Method and device for taking into account magnetic resonance signals in noise suppression

Abstract

The invention relates to a method for suppressing interference signals in image acquisition using a magnetic resonance tomography device, the magnetic resonance tomography device having an antenna and an interference signal sensor. The magnetic resonance tomography device receives a reference interference signal via the interference signal sensor, receives a magnetic resonance signal via the antenna, and reduces the component of the interference signal in the magnetic resonance signal based on the reference interference signal. The method is characterized in that, when reducing the interference signal, it is taken into account that the reference interference signal also has a signal component of the magnetic resonance signal.

Description

Technical Field

[0001] The invention relates to a method for actively suppressing interference in a magnetic resonance tomography system and to a magnetic resonance tomography system having a receiver. Background Art

[0002] A magnetic resonance tomography device is an imaging device that uses a strong external magnetic field to align the nuclear spins of the object under examination for imaging, and excites the nuclear spins to precess around the alignment by means of an alternating magnetic field. The precession or return of the spins from the excited state to a state with lower energy then generates an alternating magnetic field in response, which is received by an antenna.

[0003] With the help of the gradient magnetic field, a position encoding is applied to the signal, which can then associate the received signal with a volume element. The received signal is then analyzed and a three-dimensional imaging display of the examination object is provided. For receiving the signal, a local receiving antenna, a so-called local coil, is preferably used, which is arranged directly on the examination object to achieve a better signal-to-noise ratio. The receiving antenna can also be installed on the patient couch.

[0004] Magnetic resonance tomography systems require high-frequency shielding in two ways. On the one hand, high-frequency pulses with powers in the kilowatt range are generated to excite the nuclear spins, which are only partially absorbed in the patient. Radio waves that leave the patient tunnel are radiated into the room and therefore must be shielded in order to comply with radiation limit values.

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

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

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

[0008] The aforementioned technical problem is solved by a method according to the invention for operating a magnetic resonance tomography system.

[0009] The method according to the present invention is provided for suppressing interference signals in magnetic resonance recordings performed using a magnetic resonance tomography device. Here, not only is the passive reduction by shielding measures regarded as suppression of interference signals, but also steps and measures in the processing of received signals are utilized. The magnetic resonance tomography device has a controller and a receiver. Here, the receiver is designed to record the magnetic resonance signals required for imaging by one or more antennas and to sort them out for subsequent image reconstruction. This may include, for example, amplification and filtering. Here, the receiver is particularly designed to process magnetic resonance signals at Larmor frequencies, wherein the Larmor frequencies are predetermined by the static magnetic field B0 of the magnetic resonance tomography device and the magnetic moment or spin of the nucleus to be acquired.

[0010] The magnetic resonance signals are received by one or more antennas, for example, by a local coil or a body coil with an antenna coil. In this case, the receiver has a separate receiving channel for each antenna coil, or a receiving channel for the combined signals of multiple antennas. In this case, the signal generated at least mainly by the resonance of the excited nuclear spins of the nucleus to be examined is regarded as the magnetic resonance signal of the antenna. In this case, there will inevitably be a part of noise or other interference signals, but compared with the signal of the nuclear spin, the noise or other interference signals will be attenuated by 12dB, 18dB, 24dB, 36dB or more.

[0011] In addition, the magnetic resonance tomography apparatus also has one or more interference signal sensors. An antenna or sensor that records interference signals more strongly than the magnetic resonance signal, for example, 6 dB, 12 dB, 18 dB or more higher than the magnetic resonance signal, is considered to be an interference signal sensor. Here, the interference signal sensor can be, for example, an antenna that preferably records interference signals due to its location outside the patient tunnel. However, dedicated sensors, such as induction coils that measure interference signals from the power supply line, are also conceivable.

[0012] In the steps of the method according to the invention, the receiver receives a reference interference signal via an interference signal sensor. In a further step, the receiver receives a magnetic resonance signal via an antenna. Here, the acquisition of the reference interference signal can be carried out temporally separately from the acquisition of the magnetic resonance signal, i.e., during a non-intersecting time period, so that the interference signal sensor can also be an antenna for image acquisition. Alternatively, the spatial separation can be achieved by an interference signal sensor that is also spatially spaced apart from the antenna for receiving the magnetic resonance signal.

