, the restrictions with regard to the current strength or the power that apply in combined transmitting and receiving coils are not relevant here. These occur with transmitter coils and combined transmitter and receiver coils, since PIN diodes can only be supplied with limited currents or powers due to their design, especially in blocking mode, but high currents or powers are required for sending. When receiving, on the other hand, only the nuclear magnetic resonance signals occur at a level of a few mW. For this reason, the receiving coils according to the invention can be dimensioned much larger than conventional transmitting and receiving coils and used in this way to examine the human body, which was previously not possible with other concepts based on PIN diodes or combined transmitting and receiving coils was.

In particular, the tuning circuit has no further devices which could reduce the signal-to-noise ratio. In particular, the PIN diode is switched off when blocking, so that the circuit when the PIN diode is blocking corresponds overall to a simply tuned coil. This means that there are no losses and a high quality of detection is guaranteed. The resistance of the PIN diode does not occur when operating in reverse direction.

In one embodiment, the receiving coil comprises a plurality of tuning circuits, which are operatively connected to the coil body, for tuning the receiving coil. In this way the receiving coil is on more than two different frequencies tunable. Each of the tuning circuits can have the same structure, with different inductances or different pairs of PIN diodes and inductances being used, of course, in order to define the extent of the frequency shift of the respective tuning circuit and thus the respective frequencies to be tuned to, for example ¹ H , ¹³ C, ³¹ P and / or others.

In one embodiment, the tuning circuit is set up to tune the receiving coil to a proton frequency and to a non-proton frequency.

A proton frequency is a frequency suitable for detecting the nuclear magnetic resonance signals of protons or hydrogen atomic nuclei ( ¹ H), in particular a frequency to which the receiving coil is optimized. A non-proton frequency is a frequency that is suitable, in particular optimized, for the detection of nuclear magnetic resonance signals from atomic nuclei other than protons. Atomic nuclei that can be used as non-protons in MRT are, for example, ² H, ³ He, ⁷ Li, ¹³ C, ¹⁷ 0, ¹⁹ F, ²³ Na, ³¹ P, ³⁵ CI, ³⁹ K or ¹²⁹ Xe. These enable further examinations that are ^{not possible with a pure 1} H scan and that are used, for example, to determine metabolic or cellular information. In one embodiment, the receiving coil can be tuned to at least two frequencies that are close to one another. Frequencies that are close to one another can be frequencies of those atomic nuclei whose gyromagnetic ratios differ from one another by less than 20%, in particular less than 10% and / or whose gyromagnetic ratios differ from one another by less than 10 MHz / T, in particular less than 5 MHz / T. Conventional decoupling and / or tuning methods, for example with LC trap circuits, are often not well applicable to these frequencies. Such frequencies can also be switched particularly effectively according to the invention. With a doubly tuned coil with PIN diode, the frequency switching between closely spaced frequencies can be achieved effectively, while coils with conventional LC traps show clear disadvantages with comparable double tuning, since the peaks in this case are too close to each other so that they are mutually exclusive influence. Frequencies that are close together can be, for example, the frequencies of ¹ H and ¹⁹ F or of ² H, ¹³ C and ²³ Na.

In one embodiment, the receiving coil is tuned to the non-proton frequency when the PIN diode blocks, and tuned to the proton frequency when the PIN diode is conducting. In other words, nuclear magnetic resonance signals from protons are detected when the PIN diode is conducting, and nuclear magnetic resonance signals from atomic nuclei of a chemical element other than hydrogen are detected when the PIN diode is blocked. In the latter case, the reception coil corresponds to a simply tuned reception coil due to the omission or non-use of the tuning circuit.

Due to the lower occurrence of non-protons in comparison to protons, a high signal-to-noise ratio or high sensitivity is particularly important for the non-protons in order to obtain a good quality of the images generated. This is achieved here at the high level of a receiving coil that is simply tuned to the frequency of the non-protons. In addition, the receiving coil according to the invention enables the detection of proton signals. In particular, the tuning circuit is used to increase the resonance frequency of the receiving coil.

