DE202017004947U1 - Scalable Broadband Switching Matrix for Magnetic Resonance Imaging and Magnetic Resonance Imaging and Local Coil therefor - Google Patents

Abstract

A local coil for a magnetic resonance tomograph (1), wherein the local coil (50) has an antenna coil (51) and a detuning device (40), wherein the detuning device (40) has a control input and is designed in response to a first control signal at the control input Antenna coil (51) to detune, wherein the detuning is designed to receive the energy required for detuning substantially from a source of energy other than the control input.

Description

The invention relates to a scalable broadband switching matrix for switching magnetic resonance signals from local coils to receiver inputs in a magnetic resonance tomograph as well as a local coil for use with the broadband switching matrix and a magnetic resonance tomograph with a corresponding broadband switching matrix.

Magnetic resonance tomographs are imaging devices which, in order to image an examination subject, align nuclear spins of the examination subject with a strong external magnetic field and excite them by means of an alternating magnetic field for precession. The precession or return of the spins from this excited to a lower energy state, in turn, generates an alternating magnetic field which is received via antennas.

With the aid of magnetic gradient fields, a spatial coding is impressed on the signals, which subsequently enables an assignment of the received signal to a volume element. The received signal is then evaluated and a three-dimensional imaging of the examination subject is provided. To receive the signal preferably local receive antennas, so-called local coils are used, which are arranged to achieve a better signal-to-noise ratio directly to the examination object. The receiving antennas can also be installed in a patient bed.

Local coils are often constructed as a matrix with a plurality of antenna coils. This makes it possible, for example, to simultaneously detect magnetic resonance signals in non-overlapping sensitivity regions of different coils and thus to accelerate the imaging. However, the maximum number of simultaneously detectable channels is limited to the antenna coils that are simultaneously in the homogeneous B0 field of the recording area. With a spine coil for taking pictures of the spinal column and the torso, there are always several antenna coils not in the receiving area and do not provide usable signals. The number of receivers is thus smaller than the number of antenna coils, whereby it must be possible to couple each antenna coil to at least one receiver at certain points in time. For this purpose, switching matrices are used, which can correspondingly connect M connections for the local coils with N receivers.

From the pamphlets DE 10 2013 218226 A1 and DE 10 2014 202862 A1 are corresponding switching matrices known.

The individual antenna coils are resonantly tuned to the Larmor frequency of the magnetic resonance signals for maximum sensitivity and signal-to-noise ratio (SNR). The excitation pulses with several kilowatts of power are transmitted at the same frequency, so that the antenna coils must be protected during this time. At the same time, it must be prevented that voltages or currents in the antenna coils endanger the patient directly or as a result of heat. The antenna coils are usually detuned and / or damped by a controllable capacitance, for example in the form of PIN diodes.

The required control signals are generated because of high voltage or currents in their own units and passed directly to the local coils. For a corresponding local coil with an antenna coil matrix correspondingly many switches and cables to the antenna coil are required in order to detune them individually.

It could therefore be an object of the invention to provide a less expensive magnetic resonance tomograph with a corresponding local coil.

The object is achieved by a local coil according to the invention as claimed in claim 1, a broadband switching matrix according to the invention as claimed in claim 7 and a magnetic resonance tomograph according to the invention.

The inventive local coil for a magnetic resonance tomograph has an antenna coil and a detuning device. The detuning device has a control input and is designed to detune the antenna coil in response to a first control signal at the control input. As detuning in the sense of the invention, a change in electrical properties of the antenna coil is considered, which means that in the case where the antenna coil is in the recording area during an excitation pulse of the magnetic resonance tomograph, voltages and currents are limited to a level that is harmless for a patient. The corresponding values for maximum voltages and current-related heating can be found in the relevant regulations. This effect can be achieved in particular by changing the resonant frequency or by damping the antenna coil.