[0013] It is conceivable here that, as has already been explained for the interference signal sensor, the reference interference signal also has a small component of the magnetic resonance signal. The two signals can be received simultaneously, but it is also conceivable to receive the two signals simultaneously and separately at different times or alternately. In particular, in the case of separation in time, the radiation of the received nuclear spins is referred to as a magnetic resonance signal, even if this radiation is not further used for imaging. Since the signal of the nuclear spin decreases exponentially over time, there are also magnetic resonance signals outside the receiving window for imaging, even if their intensity is lower.

[0014] In another step, the receiver reduces the component of the interference signal in the magnetic resonance signal based on the reference interference signal. For example, the receiver can use an amplifier to amplify the reference interference signal of the interference signal detector by a factor, and use a delay element to delay it in phase, so that the reference interference signal corresponds to the component of the interference signal in the magnetic resonance signal of the antenna with its amplitude and has an opposite sign. For example, a summing element can be used to reduce the component of the interference signal in the magnetic resonance signal by adding the two signals, and in an ideal case, it is reduced to almost zero. For this purpose, the receiver and / or the controller determine the attenuation and phase shift of the interference signal in the magnetic resonance signal, for example, by the autocorrelation of the magnetic resonance signal and the reference interference signal.

[0015] However, at least when determining or adjusting the attenuation of interference signals in the magnetic resonance signal and the determination of the phase shift during imaging, a small portion of the magnetic resonance signal is always contained in the reference interference signal, since the magnetic resonance signal decreases exponentially and thus never reaches zero completely, at least in theory. In simple interference suppression, portions of the magnetic resonance signal received by the interference signal sensor would appear erroneously as interference signals, be subtracted from the magnetic resonance signal received via the antenna, and thus lead to impairments or artifacts in the imaging.

[0016] Therefore, the method according to the invention further provides for the following steps: the interference signal is reduced as a function of the proportion of the magnetic resonance signal in the reference interference signal received by the interference signal sensor, in other words, the influence of the magnetic resonance signal on the reference interference signal is determined or estimated and this influence is taken into account in the subsequent determination of parameters (such as attenuation and / or phase shift) for suppressing interference in the magnetic resonance signal. The invention also provides different possibilities for this.

[0017] Advantageously, the method according to the invention makes it possible to reduce or prevent artifacts caused by interference suppression.

[0018] The present invention also provides other advantageous embodiments.

[0019] In a conceivable embodiment of the method according to the invention, the method comprises the following steps: filling k-space with measurement data from an image acquisition by means of a magnetic resonance measurement This can be done, for example, with a conventional image acquisition by means of a gradient echo sequence, wherein k-space is scanned line by line.

[0020] In a further step, the magnetic resonance signal at the corresponding time point of the acquisition of the reference interference signal is determined based on these k-space measurement data. Since the acquisition of the reference interference signal is not necessarily performed simultaneously with the acquisition of the magnetic resonance signal, the magnetic resonance signal then corresponds to a point in k-space, and therefore it is necessary to interpolate the magnetic resonance signal between the measurement points based on the k-space data during the acquisition of the reference interference signal.