In one embodiment, the receiving coil can be tuned to a proton frequency and to the non-proton frequency of ^{19 F.}

The respective frequency depends on the atomic nucleus used. The gyromagnetic ratio of ¹ H is 42.58 MHz / Tesla and that of ¹⁹ F is 40.05 MHz / Tesla. The actual frequencies depend on the strength of the magnetic field, i.e. the magnetic flux density.

A ¹⁹ F-based MR technology, as a molecular imaging instrument, enables the direct detection and quantification of extremely specific cells that can be marked beforehand. It can be used for a number of different applications, for example for monitoring the targeted release of active substances, for tracking marked cells or nanoparticles, for measuring tumor oximetry or for visualizing inflammation.

In one embodiment, the PIN diode consists of a non-magnetic material. In other words, the PIN diode does not include magnetic materials. By non-magnetic it is meant in particular that when a magnetic field is applied there is no significant attraction or repulsion. In particular, the capacitors connected to the coil body also consist of non-magnetic material. This configuration has the advantage that the accuracy of the detection is improved since there are no interactions with the magnetic fields generated during the MRT.

In one embodiment, the receiving coil is designed for examining a human body or body part.

In other words, the size and / or the configuration with regard to the reception power are such that MRT examinations of entire human bodies or human body parts are possible. In comparison to smaller applications for animals or applications on a laboratory scale with combined transmitter and receiver coils of comparable technology, this is not possible, since the usable currents or powers are limited by the use of PIN diodes.

In particular, the coil body has a size of at least 5 cm, typically at least 10 cm, in particular at least 20 cm, preferably at least 35 cm and particularly preferably at least 50 cm. The size can be, for example, the greatest distance between two opposing areas of the coil former.

In one embodiment, the reception coil is set up for use with a transmission coil with a transmission power of at least 2 kW, in particular at least 5 kW, for example at least 10 kW and in one embodiment at least 20 kW.

In one embodiment, the receiving coil comprises at least one and optionally a plurality of preamplifiers for amplifying nuclear magnetic resonance signals or electrical voltage detected by means of the coil, in particular low-noise preamplifiers. In a further embodiment, the receiving coil comprises a preamplifier decoupling circuit. This enables a lossless or low-loss reception of the nuclear magnetic resonance signal without damaging the preamplifier or the circuit.

In one embodiment, the receiving coil has a device for impedance matching. This can be arranged between parts of the coil former and / or connected to them. In one embodiment, during the adaptation, the capacitance in a coil is set or influenced in such a way that a desired reactance is achieved. The device for impedance matching has in particular at least one and in particular several capacitors, for example capacitors, or consists of these. The device for impedance matching can be tuned to each of the different frequencies.

The embodiments and features disclosed here can also be applied to all further aspects of the invention.

A second aspect of the invention is a method for tuning a receiving coil according to the invention, in which the PIN diode is biased so that the receiving coil is tuned to one of the two frequencies by means of the tuning circuit.

The biasing takes place in particular by applying an electric current and / or an electric voltage to the tuning circuit, in particular a PIN diode contained therein. The tuning circuit is thus activated or deactivated as a function of the electric current and / or the electric voltage, so that the resonance frequency of the receiving coil or of the resonator is increased or decreased. In particular, the tuning circuit is activated or deactivated by means of a PIN diode. This can activate or deactivate the tuning circuit depending on the operation in the forward or reverse direction. In this way it is particularly easy and quick to switch back and forth between the frequencies.

A third aspect of the invention is a receiving coil arrangement for a magnetic resonance tomography and / or spectroscopy system, which comprises a plurality of receiving coils according to the invention.

