Magnetic resonance tomography apparatus and method for operating a magnetic resonance tomography apparatus

Abstract

The present invention relates to a magnetic resonance tomography system and a method for operating the same. The magnetic resonance tomography system comprises a first receiving antenna for receiving magnetic resonance signals from a patient in a patient tunnel; a second receiving antenna for receiving signals having the Larmor frequency of the magnetic resonance signals; and a receiver. The second receiving antenna is arranged outside or near the opening of the patient tunnel. The receiver is signal-connected to the first receiving antenna and the second receiving antenna and is designed to suppress interfering signals received by the second receiving antenna in the magnetic resonance signals received by the first receiving antenna.

Description

[0001] This application is a divisional application of a patent application with a filing date of October 2, 2018, Chinese patent application number 201880075857.6, and invention name “Magnetic resonance tomography equipment and method for operating magnetic resonance tomography equipment”. Technical Field

[0002] The invention relates to a method for active interference suppression in a magnetic resonance tomography system and to a magnetic resonance tomography system having a receiver. Background Art

[0003] Magnetic resonance tomography systems are imaging devices that, to image an examination subject, align the subject's nuclear spins using a strong external magnetic field and excite the nuclear spins to precess about this alignment using an alternating magnetic field. The precession of the spins from this excited state to a state with lower energy, or back again, in turn generates an alternating magnetic field, which is received by an antenna.

[0004] These signals are spatially encoded using gradient magnetic fields, which then allows the received signals to be associated with volume elements. The received signals are then analyzed to provide a three-dimensional image of the examination object. Local receiving antennas, so-called local coils, are preferably used to receive the signals. To achieve a better signal-to-noise ratio, these antennas are positioned directly above the examination object. The receiving antennas can also be installed in the patient's bed.

[0005] Magnetic resonance tomography systems require high-frequency shielding in two areas. Firstly, to excite nuclear spins, high-frequency pulses with powers in the kilowatt range are generated, which are only partially absorbed by the patient. Radio waves that leave the patient channel are radiated into the air and therefore require shielding to comply with emission limits.

[0006] On the other hand, the magnetic resonance signals to be received for imaging are extremely weak. SNR), it is necessary to shield external interference signals.

[0007] Therefore, in the prior art, an expensive shielding cabin is installed around a magnetic resonance tomography apparatus to reduce radiation and invasiveness.

[0008] A knee coil with partial shielding is known from DE 10 2014 207 843. Summary of the Invention

[0009] Therefore, the technical problem to be solved by the present invention is to reduce the expenditure for shielding.

[0010] This object is achieved by an inventive magnetic resonance tomography system according to claims 1 and 2 and by an inventive method for operating a magnetic resonance tomography system according to claims 21 and 22 .

[0011] The magnetic resonance tomography system according to the present invention comprises a patient tunnel; a first receiving antenna for receiving magnetic resonance signals from a patient, wherein the patient is located in the patient tunnel; a second receiving antenna for receiving a signal having the Larmor frequency of the magnetic resonance signal; and a receiver. The receiver is signal-connected to the first receiving antenna and the second receiving antenna and is preferably designed to prepare the magnetic resonance signals for imaging.

[0012] The second receiving antenna is arranged outside or near the opening of the patient tunnel. Specifically, the openings of the patient tunnel are considered to be those through which the patient bed, along with the patient, enters the patient tunnel and, depending on the area to be examined, exits the patient tunnel again at the opposite end. "Near" in this context is considered to be a distance from the opening that is less than 0.1 m, 0.2 m, 0.5 m, 1 m, or 2 m. "Near" can also be considered to be a distance from the opening that is less than one-quarter or half the wavelength of radio waves in air at the Larmor frequency of the magnetic resonance imaging system.

[0013] Here, the first receiving antenna preferably receives the magnetic resonance signal, but the magnetic resonance signal always also includes a small portion of interference signals. In contrast, the second receiving antenna receives not only the interference signal but also a small or negligible portion of the magnetic resonance signal. For simplicity, the signal received by the first receiving antenna will still be referred to as the magnetic resonance signal (even if it includes interference signal components to be removed), and the signal received by one or more second receiving antennas will be referred to as the interference signal.

[0014] In this case, the receiver is designed to suppress interference signals received by the second receiving antenna in the magnetic resonance signals received by the first receiving antenna. Exemplary embodiments are described in more detail in the dependent claims.

[0015] In the embodiment of claim 2, the possibility that the interference signal has a wider bandwidth than the magnetic resonance signal is taken into account. Here, the portion outside the frequency range of the magnetic resonance signal is correlated with the portion within the frequency range of the magnetic resonance signal. Therefore, according to the present invention, it may be sufficient if the second receiving antenna receives a broadband interference signal and the receiver is designed to analyze this signal only partially, for example, in a frequency range that differs from the frequency range of the magnetic resonance signal or in a frequency range outside the frequency range of the magnetic resonance signal, and then suppress the interference signal in the magnetic resonance signal received by the first receiving antenna based on this partial signal. However, alternatively or additionally, it is also conceivable that the second receiving antenna only receives frequencies outside the frequency range of the magnetic resonance signal and transmits them to the receiver. Due to the correlation, for example, the amplitude of the frequency portion of the interference signal within the frequency range of the magnetic resonance signal can be correlated with the amplitude of the frequency portion of the magnetic resonance signal outside the frequency range of the magnetic resonance signal. In this way, it is also conceivable that during the magnetic resonance measurement, the second receiving antenna, in conjunction with the receiver, monitors only the frequency portion outside the frequency range of the magnetic resonance signal for interference signals and, accordingly, suppresses the interference signal in the signal of the first receiving antenna. In this case, the receiver can, for example, determine, before the acquisition of magnetic resonance signals, for interference signals within the frequency range of the magnetic resonance signals, a relationship between an interference signal from a first receiving antenna and a portion of the interference signal from a second receiving antenna, also referred to as a transfer function, and during the acquisition of the magnetic resonance signals, adjust, for example, the amplitude or scaling as a function of the portion of the interference signal received by the second receiving antenna outside the frequency range of the magnetic resonance signals.

[0016] It is also conceivable to provide a filter between the second receiving antenna and the receiver, which preferably allows interference signals to pass while suppressing the magnetic resonance signal. For example, a filter can be provided to suppress the magnetic resonance signal for interference outside the frequency band of the magnetic resonance signal. The filter can also be adaptive or controllable. Thus, it is conceivable that the interference cancellation controller adapts the filter to the Larmor frequency of the currently acquired slice.

[0017] The following describes how interference signals in the signal from the second receiving antenna can be suppressed by the receiver. For example, the receiver can include a summing device that forms a linear combination of the magnetic resonance signal and the interference signal, which is dependent on one or more parameters. Furthermore, the receiver can include an interference cancellation controller that is designed to vary the one or more parameters so that the energy of the interference signal in the linear combination is minimized. One or more of these parameters can be complex numbers in order to model the phase shift or to provide a phase shift via its own parameters. Multiple parameters, in particular, enable effective suppression of different interference sources.

[0018] However, non-linear combinations of the signals that are dependent on one or more parameters are also conceivable.

[0019] When performing interference suppression, the interference cancellation controller can also weight interference signals with particularly large amplitudes more strongly in the parameters than weaker interference signals, since these strong interference signals can be suppressed particularly well due to a particularly large distance between the signal levels and the statistical background noise. In particular, different interference signals are considered to be interference signals that can be separated by means of multiple second receiving antennas due to different origins, occupy different frequency ranges, or can be distinguished by different temporal behavior.

[0020] Here, the receiver can be designed to perform the processing according to the present invention on the received magnetic resonance signals and interference signals in real time, for example, by means of a programmable logic circuit (FPGA) or a signal processor (DSP), to suppress the interference signals.

[0021] However, the receiver may also have a memory and initially store the received interference signals and the received magnetic resonance signals, wherein the interference signals are only suppressed at a later point in time, for example, by delaying the entire image acquisition of an echo sequence, an excitation sequence, or a single slice, or the duration of the entire image acquisition sequence. The delay may, for example, be greater than 50 ms, 100 ms, 0.5 s, 1 s, 10 s, 1 min, or even longer.

[0022] In this context, receivers within the meaning of the present invention can include hardware for performing analog and / or digital high-frequency processing in real time, such as amplifiers, filters and mixers, but can also include image analysis units for subsequently generating a mapping based on the received magnetic resonance signals.

[0023] The method according to the invention for operating a magnetic resonance tomography system according to the invention comprises the following steps: an interference signal is received by a receiver via a second receiving antenna. Since the second antenna is arranged near the opening, the interference signal received by the second antenna has little or no magnetic resonance signal component.

[0024] In a further step, the receiver receives the magnetic resonance signal via a first receiving antenna, which may be, for example, a body coil or a local coil of a magnetic resonance tomography system.

[0025] In a further step of the method, the receiver processes the magnetic resonance signal into a received signal in a manner correlated with an interference signal passing through the receiver, wherein the correlation depends on a parameter. For example, it is conceivable that the receiver uses the parameter as a factor to form a linear combination of the interference signal and the magnetic resonance signal, wherein the parameter may be complex to reflect a phase shift. Multiple parameters are also conceivable.

[0026] In another embodiment of the method according to the present invention, the receiver receives a broadband interference signal portion outside the frequency range of the magnetic resonance signal using a second receiving antenna. The interference signal portion outside the frequency range of the magnetic resonance signal is correlated with the portion within the frequency range. For example, if the source is the same, the amplitudes of the interference signals within and outside the frequency range of the magnetic resonance signal are proportional to each other. In the suppression of interference signals in the magnetic resonance signal received by the first receiving antenna, described below, the amplitude scaling of the signal using the second receiving antenna can then be correlated, for example.

[0027] Advantageously, the separate frequency ranges can prevent the magnetic resonance signal from influencing the suppression of interference signals during image acquisition. In other words, by analyzing the signal received by the second receive antenna in a frequency range different from the frequency of the magnetic resonance signal, the receiver can avoid evaluating scattered magnetic resonance signals as interference signals and suppressing them by the interference cancellation control.

[0028] The interference cancellation controller preferably also takes into account different characteristics of signals within and outside the frequency band of the magnetic resonance signal. These can be, for example, different attenuations or signal delays, which can be taken into account by different amplification factors and phase shifts. The different characteristics can be determined, for example, by calibration measurements for determining the transfer function, as described below in the dependent claims.

[0029] It is conceivable that the receiver acquires interference signals between and / or during the MR signal acquisitions. Continuous acquisition advantageously allows for better acquisition of the temporal profile of the interference signals and thus also better future estimation of their temporal profile, which enables more accurate suppression.

[0030] On the other hand, performing acquisitions during the interval, that is, between the acquisitions of MR signals, prevents the MR signals from being interpreted as interference signals. It is also conceivable that not only one or more second receive antennas acquire interference signals, but also one or more first receive antennas simultaneously. This allows for precise knowledge of how the first receive antennas acquire the interference signals received by the second receive antennas. This relationship, also known as a transfer function, then allows for more precise determination of the parameters for interference suppression, thereby enabling better interference suppression by the receiver.

[0031] Different methods (different frequencies, time limits) can also be combined with one another and / or used alternately in order to achieve improved interference cancellation overall.

[0032] Furthermore, it is also conceivable to average the results over a longer or multiple acquisition time periods and / or also between different methods.

[0033] In another step, the receiver sets parameters, for example by means of an interference cancellation controller, such that the interference signal portion of the received signal is reduced. For example, it is conceivable that in an optimization method, the interference cancellation controller sets parameters such that the energy of the interference signal in the received signal is minimized.

[0034] As already explained above with respect to the receiver, the receiver can also store magnetic resonance signals and / or interference signals so that the processing and parameter setting steps can also be performed at a time interval relative to the reception of the signals by the first and second reception antennas.