[0021] According to an embodiment of the method according to the invention, a method also known as gridding is used for this purpose. Gridding is usually used to convert the measurement data from a spiral or radial scan for simplified Fourier transformation into image space into a virtual scan in the rows of a Cartesian grid in k-space (see Bernstein, King, Zhou et al., "Handbook of MRI Pulse Sequences", Elsevier Academic Publishers, ISBN-13: 978-0-12-092861-3, Chapter 13.2). However, in an embodiment of the method according to the invention, gridding is used to determine the magnetic resonance signal at the time of acquiring the reference interference signal. Using the components of the magnetic resonance signal in the reference interference signal received by the interference signal sensor determined in this way, a reference interference signal without magnetic resonance components can be determined, for example, by forming a difference or by an adaptive filter. Then, the controller or the receiver determines parameters for suppressing interference signals in the magnetic resonance signal, such as amplification and / or phase shift, based on the filtered reference interference signal. By using the method according to the invention to determine interference signals and magnetic resonance signals separately, it is conceivable, for example, to free the interference signal received by the interference signal sensor from components of the magnetic resonance signal, for example by means of an adaptive filter or by subtracting the determined magnetic resonance signal components, before the interference signal received by the interference signal sensor is combined with the magnetic resonance signal of the antenna for interference suppression. However, it is also conceivable, for example, to parameterize the interference suppression of the magnetic resonance signal received by the antenna itself by means of an adaptive filter, so that the magnetic resonance signal components in the interference signal are not taken into account when suppressing the interference.

[0022] Artifacts caused by magnetic resonance signals which appear as interference signals are thereby advantageously reduced without having to carry out additional, time-consuming magnetic resonance measurements.

[0023] In a possible embodiment of the method according to the invention, the method has the following steps: quantitative information about the object to be examined is determined by means of magnetic resonance measurements. Such quantitative information can be extracted, for example, from T1 and / or T2 maps, which are determined within the framework of fingerprint recognition for preparing image acquisition.

[0024] In the steps of the method according to the invention, the component of the magnetic resonance signal in the reference interference signal is determined based on the quantitative information. For example, it is conceivable to simulate or synthesize the magnetic resonance signal of the examination object based on the determined quantitative information with the aid of the Bloch equation in order to subtract the magnetic resonance signal thus determined from the reference interference signal or to take the magnetic resonance signal thus determined into account when reducing the interference signal in the magnetic resonance signal.

[0025] Advantageously, the synthesized magnetic resonance signal previously obtained from the quantitative information also allows the proportion of the magnetic resonance signal in the reference interference signal to be determined and taken into account in the interference suppression in order to reduce artifacts by means of the interference suppression.

[0026] In a possible embodiment, the method has the following steps: determining a magnetic resonance signal transfer function from the examination object to the interference signal sensor. For this purpose, it is conceivable to calculate the field strength of the magnetic resonance signal at the location of the interference signal detector according to Maxwell's field equations. However, as described above, it is also conceivable to identify the magnetic resonance signal estimated at the location of the examination object by an autocorrelation in the signal of the interference signal sensor and to determine the transfer function from this.

[0027] It is also conceivable to repeat the measurement of the signal at the interference signal sensor several times under the same conditions, i.e. with the same excitation sequence and the same geometric arrangement. The statistical interference signals are then averaged, while the same magnetic resonance signal components are continuously increased by superposition, and the transfer function can be determined from this.

[0028] In particular for image acquisitions with the same examination object and the same arrangement, the transfer function determined once can then be assumed to be constant. In the event of a change, the steps for determining the transfer function can then be repeated.

[0029] The transfer function advantageously makes it possible to use the determined magnetic resonance signal to more accurately predict the proportion of the magnetic resonance signal in the signal of the interference signal sensor.

[0030] In a conceivable embodiment of the method according to the invention, the magnetic resonance tomography device has a plurality of antennas for receiving magnetic resonance signals. Here, in the step of reducing the component of the interference signal in the magnetic resonance signal of the first antenna by the receiver, this is performed based on the reference interference signal and the magnetic resonance signal of the second antenna. Regarding the suppression based on the reference interference signal, please refer to the previous implementation. In addition, the signal of the second antenna and / or another antenna is also used during the suppression. Here, the interference signal can be inferred by the correlation of the signals received by the antennas. For example, due to the different spatial arrangements of the antennas, the interference signal can be shifted in phase between the antennas respectively, so that the phase shift is determined by the correlation of the signals of the antennas, and before the signal of the interference signal sensor is subtracted from the magnetic resonance signal of the corresponding antenna to reduce the interference signal, different phase shifts are applied to the signal of the interference signal sensor accordingly.

