Circuit with a sensor for detecting a disturbance associated with the circuit

Abstract

The invention relates to a circuit with a sensor for detecting interference associated with the circuit. The invention relates to a circuit for electrical connection in a magnetic resonance tomography device and a magnetic resonance tomography device with a corresponding circuit. The circuit has an interfering electrical conductor, which can receive electromagnetic interference signals from the environment and / or radiate electromagnetic interference signals into the environment. In addition, the circuit has a sensor, which is electrically and / or magnetically coupled to the interfering circuit.

Description

Technical Field

[0001] The invention relates to a line for electrical connection in a magnetic resonance tomography system, which line has a connection to the magnetic resonance tomography system. Background Art

[0002] Magnetic resonance tomography systems are imaging devices that, in order to image the object under examination, align the nuclear spins of the object under examination using a strong external magnetic field and excite the nuclear spins to precess about the alignment using an alternating magnetic field. The precession of the spins from the excited state to a state with less energy or back again generates an alternating magnetic field in response, which is received via an antenna.

[0003] These signals are positionally encoded with the aid of gradient magnetic fields, which subsequently enables the received signals to be associated with volume elements. The received signals are then analyzed and a three-dimensional imaging display of the object under examination is provided. For receiving the signals, preferably a receiving antenna, so-called local coil, which is arranged directly on the object under examination in order to achieve a better signal-to-noise ratio is used. The receiving antenna can also be installed in the patient's bed.

[0004] Magnetic resonance tomography systems require high-frequency shielding in two aspects. On the one hand, high-frequency pulses with a power in the kilowatt range are generated to excite the nuclear spins, which are only partially absorbed in the patient. The radio waves that leave the patient channel (Patient endurchführung) are radiated into the air and therefore must be shielded in order to comply with emission limit values.

[0005] In contrast, the magnetic resonance signals to be received for imaging are extremely weak, and therefore, in order to achieve a sufficient signal-to-noise ratio (SNR), it is necessary to shield against external interfering signals.

[0006] Therefore, in the prior art, expensive shielding rooms are installed around magnetic resonance tomography devices in order to reduce emissions and radiation contamination. Summary of the invention

[0007] Therefore, the technical problem to be solved by the present invention is to reduce the expenditure for shielding.

[0008] The above-mentioned technical problem is solved by the circuit according to the invention and the magnetic resonance tomography device according to the invention.

[0009] The circuit according to the invention is provided for electrical connection in a magnetic resonance tomography device and has an electrical conductor that can conduct an electric current. Due to its electrical conductivity, the conductor also acts as an antenna for electromagnetic waves and can therefore receive or emit electrical interference capacitively or by induction and also forward it along its extension, for example into a shielded area. The circuit according to the invention has a connection line to the magnetic resonance tomography device, for example a fixed electrical connection or an electrical plug connection.

[0010] The line has an interfering electrical conductor. An interfering electrical conductor should be understood as a conductor through which an interfering signal can be transmitted. Here, any signal that does not contribute to image detection and may damage the quality of the image provided is considered an interfering signal in the sense of the present invention. That is to say, here, it may also involve signals that, although these signals are required for image acquisition, do not directly carry image information. Examples are interference on power supply lines, control lines, communication lines, such as devices that communicate with patients or lighting devices in patient channels. However, lines directly related to image generation, such as gradient coil connection lines, shim current lines (Shim-Stromleitung) and their signals may also cause artifacts in image detection, and in this sense also interfering conductors.

[0011] In this case, the interfering electrical conductor can also be a conductor of a line which is actually provided for protecting the signal conductor of the line from interfering signals. For example, the outer conductor of a coaxial line itself can also introduce interfering signals into the shielding room as a conductor. Multiple conductors or cores of a line can also be interfering conductors.

[0012] Here, the interference conductor is designed to receive electromagnetic interference signals from the environment and / or radiate electromagnetic interference signals into the environment, which can only be achieved by the electrical characteristics and arrangement of the interference conductor, and the interference conductor is thus a potential source of introduced interference. However, in the sense of the present application, the interference conductor does not apply any additional interference signal or does not need to apply any additional interference signal to the interference conductor.

[0013] Furthermore, the circuit according to the invention has a sensor which is electrically and / or magnetically coupled to the interfering circuit. Different embodiments of conceivable couplings are described in detail below.

[0014] The sensor is connected or connectable to the magnetic resonance tomography system via a signal connection, via which received interference signals can be forwarded from the interference conductor to a controller of the magnetic resonance tomography system. This enables the controller to identify and suppress interference signals in the magnetic resonance signals thus known.