The receiving coil arrangement allows the arrangement of a number and possibly a shape and / or size of receiving coils adapted to the respective case, in other words it is a personalized receiving coil arrangement. A receiving coil arrangement is also referred to as a multi-channel coil, with one channel corresponding to a coil according to the invention. The receiving coil arrangement comprises a plurality of doubly tuned or tunable receiving coils. For small bodies or body parts to be examined, fewer and / or smaller receiving coils can accordingly be provided, while for larger ones to be examined Body or body parts more and / or larger receiving coils can be provided.

In one embodiment, at least two receiving coils, in particular adjacent receiving coils, are electromagnetically decoupled. The decoupling serves to reduce the mutual electromagnetic influence between the individual receiving coils, which would otherwise increase the noise. Decoupling can be implemented, for example, by overlapping receiving coils, common conductor tracks of receiving coils, capacitive decoupling and / or inductive decoupling. Alternatively or additionally, it can be implemented by means of a high-resistance configuration of the receiving coils, that is to say by means of high impedances, and / or by means of self-decoupling approaches. The receiving coil arrangement can have at least one decoupling unit for the electromagnetic decoupling of at least two, in particular, adjacent receiving coils. In particular, each pair of adjacent receiving coils has a decoupling unit.

In one embodiment, the receiving coil arrangement comprises a positioning unit for positioning the receiving coils in relation to one another and / or to a body to be examined. To adapt to the shape and / or size of the body or body part to be examined, the positioning unit can be adapted to the shape and / or size of the body or body part to be examined. In this way, the receiving coils can be used flexibly with different positioning units in different applications. Compared to conventional receiving coil arrangements, which are intended for a certain size and achieve inadequate results with different sizes, for example due to low signal-to-noise ratios and poor performance with parallel imaging, good results can be achieved with the receiving coil arrangement according to the invention by adapting to any size will. This is particularly advantageous when using non-proton nuclei.

The positioning does not necessarily have to be a fixed positioning; for example, the positioning unit can be designed as a movable or flexible part, for example textile, for covering at least one body part to be examined. It can be designed, for example, as a flexible object that can be worn on the body of a patient, such as a glove or a shirt be. The positioning unit can be designed as a holding device for holding the receiving coils. It can be designed for the fixed positioning of the receiving coils on one another or in relation to one another. It can be a solid object which can be arranged on a body or body part or into which a part of a body can be introduced. The positioning unit can be designed as a fastening unit for mechanically fastening the receiving coils to one another. In particular, the receiving coils are arranged next to one another.

A fourth aspect of the invention is a magnetic resonance tomography and / or spectroscopy system. This comprises at least one receiving coil according to the invention and / or at least one receiving coil arrangement according to the invention. In particular, the magnetic resonance tomography and / or spectroscopy system is designed for examining a human body or body part.

The design for examining a human body or body part means that the magnetic resonance tomography and / or spectroscopy system in terms of its size and / or design, in particular including the size and / or design of its transmitting and receiving coils, for MRT examinations of whole human bodies and human body parts is suitable and in particular is manufactured for this purpose.

In one embodiment, the magnetic resonance tomography and / or spectroscopy system also has at least one transmission coil, the transmission power of the transmission coil or coils being at least 2 kW, in particular at least 5 kW, preferably at least 10 kW and particularly preferably at least 20 kW.

In other words, the transmission power is adapted to the examination of human bodies and / or body parts. The transmission coil can be arranged as part of a transmission coil arrangement. The power supply or amplification must also be provided accordingly.

In one embodiment, the magnetic resonance tomography and / or spectroscopy system and / or the receiving coil is for a magnetic one Flux density between 0.1 Tesla and 25 Tesla, in particular between 1 T and 20 T, preferably between 2 Tesla and 12 Tesla, particularly preferably between 3 Tesla and 9 Tesla, for example between 4 Tesla and 8 Tesla.

A fifth aspect of the invention is the use of a PIN diode for tuning a receiving coil for a magnetic resonance tomography and / or spectroscopy system for receiving two different frequencies. The receiving coil comprises a coil body for the detection of nuclear magnetic resonance signals with a capacitance arranged in or on the coil body as well as a tuning circuit which is operatively connected to the coil body for tuning the receiving coil. The tuning circuit has the PIN diode and an inductance, and the PIN diode is connected in series with the inductance and in parallel with the capacitance. In particular, the PIN diode is used to selectively activate and deactivate the tuning circuit.