In this case, the detuning device is designed to receive the energy required for detuning substantially from a source of energy different from the control input. In this case, it is to be understood that an energy source is essentially unequal to the control input such that the one of the Detuning energy required to detune more than half, more than 80%, 90% or 95% from another energy source. For example, it is conceivable that the energy for detuning is provided by an energy store or energy supply common to a plurality of antenna coils and detuning devices. For example, switching elements may be provided in the detuning device which, with a small amount of energy supplied via the control input, bring about an energy flow from the energy store or the energy supply to the detuning device and thus the detuning. Further possible embodiments are set forth in the subclaims.

If the control input only a small proportion of the energy required for detuning must be provided, it is also possible in an advantageous manner to transmit the control signals with low currents and / or voltages. This makes it possible to route the control signals for example via a broadband switching matrix for small signals and thus over the existing broadband switching matrix for magnetic resonance signals.

The broadband switching matrix according to the invention has N first matrix connections, M second matrix connections, where N is greater than M, and a matrix control connection. The broadband switch matrix is configured to establish a detachable signal connection between a first matrix connection and a second matrix connection in dependence on a control signal received via the matrix control input. The detachable signal connection is designed to transmit a magnetic resonance signal from a first matrix connection to a second matrix connection. This means in particular that the signal connection for the frequency range of the magnetic resonance signal has an attenuation of less than 3 dB, 6 dB, 12 dB or 18 dB. Preferably, crosstalk between individual signal connections is less than -20 dB, -40 dB or -60 dB. The signal connection degrades the signal-to-noise ratio for a transmitted magnetic resonance signal by at most 1 dB, 3 dB, 6 dB or 12 dB. Preferably, the magnetic resonance signal is an analog magnetic resonance signal that has not yet been digitized by an analog-to-digital converter.

The signal connection is furthermore designed to transmit a first control signal for a control input of a detuning device of a local coil according to the invention from the second matrix connection to the first matrix connection. In particular, the attenuation is also less than 3 dB, 6 dB or 12 dB, and the broadband switching matrix is designed to transmit levels and currents of the control signal without damage or degradation. Currents for a control signal are for example up to 1 mA, 2 mA, 5 mA or 10 mA and voltages up to 1 V, 3 V, 5 V or 10 V.

Advantageously, the broadband switching matrix according to the invention allows simultaneous transmission of magnetic resonance signals from a local coil to a receiver and, conversely, control signals for the detuning device of the local coil. Thus, it is only necessary for M instead of N local coils to provide control signals for the detuning. Advantageously, N minus M signal generators can thus be saved.

The magnetic resonance tomograph according to the invention has a local coil according to the invention and a broadband switching matrix according to the invention.

The magnetic resonance tomograph according to the invention can be used with only M signal generators for the detuning all activated detuning the maximum M of a total of N antenna coils activate and are thus provided easier and cheaper.

Further advantageous embodiments of the invention are specified in the subclaims.

In a conceivable embodiment of the local coil according to the invention, the local coil is designed to receive the energy required for detuning substantially from a source of energy different from the control input. For example, by rectifying the excitation pulse received by the antenna coil, a direct current for supplying the detuning device can be obtained. It is conceivable that the detuning detuned the antenna coil so far that the voltage obtained from the antenna coil voltage decreases and thus adjusts a balance with the decreasing detuning effect with decreasing voltage.

Advantageously, a power supply by means of the antenna coil and the excitation pulse requires no additional lines for the detuning. A self-regulating equilibrium can limit the energy extraction from the high-frequency alternating field to a necessary minimum.

In one possible embodiment of the local coil according to the invention, the detuning device is designed to trigger a detuning of the antenna coil as a function of an alternating current signal at the control input. It may be at the AC signal to a carrier frequency act, in the simplest case even an unmodulated.

Advantageously, AC signals can be separated based on their frequency. In addition, magnetic resonance signals are high-frequency AC signals, so that it is possible to provide a broadband switching matrix for both types of signals with less change.