[0015] The connecting line with the sensor according to the invention advantageously makes it possible to identify and / or detect interference signals on the line as close to the source as possible or at a location where the interference signals on the line are well separated from the useful signals, so that the interference signals can then be effectively suppressed in the image acquisition.

[0016] Other advantageous embodiments are given below.

[0017] In one possible embodiment of the circuit according to the invention, the sensor has a coil or induction coil for inductive coupling with the interference conductor. In this case, the coil is preferably aligned with a surface surrounded by one or more coil windings and substantially perpendicular to the magnetic field vectors generated by the current of the interference signal on the interference signal conductor. In this case, it is considered to be substantially perpendicular when the angle enclosed by the normal vector of the surface and the magnetic field vector is less than 30 degrees, 20 degrees or 10 degrees.

[0018] The inductive coupling by means of the coil advantageously provides a coupling that is electrically isolated from interfering conductors.

[0019] In one conceivable embodiment of the connecting line according to the invention, the interfering conductor is arranged in a surface which is surrounded by one or more coil windings.

[0020] Arrangement around the line enables simple mechanical fixing and is insensitive to small position changes.

[0021] In a possible embodiment of the circuit according to the invention, the coil is a toroidal coil surrounding an interfering conductor. In other words, the conductor of the coil is wound around a toroidal shape in a closed trajectory, which in turn surrounds the interfering conductor and / or the circuit. Here, the toroidal shape can be a solid or hollow winding body, or it can also only give a virtual geometric shape, with which the conductor of the coil is wound. Here, the toroidal part preferably does not have ferrite or other materials that are not suitable for large magnetic fields or otherwise impair the magnetic resonance measurement.

[0022] Advantageously, the toroidal coil is particularly sensitive to a magnetic field which is generated by an interfering conductor through which current flows and which surrounds the interfering conductor in a toroidal manner and at the same time allows an electrically and mechanically robust fixing.

[0023] In one conceivable embodiment of the circuit according to the invention, the sensor has a capacitive coupling element for coupling to the interfering conductor. For example, a planar conductive element is conceivable, which is pressed onto the circuit in a dielectrically isolated manner or surrounds the circuit as a tube or as two half shells.

[0024] Capacitive coupling is advantageously particularly sensitive to interferences whose sources have a high impedance.

[0025] In one embodiment of the circuit according to the invention, it is conceivable that the sensor has a directional coupler. A directional coupler is understood to be any coupling device that, as a coupling element, provides a signal related to the propagation direction of the interference signal on the interference conductor. For example, a directional coupler can be realized by a strip line parallel to the interference conductor or a transformer.

[0026] Directional couplers can distinguish whether a signal originates from a local coil or moves in the direction of a local coil. If interference moving in the direction of a local coil is problematic in image acquisition, the parasitic magnetic resonance signal will only lead to artifacts if it is mistakenly interpreted as an interference signal and attempts are made to compensate for it. In this case, a directional coupler makes it possible to separate the two signals in an advantageous manner and suppress only the interference signal.

[0027] In a possible embodiment of the circuit according to the invention, the sensor resonates at the Larmor frequency of the magnetic resonance tomography device. Here, the magnetic resonance frequency of the nuclear spins to be detected in the static magnetic field B0 of the magnetic resonance tomography device is called the Larmor frequency. In the case of inductive coupling by means of a coil, the resonance can be achieved, for example, by a capacitor connected to the coil.

[0028] For imaging, magnetic resonance signals of nuclear spins with the Larmor frequency are detected in magnetic resonance tomography devices. Image detection is therefore particularly sensitive to interference with this frequency. By means of sensors that resonate at this frequency, particularly important interference signals can be detected with greater amplitudes and therefore better.

[0029] In one conceivable embodiment of the circuit according to the invention, the sensor has a protection device against excitation pulses of a magnetic resonance tomography device. Excitation pulses for nuclear spins at the Larmor frequency with a power of up to kilowatts can lead to damage to input elements, especially in the case of sensors that resonate at this frequency. Therefore, the sensor can have, for example, a passive diode for short-circuiting voltages above the cut-off voltage that occur. It is also possible to use an active circuit that detunes the sensor under the control of a controller.

[0030] Advantageously, the protective element prevents damage to the sensor caused by the magnetic resonance tomography system.

[0031] In one possible embodiment of the magnetic resonance tomography system according to the invention, the sensor is arranged adjacent to the patient channel. The patient channel provides a position at which the magnetic resonance signals are received for image acquisition, which is therefore particularly sensitive to interference. A distance is considered adjacent if it is less than 50%, 20% or 10% of the length of the line or the vacuum wavelength of the radio waves at the Larmor frequency of the magnetic resonance tomography system.