[0035] The magnetic resonance tomography system and operating method according to the invention advantageously allow the external interference signal portion in the magnetic resonance signal to be reduced by the second receiving antenna and the receiver according to the invention, so that simpler and less expensive shielding measures are sufficient.

[0036] Further advantageous embodiments are given in the dependent claims.

[0037] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system is designed to receive magnetic resonance signals having a Larmor frequency in an industrial frequency band. The Larmor frequency of the magnetic resonance tomography system is the resonant frequency of the nuclear spins used for imaging in the magnetic resonance tomography system in the static magnetic field B0 of the field magnet of the magnetic resonance tomography system. Frequency bands open for use in medical or technical equipment are referred to as industrial frequency bands, for which simplified issuance and approval regulations exist. These frequency bands are also referred to as ISM bands (Industrial, Scientific, Medical Bands). Exemplary frequency bands that also allow high-power transmission are between 26.9 and 27.3 MHz. Other such frequency bands are between 6.7 and 6.8 MHz, 13.5 and 13.6 MHz, 40.6 and 40.7 MHz, and 433.0 and 434.8 MHz.

[0038] Magnetic resonance tomography systems rely not only on receiving minimal interference but also on ensuring that powerful excitation pulses do not interfere with other devices. In the ISM band, legal tolerance limits are much higher, making it easier to comply with legal restrictions at this frequency by shielding the transmitted excitation pulses, or even eliminating them altogether. Therefore, in conjunction with active shielding, it is advantageous to implement a completely shielded MRI system in the ISM band to suppress receiver-side interference caused by other devices.

[0039] In one possible embodiment, the magnetic resonance tomography system includes a transmission path for emitting excitation pulses, which includes a filter. The filter is designed to suppress signals outside the ISM band. For example, the filter can be a bandpass filter for the used ISM band, which attenuates frequencies outside the ISM band by more than 12 dB, 24 dB, 40 dB, or 60 dB relative to signals with minimal attenuation within the ISM band. Depending on the embodiment of the high-frequency generation in the magnetic resonance tomography system, the filter can be arranged, for example, between the end stage and the hybrid coupler, between the hybrid coupler and the transmit / receive switch, or between the transmit / receive switch and the transmitting antenna.

[0040] The filter advantageously allows the emitted high-frequency power to be substantially limited to the ISM band, thereby adhering to stricter limit values ​​outside the ISM band. Magnetic resonance tomography systems can therefore also be operated in the ISM band without an RF cabin.

[0041] However, it is also conceivable to use the ISM band on the receiver side without active interference suppression and in a shielded cabin, in particular if the transmission of the excitation pulses is essential for operational compliance. This also applies to the embodiments described below that limit or optimize the excitation pulses in the ISM band.

[0042] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes a transmitting antenna for emitting excitation pulses, wherein the magnetic resonance tomography system includes a nonlinear component for detuning the transmitting antenna. This can be, for example, a PIN diode, or other diodes, or active components such as transistors or FETs. The nonlinear component is arranged in an area of ​​the magnetic resonance tomography system that is shielded from high frequencies by the patient tunnel, and a filter for the ISM frequency band or an ISM filter is arranged in the signal connection between the nonlinear component and the antenna, preferably in the shielded area.

[0043] Advantageously, shielding the nonlinear component from the patient tunnel and the surroundings prevents the emission of frequency components generated by the components used for detuning during the excitation pulse due to nonlinearities, and these frequency components no longer exist as harmonics in the ISM frequency band. The filter prevents the transmission of harmonics via the signal connection between the nonlinear component and the transmitting antenna. The arrangement of the nonlinear component thus contributes to compliance with radiation limit values ​​and enables or simplifies the need to dispense with shielding the entire magnetic resonance tomography system by a high-frequency cabin.

[0044] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes a radio-frequency unit having a predistorter. The predistorter is designed to predistort the excitation pulses used to excite nuclear spins so that, when emitted, particularly after amplification by a radio-frequency power amplifier, the signal portion of the excitation pulses outside the ISM band is reduced compared to an excitation pulse without predistortion. For example, it is conceivable that the predistorter generates and mixes in a signal portion that, after amplification by the radio-frequency unit, corresponds to harmonics generated by the excitation pulses due to the nonlinearity of the radio-frequency unit, but has the opposite sign, thereby reducing or eliminating the harmonics. The predistorter can be implemented, for example, in digital signal generation, or analog components can generate the corresponding signal from the input signal of the power amplifier. The predistorter can also be adaptive, for example, its characteristics can be controlled depending on the load of the patient tunnel. It is also conceivable that partial regulation can be performed using fast feedback from sensors in the transmission path, such as directional couplers.

[0045] The predistorter advantageously reduces harmonics outside the ISM band, thus facilitating or enabling compliance with emission limit values ​​even without a shielding cabin.

[0046] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the cutoff frequency for radio waves propagating in the patient tunnel is greater than the Larmor frequency of the magnetic resonance tomography system. The cutoff frequency is defined as the frequency at which, in the patient tunnel serving as a waveguide, radio waves can still be formed that propagate through the patient tunnel in the longitudinal direction (z direction). The cutoff frequency is also referred to as the waveguide, and in this case, it is the cutoff frequency of the patient tunnel serving as a waveguide.

[0047] If the frequency of the radio signal is below this frequency, the field strength of the external interference signal inside the patient tunnel advantageously decreases exponentially with the distance from the opening, so that the interference signal is significantly reduced in the examination area (Field of View, FoV).

[0048] In one possible embodiment of the magnetic resonance tomography apparatus according to the present invention, the second receiving antenna is arranged at the opening of the patient tunnel or at the patient bed. For example, the second receiving antenna can be arranged directly at the edge of the opening or below the surface of the patient bed.

[0049] In particular, if the frequency of the interfering signal is below the cutoff frequency of the free-wavelength wave, the patient and the patient tunnel form a coaxial conductor for the interfering signal. The patient and the second receiving antenna near the opening can advantageously detect interfering signals coupled into the patient tunnel via the patient, thus enabling particularly effective suppression by the receiver.

[0050] In one possible embodiment, the magnetic resonance tomography system includes a waveguide surrounding the magnetic resonance tomography system, wherein the waveguide has a cutoff frequency or cut-off frequency that is greater than the Larmor frequency of the magnetic resonance tomography system. A waveguide is defined as any electrically conductive structure that surrounds the magnetic resonance tomography system in at least four spatial directions on its outer circumference, for example, in the form of a tube or prism, and whose electrical conductivity substantially suppresses the propagation of radio waves or electric fields through the conductive structure at the Larmor frequency of the magnetic resonance tomography system. In other words, on the side of the electrically conductive structure of the waveguide facing away from the magnetic resonance tomography system, signals at the Larmor frequency are attenuated by more than 30 dB, 40 dB, 60 dB, or more relative to signals on the side facing the magnetic resonance tomography system.

[0051] It is also conceivable that, in one embodiment, the waveguide according to the invention or a conventional shielded cabin also surrounds the magnetic resonance tomography apparatus according to the invention. However, in this case, the high-frequency sealing door leading to the shielded cabin or waveguide is replaced by a conductive tunnel, which in turn is a waveguide with a cutoff frequency greater than the Larmor frequency.

[0052] Due to the attenuation of the alternating field in the tunnel, the radiation into the surroundings is reduced, so that expensive, cumbersome to use and prone to failure HF sealing doors can be omitted, especially at high frequency limits in the ISM band.

[0053] In principle, it is also conceivable here to use a waveguide as a gate or shield without active interference suppression in the reception path.

[0054] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the waveguide has an electrically conductive connection to the patient tunnel. It is conceivable that the waveguide and the patient tunnel together form an uninterrupted or continuous waveguide. The waveguide can also be electrically connected to the patient tunnel at both ends, or both waveguides can be electrically conductively connected to the patient tunnel at opposite ends. The waveguide can also have a cutoff frequency or cutoff frequency that differs from the cutoff frequency of the patient tunnel, but still lies above the Larmor frequency of the magnetic resonance tomography system.

[0055] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the second receiving antenna has a substantially omnidirectional reception characteristic. A substantially omnidirectional reception characteristic is defined as a sensitivity distribution of the receiving antenna in all spatial directions, wherein the difference between the maximum sensitivity and the minimum sensitivity depending on the direction is less than 6 dB, 12 dB, 18 dB, or 24 dB. This preferably also applies to different polarizations of the interfering signal.

[0056] Interference signals may enter from different directions and with different polarizations, so that an antenna with directional or preferred polarization cannot detect all interference signals. In contrast, an antenna with omnidirectional reception characteristics can advantageously detect all interference signals.

[0057] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes a plurality of second antennas, and the receiver is configured to suppress interference signals in the magnetic resonance signal based on reception signals from the plurality of second reception antennas. Preferably, the plurality of second reception antennas are spaced apart from one another, for example, at intervals greater than one-quarter or one-half the wavelength of a radio wave having the Larmor frequency.

[0058] A plurality of antennas distributed in space are also advantageously suitable for better detection of one or more interference sources, thereby improving interference suppression.

[0059] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the plurality of receiving antennas are arranged symmetrically about the patient tunnel. For example, it is conceivable that they are arranged at two opposite points on the edge of the opening of the patient tunnel, or at the vertices of a regular polygon or polyhedron.

[0060] Advantageously, the symmetry of the antenna can also be used to produce a symmetrical relationship between the parameters, thereby simplifying and / or accelerating the optimization method for reducing interference signals.

[0061] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes an interference suppression transmitter and an interference suppression antenna. The interference suppression antenna is arranged at a certain distance from the patient tunnel. The interference suppression transmitter is designed to generate a signal within the frequency range of the excitation pulses of the magnetic resonance tomography system and output this signal via the interference suppression antenna so that the field strength of the excitation pulses is reduced in the area surrounding the magnetic resonance tomography system due to destructive interference. A reduction in the field strength of the excitation pulses in this area, or a signal attenuation of the excitation pulses exceeding 6 dB, 12 dB, 24 dB, 40 dB, or 60 dB, is considered a reduction.

[0062] Advantageously, the interference suppression transmitter and the interference suppression antenna, in particular in conjunction with the other proposed measures, can reduce the field strength of electromagnetic waves emitted by the excitation pulses into the surroundings of the magnetic resonance tomography system, so that legal limit values ​​can be observed even without an RF cabin.

[0063] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes multiple interference suppression antennas, wherein the interference suppression antennas are arranged at a certain distance from the patient tunnel and at certain distances relative to one another. These distances are preferably less than the wavelength of a free radio wave having the Larmor frequency and / or greater than one-tenth of this wavelength. For example, the interference suppression antennas can be arranged in a plane surrounding the opening of the patient tunnel. The interference suppression transmitter is designed to output signals in the frequency range of the excitation pulses of the magnetic resonance tomography system via the interference suppression antennas, such that the field strength of the excitation pulses is reduced in multiple regions of the surroundings of the magnetic resonance tomography system due to destructive interference.

[0064] Advantageously, multiple interference suppression antennas and control signals for interference suppression transmitters can be used to reduce electromagnetic fields in multiple regions or to reduce or, ideally, eliminate radiation in multiple directions. The number of directions without radiation corresponds to the zero points of a multipole radiation pattern. The electromagnetic waves formed by the signals from the local transmitting antennas and the excitation pulses from the interference suppression antennas are thus multipole fields (e.g., quadrupole fields), which advantageously decrease significantly faster with increasing distance from the source, compared to, for example, a dipole field. This makes it possible to adhere to emission limits without an RF cabin.

[0065] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the interference suppression transmitter is designed to generate signals for one or more interference suppression antennas by phase shifting and / or adjusting the amplitude as a function of one or more transmit interference cancellation parameters. Preferably, the one or more corresponding signals for the one or more interference suppression antennas are generated from the excitation pulses by means of adjustable amplifiers or attenuators and phase shifting elements in the interference suppression transmitter. The amplitude relationships and phase shifts can be transmit interference cancellation parameters or can be derived from the one or more transmit interference cancellation parameters, for example, using analytical functions, tables, or iterative methods.