In the following, further exemplary embodiments of the invention will also be explained in more detail with reference to figures.

Show it:

FIG. 1: a schematic representation of an embodiment of a receiving coil according to the invention;

Figure 2: a schematic representation of a further embodiment of an inventive

Receiving coil;

FIGS. 3A and 3B: two diagrams with representations of the performance of a receiving coil according to the invention in a first state;

FIGS. 4A and 4B: two diagrams with representations of the performance of the receiving coil according to the invention in a second state;

FIGS. 5A and 5B: two diagrams with superimposed representations of the performance of the receiving coil according to the invention in the first and second state; and

FIG. 6: a schematic representation of an embodiment of a receiving coil arrangement according to the invention. FIG. 1 shows a receiving coil arrangement 1 according to the invention. The coil body 2 is essentially square in shape and is composed of five parts, between which respective capacitors 3 are arranged in the form of capacitors. Coil body 2 and capacitance 3 together form a resonator. The receiving coil 1 is thus set up to receive nuclear magnetic resonance signals. The capacitors 3 tune the receiving coil 1 to a desired frequency.

The receiving coil 1 has a tuning circuit 9 for tuning the receiving coil 1, which is in operative connection with the coil body 2 and with which the receiving coil 1 can be tuned to two different frequencies. The tuning circuit 9 comprises an inductance 7 in the form of a coil as well as a PIN diode 8 connected in series with the inductance 7, which can be switched between conductive and non-conductive operation by biasing Capacitance 3 of the bobbin 2 is switched, whereby the resonance frequency of the receiving coil 1 changes. The PIN diode 8 does not contain any magnetic materials, so that any influence of magnetic fields or magnetic fields during the MRT is excluded.

The receiving coil 1 also includes an interface unit 16, which is also referred to as an interface unit. This serves as an interface to the environment, in particular for the purpose of transmitting or forwarding the received and possibly pre-amplified signals. The interface unit can have a preamplifier for amplifying the received signals. This can be designed as a broadband preamplifier, in particular with frequencies that are close together, or it can be implemented by means of two narrowband preamplifiers. The interface unit 16 may comprise a balun, a double-tuned matching circuit and / or a preamplifier decoupling unit.

The receiving coil 1 is set up in such a way that, depending on the bias voltage of the PIN diode 8, it is possible to switch back and forth ^{between a proton frequency and the non-proton frequency of 31 P.} The receiving coil 1 is tuned to the non-proton frequency when the PIN diode 8 blocks, and tuned to the proton frequency when the PIN diode 8 conducts. In Figure 2, instead of the interface unit 16, a specific circuit is shown. The receiving coil 1 shown here comprises a device for impedance matching with capacitors 4, a low-noise preamplifier 6 and a balun 5 arranged between the device for impedance matching and the preamplifier 6, which also serves to decouple the preamplifier 6. This embodiment with a single broadband preamplifier 6 is particularly suitable for frequencies that are close together. In the case of frequencies that are further apart, separate narrow-band preamplifiers can instead be used for each of the frequencies, with slight modifications of the respective circuits being possible.

In FIG. 3, two diagrams arranged next to one another show the reactions of a receiving coil according to the invention, in particular the receiving coil from FIG. 1, when the PIN diode is conducting or switched on. The data shown were measured using a vector network analyzer. The so-called S21 measurements were carried out with a double recording loop. These are a measure of the signal emerging at connection 2 in relation to the RF signal level at connection 1. As in FIGS. 4 and 5, frequency 10 is shown in MHz on the x-axis in the diagrams shown here. In the center of the x-axis in all diagrams is the frequency 10, which is to be tuned to. The total frequency range shown is 100 MHz and each vertical division corresponds to 10 MHz. The power 13 in dB, that is to say as a power level, is shown on the y-axes. A difference of -3 dB thus means roughly halving the power. The horizontal tick marks each correspond to 10 dB.