[0032] Advantageously, the arrangement of the sensor in the vicinity of the patient passage or on a line adjacent thereto ensures that as few disturbances as possible are introduced between the sensor and the patient passage and are not detected by the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The characteristics, features, and advantages of the present invention described above and their implementation methods will become clearer and easier to understand with reference to the following detailed description of the embodiments with reference to the accompanying drawings.

[0034] Figure 1 A schematic diagram of a magnetic resonance tomography apparatus having a circuit according to the present invention is shown;

[0035] Figure 2 A schematic diagram showing an embodiment of a circuit with a sensor according to the invention;

[0036] Figure 3 A schematic diagram showing an embodiment of a circuit with a sensor according to the invention;

[0037] Figure 4 A schematic diagram showing an embodiment of a circuit with a sensor according to the invention;

[0038] Figure 5 A schematic diagram showing an embodiment of a circuit with a sensor according to the invention;

[0039] Figure 6 A schematic diagram of a sensor showing an embodiment of a circuit according to the present invention;

[0040] Figure 7 A schematic diagram of a sensor showing an embodiment of a circuit according to the invention is shown. DETAILED DESCRIPTION

[0041] Figure 1 The schematic diagram shows an embodiment of a magnetic resonance tomography system 1 having a circuit 33 according to the invention with a sensor 60 .

[0042] The magnet unit 10 has a field magnet 11, which generates a static magnetic field B0 in the recording area for aligning the nuclear spins of the sample or patient 100. The recording area is characterized by an extremely uniform static magnetic field B0, wherein the uniformity particularly relates to the magnetic field strength or magnitude. The recording area is almost spherical and is arranged in a patient channel 16, which extends through the magnet unit 10 along the longitudinal direction 2. The patient bed 30 can be moved in the patient channel 16 by a movement unit 36. The field magnet 11 is usually a superconducting magnet that can provide a magnetic field with a magnetic flux density of up to 3 T, and even higher in the case of the latest devices. However, for lower field strengths, permanent magnets or electromagnets with normally conductive coils can also be used.

[0043] In addition, the magnet unit 10 has a gradient coil 12, which is designed to superimpose the magnetic field B0 with the variable magnetic field in three spatial directions to spatially distinguish the imaging area in the acquired examination volume. The gradient coil 12 is usually a coil composed of a normally conductive metal wire, which can generate mutually orthogonal fields in the examination volume.

[0044] The magnet unit 10 further has a body coil 14 , which is designed to radiate high-frequency signals fed via signal lines into an examination volume, receive resonance signals emitted by the patient 100 , and output them via the signal lines.

[0045] The control unit 20 supplies the magnet unit 10 with various signals for the gradient coil 12 and the body coil 14 , and analyzes the received signals.

[0046] The control unit 20 therefore has a gradient controller 21 which is designed to supply the gradient coils 12 via supply lines with variable currents which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0047] The control unit 20 also has a radio-frequency unit 22, which is designed to generate radio-frequency pulses with a predetermined time course, amplitude and spectral power distribution for exciting magnetic resonance of nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation pulses can be radiated into the patient 100 via the body coil 14 or also via local transmission antennas.

[0048] The controller 23 communicates with the gradient controller 21 and the high-frequency unit 22 via a signal bus 25 .

[0049] A local coil 50 is arranged on the patient 100 and is connected to the high-frequency unit 22 and its receiver 70 via a line 33 . However, it is also conceivable for the magnetic resonance signals to be received by the body coil 14 and forwarded to the receiver 70 .

[0050] The patient access preferably has a radius R, for which:

[0051] R<(Lambda L *1.841) / (2*Pi)

[0052] Here, Lambda L Lambda gives the wavelength of the radio waves in air at the Larmor frequency of the magnetic resonance tomograph 1. If the radius R is smaller than the term on the right, the radio waves propagate in the patient channel 16 in an exponentially decaying manner and the interfering signals are strongly attenuated in the center of the examination region FoV. L It is also called the limiting wavelength of a circular hollow conductor and the frequency associated with it is called the limiting frequency.

[0053] However, electromagnetic signals entering the patient channel 16 via an electrical conductor such as line 33 do not decay exponentially, since line 33 acts like a coaxial conductor together with the conductive walls of the patient channel. Interference may enter, for example, the shielding of line 33 via inductance or capacitance external to the patient channel 16. Line 33 acts as an interference conductor in the sense of the present invention.