[0066] The excitation pulses can be detected, for example, by a sensor, such as a directional coupler in the line between the high-frequency power amplifier and the transmitting antenna, or a sensor antenna in the patient tunnel. It is also conceivable to generate the signal for the interference suppression antenna directly from the digital data of the excitation pulses by scaling and phase shifting using an A / D converter and an amplifier.

[0067] The transmit interference cancellation parameters advantageously simplify the determination of the settings of the interference suppression transmitter given below by reducing the number of variables and enable faster adaptation to changing conditions, such as other excitation pulses or the patient or operator environment.

[0068] In one possible embodiment of the magnetic resonance tomography system, transmission interference elimination parameters are set during production or installation.

[0069] In one conceivable embodiment of a magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes a calibration element and an interference suppression controller in the environment of the magnetic resonance tomography system. The calibration element is preferably an antenna or a sensor, which can be used to detect the electric field strength and / or magnetic field strength of an alternating electric field and / or alternating magnetic field at the frequency of the excitation pulse and transmit it to the interference suppression controller. The interference suppression controller is designed to detect the field strength within the frequency range of the excitation pulse at the location of the calibration element using the calibration element. For example, the interference suppression controller can include a calibration receiver. In addition, the interference suppression controller is designed to set transmission interference cancellation parameters based on the detected field strength so that the field strength of the excitation pulse in the predetermined environment of the calibration element is reduced. For example, the interference suppression controller can change or optimize the amplitude and / or phase of one or more interference suppression antennas so that a reduction in field strength and / or a local minimum is achieved at the location of the calibration element due to destructive interference.

[0070] Advantageously, by adaptively setting one or more emission interference cancellation parameters, it is possible to react to changes in the environment caused by people or associated equipment in the vicinity of the magnetic resonance tomography system, so that emission limit values ​​are maintained even under changing conditions. If necessary, emission can be interrupted and / or parameter redefinition initiated if a limit value is exceeded.

[0071] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the interference suppression antenna has a high-frequency power amplifier. The high-frequency power amplifier is preferably designed to generate an alternating electromagnetic field sufficient to suppress stray fields of the excitation pulse via the interference suppression antenna in response to a control signal having a low high-frequency power, for example, less than 10 mW, 50 mW, or 100 mW.

[0072] Compared to purely passive interference suppression antennas, HF power amplifiers enable the connection of passive interference suppression antennas to interference suppression transmitters via thin, flexible HF cables, thus simplifying installation. In conjunction with the patient tunnel acting as a waveguide and the advantageous interaction of multiple interference suppression antennas, only a few watts of power are required. This allows the locally located HF power amplifier to be small and lightweight, simplifying installation.

[0073] The transmission interference cancellation according to the invention by destructive interference can also be used independently of the other features of the magnetic resonance tomography system according to the invention. For example, in particular when the permitted electromagnetic radiation is a limiting factor, it is also conceivable to use an active interference suppression transmitter without active interference suppression on the receiving side.

[0074] However, in the ISM band, special synergies arise due to the higher permissible limit values, combined with interference suppression on the reception side, which enables operation without a closed shielded cabin.

[0075] In one conceivable embodiment of the method according to the invention, the step of setting the parameter comprises a step of temporal averaging by temporal averaging based on the interference signal. For example, the amplitude and / or phase of the interference signal can be acquired and averaged using a low-pass filter or window averaging, so that the parameter changes only slowly.

[0076] The temporal averaging advantageously ensures that the interference cancellation is not falsified by short-term, possibly accidental influences and that high-frequency noise components are not artificially generated by the interference cancellation.

[0077] In one possible embodiment of the method according to the invention with a magnetic resonance tomography system having a calibration element, the setting step has the following substeps:

[0078] In one step, the receiver measures a first transfer function between a first receiving antenna and a calibration element. The measurement can be performed, for example, by the receiver or the interference cancellation controller instructing the interference suppression transmitter via a signal connection to transmit, via the calibration antenna, a signal having a predetermined amplitude and / or a predetermined phase within the frequency range of the magnetic resonance signal and / or an adjacent frequency range. In this case, a signal connection is required between the interference suppression transmitter and the calibration element. The receiver can then receive the signal via the first receiving antenna and thereby determine the first transfer function. This can also be performed simultaneously for multiple first receiving antennas. However, in principle, it is also conceivable to acquire the transfer function by transmitting via the first receiving antenna and receiving via the calibration element.

[0079] In a further step, the receiver measures a second transfer function between the second receiving antenna and the calibration element. This can be done in the same manner as previously described. If the signal is emitted via the calibration element, both transfer functions can advantageously be acquired simultaneously.

[0080] The signals emitted for acquiring the first and second transfer functions are preferably encoded so that the receiver can determine the amplitude and phase relationship in a simple manner. For example, pseudo-random codes are conceivable, which enable the signals to autocorrelate quickly and reliably. In this case, the signal can be modulated in amplitude, frequency and / or phase. Spread spectrum modulation is also conceivable, in which the signal for determining the transfer function can also be kept below the noise limit of the MR signal and can be emitted simultaneously during the acquisition of the MR signal. In this way, it is possible to react continuously to changes in the environment. Continuous emission of the signal can also be achieved by using a frequency range adjacent to the MR signal. However, in this case, different propagation conditions must be taken into account by using different frequencies when determining the transfer function.

[0081] In another step, interference cancellation parameters are set based on the measured one or more first transfer functions and one or more second transfer functions, or in the case of multiple first and second receive antennas, multiple interference cancellation parameters are set so that the portion of interference signals received by the one or more second receive antennas in the signal received by the receiver via the first receive antenna is reduced. Interference signals received by the one or more second receive antennas are preferably also taken into account. The transfer function is applied so that the signals of individual receive antennas are considered in this manner. This can be achieved, for example, by having the interference cancellation controller set the interference cancellation parameters using a variation method or a linear optimization method for interference signals separated by autocorrelation in the received MR signals so that the interference signal portion is minimized. The transfer function is incorporated as a predetermined phase shift and attenuation between the receive antenna and the receiver. For the calibration element, a transfer function that is valid only for interference sources in a specific position or direction is used. However, if a sufficient number of appropriately positioned calibration elements are used to determine the transfer function, a transfer function that is independent of the respective position of the calibration elements can also be determined.

[0082] The calibration element is used to determine the transfer function so that the reception interference cancellation can react advantageously to different conditions in the environment, such as the position of persons or associated devices, and to the resulting changed propagation conditions, and adjust the interference cancellation.

[0083] In one possible embodiment of the method according to the present invention, the setting step is performed during a sequence of time periods during which no magnetic resonance signals are received, in particular no signals for exciting spins are transmitted. Within the sequence for image acquisition, there are time periods during which no excitation pulses are transmitted and no magnetic resonance signals for imaging are acquired. These are preferably also time periods during which the examination subject or patient emits no significant magnetic resonance signals, i.e., the signal level is at least 12 dB, 24 dB, 36 dB, 48 dB, or 60 dB below the maximum magnetic resonance signal. In this embodiment of the method, the setting step is performed during such time periods.

[0084] The interference cancellation controller of the receiver is accordingly designed to perform the setting step in such a time period. For example, the interference cancellation controller can receive a trigger signal from a controller of the magnetic resonance tomography system.

[0085] Advantageously, in the absence of magnetic resonance signals, parameter setting can be simplified, for example, by minimizing the energy of the signal received by the first receiving antenna according to the parameters. Even if, for example, the amplitude of the interfering signal changes over time, the set parameters remain applicable and effective in the same spatial arrangement.

[0086] However, in another possible embodiment of the method according to the invention it is also conceivable to set the parameters continuously, ie in short intervals of 1 ms, 10 ms or 100 ms, or in particular in real time with a delay of less than 10, 100 or 500 microseconds.

[0087] Continuous real-time or near-real-time parameter setting advantageously allows for rapid reaction to newly occurring interference signals and minimizes the negative impact of interference signals on the imaging.

[0088] In another conceivable embodiment, the receiver has a memory and stores the received magnetic resonance signals and the received interference signals. In this case, within the meaning of the present invention, the receiver may also include, for example, an image analysis computer. However, in one embodiment, it is also conceivable that the receiver in the narrow sense, i.e., the device for preparing the received high-frequency magnetic resonance signals, has a memory. Parameters can then be set with a delay relative to reception, and the receiver processes the magnetic resonance signals with the interference signals according to the parameters to form the received signals in order to reduce the interference signals. The delay can, for example, include the duration of an echo sequence, an excitation sequence, or the entire image acquisition sequence, for example, greater than 10 ms, 100 ms, 0.5 s, 10 s, or can also be several minutes, several hours, or in principle, several days.

[0089] Advantageously, the storage allows the use of existing magnetic resonance tomography system resources or, because real-time processing is not required, interference suppression can be provided at lower costs with less computing power. Subsequent interference suppression also allows the results of different parameter settings and suppression methods to be compared, thereby optimizing the interference cancellation.

[0090] In one conceivable embodiment of the method according to the invention, the receiver or the interference cancellation controller has an autocorrelation device, by means of which the interference cancellation controller can determine interference signal components in the magnetic resonance signal, for example amplitude and phase shift.

[0091] In another possible embodiment, the interference cancellation controller has an estimation device, which determines the interference signal portion, for example by means of an optimization method, such as the Least Mean Square Root (LSR) or a similar method, in which the interference portion in the magnetic resonance signal is minimized by changing one or more parameters.

[0092] In the case of multiple parameters, the interference cancellation controller optimizes the multiple parameters so that the largest possible portion of the interference signal is reduced. This can be advantageous in particular in the case of multiple interference sources or reflections.

[0093] The autocorrelation or estimation advantageously enables flexible adaptation to different interference sources.

[0094] In a possible embodiment of the method according to the present invention, the step of setting parameters has the following sub-steps:

[0095] In a sub-step, the received magnetic resonance signals are transformed into image space. Methods commonly used in MRT imaging, such as Fourier transformation, can be used here, but other methods such as compressed sensing are also conceivable.

[0096] In another substep of the method, interference signals are separated from the magnetic resonance data in image space. This can be done, for example, by comparing two adjacent volumes or two image data of the same volume acquired at different times. Although the image data are identical or similar, the image artifacts caused by the interference signals are clearly distinct due to the lack of correlation.

[0097] It is also conceivable that the acquired image space or the associated volume is larger than the examination object. Then, in the image space, regions with no magnetic resonance signals but only interfering signals are acquired. By means of this segmentation, interfering signals can be separated and determined.

[0098] In a further sub-step, the interference signal separated in the image space is transformed back into the original data space or k-space, for example again using a Fourier transform.

[0099] In another sub-step, parameters for suppressing the interference signal are determined based on the transformed interference signal in the raw data space. For example, the coordinates in k-space provide information about the phase and frequency of the interference signal. This allows for determining an attenuation and signal delay, taking into account the arrangement of the first and second receive antennas, as well as the attenuation factors and phase shifts of the signal paths. After applying this attenuation and signal delay to the interference signal of the second receive antenna in the sum signal with the receive signal of the first receive antenna, interference in the magnetic resonance signal is reduced.

[0100] However, it is also conceivable to suppress interference signals directly in image space, for example by omitting the corresponding image data. This is particularly useful when the image data does not lie within the examination region or when it can be replaced by previously acquired interference-free data from this region. It is also conceivable to mark the interference-free data in image space with a special marker, such as a color or brightness value, so that image artifacts caused by interference cannot be perceived as features of the examination object.