[0031] In a possible embodiment of the method according to the invention, the magnetic resonance tomography device has a field camera. Here, the following device is called a field camera, which is designed to record the magnetic field in the environment of the examination object, in particular the gradient field that changes in time, in order to detect deviations caused by eddy currents or the examination object itself, for example. During the magnetic resonance measurement, the field camera records the time course of the gradient field. The controller or the receiver then determines the component of the magnetic resonance signal in the reference interference signal based on the time course of the gradient field recorded by the field camera. This can be done, for example, by the gridding that has already been described, in which the measured k-space position is corrected according to the magnetic field recorded by the field camera. In the simulation of the magnetic resonance signal with the help of quantitative information, the corrected magnetic field value is used for the Bloch equation, for example, corresponding to the recording of the field camera.

[0032] The acquisition of the gradient fields by means of a field camera advantageously allows a more precise determination of the proportion of the magnetic resonance signal in the reference interference signal and thus allows for a better correction.

[0033] In a conceivable embodiment of the method according to the invention, the magnetic resonance tomography system has a plurality of antennas for receiving magnetic resonance signals. These antennas can be, for example, a plurality of antenna coils of a local coil matrix, a plurality of individual local coils arranged at different locations, or also one or more local coils and a body coil.

[0034] Regarding the reduction of the component of the interference signal in the magnetic resonance signal of the first antenna by the receiver, please refer to the previous implementation. In addition, in the current implementation, at least the magnetic resonance signal recorded by the second antenna is also used for interference suppression. Here, interference suppression is performed based on the reference interference signal and the magnetic resonance signal of the second antenna. Here, the following fact is fully utilized: the first antenna and the second antenna are spatially offset from each other, especially related to the distance from the interference signal sensor. As a result, when received by the first and second antennas, the interference signal recorded by the interference signal sensor is offset by a certain phase amount, which corresponds to the distance difference divided by the propagation speed. In the opposite direction, the magnetic resonance signals collected by the first antenna and the second antenna arrive with corresponding phase delays. Thus, for example, the magnetic resonance signal at the interference signal sensor can be approximately estimated by the weighted sum of the first antenna, the second antenna and possible other antennas with different phase shifts, so as to then subtract the magnetic resonance signal from the received signal of the interference signal sensor.

[0035] Including the signal of the second or further antenna while reducing interfering signals in the magnetic resonance signal of the first antenna advantageously allows a more accurate estimation and thus a reduction in image artifacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The characteristics, features and advantages of the present invention described above and the implementation methods thereof will be more clearly understood with reference to the following description of the embodiments described in detail with reference to the accompanying drawings.

[0037] In the attached figure:

[0038] Figure 1 A schematic diagram of a magnetic resonance tomography apparatus for carrying out the method according to the invention is shown;

[0039] Figure 2 A schematic diagram showing an exemplary flow chart of a method according to the present invention;

[0040] Figure 3 A schematic diagram showing an exemplary flow chart of a method according to the invention is shown. DETAILED DESCRIPTION

[0041] Figure 1 A schematic diagram of an embodiment of a magnetic resonance tomography system 1 having a local coil 50 according to the invention is shown.

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

[0043] Furthermore, the magnet unit 10 has gradient coils 12, which are designed to superimpose variable magnetic fields in three spatial directions on the magnetic field B0 for spatial differences in the acquired imaging region in the examination volume. The gradient coils 12 are usually coils made of normally conducting wires, which can generate mutually orthogonal fields in the examination volume.

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

[0045] The control unit 20 supplies different signals for the gradient coil 12 and the body coil 14 to the magnet unit 10 , 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 to excite nuclear spin magnetic resonance in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation pulses can be transmitted 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] Arranged on the patient 100 is a local coil 50 as a first antenna, which is connected to the high-frequency unit 22 and its receiver via a connecting line 33. However, it is also conceivable for the body coil 14 to be the first antenna within the meaning of the invention.