[0054] The local coil 50 thus receives a mixture of magnetic resonance signals and interference signals, which in particular enter the patient channel 16 via interference conductors. By means of active interference suppression, which scales the interference signal and adds it with the opposite sign to the signal of the local coil 50 by the receiver 70, the interference signal in the received signal of the local coil can be reduced or, in the ideal case, completely suppressed. However, for this purpose, the interference signal itself must be known as accurately as possible. Then, for example, the interference signal portion in the received signal of the local coil 50 can be determined by autocorrelation and, by suitable selection of the phase shift and amplification or attenuation, the interference signal portion can be significantly reduced or completely eliminated.

[0055] According to the invention, a sensor 60 is therefore arranged on the interference line in order to detect interference signals which are captured by the interference line and enter the patient channel 16 as accurately as possible. In the following, different embodiments of the sensor are shown.

[0056] exist Figure 2 FIG. 3 shows, by way of example, a line 33 between a local coil 50 and a receiver 70 as an interference conductor. The alternating current I induced by the electromagnetic interference field ST Flows on the outer conductor of the coaxial line. The source may be equipment in other rooms or buildings. Alternating current I ST Again, an alternating magnetic field B is generated which surrounds the signal conductor 33 or the interference conductor. STThe sensor 60 according to the invention is coupled to the interfering magnetic field B via a coil or induction coil 61. ST Ideally, the induction coil 61 is oriented relative to the interfering conductor so that the normal vector of the surface surrounded by the induction coil 61 is aligned with the magnetic field B extending in a circle around the signal line. ST The sensor 60 is oriented in a tangential manner to the magnetic field lines of the induction coil 61. In this way, the voltage induced in the induction coil 61 is maximal and the sensor 60 provides a disturbance signal that is as large as possible and has little interference. In addition, the sensor 60 preferably has a low-noise preamplifier 62 (LNA), which amplifies the induction signal before forwarding it to the receiver 70 via the sensor line 63. In this case, the induction coil 61 can also have multiple windings in order to increase the induced voltage. In this case, the induction coil 61 is electrically isolated from the interfering conductor.

[0057] In principle, instead of coils or induction coils, other sensors 60 that can detect the amplitude and / or phase of a high-frequency alternating magnetic field are also conceivable, such as Hall detectors or Josephson contact devices or SQIDs (superconducting quantum interference devices).

[0058] Figure 3 A further embodiment of a sensor 60 according to the invention is shown. In this case, the sensor 60 is arranged, by way of example, on a line 31 for supplying energy to a lighting device, for example for a patient channel 16 .

[0059] Here, the sensor 60 has an induction coil 61, whose winding is wound around a winding body that surrounds the line 33 or the interfering conductor on the periphery. It is also conceivable that the winding body itself is virtual, that is, the winding is arranged in this way without support without the winding body. Here, the winding body preferably has the shape of a ring or a cylindrical ring, but it is also conceivable that instead of a ring, the interfering conductor is surrounded by an ellipse, an oval or a polygon. It is also conceivable that the cross-section of the winding body, and thus the shape of the individual windings of the induction coil 61, is not only circular, but also, for example, elliptical, polygonal, or has a mixed shape, such as a D-shape. In other words, the individual windings extend around the winding body and are arranged around the interfering conductor along the periphery, so that, as shown, the two terminals of the induction coil 61 are placed side by side, so that they can return to the low-noise preamplifier 62 with a small distance and a small closed surface.

[0060] Since along the magnetic field line B STThe magnetic field lines extend through the largest closed surface, so that an induction coil 61 with this shape has the maximum induced voltage. At the same time, the sensor is easy to push open and is insensitive to position changes and external interference signals, ie, not conducted on the interfering conductor.

[0061] Figure 4 Another variant is shown. Here, it is assumed by way of example that the gradient connecting lines connecting the controller 20 with the gradient coils 12 are interference lines.

[0062] Here, the reception of the interference signal is not by induction, but by the electric field component of the interference signal in a capacitive manner. Here, in a possible embodiment, the sensor 60 may have one or two capacitive coupling elements 64 as shown here. It is arranged near the insulator of the interference conductor, preferably arranged outside the insulator of the interference conductor, and electrically isolated from it. Among them, the electric field component of the high-frequency interference propagating along the interference conductor causes a voltage difference, which is amplified by the low-noise preamplifier 62 and transmitted to the receiver 70. It is also conceivable that only one capacitive coupling element 64 is provided, and the reference potential is the signal ground.

[0063] exist Figure 5 The variant of the sensor shown in FIG. 1 again has a directional coupler. In this case, any form of signal collector of the interfering conductor is regarded as a directional coupler, which provides a signal related to the propagation direction of the interfering signal on the interfering conductor. This can be a general directional coupler, but it is also conceivable to combine multiple inductive or capacitive coupling elements that provide direction-dependent signals.