[0101] Identifying interference signals in image space advantageously enables separation or segmentation of magnetic resonance data from interference. This allows interference signals to be detected separately in a simple manner and better characterized, which leads to better and more effective suppression.

[0102] In one conceivable embodiment of the method according to the invention, the sub-steps of transforming, separating, inversely transforming and determining parameters are performed in the raw data space per row of data of the received magnetic resonance signal.

[0103] By applying the method according to the invention to individual lines of the raw data space and transforming them into image space, parameters can advantageously be changed more quickly than when acquiring an entire slice, thereby enabling a faster response to changes in interference signals. Repeated acquisitions of entire slices can thus be avoided.

[0104] In one possible embodiment of the method according to the present invention, the receiver monitors changes in the interference signal in one step and, if changes occur, adjusts parameters in another step. For example, the phase and amplitude of the interference source's field distribution may change due to movement of an interference source or a reflective object in the environment of the magnetic resonance tomography system. The receiver can then detect these changes in the interference signal and adjust one or more parameters accordingly, so that, for example, the interference signal received by one or more second receiving antennas is summed with the MRI signal with an appropriate gain and / or phase shift. It is conceivable that the receiver considers a threshold value during monitoring and only considers a change if the threshold value is exceeded. It is also conceivable that the receiver performs temporal averaging to suppress short-term fluctuations. The averaging can, for example, involve characteristics of the interference signal, such as amplitude, phase, frequency, and / or frequency distribution, to mitigate short-term fluctuations and minimize the introduction of additional noise into the magnetic resonance signal through interference suppression. It is also conceivable that the parameters are averaged over a certain time period or filtered using a low-pass filter in the setting step.

[0105] The receiver monitors the interference signal and advantageously reacts to changes in the interference signal, thus ensuring effective interference cancellation of the changing interference signal over a longer period of time. Threshold values ​​and averaging limit the changes and avoid fluctuations resulting from instabilities or artifacts caused by excessive compensation.

[0106] In one possible embodiment of the method according to the present invention, in one substep, the receiver stores the received first magnetic resonance signal in a memory. In another substep, the receiver stores the received second magnetic resonance signal in a memory. In a further substep, the receiver compares the received first magnetic resonance signal with the received second magnetic resonance signal. If the receiver detects a deviation attributable to external interference, the receiver performs interference suppression measures or signals the controller of the magnetic resonance tomography system to notify the controller of the interference, causing it to initiate interference suppression measures. Sudden amplitude differences in magnetic resonance signals of closely adjacent slices or, for example, measurements of the same slice based on calibration measurements, can be interference signals.

[0107] Advantageously, interference signals can be identified by comparing magnetic resonance signals of adjacent regions or the same region at different times. This is also conceivable in applications without a second receiving antenna for receiving interference signals.

[0108] In one conceivable embodiment of the method according to the present invention, the interference suppression measure comprises discarding the received first and / or second magnetic resonance signals. It is also conceivable, additionally or alternatively, to repeat the acquisition of the first and / or second magnetic resonance signals. The interference suppression measure may also comprise setting parameters.

[0109] By means of the proposed interference suppression measures, image artifacts can be avoided in magnetic resonance recordings after the interfering signals have been identified.

[0110] In one possible embodiment of the method for operating a magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system comprises: a patient tunnel; a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel; a second receiving antenna for receiving signals having the Larmor frequency of the magnetic resonance signals; and a receiver, wherein the second receiving antenna is arranged outside the patient tunnel or near the opening of the patient tunnel. The method includes the step of receiving an interfering signal by the receiver via the second receiving antenna. The arrangement of the second receiving antenna makes it more sensitive to signals outside the patient tunnel, which are not magnetic resonance signals solely due to their spatial origin. In principle, the signal from the second receiving antenna may still contain a small portion of the magnetic resonance signal, but these portions, due to their small proportion, can be initially disregarded in interference suppression or further reduced or avoided using the devices and methods described in the dependent claims.

[0111] In another step, the receiver receives magnetic resonance signals via a first receiving antenna. Here, the signals primarily used for image acquisition are referred to as magnetic resonance signals. For example, the first receiving antenna can be a local coil on the patient's body. The magnetic resonance signals may contain interfering signal components, which are further reduced using the apparatus and method according to the present invention described below.

[0112] In another step, the magnetic resonance signals received by the first receive antenna are discarded based on an interference signal received by the second antenna. For example, the interference signal received by the second receive antenna may be above a threshold level, so that despite propagation attenuation between the position of the second receive antenna and the position of the first receive antenna, interference in the mapping obtained from the magnetic resonance signals can be expected. The receiver or a controller of the magnetic resonance tomography system can then discard the signal from the first receive antenna. It is then conceivable that the magnetic resonance tomography system subsequently repeats the acquisition of the discarded signal.

[0113] Advantageously, due to the different arrangements of the first and second receiving antennas, interfering signals can be detected, in particular based on the signal amplitudes.

[0114] In one conceivable embodiment of the method according to the present invention for operating a magnetic resonance tomography system with a Larmor frequency in the ISM band, the method includes the step of determining an excitation pulse for exciting nuclear spins in the examination subject. This determination is performed based on predetermined frequency limits of the ISM band. Preferably, the excitation pulse is determined such that it only has spectral portions outside the ISM band that are below a predetermined limit value. Limiting the ISM band can be achieved, for example, by the measures described in the following claims.

[0115] In a further step of the method, the magnetic resonance tomography system emits an excitation pulse.

[0116] In a further step of the method, the magnetic resonance tomography system receives magnetic resonance signals, and in a further step, a map of the distribution of nuclear spins in the examination subject is determined. This map can then be output on a display.

[0117] In the ISM band, significantly higher limits for radio waves radiated into the environment are generally permitted. Depending on the slice density and duration, the excitation pulse can be broadband, thus also including components outside the ISM band, also because the Larmor frequency lies within the ISM band. If this is avoided by the measures described below, additional shielding measures such as an RF cabin can be dispensed with without exceeding the limit values.

[0118] In one possible embodiment of the method according to the invention, the step of determining the excitation pulse comprises the following substep: determining the excitation pulse for exciting the nuclear spins in the slice of the examination object as a function of the relative position of the slice relative to the magnet unit, the predetermined gradient strength, the slice thickness, and the type of measurement. This can be done, for example, by using a library of parameterized excitation pulses.

[0119] In a further checking step, the magnetic resonance tomography system determines whether the excitation pulse lies within predetermined frequency limits. This can be done, for example, by means of a spectral analysis using an FFT.

[0120] If the excitation pulse is not within the predetermined frequency limits, the determination step is repeated. In this case, pulse parameters that influence the frequency distribution of the spectrum of the excitation pulse are changed during the determination of the excitation pulse.

[0121] If the excitation pulse lies within the predetermined frequency limits, then in a further step the magnetic resonance tomography system emits the excitation pulse.

[0122] In one conceivable embodiment of the method according to the invention, the pulse parameter influencing the determination of the excitation pulse is one of the following parameters: the duration of the excitation pulse, the slice thickness, the relative position of the slices, or the gradient strength. In other words, to obtain another excitation pulse within the ISM frequency band with the Larmor frequency of the magnetic resonance tomography system, for example, the duration of the excitation pulse, the thickness of the slice to be excited, or also the position of the slice or the gradient strength can be varied. Simultaneous variation of multiple parameters is also conceivable.

[0123] By varying one or more pulse parameters, an excitation pulse can advantageously be determined which does not exceed the limits of the frequency band and thus enables operation within the permitted framework.

[0124] In one possible embodiment of the method according to the invention, the step of emitting has a sub-step of changing the relative position of the examination object with respect to the magnet unit before the step of emitting the pulses.

[0125] Due to the gradient fields, the resonance frequencies of nuclear spins at the edges of the Field of View (FOV) can deviate significantly from the average Larmor frequency of the magnetic resonance tomography system determined by the B0 field. By repositioning the slice to be acquired closer to the center of symmetry of the B0 field, full excitation of the slice can be achieved without leaving the ISM band boundaries, while maintaining the same bandwidth of the excitation pulses.

[0126] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system includes a control unit for controlling image acquisition. The control unit can, in particular, influence image acquisition parameters, such as the timing of the excitation pulse and / or the timing of the acquisition of the magnetic resonance signals, upon receiving magnetic resonance signals, or can also influence the frequency of the excitation pulse and / or the frequency range of the receiver. Furthermore, the magnetic resonance tomography system includes an interface for signal connection to the control unit. As will be explained below, this interface can be an interface for exchanging data with other magnetic resonance systems or a high-frequency interface. The control unit is designed to synchronize image acquisition based on signals received via the interface from another magnetic resonance tomography system. Synchronization is considered any activity that reduces mutual interference. This can include temporal coordination, but can also include, for example, frequency changes.

[0127] In the magnetic resonance tomography system according to the present invention, the control unit can also be designed to transmit a signal containing information about an upcoming image acquisition to another magnetic resonance tomography system. This feature is equivalent to a plug-and-socket combination, supplementing the magnetic resonance tomography system previously designed to receive signals from another magnetic resonance tomography system. This information preferably relates to the emission time and / or frequency of the excitation pulses. As will be explained below, the magnetic resonance tomography system according to the present invention is preferably designed for both transmitting and receiving signals. This magnetic resonance tomography system will also be referred to below as the first magnetic resonance tomography system.

[0128] The first magnetic resonance tomography system according to the present invention can also be signal-connected to the second magnetic resonance tomography system according to the present invention. To this end, the first and second magnetic resonance tomography systems each have an interface and a control unit. The first and second magnetic resonance tomography systems are signal-connected via the interface. The signal connection enables at least signal transmission from the first magnetic resonance tomography system to the second magnetic resonance tomography system, but bidirectional information exchange is also conceivable. Point-to-point connections via electrical, optical, or wireless paths are conceivable. In particular, networks such as LANs and WANs under TCP / IP can also serve as signal connections. The control unit of the first magnetic resonance tomography system is designed to send information about an upcoming image acquisition process to the second magnetic resonance tomography system via the interface. This information can be in absolute time or relative to the signal, or relative to the frequency or frequency range of the excitation pulses, indicating the planned emission time of the excitation pulses. The control unit of the second magnetic resonance tomography system is designed to receive this information via the interface and perform image acquisition based on the received information. For example, the controller of the second magnetic resonance tomography system can be designed to temporally shift the magnetic resonance signal acquisition, i.e., the sequence or a portion of the sequence, so as not to interfere with the excitation pulses of the first magnetic resonance tomography system. The second magnetic resonance tomography system will also be referred to below as another magnetic resonance tomography system.

[0129] The method for operating a magnetic resonance tomography system according to the present invention can also be extended to operate a first magnetic resonance tomography system having a control unit for controlling image acquisition and an interface for signal connection to the control unit. The method then includes a step in which the control unit receives a signal from a second magnetic resonance tomography system via the interface. This may involve a targeted information exchange, wherein the first magnetic resonance tomography system receives information or messages from the second magnetic resonance tomography system via the data interface, the information or messages including parameters such as the time and / or frequency of the intended image acquisition. However, it is also conceivable for the first magnetic resonance tomography system to monitor the environment, for example, via a receiver, for magnetic resonance signals.

[0130] In a further step, the control unit of the first magnetic resonance tomography device sets parameters for the image acquisition as a function of the received signal. For example, a temporal shifting of the sequence is conceivable.

[0131] In a further step, the first magnetic resonance tomography system performs an image acquisition according to the set parameters. For example, the sequence can be started at a modified time such that the excitation pulses of the two magnetic resonance tomography systems occur simultaneously, or the excitation pulse of the first magnetic resonance tomography system occurs at a time at which the second magnetic resonance tomography system does not receive any image-related magnetic resonance signals.

[0132] Advantageously, the magnetic resonance tomography apparatus and the operating method according to the invention in combination with a second magnetic resonance tomography apparatus allow mutual interference between the two magnetic resonance tomography apparatuses to be reduced during simultaneous operation.