[0050] Four interference signal sensors 60 are arranged at the edge of the opening of the patient tunnel 16, which are arranged at the corners of a square embedded in the circular opening, so that these corners are located on the edge of the opening. The four interference signal sensors 60 are connected to the receiver 70 of the high-frequency unit 22. Here, based on the plurality of interference signal sensors 60, it is conceivable that the interference signal sensors 60 do not all have omnidirectional receiving characteristics, but are, for example, dipoles and are supplemented with omnidirectional characteristics by different orientations. However, it is also conceivable, for example, to set a cross dipole as the only second antenna with omnidirectional characteristics.

[0051] Alternatively or additionally, the interference signal sensor 60 can also be arranged in the patient couch 30 .

[0052] The patient tunnel preferably has a radius R, which applies to:

[0053] R<(λ L *1.841) / (2*π)

[0054] Here, λ L The wavelength of the radio waves in the air at the Larmor frequency of the magnetic resonance tomograph 1 is indicated. If the radius R is smaller than the right-hand term, the radio waves propagate exponentially in the patient tunnel 16 and the interfering signals are strongly attenuated in the center of the examination region FoV. L It is also called the cut-off wavelength of the circular waveguide, and the corresponding frequency is called the cut-off frequency.

[0055] Due to the limited electrical conductivity of the patient, the patient 100 acts only as the core of a coaxial cable, the outer shell of which is the wall of the patient tunnel 16 and transmits electromagnetic signals coupled at the leg or head end into the examination area. In this case, one or more interference signal sensors 60 close to the opening or the patient couch 30 advantageously register interference signals transmitted by the patient 100 into the FoV and thus make the compensation in the receiver 70 particularly effective.

[0056] However, the patient 100 also conducts magnetic resonance signals in the opposite direction from the patient tunnel 16 to one or more interference signal sensors 60. If the interference signal sensors 60 register these magnetic resonance signals and process them like external interference signals, i.e., for example, by subtracting them from the magnetic resonance signals received by the local coil 50 and / or the body coil 14, this leads to distortions of the magnetic resonance signals and, due to the imaging-related magnetic resonance signals, to image artifacts.

[0057] Therefore, the controller 23 and / or the receiver 70 of the magnetic resonance tomography apparatus according to the present invention is designed to reduce the interference signal as a function of the portion of the magnetic resonance signal in the reference interference signal received by the interference signal sensor 60 .

[0058] To this end, the receiver 70 and / or the controller 23 executes Figure 2 The method according to the invention is shown in FIG. It is conceivable that the method is executed in a program-controlled manner by a processor, preferably a signal processor. However, it is also conceivable that the invention is implemented by logic in an FPGA (field-programmable gate array) or an ASIC (Application Specific Integrated Circuit).

[0059] In step S10 of the method according to the invention, the receiver 70 receives a reference interference signal via the interference signal sensor 60. The reference interference signal also has a component of the magnetic resonance signal emitted by the patient 100, which is present for a long time in a weakened manner due to the exponential drop of the magnetic resonance signal, even if no magnetic resonance signal is received via the local coil 50 or the body coil at the same time.

[0060] In step S20, the magnetic resonance tomography device 1 receives magnetic resonance signals from the patient 100 using the receiver 70 via an antenna, such as a local coil 50 (which can also be designed as a local coil matrix with multiple antenna coils) or a body coil 14. Steps S10 and S20 do not necessarily have to be performed simultaneously, but can also be performed sequentially. After processing according to the method according to the present invention, the controller 23 or a separate unit for image reconstruction uses the received magnetic resonance signals for further imaging and, for example, finally outputs them on a screen.

[0061] In step S30, the receiver 70 reduces the component of the interference signal in the magnetic resonance signal based on the reference interference signal. This can be done, for example, by adding the signal received by the interference signal sensor 60 to the signal of the local coil 50 with a predetermined weighting and phase shift, so that the component of the interference signal in the signal of the local coil 50 exactly cancels out the weighted signal. The phase shift and the weighting can be determined, for example, by the signal autocorrelation of the interference signal and the signal autocorrelation of the local coil 50.