[0064] The directional coupler enables a distinction to be made between signals whose propagation direction is directed away from the local coil 50 and signals entering the local coil. Parasitic magnetic resonance signals on the outer conductor of the coaxial cable can thus be distinguished from incoming interference signals in an advantageous manner, so that magnetic resonance signals are not erroneously identified as interference signals and, during image evaluation, no artifacts are generated as a result of interference suppression.

[0065] exist Figure 6In an embodiment of the invention, the sensor 60 has a resonant element 66 so that the sensor 60 is particularly sensitive to a predetermined frequency, preferably to the Larmor frequency of the magnetic resonance tomography device 1. Since the image detection is performed by means of magnetic resonance signals from nuclear spins, the frequency of these magnetic resonance signals corresponds in the static magnetic field B0 to the Larmor frequency of the spins in the magnetic field, and therefore the image detection reacts particularly sensitively to interferences in this frequency range. That is to say, better interference suppression is particularly effective here and can be achieved in this frequency range by a higher output signal of the sensor 60. This can be achieved, for example, by the resonance of the sensor having a maximum amplitude at the Larmor frequency. For Figure 6 With the toroidal coil shown by way of example in FIG. 1 , this can be achieved by means of a capacitor as resonant element 66 in a parallel resonant circuit.

[0066] Due to the large dynamic range between the interference signal and the magnetic resonance signal on the one hand and the high-frequency pulse for exciting the nuclear spins on the other hand, in particular in resonant sensors, the sensor, in particular the low-noise amplifier 62, can be damaged, for example, due to large input amplitudes during the excitation pulse. Therefore, as protection, an active protection element 67, here in the form of a PIN diode, can be provided, which, under the control of the controller 20, reduces the input signal of the low-noise amplifier 62. As in Figure 6 As shown in FIG. 1 , this can be achieved by using a PIN diode as a variable capacitor to detune the resonant circuit consisting of the induction coil 61 and the resonant element 66. However, it is also conceivable, for example, that the PIN diode is operated as a switch, which short-circuits the resonant circuit or detunes it due to an inserted capacitance or inductance. Other mechanical or electronic switches can also be used for this purpose.

[0067] Figure 7 Another conceivable embodiment of a sensor 60 is shown with a capacitive coupling element 64 which is tuned to the Larmor frequency via an inductor as a resonant element 66. Also implemented in this figure is an exemplary passive protection element 68 consisting of two antiparallel diodes which short-circuit any signal greater than a threshold voltage and thus limit it.

[0068] Other combinations of inductive pick-up or induction coil 61 or capacitive coupling element 64 with active protective element 67 and / or passive protective element 68 are also conceivable within the meaning of the present invention.

[0069] Although the present invention has been further shown and described in detail through preferred embodiments, the present invention is not limited to the disclosed examples, and those skilled in the art may derive other variations therefrom without departing from the scope of protection of the present invention.

Claims

1. A line for an electrical connection in a magnetic resonance tomography device (1), the line having a connection leading to the magnetic resonance tomography device (1), wherein: The line (33) has an interference conductor, which is designed to receive electromagnetic interference signals from the environment and / or radiate electromagnetic interference signals into the environment, wherein the line (33) has a sensor (60) which is electrically and / or magnetically coupled to the interference line, wherein the line (33) has a signal connection, which is designed to provide the interference signal received by the sensor to the magnetic resonance tomography device (1) at a connector for processing, and wherein The sensor (60) has a directional coupler (65).

2. The circuit according to claim 1, wherein: The sensor (60) has a coil for inductive coupling to an interfering conductor.

3. The circuit according to claim 2, wherein: The interfering conductor extends through the area surrounded by the coil.

4. The circuit according to claim 3, wherein: The coil is a toroidal coil which surrounds the interfering conductor.

5. The circuit according to claim 1, wherein: The sensor (60) has a capacitive coupling element (64) for coupling to the interfering conductor.

6. The circuit according to claim 1 or 2, wherein: The sensor (60) resonates at the Larmor frequency of the magnetic resonance tomography system (1).

7. The circuit according to claim 1 or 2, wherein: The sensor (60) has a protection device against excitation pulses of the magnetic resonance tomography system (1).

8. A magnetic resonance tomography apparatus having a circuit (33) according to any one of claims 1 to 7, wherein: The magnetic resonance tomography device (1) has a controller (23) which is designed to generate a magnetic resonance image based on the received magnetic resonance signals and in accordance with the interference signals received by the sensor (60).

9. The magnetic resonance tomography apparatus according to claim 8, wherein: The sensor (60) is arranged adjacent to the patient passage (16).

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