In FIG. 3A shown on the left, the proton frequency 11 is located in the center of the x-axis, which is 300 MHz and ^{corresponds to the frequency tuned to 1} H with a magnetic flux density of 7 Tesla. In FIG. 3B shown on the right, the non-proton frequency 12 is located in the center of the x-axis, which is 120.5 MHz and ^{corresponds to the frequency tuned to 31} P at the same magnetic flux density of 7 Tesla. This also applies to FIGS. 4A and 4B as well as 5A and 5B.

FIG. 4 thus shows the response of the receiving coil, which is tuned ^{to 300 MHz, that is to say to 1 H.} In FIG. 3A it can be seen that a maximum occurs at the proton frequency 11 of 300 MHz, which is referred to as the first power at the proton frequency M1A. FIG. 3B shows that at the non-proton frequency 12 of 120.5 MHz, on the other hand, no maximum occurs. This position is designated as the first power at non-proton frequency M1B. It becomes clear that the receiving coil is tuned to the proton frequency 11 when the PIN diode is switched on or conducting, but not to the non-proton frequency 12.

FIGS. 4A and 4B show corresponding representations for the case that the PIN diode is switched off or blocked. FIG. 4A shows that no maximum occurs at the proton frequency 11 of 300 MHz. This position is designated as the second power at proton frequency M2A. Accordingly, when the PIN diode is switched off, the receiving coil is not tuned to the proton frequency. In contrast, it becomes clear in FIG. 4B that a maximum occurs at the non-proton frequency 12 of 120.5 MHz, which is referred to as the second power at the non-proton frequency M2B. In this case, the receiving coil is tuned ^{to the non-proton frequency 12 of 31 P.}

FIG. 5A shows a superimposition of the diagrams from FIGS. 3A and 4A, that is to say shows the behavior of the proton frequency 11 of 300 MHz in the conductive and non-conductive operation of the PIN diode. It becomes clear here that a first difference 14 of more than 20 dB is achieved between the positions M1A and M2A, which shows the effective selective tuning to the proton frequency 11 of 300 MHz. Analogously to this, FIG. 5B shows a superimposition of the diagrams from FIGS. 3B and 4B, so that the behavior of the non-proton frequency 11 of 120.5 MHz in the conductive and non-conductive operation of the PIN diode is shown. The second difference 15 resulting between the positions M1B and M2B is also more than 20 dB, which also shows the effective selective tuning in the range of the non-proton frequency 12. The “non-tuning” shown in positions M2A and M1 B are also referred to as “detuning”. They are required in pure receiving coils in order to protect them from increased current flow during the transmission phase, which otherwise leads to damage to the preamplifier, which results in an interruption of the MRI operation.

In particular, the receiving coil according to the invention, based on the receiving frequency, must be detuned during transmission. This can be achieved in that one frequency 10 is switched over to the other as shown in FIG. 5 and in this way - for example - a detuning of approximately -20 dB can be achieved. In other words, to receive the nuclear magnetic resonance signals from ¹ H requires the proton frequency. During the ¹ H transmission, the doubly tuned receiving coil according to the invention is tuned to the non-proton ^{frequency, that is to say the 31} P frequency, by switching off the PIN diode. The receiving coil is thus ^{detuned from the perspective of the 1} H receiving coil.

FIG. 6 shows a receiving coil arrangement 20 according to the invention, which is also referred to as a multi-channel coil or “array”. This comprises six similarly constructed receiving coils 1, which can accordingly also be referred to as channels. The receiving coils 1 are designed in particular as shown in FIG. For a better clarity, the designation of the individual components has been omitted and reference is made to FIG. 1 in this regard. The receiving coil arrangement 20 shown here is suitable, for example, for an areal arrangement on a human thorax for the purpose of an MRT examination of the same. The number of six receiving coils is purely exemplary; Depending on the requirements, more or fewer receiving coils can also be used.