[0062] However, the method according to the invention is characterized in particular in that, in step S30, it is also taken into account that, at least during the image acquisition of the patient 100, a component of the magnetic resonance signal is always contained in the signal of the interference signal sensor 60. Therefore, the method according to the invention provides that step S30 is performed as a function of the component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor 60.

[0063] This can be achieved in the following way: In an embodiment of the method according to the invention, k-space is filled with measurement data of an image acquisition, such as a gradient echo sequence, by means of a magnetic resonance measurement S31. Here, the magnetic resonance measurement can be performed as part of a sequence or as a preparatory measurement. In the simplest case, this can be a Cartesian grid in k-space, the nodes of which are filled row by row and column by column with magnetic resonance signals by a suitable sequence. However, other scanning schemes along radial or spiral trajectories are also conceivable.

[0064] In step S32, the magnetic resonance signal at any point in time can then be interpolated by interpolating at these k-space points. Corresponding methods have been developed, for example, in order to determine the measured values ​​in a Cartesian coordinate system in the case of a spiral trajectory (also known as "gridding") and then use a simpler inverse transformation to image space. Such methods are described, for example, in "Handbook of MRI Pulse Sequences" by Bernstein, King, Zhou et al.; Elsevier Academic Publishers, ISBN-13: 978-0-12-092861-3, Chapter 13.2. In this way, the magnetic resonance signal emitted by the patient 100 can be determined at least approximately, while in step S10, a reference interference signal is recorded using the interference signal sensor 60.

[0065] exist Figure 3 In a further exemplary embodiment shown in , it is conceivable to acquire quantitative information about the object to be examined by means of a magnetic resonance measurement S33. This can be, for example, the spin density of the nuclear spins of each volume element. Based on this quantitative information, the component of the magnetic resonance signal in the reference interference signal received in step S10 is determined in step S33. Here, in step S34, the magnitude of the component of the magnetic resonance signal received during step S10 can be determined with the help of the quantitative information, for example by a Bloch simulation based on this spin density and a transfer function subsequently applied thereto.

[0066] Such a transfer function can be determined in step S35. It is conceivable, for example, to simulate the transfer function using Maxwell's field equations if the reception characteristic of the interference signal sensor 60, the arrangement of the interference signal sensor relative to the examination object and the properties of the examination object are known.

[0067] However, the transfer function can also be determined by measurement in step S35. It is conceivable that, for a known magnetic resonance signal at the position of the examination object, the magnetic resonance signal is detected by the receiver 70 by means of an autocorrelation in the received signal of the interference signal sensor 60 and in this way the transfer function is determined using its essential parameters, in particular the attenuation and the phase shift.

[0068] It is also conceivable to repeatedly measure the signal of the interference signal sensor 60 with identical excitation of the spins, for example in the same sequence, and to sum or average them. In this case, as the number of repetitions increases, the statistical interference signals are emphasized by the averaging, while the intensity of the magnetic resonance signal also increases relative to this, so that in the case of sufficiently long averaging, the transfer function of the magnetic resonance signal can be determined with sufficient accuracy.

[0069] In this case, step S35 can also include a combination of the described methods, so that, for example, periodic interference signals do not interfere with the method.

[0070] Step S35 can also be performed at different points in time. For example, the transfer function can be determined once for one type of magnetic resonance tomography device 1. However, it is also conceivable that the transfer function is newly determined or adjusted before or before each image acquisition or between individual sequences in order to take into account changes caused by the movement of the patient 100 being examined.

[0071] Based on the determined magnetic resonance signal and the transfer function, the component of the expected magnetic resonance signal in the signal of the interference signal sensor 60 can then be determined at each time point. If this determined component is then added to the signal of the interference signal sensor, for example with an opposite sign, i.e. with a phase shift of 180 degrees, then in an ideal case the magnetic resonance signal components cancel each other out and a pure interference signal is obtained. However, it is also conceivable that in the receiver 70, the determined magnetic resonance signal components are taken into account or suppressed in the subsequent signal path in analog or digital signal processing by corresponding filtering measures. This can be achieved, for example, by means of an adaptive filter.