[0133] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the interface is designed for data exchange. In other words, the first magnetic resonance tomography system is designed to both send data to the second magnetic resonance tomography system via the interface and receive data from the second magnetic resonance tomography system via the interface. The control unit is designed to synchronize image acquisition with the second magnetic resonance tomography system by exchanging information via the interface. In other words, the control unit coordinates image acquisition using messages to minimize interference.

[0134] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the signal contains information about the time and / or frequency of the transmission process. For example, the time can be specified absolutely or relative to the time of the message transmission. The frequency specification can be a center frequency and / or a bandwidth, a frequency range, or even a channel specification encoding the frequency range.

[0135] In a possible embodiment of the method according to the invention for operating a first magnetic resonance tomography system and a second magnetic resonance tomography system, the method further comprises the following steps: a control unit of the second magnetic resonance tomography system determines information about an upcoming image acquisition of the second magnetic resonance tomography system and, in a further step, sends a signal containing this information to the first magnetic resonance tomography system.

[0136] For example, the control unit can receive a message from the second MRI scanner via an interface, instructing the second MRI scanner to send an excitation pulse with a center frequency equal to the Larmor frequency + 100 kHz and a bandwidth of 200 kHz within 2 seconds. The first MRI scanner can then, for example, interrupt the sequence before its own excitation pulse and continue it after the second MRI scanner has finished its sequence, or send the next excitation pulse simultaneously with the excitation pulse of the second MRI scanner. Mutual interference caused by the excitation pulses of the second MRI scanner can thus be advantageously avoided during the reception phase.

[0137] In one possible embodiment of the magnetic resonance tomography system according to the present invention, the signal includes information about the time and / or frequency of the reception process. This information can, for example, specify the start, duration, and frequency, such that, for example, the second magnetic resonance tomography system starts within one second and receives within two seconds at a center frequency equal to the Larmor frequency minus 300 kHz and a bandwidth of 200 kHz. The first magnetic resonance tomography system can then, for example, interrupt the sequence so that it does not transmit excitation pulses within the aforementioned frequency band during this time.

[0138] Advantageously, upon receiving a message about the planned reception in another unit, the emission of the first magnetic resonance tomograph can also be shifted, so that interference is reduced.

[0139] In one possible embodiment, it is conceivable that the control unit of the first magnetic resonance tomography system is designed to change the frequency of the image acquisition process based on the received information. For example, it is conceivable that the image acquisition includes different slices, where the slices are differentiated by the effective Larmor frequency of the magnetic resonance signal via a gradient magnetic field on the z-axis. Therefore, if the image acquisition sequence is arranged so that the two systems do not simultaneously acquire data in the same frequency range, simultaneous operation can be achieved with minimal mutual influence.

[0140] Advantageously, differentiation by frequency enables simultaneous acquisition of magnetic resonance signals in adjacent magnetic resonance tomographs, thereby making better use of the examination time.

[0141] In one conceivable embodiment of the magnetic resonance tomography system according to the present invention, the first magnetic resonance tomography system has a receiver as an interface. In particular, the receiver is considered to be a receiver for magnetic resonance signals, including an antenna such as a local coil or a body coil. The first magnetic resonance tomography system is designed to acquire excitation pulses from the second magnetic resonance tomography system outside of image acquisition and to perform image acquisition based on the acquired excitation pulses. For example, it is conceivable that the first magnetic resonance tomography system first acquires magnetic resonance signals from a slice having a different effective Larmor frequency or waits until a maximum duration for acquiring magnetic resonance signals in the second magnetic resonance tomography system that emits the excitation pulses has expired.

[0142] Thus, synchronization can advantageously also be performed without a data connection or a change in the second magnetic resonance tomography scanner.

[0143] In a possible embodiment of the method according to the invention for operating a first magnetic resonance tomography system and a second magnetic resonance tomography system, the method further comprises the following steps: a control unit of the second magnetic resonance tomography system determines information about an upcoming image acquisition of the second magnetic resonance tomography system and, in a further step, sends a signal containing this information to the first magnetic resonance tomography system.

[0144] In principle, it is also conceivable to combine the various measures described. A protocol for exchanging information between the two magnetic resonance tomography systems can also be provided, which allows the image acquisitions of the two systems to be optimally interleaved, with only slight variations in acquisition duration, without mutual interference. In the simplest case, for example, all excitation pulses can be emitted simultaneously, as long as the image acquisitions in both magnetic resonance tomography systems occur within the same time period.

[0145] The magnetic resonance tomography apparatus according to the present invention comprises: a patient tunnel; a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel; a second receiving antenna for receiving a signal having the Larmor frequency of the magnetic resonance signal; and a receiver, wherein the second receiving antenna is arranged outside or near an opening of the patient tunnel, wherein the receiver is signal-connected to the first receiving antenna and the second receiving antenna, and the receiver is designed to suppress interference signals received by the second receiving antenna in the magnetic resonance signals received by the first receiving antenna.

[0146] In one conceivable embodiment, the magnetic resonance tomography apparatus according to the present invention comprises: a patient tunnel; a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel; a second receiving antenna for receiving signals near the Larmor frequency of the magnetic resonance signals; and a receiver, wherein the second receiving antenna is arranged outside or near the opening of the patient tunnel, wherein the receiver is signal-connected to the first receiving antenna and the second receiving antenna, and the receiver is designed to suppress broadband interference signals in the magnetic resonance signals received by the first receiving antenna that are received by the second receiving antenna outside the frequency range of the magnetic resonance signals.

[0147] In one possible embodiment, the magnetic resonance tomography system according to the present invention is designed to receive magnetic resonance signals having Larmor frequencies in the industrial frequency band.

[0148] In one conceivable embodiment, the magnetic resonance tomography system according to the invention has a transmission path for emitting excitation pulses, the transmission path having an ISM filter, wherein the ISM filter is designed to suppress signals outside the ISM frequency band.

[0149] In one possible embodiment, the magnetic resonance tomography system according to the invention comprises a transmitting antenna for emitting excitation pulses, wherein the magnetic resonance tomography system comprises a nonlinear component for detuning the transmitting antenna, wherein the nonlinear component is arranged in a region of the magnetic resonance tomography system that is shielded from high frequencies by the patient tunnel, wherein the ISM filter is arranged between the nonlinear component and the antenna.

[0150] In one conceivable embodiment, the magnetic resonance tomography system according to the invention comprises a radio-frequency unit, wherein the radio-frequency unit comprises a predistorter which is designed to predistort excitation pulses for exciting nuclear spins in such a way that the signal portion of the emitted excitation pulses outside the ISM band is reduced compared to non-predistorted excitation pulses.

[0151] In one possible embodiment of the magnetic resonance tomography system according to the invention, the cutoff frequency of the radio waves propagating in the patient tunnel is greater than the Larmor frequency of the magnetic resonance tomography system.

[0152] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the magnetic resonance tomography system comprises a waveguide surrounding the magnetic resonance tomography system, wherein the waveguide has a cutoff frequency which is greater than the Larmor frequency of the magnetic resonance tomography system.

[0153] In one possible embodiment of the magnetic resonance tomography system according to the invention, the waveguide has an electrically conductive connection to the patient tunnel.

[0154] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the second receiving antenna is arranged at the opening of the patient tunnel or on the patient bed.

[0155] In one possible embodiment of the magnetic resonance tomography apparatus according to the present invention, the second receiving antenna has an omnidirectional receiving characteristic.

[0156] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the magnetic resonance tomography system has a plurality of second receiving antennas, and the receiver is designed to suppress interference signals in the magnetic resonance signal based on the reception signals of the plurality of second receiving antennas.

[0157] In one possible embodiment of the magnetic resonance tomography system according to the invention, the plurality of second receiving antennas are arranged symmetrically with respect to the patient tunnel.

[0158] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the receiver has an autocorrelation device, and the autocorrelation device is designed to determine the signal portion of the magnetic resonance signal received by the first receiving antenna that is received by the second receiving antenna.

[0159] In one possible embodiment of the magnetic resonance tomography system according to the invention, the receiver has an estimation device, and the estimation device is designed to estimate the signal portion of the magnetic resonance signal received by the first reception antenna that is received by the second reception antenna.

[0160] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the magnetic resonance tomography system comprises an interference suppression transmitter and an interference suppression antenna, wherein the interference suppression antenna is arranged at a certain distance from the patient tunnel, and wherein the interference suppression transmitter is designed to output a signal in the frequency range of the excitation pulses of the magnetic resonance tomography system via the interference suppression antenna, depending on a transmission interference cancellation parameter, so that in a predetermined area of ​​the environment of the magnetic resonance tomography system the field strength of the excitation pulses is reduced by destructive interference.

[0161] In one possible embodiment of the magnetic resonance tomography device according to the present invention, the magnetic resonance tomography device has a calibration element located in the environment of the magnetic resonance tomography device and has an interference suppression controller, wherein the interference suppression controller is designed to, with the help of the calibration element, detect the field strength within the frequency range of the excitation pulse at the position of the calibration element, and to set the transmission interference elimination parameters based on the detected field strength so that the field strength of the excitation pulse is reduced in a predetermined environment of the calibration element.

[0162] In one conceivable embodiment of the magnetic resonance tomography apparatus according to the invention, the interference suppression transmitter is designed to generate signals for one or more interference suppression antennas by phase shifting and / or amplitude adjustment as a function of one or more transmit interference cancellation parameters.

[0163] In one possible embodiment of the magnetic resonance tomography system according to the invention, the interference suppression antenna has a high-frequency power amplifier.

[0164] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the magnetic resonance tomography system comprises a calibration element in the environment of the magnetic resonance tomography system, wherein the receiver is designed to measure a first transfer function between a first receiving antenna and the calibration element and a second transfer function between a second receiving antenna and the calibration element, and to set one or more interference cancellation parameters as a function of the measured first and second transfer functions, such that an interference signal received by the second receiving antenna is reduced in the magnetic resonance signal received by the first receiving antenna.

[0165] In a method for operating a magnetic resonance tomography system according to the present invention, the magnetic resonance tomography system comprises: a patient tunnel; a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel; a second receiving antenna for receiving a signal having a Larmor frequency of the magnetic resonance signals; and a receiver, wherein the second receiving antenna is arranged outside the patient tunnel or near an opening of the patient tunnel, wherein the method comprises the following steps:

[0166] The receiver receives the interference signal via the second receiving antenna;

[0167] The receiver receives the magnetic resonance signal via the first receiving antenna;

[0168] The receiver processes the magnetic resonance signal in correlation with the interference signal to form a received signal, wherein the correlation depends on a parameter;

[0169] The receiver sets parameters so that the interference signal portion of the received signal is reduced.

[0170] In one conceivable embodiment of the method according to the invention for operating a magnetic resonance tomography system, the magnetic resonance tomography system comprises a patient tunnel, a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel, a second receiving antenna for receiving signals near the Larmor frequency of the magnetic resonance signals, and a receiver, wherein the second receiving antenna is arranged outside the patient tunnel or near an opening of the patient tunnel, wherein the method comprises the following steps:

[0171] The receiver receives a frequency portion of the interference signal near the Larmor frequency via the second receiving antenna;

[0172] The receiver receives the magnetic resonance signal via the first receiving antenna;

[0173] The receiver processes the magnetic resonance signal in correlation with a frequency component of the interfering signal to form a received signal, wherein the correlation depends on a parameter;

[0174] The receiver sets parameters so that the interference signal portion of the received signal is reduced.

[0175] In a possible embodiment of the method according to the invention, the step of setting parameters comprises a step of temporal averaging by temporal averaging based on the interference signal.