In a conceivable embodiment of the local coil according to the invention, the local coil has a diplexer. As a diplexer according to the invention, a device is considered which makes it possible to combine the control signal and a magnetic resonance signal for transmission on a common signal line or to separate it again for further processing. An exemplary diplexer can perform, for example, the separation based on different frequency ranges or propagation direction of magnetic resonance signal and control signal. The diplexer has a first signal terminal, a second signal terminal and a third signal terminal. In this case, the first signal terminal with the control input in signal connection, the second signal terminal with the antenna coil for receiving a magnetic resonance signal and the third signal terminal with a local coil terminal for connection to the magnetic resonance tomograph. It is conceivable that additional signal processing units are connected in between, for example a preamplifier, AD converter or frequency converter between antenna coil and diplexer. The diplexer is designed to output a first control signal arriving at the third signal terminal, preferably at the first signal terminal, and to output a magnetic resonance signal arriving at the second signal terminal via the third signal terminal. For the purposes of the invention, preference is hereby given for the attenuation between the preferred signal terminal and the other, non-preferred signal terminal to be at least 6 dB, 12 dB, 18 dB 30 dB or more. For example, for the control signal, the first signal terminal is the preferred signal terminal and the second signal terminal is the non-preferred signal terminal.

The diplexer advantageously offers a simple possibility of uniting the different signals for transport via the broadband switching matrix and subsequently separating them again.

In one possible embodiment of the local coil according to the invention, the diplexer has a fourth signal connection. The diplexer is designed to output a second control signal arriving via the third signal connection, preferably at the fourth signal connection. It is preferable to interpret as already described. The second control signal may differ from the first control signal and the magnetic resonance signal, for example, by a different, disjoint frequency range.

Advantageously, further control signals can be transmitted simultaneously and separated again with the diplexer.

In a conceivable embodiment of the local coil according to the invention, the detuning device is designed to detune the antenna coil without a first control signal at the local coil connection. When detuning, it is to be regarded as if the resonant frequency of the antenna coil in the detuned state is not equal to the Larmor frequency of a magnetic resonance signal to be detected with the local coil, ie deviates, for example, by 1%, 2%, 5%, 10%, 20% or more. As a Larmor frequency, for example, the frequency of the hydrogen nucleus at 1.5 T or 3 T are considered. In particular, the antenna coil is detuned to such an extent that, in the case of an excitation pulse of the magnetic resonance tomograph, the local coil in a patient tunnel of the magnetic resonance tomograph does not present a danger to a patient, d. H. in particular, that the voltage and the currents in the antenna coil neither pose a danger to the patient according to the safety guidelines, neither by electrical nor by heat effect, nor damage any electronics of the local coil.

Advantageously, such a local coil according to the invention can also be separated in the receiving area by the broadband switching matrix from a signal generator for the first control signal, without the patient or local coil being endangered. No active detuning is necessary, passive measures in the local coil replace an active detuning by an external control signal.

In one possible embodiment of the broadband switching matrix according to the invention, the broadband switching matrix is designed to transmit an AC signal as the first control signal. In particular, a frequency range of the first control signal is not equal to a frequency range of the magnetic resonance signal, for example between 1 kHz and 1 MHz. Preferably, the first control signal is a small signal having a maximum amplitude of less than 10V, 5V, 2V or 1V and a maximum current of less than 20mA, 10mA, 5mA. 2mA or 1mA.

Advantageously, AC signals can be separated based on their frequency. A broadband switching matrix for AC signals, especially for small signals with different frequency range can be with little realize additional effort and allows the simultaneous switching and transmission of magnetic resonance signal and control signal by means of the broadband switching matrix.

The magnetic resonance tomograph according to the invention shares the advantages of the inventive local coil and broadband switching matrix.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which will be described in detail in conjunction with the drawings.

Show it:

1 a schematic representation of a system according to the invention of magnetic resonance tomograph, receiving antenna and connecting cable.

2 a schematic representation of an embodiment of a local coil according to the invention;

3 a schematic representation of a detuning device according to the invention;

4 a control unit of a magnetic resonance tomograph according to the invention.