[0072] Here, due to undesirable side effects, such as changes in the gradient field caused by eddy currents, the magnetic resonance signal may deviate from the ideal magnetic resonance signal. Therefore, in a conceivable embodiment, it is provided that the magnetic resonance tomography device 1 has a field camera 65, preferably during steps S10 and / or S20, the field camera is used to measure the magnetic field composed of the static component B0 and the gradient field. The field camera 65 can, for example, have a plurality of samples, which have materials that are sensitive to nuclear spin excitation distributed on the patient tunnel, and whose magnetic resonance signals are collected and thus allow the magnetic field at the position of the field sample to be accurately determined. Thus, the field strength between the samples can also be determined by interpolation. It is also conceivable to determine the magnetic field by a magnetic field sensor such as a Hall sensor. Then, for example, the determined field strength can be used to more accurately perform a Bloch simulation of the magnetic resonance signal in the receiver 70 or the controller 23, and then the component of the magnetic resonance signal in the signal of the interference signal sensor 60 can also be better suppressed in this way.

[0073] In a conceivable embodiment of the method according to the invention, the magnetic resonance tomography system has a plurality of antennas for receiving magnetic resonance signals. The plurality of antennas, preferably the antenna coils of the local coil 50 or the local coil array, can make it possible to analyze different mixtures of the same interference signal with the magnetic resonance signal due to different relative positions relative to each other and relative to the patient 100 or the object under examination, so that on the one hand, interference signals can be better distinguished and filtered out in the signals of the antennas, and conversely, magnetic resonance signal components can be identified and filtered out in the signals of the interference signal sensors in other directions. For example, for adjacent antennas of the local coil array, the interference signals are almost identical due to the smaller distances between each other compared to interference signal sources outside the patient tunnel 16, while the magnetic resonance signals of different volumes of the patient 100 can be distinguished. As a result, when simulating magnetic resonance components, these magnetic resonance components can then be modeled more accurately for different starting positions and then better suppressed or compensated.

[0074] Although the present invention has been illustrated 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 method for suppressing interference signals in a magnetic resonance recording using a magnetic resonance tomography device (1), wherein the magnetic resonance tomography device (1) has a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the method comprises the following steps: (S10) using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); (S20) using the receiver (70) to receive magnetic resonance signals of the object under examination via the antenna; (S30) reducing the interference signal component in the magnetic resonance signal according to the reference interference signal by the receiver (70), in, The interference signal is reduced according to the component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), It is characterized in that (S31) filling k-space with measurement data acquired by the image by means of magnetic resonance measurement, and ( S32 ) Interpolating the component of the magnetic resonance signal in the reference interference signal on the measurement data in k-space by means of gridding.

2. A method for suppressing interference signals in a magnetic resonance recording using a magnetic resonance tomography device (1), wherein the magnetic resonance tomography device (1) has a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the method comprises the following steps: (S10) using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); (S20) using the receiver (70) to receive magnetic resonance signals of the object under examination via the antenna; (S30) reducing the interference signal component in the magnetic resonance signal according to the reference interference signal by the receiver (70), in, The interference signal is reduced according to the component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), It is characterized in that (S33) determining quantitative information about the object to be examined by means of magnetic resonance measurements, and ( S34 ) Using the quantitative information, a component of the magnetic resonance signal in the reference interference signal is determined by means of a simulation of the magnetic resonance signal.

3. The method according to claim 1 or 2, wherein the method comprises the following step (S35): determining a magnetic resonance signal transfer function from the examination object to the interference signal sensor (60).