[0176] In one conceivable embodiment of the method according to the invention for operating a magnetic resonance tomography system, the method comprises the following steps:

[0177] measuring a transfer function between the first receiving antenna and the calibration element;

[0178] measuring a transfer function between the second receiving antenna and the calibration element;

[0179] Based on the measured transfer function, interference cancellation parameters are set so that the portion of the interference signal received by the second receiving antenna in the signal received by the receiver via the first receiving antenna is reduced.

[0180] In one possible embodiment of the method according to the present invention, the step of receiving the interference signal is performed during a time period in which a sequence of magnetic resonance signals for imaging is not received.

[0181] In one conceivable embodiment of the method according to the invention, the receiver has a memory and the method has a storing step in which the receiver stores the interference signal and the magnetic resonance signal in the memory.

[0182] In this case, the processing step is performed with a delay relative to the reception of the interference signal and / or the magnetic resonance signal.

[0183] In one possible embodiment of the method according to the invention, the receiver has an autocorrelation device, and in the step of setting parameters, the autocorrelation device determines an interference signal portion in the magnetic resonance signal and sets the parameters depending on the determined interference signal portion.

[0184] In one conceivable embodiment of the method according to the invention, the receiver has an estimation device and, in the step of setting the parameters, the estimation device determines the interference signal portion in the magnetic resonance signal and sets the parameters as a function of the determined interference signal portion.

[0185] In a possible embodiment of the method according to the present invention, the step of setting parameters has the following sub-steps:

[0186] transforming the received magnetic resonance signals into image space;

[0187] separating interfering signals from magnetic resonance data;

[0188] Transform the interference signal into the original data space;

[0189] Parameters are determined based on the interference signal in the transformed original data space.

[0190] In one conceivable embodiment of the method according to the invention, the transformation step, the separation step, the inverse transformation step and the parameter determination step are performed according to rows of data of the received magnetic resonance signal in the raw data space.

[0191] In one possible embodiment of the method according to the invention, the receiver monitors changes in the interfering signal in one step and, if a change is present, adjusts the parameter in one step.

[0192] In a conceivable embodiment of the method according to the invention, the receiver stores the received first magnetic resonance signal in a memory in one step;

[0193] In one step, the received second magnetic resonance signal is stored; and

[0194] In one step, a first received magnetic resonance signal is compared with a second received magnetic resonance signal, and if there is a deviation attributable to external interference, interference suppression measures are performed.

[0195] In a possible embodiment of the method according to the present invention, the interference suppression measure is one of the following measures: discarding the received first and / or second magnetic resonance signals, repeating acquisition of the first and / or second magnetic resonance signals, or setting parameters.

[0196] In one conceivable embodiment of the method according to the invention for operating a magnetic resonance tomography system, the magnetic resonance tomography system comprises a patient tunnel, a first receiving antenna for receiving magnetic resonance signals from a patient in the patient tunnel, a second receiving antenna for receiving signals having the Larmor frequency of the magnetic resonance signals, and a receiver, wherein the second receiving antenna is arranged outside the patient tunnel or near an opening of the patient tunnel, wherein the method comprises the following steps:

[0197] The receiver receives the interference signal via the second receiving antenna;

[0198] The receiver receives the magnetic resonance signal via the first receiving antenna;

[0199] The magnetic resonance signal is discarded based on the interference signal received by the second receiving antenna.

[0200] In one possible embodiment of the method according to the invention for operating a magnetic resonance tomograph with a Larmor frequency in the ISM band, the method comprises the following steps:

[0201] determining an excitation pulse for exciting nuclear spins in the examination object;

[0202] Sending an excitation pulse;

[0203] receiving magnetic resonance signals;

[0204] determining a map of the distribution of nuclear spins in the examination object;

[0205] In the step of determining the excitation pulse, the determination is performed based on a predetermined frequency boundary of the ISM band.

[0206] In one conceivable embodiment of the method according to the invention, the step of determining the excitation pulse has the following substeps:

[0207] determining an excitation pulse for exciting nuclear spins in a slice of the examination object as a function of the relative position of the slice with respect to the magnet unit, a predetermined gradient strength, a thickness of the slice, and a type of measurement;

[0208] checking whether the determined excitation pulse is located within predetermined frequency boundaries of the ISM band;

[0209] Repeating the determining step while varying a pulse parameter, wherein when determining the excitation pulse, the pulse parameter has an influence on the spectral frequency distribution of the excitation pulse when the excitation pulse is not within predetermined frequency limits, or

[0210] In step, the determined excitation pulse is emitted.

[0211] In one possible embodiment of the method according to the invention, the pulse parameter influencing the determination of the excitation pulse is one of the following parameters: duration of the excitation pulse, slice thickness, relative position of the slices or gradient strength.

[0212] In one conceivable embodiment of the method according to the invention, the step of emitting has the sub-step of changing the relative position of the examination object with respect to the magnet unit before the step of emitting the pulses.

[0213] In one possible embodiment of the magnetic resonance tomography apparatus according to the present invention, the magnetic resonance tomography apparatus comprises: a control unit for controlling image acquisition; and an interface signal-connected to the control unit, wherein the control unit is designed to synchronize the image acquisition based on a signal received from a second magnetic resonance tomography apparatus via the interface.

[0214] In one conceivable embodiment of the magnetic resonance tomography device according to the invention, the magnetic resonance tomography device comprises a control unit for controlling image acquisition and an interface for signal connection to the control unit, wherein the control unit is designed to send a signal containing information about the upcoming image acquisition to a second magnetic resonance tomography device.

[0215] In one possible embodiment of the magnetic resonance tomography system according to the invention, the interface is designed for data exchange, wherein the control unit is designed to synchronize the image acquisition with the second magnetic resonance tomography system by means of information exchange via the interface.

[0216] In one conceivable embodiment of the magnetic resonance tomography system according to the invention, the signal has information about the time and / or frequency of the transmission process.

[0217] In one possible embodiment of the magnetic resonance tomography system according to the invention, the signal has information about the time and / or frequency of the acquisition process.

[0218] One possible embodiment of the present invention comprises a computer program product that can be loaded directly into a processor of a programmable controller, the computer program product comprising program code means for carrying out all steps of the method according to the present invention for operating a magnetic resonance tomography system when the program product is executed on the controller.

[0219] One possible embodiment of the present invention comprises a computer-readable storage medium having electronically readable control information stored thereon, the electronically readable control information being designed such that, when the storage medium is used in a controller of a magnetic resonance tomography system according to the present invention, the electronically readable control information executes the method according to the present invention for operating a magnetic resonance tomography system. BRIEF DESCRIPTION OF THE DRAWINGS

[0220] The above-described characteristics, features, and advantages of the present invention and their implementation methods will become clearer and more easily understood when combined with the following description of the embodiments in detail with reference to the accompanying drawings.

[0221] Figure 1 A schematic diagram of a magnetic resonance tomography apparatus with an apparatus according to the invention is shown;

[0222] Figure 2 A schematic diagram showing a receiver and a first receiving antenna and a second receiving antenna;

[0223] Figure 3 A schematic diagram showing a flow chart of one embodiment of the method according to the present invention;

[0224] Figure 4 A schematic diagram showing a high-frequency unit of a magnetic resonance tomography apparatus according to the present invention;

[0225] Figure 5 A schematic diagram of a magnetic resonance tomography apparatus according to the present invention surrounded by a waveguide is shown;

[0226] Figure 6 A schematic diagram of a magnetic resonance tomography apparatus according to the invention with an interference suppression transmitter is shown;

[0227] Figure 7 A schematic diagram showing a flow chart of a partial aspect of a method according to the present invention;

[0228] Figure 8 A schematic diagram showing a flow chart of a partial aspect of a method according to the present invention;

[0229] Figure 9 A schematic diagram showing a flow chart of a partial aspect of a method according to the present invention;

[0230] Figure 10 A schematic diagram showing a flow chart of a partial aspect of a method according to the present invention;

[0231] Figure 11 A schematic diagram of a magnetic resonance tomography apparatus according to the invention connected to another magnetic resonance tomography apparatus is shown. DETAILED DESCRIPTION

[0232] Figure 1 A schematic diagram of an embodiment of a magnetic resonance tomography system 1 with a local coil 50 according to the invention is shown.

[0233] The magnet unit 10 has a field magnet 11 that generates a static magnetic field B0 in a recording region for aligning the nuclear spins of a sample or patient 100. The recording region is characterized by a highly uniform static magnetic field B0, where the uniformity particularly relates to the magnetic field strength or magnitude. The recording region is nearly spherical and is arranged in a patient tunnel 16 that extends through the magnet unit 10 in the longitudinal direction 2. A movement unit 36 ​​enables the patient bed 30 to be moved in the patient tunnel 16. The field magnet 11 is typically a superconducting magnet that can provide a magnetic field with a flux density of up to 3 T, or even higher with the latest equipment. However, for lower field strengths, permanent magnets or electromagnets with normally conductive coils can also be used.

[0234] The magnet unit 10 also includes gradient coils 12 designed to superimpose a magnetic field B0 with a variable magnetic field in three spatial directions to spatially differentiate acquired imaging regions in the examination volume. The gradient coils 12 are typically coils made of normally conductive metal wires that can generate mutually orthogonal fields in the examination volume.

[0235] The magnet unit 10 also has a body coil 14 , which is designed to radiate high-frequency signals fed via signal lines into an examination volume, to receive resonance signals emitted by the patient 100 , and to output them via the signal lines.

[0236] 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.

[0237] The control unit 20 therefore has a gradient controller 21 which is designed to supply the gradient coils 12 via feed lines with variable currents which provide the desired gradient fields in the examination volume in a time-coordinated manner.

[0238] The control unit 20 also includes 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 transmitting antennas.

[0239] The controller 23 communicates with the gradient controller 21 and the high-frequency unit 22 via a signal bus 25 .

[0240] A local coil 50 is arranged on the patient 100 as a first receiving coil and is connected to the high-frequency unit 22 and its receiver via a connecting line 33. However, it is also conceivable that the body coil 14 is the first receiving antenna within the meaning of the present invention.

[0241] Four second receiving antennas 60 are arranged at the edge of the opening of the patient tunnel 16 . These four second receiving antennas 60 are arranged at the corners of a square inscribed in the circular opening, so that the corners are located at the edge of the opening. The four second receiving antennas 60 are signal-connected to the receiver 70 of the high-frequency unit 22 . Given the plurality of second receiving antennas 60 , it is conceivable that not all of these second receiving antennas 60 have omnidirectional reception characteristics, but rather, for example, they may be dipoles, supplemented by different orientations to achieve omnidirectional characteristics. However, it is also conceivable, for example, to provide a crossed dipole as the only second antenna with omnidirectional characteristics.

[0242] Alternatively or additionally, the second receiving antenna 60 can also be arranged in the patient bed 30 .

[0243] The patient tunnel preferably has a radius R, for which:

[0244] R<(LambdaL*1,841) / (2*Pi)

[0245] Here, Lambda L Lambda gives the wavelength of the radio wave 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 wave propagates exponentially in the patient tunnel 16, and the interference signal is strongly attenuated in the middle of the examination region FoV. L Also known as the cutoff wavelength of a circular waveguide, the frequency associated with it is called the cutoff frequency.

[0246] Due to its limited electrical conductivity, the patient 100 serves solely as the core of the coaxial cable, whose outer sheath forms the wall of the patient tunnel 16 and transmits electromagnetic signals coupled from the legs or the top of the head into the examination region. Advantageously, one or more second receiving antennas 70 near the opening or in the patient bed 30 record interfering signals transmitted from the patient 100 into the FoV, thereby making compensation in the receiver 70 particularly effective.

[0247] Figure 2 A schematic diagram of the functional units of a possible embodiment of a receiver 70 is shown.