1 shows a schematic representation of an embodiment of a magnetic resonance tomograph 1 with a local coil according to the invention 50 ,

The magnet unit 10 has a field magnet 11 a static magnetic field B0 for aligning nuclear spins of samples or the patient 100 generated in a recording area. The recording area is characterized by an extremely homogeneous static magnetic field B0, wherein the homogeneity relates in particular to the magnetic field strength or the magnitude. The receiving area is almost spherical and in a patient tunnel 16 arranged in a longitudinal direction 2 through the magnet unit 10 extends. A patient bed 30 is in the patient tunnel 16 from the track unit 36 movable. Usually, it is the field magnet 11 a superconducting magnet that can provide magnetic fields with a magnetic flux density of up to 3 T, even more with the latest devices. For lower field strengths, however, it is also possible to use permanent magnets or electromagnets with normally conducting coils.

Furthermore, the magnet unit 10 gradient coils 12 auf, which are adapted to superimpose the magnetic field B0 variable magnetic fields in three spatial directions for the spatial differentiation of the detected imaging areas in the examination volume. The gradient coils 12 are usually coils of normal conducting wires that can generate mutually orthogonal fields in the examination volume.

The magnet unit 10 also has a body coil 14 configured to radiate a high frequency signal supplied via a signal line into the examination volume and from the patient 100 to receive emitted resonance signals and output via a signal line.

A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

This is how the control unit points 20 a gradient control 21 which is designed to be the gradient coils 12 To supply over supply lines with variable currents, which provide time coordinated the desired gradient fields in the examination volume.

Furthermore, the control unit 20 a radio frequency unit 22 which is adapted to a high-frequency pulse having a predetermined time course, amplitude and spectral power distribution for exciting a magnetic resonance of the nuclear spins in the patient 100 to create. In this case, pulse powers in the range of kilowatts can be achieved. The excitation pulses can via the body coil 14 or via a local transmitting antenna in the patient 100 be radiated.

A controller 23 communicates via a signal bus 25 with the gradient control 21 and the radio frequency unit 22 ,

On the patient 100 is a local coil 50 arranged, which via a connecting cable according to the invention 33 with the radio frequency unit 22 connected is.

A possible embodiment of a local coil according to the invention 50 is in 2 shown schematically in detail.

An antenna coil 51 receives the magnetic resonance signal, which is subsequently passed through a low-noise preamplifier 52 (Low noise amplifier, LNA) is amplified. The output signal of the preamplifier 52 becomes a diplexer 54 fed. The diplexer 54 performs a signal separation / mixing between the amplified magnetic resonance signal, the via the local coil connection 59 to the magnetic resonance tomograph 1 is forwarded, and one of the magnetic resonance tomograph 1 via the local coil connection 59 incoming first control signal. This can be done, for example, based on the frequency ranges. In 2 is in the diplexer 54 indicated by the capacitor, a high pass for the magnetic resonance signal and for the first control signal through the inductance a low pass. Such a simple embodiment may operate at a Larmor frequency of 30 MHz or higher and for a first control signal with an AC voltage having a frequency less than 1 MHz, for example 100 kHz. For example, a diplexer would also be conceivable 54 which utilizes a running direction of the signal and executed as a directional coupler separates an incoming from an outgoing signal. However, several control signals with different frequencies such as 100 kHz and 300 kHz would be conceivable.

An incoming first control signal is from a signal connection from the first signal terminal of the diplexer 54 the control input of the detuning device 40 fed, so the magnetic resonance tomograph 1 via a control signal via the local coil connection 59 the antenna coil 51 can be upset.

The detuning device 40 refers to the energy for detuning substantially over the antenna coil 51 from the excitation pulse of the magnetic resonance tomograph 1 itself. The first control signal from the magnetic resonance tomograph 1 on the other hand, preferably only activates a switch which suppresses or activates the detuning.