4. A method for suppressing interference signals in a magnetic resonance recording using a magnetic resonance tomography device (1), wherein the magnetic resonance tomography device (1) has a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the method comprises the following steps: (S10) using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); (S20) using the receiver (70) to receive magnetic resonance signals of the object under examination via the antenna; (S30) reducing the interference signal component in the magnetic resonance signal according to the reference interference signal by the receiver (70), in, The interference signal is reduced according to the component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), The invention is characterized in that the magnetic resonance tomography device (1) has a plurality of antennas for receiving magnetic resonance signals. wherein in the step (S30) of reducing the component of the interference signal in the magnetic resonance signal of the first antenna by the receiver (70), this is performed based on the reference interference signal and the magnetic resonance signal of the second antenna, The magnetic resonance signals acquired by the first antenna and the second antenna arrive with corresponding phase delays, so that the magnetic resonance signal at the interference signal sensor (60) is approximately estimated by a weighted sum of the first antenna and the second antenna, each having a different phase shift, so that the magnetic resonance signal is then subtracted from the received signal of the interference signal sensor.

5. A method according to claim 1 or 2 or 4, wherein the magnetic resonance tomography device (1) has a field camera (65), and the method further comprises the following steps: recording the time course of a gradient field with the aid of the field camera (65) during reception of a magnetic resonance signal (S20), wherein a component of the magnetic resonance signal in a reference interference signal is determined based on the time course of the gradient field recorded by the field camera (65).

6. A magnetic resonance tomography device comprising a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the magnetic resonance tomography device (1) is designed to: Using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); Using the receiver (70) to receive magnetic resonance signals of an object under examination via the antenna; The receiver (70) is used to reduce a component of an interference signal in a magnetic resonance signal based on a reference interference signal, wherein the interference signal reduction is performed based on a component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), characterized in that: The controller (23) is further designed to: Filling k-space with measurement data from image acquisition using magnetic resonance measurements, and The components of the magnetic resonance signal in the reference interference signal are interpolated on the measurement data in k-space using gridding.

7. A magnetic resonance tomography device comprising a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the magnetic resonance tomography device (1) is designed to: Using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); Using the receiver (70) to receive magnetic resonance signals of an object under examination via the antenna; The receiver (70) is used to reduce a component of an interference signal in a magnetic resonance signal based on a reference interference signal, wherein the interference signal reduction is performed based on a component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), characterized in that: The controller (23) is further designed to: determining quantitative information about the object to be examined by means of magnetic resonance measurements, and The quantitative information is used to determine the proportion of the magnetic resonance signal in the reference interference signal by means of a simulation of the magnetic resonance signal.

8. A magnetic resonance tomography device comprising a controller (23), a receiver (70), an antenna and an interference signal sensor (60), wherein the magnetic resonance tomography device (1) is designed to: Using the receiver (70) to receive a reference interference signal via the interference signal sensor (60); Using the receiver (70) to receive magnetic resonance signals of an object under examination via the antenna; The receiver (70) is used to reduce a component of an interference signal in a magnetic resonance signal based on a reference interference signal, wherein the interference signal reduction is performed based on a component of the magnetic resonance signal in the reference interference signal received by the interference signal sensor (60), characterized in that: The controller (23) is further designed to: In the step (S30) of reducing the component of the interference signal in the magnetic resonance signal of the first antenna by the receiver (70), this is performed based on the reference interference signal and the magnetic resonance signal of the second antenna, The magnetic resonance signals acquired by the first antenna and the second antenna arrive with corresponding phase delays, so that the magnetic resonance signal at the interference signal sensor (60) is approximately estimated by a weighted sum of the first antenna and the second antenna, each having a different phase shift, so that the magnetic resonance signal is then subtracted from the received signal of the interference signal sensor.

9. A computer program product which can be directly loaded into a processor of a programmable controller (23) of a magnetic resonance tomography device (1) according to any one of claims 6 to 8, the computer program product having program code means for executing all steps of the method according to any one of claims 1 to 5 when the program product is executed on the controller (23).

10. A computer-readable storage medium having electronically readable control information stored thereon, wherein the electronically readable control information is designed to execute the method according to any one of claims 1 to 5 when the storage medium is used in a controller (23) of a magnetic resonance tomography device (1) according to any one of claims 6 to 8.

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