The coil formers 2 of respectively adjacent receiving coils 1 have overlapping areas which are used for the electromagnetic decoupling of the respective receiving coils 1.

List of reference symbols

Receiving coil 1

Bobbin 2

Capacity 3

Capacitor 4

Balun 5

Preamplifier 6

Inductance 7

PIN diode 8

Tuning circuit 9

Frequency 10

Proton frequency 11

Non-proton frequency 12

Performance 13 First difference 14

Second difference 15

Interface unit 16

Receiving coil arrangement 20

First performance at proton frequency M1A

First performance at non-proton frequency M1B

Second power at proton frequency M2A

Second performance at non-proton frequency M2B

Another advantage of the configuration as a pure receiving coil is that in this way a preamplifier decoupling is possible, which is not possible with combined transmitting and receiving coils. This technique helps reduce interference between adjacent array elements and is essential when designing arrays.

Claims

Expectations

1. Reception coil (1) for a magnetic resonance tomography and / or spectroscopy system, which can be tuned to receive two different frequencies (10), comprising a coil body (2) for the detection of nuclear magnetic resonance signals with a coil body (2) arranged in or on the coil body (2) Capacitance (3) and a tuning circuit (9) that is operatively connected to the coil body (2) for tuning the receiving coil (1), the tuning circuit (9) having a PIN diode (8) and an inductance (7), the PIN diode (8) is connected in series with the inductance (7) and in parallel with the capacitance (3).

2. Receiving coil (1) according to the preceding claim, characterized in that the tuning circuit (9) is set up to tune the receiving coil (1) to a proton frequency (11) and to a non-proton frequency (12).

3. receiving coil (1) according to the preceding claim, characterized in that the receiving coil (1) is tuned to the non-proton frequency (12) when the PIN diode (8) blocks, and is tuned to the proton frequency (11) when the PIN diode (8) conducts.

4. receiving coil (1) according to one of the two preceding claims, characterized in that the receiving coil (1) to a proton frequency (11) and to the non-proton frequency (12) of ³¹ P can be tuned.

5. receiving coil (1) according to any one of the preceding claims, characterized in that the PIN diode (8) consists of non-magnetic material.

6. receiving coil (1) according to any one of the preceding claims, characterized in that the receiving coil (1) is designed for examining a human body or body part.

7. A method for tuning a receiving coil (1) according to any one of claims 1-6, characterized in that the PIN diode (8) is biased so that the receiving coil (1) is tuned to one of the two frequencies (10) by means of the tuning circuit (9).

8. receiving coil arrangement (20) for a magnetic resonance tomography and / or spectroscopy system, comprising a plurality of receiving coils (1) according to any one of claims 1-6.

9. Magnetic resonance tomography and / or spectroscopy system, comprising at least one receiving coil (1) according to one of claims 1-6 and / or at least one receiving coil arrangement (20) according to claim 8, wherein the magnetic resonance tomography and / or spectroscopy system is designed in particular for examining a human body or body part.

10. Magnetic resonance tomography and / or spectroscopy system according to the preceding claim, characterized in that the magnetic resonance tomography and / or spectroscopy system further comprises at least one transmission coil, the transmission power of the transmission coil or transmission coils at least 2 kW, in particular at least 5 kW , preferably at least 10 kW and particularly preferably at least 20 kW.

11. Use of a PIN diode (8) to tune a receiving coil (1) for a magnetic resonance tomography and / or spectroscopy system for receiving two different frequencies (10), the receiving coil having a bobbin (2) for the detection of nuclear magnetic resonance signals a capacitance (3) arranged in or on the bobbin (2) as well as a tuning circuit (9) in operative connection with the bobbin (2) for tuning the receiving coil (1), the tuning circuit (9) comprising the PIN diode (8) and an inductance (7) and wherein the PIN diode (8) is connected in series with the inductance (7) and in parallel with the capacitance (3).