[0248] A summing device 71 uses a parameter, which can also be complex, to weight the signals entering from the first receiving antenna or local coil 50 and from the second receiving antenna 60 to provide a phase shift. In an analog receiver 70, this can be accomplished using an adjustable amplifier in combination with an adjustable phase shifter. The real part of the parameter then corresponds to the amplification factor, and the imaginary part corresponds to the phase shift. In a preferred embodiment, the weighted signals are then summed, but other nonlinear signal operations are also conceivable for combining the individual signals.

[0249] The interference cancellation controller 72 obtains the composite signal and the individual signals of the first and second receive antennas 60. To determine the interference signal portion of the composite signal, the interference cancellation controller 72 can, for example, perform an autocorrelation on the signals. However, it is also conceivable to determine the energy of the composite signal. In one conceivable embodiment, the interference cancellation controller 72 determines the interference signal portion in segments of a magnetic resonance tomography sequence in which no magnetic resonance signals are expected to be used for imaging, so that the composite signal contains only interference signals. This can be the case, for example, in dephased segments of an echo sequence, because the amplitudes of the individual nuclear spins cancel each other due to their different phases, and overall no signal is generated.

[0250] Then, the interference cancellation controller 72 optimizes the parameters in the summing device, for example, according to the least square root method (LSR), so as to minimize the interference signal portion or energy in the composite signal.

[0251] In principle, the receiver 70 can be implemented using analog signal processing technology, whereby, for example, gain adjustment and phase shift are controlled by parameters and then an analog conversion is performed, or the receiver 70 can be implemented as a digital receiver, which receives already digitized signals from the first receiving antenna and / or the second receiving antenna 60 or which already digitizes the signals at the signal input with the aid of an A / D converter.

[0252] The receiver 70 transmits the synthesized signal in which the interference signal is largely suppressed to the controller 23 of the magnetic resonance tomography apparatus for imaging.

[0253] It is also possible that the interference signal has a wider bandwidth than the magnetic resonance signal. In this case, the frequency portion of the magnetic resonance signal outside the frequency range is often correlated with the frequency portion within the magnetic resonance signal. Therefore, according to the present invention, it may be sufficient for the second receiving antenna 60 to only partially receive the broadband interference signal, for example, within a frequency range different from or outside the frequency range of the magnetic resonance signal. Additionally or alternatively, the receiver 70 may be designed to receive only frequencies within this frequency range from the second receiving antenna. In this case, the receiver 70 is designed to suppress interference signals in the magnetic resonance signal received from the first receiving antenna based on this partial signal. Due to correlation, for example, the amplitude of the frequency portion of the interference signal within the frequency range of the magnetic resonance signal may be correlated with the amplitude outside this frequency range. In this way, it is also conceivable that the second receiving antenna 60, in conjunction with the receiver 70, monitors only the frequency portion outside the frequency range of the magnetic resonance signal for interference signals during a magnetic resonance measurement and, accordingly, suppresses the interference signal in the signal from the first receiving antenna. In this case, the receiver 70 can, for example, determine, before the acquisition of magnetic resonance signals, for interference signals within the frequency range of the magnetic resonance signals, a relationship between the interference signal from the first receiving antenna and the interference signal portion from the second receiving antenna 60, which is also referred to as a transfer function, and during the acquisition of the magnetic resonance signals, adjust the amplitude or scaling, for example, as a function of the interference signal portion from the second receiving antenna received outside the frequency range of the magnetic resonance signals.

[0254] In another conceivable embodiment of the magnetic resonance tomography system (1) according to the invention, the suppression of interference signals in the received signal is not performed in real time, i.e., not immediately upon receiving the interference signal and / or magnetic resonance signal, but the magnetic resonance signal and the interference signal are stored in a memory by the receiver 70, which can also comprise the controller 23 or the image analysis part of the magnetic resonance tomography system 1. The steps described below with respect to the method are then no longer performed in real time or almost in real time, but can be performed with a delay, for example in a preparatory phase for the image analysis, on the stored data.

[0255] In this case, for example, a combination of reception outside the frequency band of the MR signal with the second antenna and interference suppression in real time or at a later point in time, for example during image analysis, is also conceivable.

[0256] exist Figure 2The interference suppression in the receiver shown in FIG can also be performed using a single second antenna 60. Instead, the receiver 70 can have multiple channels, or multiple receivers 70 can be provided in the magnetic resonance tomography system 1 to suppress interference with the magnetic resonance signals of multiple local coils 50. In this case, it is conceivable that multiple receivers 70 or multiple channels of the receiver 70 use the signal of the second receiving antenna 60 to suppress interference.

[0257] Here, it is conceivable that the correlation between the interference signal received by the second antenna and the interference suppression is not only linear but also nonlinear. Here, the linear correlation can be a phase shift of a specific value or a linear scaling having a value determined based on the signal of the second antenna. However, it is also conceivable that the transfer function of the interference signal has nonlinearity on the path from the first receive antenna and / or the second receive antenna, for example due to a mixer or a nonlinear amplifier. Therefore, a nonlinear operation must also be applied to the interference signal received from the second receive antenna 60 in the receiver 70 to suppress the interference.

[0258] Figure 3 A schematic flow chart of the method according to the present invention is shown.

[0259] In step S10, the receiver 70 receives the interference signal via the second receiving antenna 60 or via a plurality of second antennas 60. The interference signal is transmitted via a signal connection to the receiver 70. It is also conceivable that the interference signal is first digitized by an A / D converter before being transmitted to the receiver 70, in which case the receiver 70 is designed as a digital receiver 70.

[0260] In step S20, the receiver 70 receives magnetic resonance signals via a first receiving antenna, such as a local coil 50. In the case of multiple local coils 50, multiple receivers 70 can be provided accordingly, or a receiver 70 with multiple channels can be provided, each channel having a summing device 71. In this case, the interference cancellation controller 72 can be provided separately or jointly, which can speed up subsequent setup since the parameters for different channels are similar.

[0261] In step S30, the receiver 70 processes the magnetic resonance signal based on the interference signal, or, in the case of multiple second receive antennas 60, based on multiple interference signals, to form a received signal. For example, one or more interference signals from one or more second receive antennas 60 and the magnetic resonance signal from the first receive antenna are weighted using different parameters, delayed, and then combined. This can be, for example, a linear combination. The generated received signal or sum signal is dependent on one or more parameters.

[0262] In another step S40, the receiver 70, in particular the interference cancellation controller 72, sets one or more parameters to reduce the interference signal portion in the received signal. For example, if the interference signal received from the second receiving antenna 60 is scaled by the set parameters so that it has the same amplitude as the interference signal portion via the first receiving antenna, and a 180-degree phase shift is set for the interference signal relative to the interference signal portion, the interference signal in the resulting received signal is exactly canceled. Here, one or more parameters can be determined by an optimization method, such as Least Square Root (LSR) or Wiener Filter.

[0263] Here, step S40 may also include a sub-step S41 for forming a time average value and setting parameters for interference suppression based on the average value. For example, the amplitude or phase of the interference signal may be averaged to balance statistical fluctuations, and by performing interference suppression, less noise is introduced into the magnetic resonance signal.

[0264] It is also conceivable to carry out steps S10 to S30 in real time for each of the received magnetic resonance signals and the received interference signals, in particular in the case of an analog receiver 70. However, it is also conceivable to carry out steps S10 to S30 for each of the stored interference signals and magnetic resonance signals, for example to digitize the interference signals and the magnetic resonance signals for a single sequence or individual segments thereof.

[0265] In one possible embodiment of the method according to the present invention, step S40 is performed for interference signals during a time period in which no magnetic resonance signals used for imaging are received. For example, the interference cancellation controller 72 may determine parameters using the interference signal from the second receive antenna 60 and the signal from the first receive antenna during a time period in which the nuclear spins are dephased and no magnetic resonance signals are generated. However, it is also conceivable that only the interference signal and the signal from the first receive antenna are digitally acquired during this time period in which no magnetic resonance signals are generated, and these signals are subsequently analyzed.

[0266] Here, it is contemplated that, in step S50, the interference cancellation controller 72 monitors changes in the interference signal, such as different amplitudes, frequencies, or phases. Upon identifying such changes, or if the changes exceed a predetermined threshold, the interference cancellation controller 72 may, in step S51, change the steps of receiving the interference signal (S10) and receiving the magnetic resonance signal (S20), as well as the settings of the interference cancellation parameters based on the received interference signal, to adapt the interference cancellation to the changed interference signal.

[0267] In principle, in one embodiment of the method according to the present invention, it is also conceivable that in step S25, the receiver 70 stores the received interference signals and / or magnetic resonance signals. The receiver 70 can also comprise part of the controller 23 of the magnetic resonance tomography system 1 or an external image analysis computer. Steps S20 to S40 are then performed later, for example, at the end of the echo sequence, the excitation sequence, or the acquisition of signals for a slice of the examination object, or after all data has been acquired.

[0268] Thus, decoupling the signal acquisition of interference signals and magnetic resonance signals from interference suppression allows for the advantageous use of low-cost components with reduced computing power, or for the dual use of existing resources, such as those used in image analysis. It is also conceivable to compare and select different parameter settings, or to subsequently optimize them. Applications can also be restricted to time periods with interference.

[0269] Figure 4 A schematic diagram of a radio-frequency unit of a magnetic resonance tomography system according to the invention is shown. This diagram does not show all details of the radio-frequency unit, but only details of the transmission path relevant to the interference suppression according to the invention.

[0270] In this case, the transmission path of the radio-frequency unit 22 has a pulse generator 220 , a predistorter 221 , a power amplifier 222 and an ISM filter 223 .

[0271] The pulse generator 220 can, for example, have an oscillator, a modulator, and a mixer, with which pulses are generated in baseband and then converted to the Larmor frequency.

[0272] Predistorter 221 is designed to predistort the excitation pulse used to excite nuclear spins, thereby reducing the signal portion of the excitation pulse outside the ISM band compared to an unpredistorted excitation pulse. For example, it is conceivable that predistorter 221 generates and mixes signal portions that, after amplification by the power amplifier, correspond to harmonics generated by the excitation pulse due to the nonlinearity of the power amplifier, but have opposite signs, thereby reducing or eliminating the harmonics. A similar approach can be considered for intermodulation of signal portions generated due to nonlinearity. Predistorter 221 can be implemented, for example, in digital signal generation, or by analog components generating a corresponding signal from the power amplifier input signal. It is also conceivable that predistorter 221 be integrated into digital pulse generator 220, for example.

[0273] The output signal of predistorter 221 is amplified in power amplifier 222. A power amplifier 22 having a linear characteristic curve is conceivable. However, predistorter 222 can also modify the input signal of power amplifier 222 so that, after amplification by power amplifier 222, a signal without undesirable harmonics is generated. In other words, ideally, the characteristic curve of predistorter 221 multiplied by the characteristic curve of power amplifier 222 yields a linear characteristic curve, so that the system consisting of predistorter 221 and power amplifier 222 amplifies the pulses of the pulse generator without undesirable harmonics.

[0274] In one embodiment, as in Figure 4 As shown by the dotted line starting from the output of the ISM filter 223, the predistorter 221 can also be adaptive in the sense that it adjusts the predistortion by monitoring the output signal of the power amplifier 222 so that the entire system consisting of the predistorter and the power amplifier has linear characteristics.

[0275] After the power amplifier 222, the signal is preferably further filtered by an ISM filter 223. The filter preferably suppresses frequency components outside the ISM band used by the magnetic resonance tomography system 1 for image acquisition. For example, the filter can be a bandpass filter for the used ISM band, which attenuates frequencies outside the ISM band by more than 12 dB, 24 dB, 40 dB, or 60 dB relative to signals with minimal attenuation within the ISM band. However, a low-pass filter can also be used. Depending on the embodiment of the high-frequency generation in the magnetic resonance tomography system, the filter can be arranged, for example, between the power amplifier 222 and a hybrid coupler (not shown), between the hybrid coupler and a transmit / receive switch (not shown), or between the transmit / receive switch and the transmitting antenna.