A highly simplified embodiment of such detuning 40 is in 3 shown. In the antenna coil 51 is a capacitance diode in this conceivable embodiment 41 shown having a parallel resonant circuit with the antenna coil 51 forms and whose capacity is the resonant frequency of the parallel resonant circuit with the antenna coil 51 changed. The antenna coil 51 is about capacity 42 to a subsequent balun 55 coupled, which is the balanced output signal of the antenna coil 51 converted into an asymmetric signal with respect to a ground. From the output of the balun 55 is by a rectification, represented by a diode 43 and capacity 44 , a DC voltage obtained for decoupling from the received radio frequency of the antenna coil 51 via inductances 45 the capacitance diode is supplied. The voltage then caused by the capacitance change detuning the parallel resonant circuit of antenna coil 51 and the varactor diode 41 , Due to the non-linearity of the rectifier diode 43 It uses the detuning only at a value of the received high-frequency signal, which is far above the imaging magnetic resonance echo, but also far below a signal level, which is dangerous for the patient 100 or the local coil 50 is. With increasing voltage at the varactor diode 41 increases the detuning of the resonant frequency, which in turn increases the amplitude of the diode 43 reduces high frequency signal supplied and leads to an equilibrium. No external signal is required for detuning.

However, an AC signal as the first control signal of the diode 46 supplied and rectified, so is due to the capacitor 47 a DC voltage, which is a transistor 48 turns on and off the diode 43 short-circuited voltage for detuning. In this way, by a first control signal in the circuit of 3 the detuning can be deactivated or the capacitance diode can be set to a defined capacitance value. Also, the transistor reduces 48 Advantageously, the switching time in a non-detuned state, otherwise the voltage to detun only by leakage currents of the diodes can flow.

The circuit of 3 is only an exemplary embodiment, there are also other elements and circuits for detuning conceivable. For example, instead of the transistor 48 also a MOS-FET or other switch can be used.

In 4 is an exemplary embodiment of a control unit 20 a magnetic resonance tomograph according to the invention 1 exemplified. The radio frequency unit 22 has connections for signal connections to local coils according to the invention 50 on. The signal connections can be used, for example, as cables or as internal connections, for example in a patient couch 30 be executed.

The receiving unit 22 has a number of M recipients 26 for receiving magnetic resonance signals of the local coils 50 on. The number M is the recipient 26 less than the number N of signal connections to the local coils 50 , For example, a spine coil 64 or 128 antenna coils 51 exhibit. Because of the extension along the spine, however, only a small proportion of it is always in the receiving area (FoV) at the same time. To the N antenna coils 51 with the M receivers 26 flexible to connect, there is a broadband switching matrix 24 between the recipients 26 and the signal lines for the local coils. The broadband switch matrix is designed to receive magnetic resonance signals from the local coils 50 to the recipients 26 switch through flexibly.

The broadband switching matrix according to the invention 24 In addition, it is also capable of receiving a first control signal from one of the M terminals of the receivers 26 to one of the N terminals for the signal lines to the local coils 50 to switch. For example, the first control signal differs from a magnetic resonance signal in that it lies in a different, disjoint frequency range. For example, magnetic resonance signals, also converted into an intermediate frequency, are located above 1 MHz, 10 MHz or 20 MHz, while a control signal has, for example, a frequency below 1 MHZ, 100 kHz or 10 kHz. Preferably, the first control signal is an AC signal. The magnetic resonance signal and the first control signal also differ in their amplitude. Magnetic resonance signals usually only amplitudes in the milli or microvolt range, while the first control signal can have an amplitude of a few volts and a current of a few mA. For example, the amplitude of the first control signal may be less than 10 V (effective, RMS) 5 V, 2 V or 1 V, and the current may be less than 10 mA, 5 mA or 1 mA.

The first control signal is from a control signal generator 27 generated and via a diplexer 28 the broadband switching matrix 24 fed. The broadband switching matrix 24 then flexibly switches the maximum M first control signals to M of the N local coils 51 further. In the opposite way, the magnetic resonance signals of M become the N local coils 51 to the M recipients 26 switched through, the diplexer 28 prevents the receiver 26 be disturbed by the first control signals by sending these towards the receiver 26 sufficiently suppressed, for example by 12 dB, 24 dB, 36 dB, 48 dB or more. For the diplexers, please also refer to the notes to 2 directed.

In the magnetic resonance tomograph according to the invention, it is also conceivable to use the magnetic resonance signals from an antenna coil 51 for transmission via the signal line to the receivers 26 also be multiplexed, for example by a frequency division. In such a case, it is also conceivable that the signal generator 27 is designed, for example, to generate 2 × M first control signals, conceivable with two different carrier frequencies in said frequency range for the first control signals. The diplexer 28 is then designed, these first control signals to the M terminals of the broadband switch matrix 24 to apply. The broadband switching matrix 24 is then further designed, these two first control signals to one of the N terminals to the local coils 50 turn on.

Although the invention has been further illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013218226 A1 [0005]
• DE 102014202862 A1 [0005]

Claims (10)

Local coil for a magnetic resonance tomograph ( 1 ), wherein the local coil ( 50 ) an antenna coil ( 51 ) and a detuning device ( 40 ), wherein the detuning device ( 40 ) has a control input and is designed, in dependence on a first control signal at the control input, the antenna coil ( 51 ), wherein the detuning device is adapted to receive the energy required for detuning substantially from a source of energy other than the control input. A local coil according to claim 1, wherein the power source for the detuning device ( 40 ) the antenna coil ( 51 ). A local coil according to claim 1 or 2, wherein the first control signal is an AC signal. Local coil according to claim 3, wherein the local coil ( 50 ) a diplexer ( 54 ), wherein the diplexer ( 54 ) has a first signal terminal, a second signal terminal and a third signal terminal and the first signal terminal with the control input, the second signal terminal with the antenna coil ( 51 ) for receiving a magnetic resonance signal and the third signal terminal having a local coil connection ( 59 ) for connection to the magnetic resonance tomograph ( 1 ) is in electrical signal connection, the diplexer ( 54 ) is configured to output a first control signal arriving at the third signal terminal, preferably at the first signal terminal, and outputting a magnetic resonance signal arriving at the second signal terminal via the third signal terminal. A local coil according to claim 4, wherein the diplexer ( 54 ) has a fourth signal terminal and the diplexer is designed to output a second control signal incoming via the third signal terminal, preferably at the fourth signal terminal. Local coil according to one of the preceding claims, wherein the detuning device ( 40 ), the antenna coil ( 40 ) without detuning a first control signal at the local coil connection in such a way that during an excitation pulse of the magnetic resonance tomograph ( 1 ) the local coil in a patient tunnel ( 16 ) of the magnetic resonance tomograph ( 1 ) no danger to a patient ( 100 ). Broadband switch matrix for a magnetic resonance tomograph ( 1 ), where the broadband switching matrix ( 24 ) N first matrix connections, M second matrix connections and a matrix control connection, where N is greater than M, wherein the broadband switching matrix ( 24 ) is adapted to establish a detachable signal connection between a first matrix terminal and a second matrix terminal in response to a control signal received via the matrix control input, the detachable signal connection being adapted to transmit a magnetic resonance signal from a first matrix terminal to a second matrix terminal and a first control signal from the second matrix terminal to the first matrix terminal. A broadband switching matrix according to claim 7, wherein the first control signal is an AC signal. Magnetic resonance tomograph with a broadband switching matrix ( 24 ) according to claim 7 and a local coil ( 50 ) according to one of claims 1 to 6, wherein the control input of the detuning device ( 40 ) is electrically connectable to a first matrix terminal of the broadband switching matrix. Magnetic resonance tomograph according to Claim 9 with a broadband switching matrix ( 24 ) according to claim 8 and a local coil ( 50 ) according to one of claims 4 to 6, wherein the local coil connection ( 59 ) is electrically connectable to a first matrix terminal.

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