[0276] In one embodiment, the MRI system also includes a detuning element for the transmitting antenna. This can be, for example, a PIN diode, or other diodes or active components such as transistors or FETs. These detuning elements are provided to detune the transmitting antenna during reception and prevent interaction with the receiving antenna. Detuning elements typically have nonlinear characteristic curves and therefore can generate harmonics during transmission. Therefore, in a preferred embodiment, an ISM filter 223 is arranged between the detuning element and the transmitting antenna. The nonlinear component is also preferably arranged in an area of ​​the MRI system that is shielded from high frequencies by the patient tunnel.

[0277] The arrangement of the nonlinear components therefore contributes to compliance with radiation limit values ​​and makes it possible to dispense with or simplify shielding of the entire magnetic resonance tomography system by means of a high-frequency cabin.

[0278] exist Figure 5 Schematically depicts an embodiment of an MRI system 1 according to the present invention surrounded by a waveguide. The waveguide 260 can be provided by any electrically conductive surface surrounding the MRI system 1 on its periphery in at least four spatial directions. Conductive surfaces are particularly considered to be metal or metalized surfaces or fabrics, which, when passing through them, attenuate electromagnetic waves having the Larmor frequency by 60 dB, 80 dB, 100 dB, or more. The conductivity of the surface can also be anisotropic due to geometrical divisions, such as gaps, as long as the conductivity parallel to the electric field vector of the alternating field is sufficient to achieve attenuation.

[0279] The waveguide 260 is preferably formed as a tunnel surrounding the magnetic resonance tomograph, for example, in the shape of a cylinder, cube, or prism. The cylinder, cube, or prism has a width that does not allow the formation of free-flowing waves with the Larmor frequency. In the case of a cube, this is the case, for example, when the longer dimension of the cross section is less than half the wavelength of the electromagnetic wave with the Larmor frequency. In other words, the cut-off frequency, or cutoff frequency, of the waveguide 260 is greater than the Larmor frequency. As a result, the electromagnetic field decreases exponentially with distance from the source, causing the alternating field escaping from the patient tunnel 16 to decrease rapidly. It is conceivable that the waveguide 260 is open at one or both ends, as the exponential decay is sufficiently strong due to the distance from the patient tunnel 16 to adhere to the permissible limits in the ISM frequency band.

[0280] It is also conceivable that the magnetic resonance tomography system 1 is surrounded by a shield having dimensions greater than half the wavelength. However, instead of a high-frequency sealing door, the magnetic resonance tomography system 1 can be provided with a tunnel-shaped access opening 261 made of a conductive material with a correspondingly small cross-section. The dimensions of the access opening 261 prevent the free propagation of waves due to a cutoff frequency greater than the Larmor frequency. The access opening 261 is preferably connected to the shield and / or waveguide in a manner that is electrically conductive to high frequencies. In one embodiment, the waveguide 260 is also connected to the patient tunnel 16 in a manner that is electrically conductive to high frequencies.

[0281] Figure 6A schematic diagram shows an embodiment of a magnetic resonance tomography system 1 according to the present invention having an interference suppression transmitter 80. Electric waves or alternating fields can also be suppressed by electric fields having the same frequency and amplitude, but opposite polarity or a 180-degree phase shift. If the amplitude or phase are not perfectly matched, a reduction is achieved at least by destructive interference. To generate such an alternating field for interference suppression, the magnetic resonance tomography system 1 according to the present invention has interference suppression antennas 81 arranged around the source of the field, in this case, the patient tunnel 16. Preferably, the interference suppression antennas 81 cover all spatial directions around the opening, and symmetry, such as a distribution at the same distance and / or the same angular distance from the opening of the patient tunnel 16, simplifies the control of the individual interference suppression antennas 81. However, since the amplitude and phase can be set individually for each interference suppression antenna 81, any desired distribution is also conceivable. Depending on the type of alternating field, the interference suppression antennas can be antennas that preferably utilize electric fields, such as dipoles, or antennas that utilize magnetic fields, such as transmitting coils. In this case, the orientation of the antenna or the polarization of the generated field is preferably oriented with respect to the field direction of the alternating field to be suppressed.

[0282] The signal emitted by interference suppression antenna 81 is intended to reduce the radiation from the excitation pulse and therefore must have a predetermined amplitude and phase relationship with the excitation pulse. Therefore, the signal is preferably derived analogically from the excitation signal or generated by digital pulse generation. However, it is also conceivable to provide the signal independently of the pulse generation by a separate unit, as long as the required amplitude and phase relationship is established.

[0283] exist Figure 6 , the connection line between body coil 14, serving as the source of electromagnetic waves, and the interference suppression transmitter is shown symbolically. A direct connection via a power splitter or, for example, a directional coupler is conceivable, as is a sensor in the patient tunnel for directly acquiring the electromagnetic field. However, a reference signal can also be obtained from power amplifier 222 or pulse generator 220, which is used to generate the signal for interference suppression.

[0284] Subsequently, before the reference signal for interference suppression derived from the excitation pulse is transmitted via the interference suppression antenna 81 , the reference signal is delayed or phase-shifted for each interference suppression antenna 81 via an adjustable phase adjuster 82 and then amplified in amplitude via an adjustable amplifier 83 .

[0285] The interference suppression controller 84 sets the phase adjuster 82 and the amplifier 83 via a signal connection. It is conceivable that the interference suppression controller 84 sets a predetermined phase shift and amplitude, which are determined, for example, during installation of the magnetic resonance tomography system 1 .

[0286] However, the setting can also be performed by calibration measurements. In this case, it is conceivable that the calibration receiver 85 records the alternating field to be suppressed using one or preferably a plurality of calibration elements 86 distributed in space. At the same time, the calibration receiver 85 acquires the signal fed to the interference suppression antenna 81 and transmits the acquired values ​​to the interference suppression controller 84. The interference suppression setting 84 can then, for example, cause the interference suppression controller 84 to set the phase and amplitude of each interference suppression antenna using a linear optimization method such as LSR so that the field strength is zero at the location of the calibration antenna 86. If n calibration elements 86 are distributed over a spatial angle, the body coil 14 and the interference suppression antenna 81 can transform the generated alternating field into a multipole field with n zero points or radiation lobes (Abstrahlkeule), which decreases in a high-order manner with distance and enables effective suppression.

[0287] In principle, the propagation of the field is reversible. That is, for calibration purposes, it is also conceivable that one or more calibration elements 86 emit a signal, and the body coil 14 and the interference suppression antenna 84 receive the signal, and the interference suppression controller 84 then determines the appropriate phase relationship and amplitude.

[0288] Furthermore, calibration element 86 can also be used to emit a reference signal for reception interference suppression. The reference signal must be encoded or modulated so that receiver 70 can distinguish it from the magnetic resonance signal. For example, this can be achieved using spread spectrum modulation below the noise limit of the magnetic resonance signal. Emission within adjacent frequency ranges is also conceivable. This requires that receiver 70 be able to establish a correlation between the reference signal and the signals received via the second and first receiving antennas in order to optimize interference suppression. This allows, for example, the settings for suppressing interference signals from a specific direction to be determined.

[0289] Figure 7 A flow chart of a possible embodiment of the method according to the invention for running the method according to the invention is schematically shown. Figure 7 In particular, the following aspects are considered: how the excitation pulses must be designed and emitted in order to comply with the regulatory limit values ​​for high-frequency radiation even without a shielding cabin, in particular when the Larmor frequency lies in the ISM band. Figure 7 In step S130, the data on Figure 3 The steps of the method according to the present invention are described in detail and are not described again. However, in principle, it is also possible to Figure 3 In the case of receiving interference suppression in Figure 7Described are measures for emission limitation in excitation pulses.

[0290] In step S110, the controller 23 determines an excitation pulse for exciting nuclear spins in the examination subject. To this end, first, in S111, the controller 23 determines an excitation pulse for exciting nuclear spins in a slice of the examination subject. This can be done, for example, by selecting from a library of excitation pulses, depending on the selected sequence or examination type. The frequency, duration, power, and spectral distribution are dependent on multiple parameters. The center frequency is determined by the nuclear spins to be acquired, the strength of the uniform static magnetic field B0, the position of the slice relative to the gradient field, and the gradient field strength. The spectral distribution and bandwidth are determined by the gradient field strength and the slice thickness in the direction of the field gradient. The amplitude is, in turn, dependent on the duration of the excitation pulse, the volume to be excited, and the desired excitation intensity, also known as the flip angle. In substep S111, a set of parameters is determined based on these boundary conditions, describing possible excitation pulses for these boundary conditions. It is conceivable to predefine a library or table of different parameter sets for specific standard situations, such as image acquisition of a specific organ, and select from them.

[0291] In a further substep S112, the controller 23 checks whether the determined excitation pulse lies within predetermined frequency limits. In the simplest case, for example, the highest and lowest frequencies of the excitation pulse can be calculated using the center frequency and the spectral frequency distribution. It is also conceivable to calculate the power distribution and evaluate the frequency-dependent power limit values.

[0292] If the evaluation determines that the determined excitation pulse exceeds a limit value, in particular a limit value for the permissible emission of high-frequency lines, substep S111 is repeated. This applies in particular to emissions outside the ISM band, which are subject to more stringent restrictions, when the magnetic resonance tomograph is operated in the ISM band.

[0293] Here, when sub-step S111 is repeated, the parameters that affect it are changed. For example, a longer pulse can achieve the same excitation with a lower power. When the gradient is small, a smaller frequency bandwidth is required to excite the same layer thickness.

[0294] If the excitation pulse determined in substep S111 complies with the limit value, then in step S120 of the method the high-frequency unit 22 emits this excitation pulse.

[0295] In step S130, as already mentioned Figure 3 In one exemplary embodiment described, receiver 70 receives magnetic resonance signals.

[0296] Then, in step S140, the controller 23 determines a map of the distribution of nuclear spins based on the received magnetic resonance signals. Finally, the map is preferably reproduced on a display.

[0297] Figure 8 Schematically shows the Figure 3 , a flow chart of a further sub-aspect of the method according to the invention is shown in FIG. 1 , which relates to possible interference suppression using previously acquired image information.

[0298] In step S21, the receiver 70 receives the received first magnetic resonance signal and stores it in a memory. It is also conceivable that the signal acquired in step S21 originates from a calibration measurement or a prescan, and that the calibration measurement or prescan is also acquired with other parameters or a lower resolution.

[0299] In another step S22 , the receiver 70 receives the received second magnetic resonance signal and stores it. Preferably, the second magnetic resonance signal is a signal used for image acquisition.

[0300] In step S23, the received first magnetic resonance signal and the received second magnetic resonance signal are compared. This can be performed, for example, already in the raw data or, for example, in image space after a Fourier transform. In a preferred embodiment, the comparison is performed on a line-by-line basis in k-space. If the first and second magnetic resonance signals differ significantly, particularly if possible different recording conditions are taken into account during the comparison, interference suppression measures are implemented if the deviation is attributable to external interference. Interference signals can be characterized, for example, by frequency, amplitude, characteristic curve, or duration.

[0301] Interference suppression measures can be, for example, repeated acquisitions, which lead to a small delay, particularly within a line in k-space. It is also conceivable to set the signal to zero, particularly when it comes to regions where no image signal is expected.

[0302] Figure 9 A flow chart schematically shows a further sub-aspect of the method according to the invention for interference suppression, here a possible interference suppression by evaluating the acquired image information in image space.

[0303] In this possible embodiment of the method according to the present invention, the magnetic resonance signals are examined in image space to identify interfering signals and determine parameters for eliminating them. To this end, in substep S42, the controller 23 transforms the received magnetic resonance signals into image space, for example by performing a Fourier transform. As with subsequent steps, this step can also be performed on individual rows in the raw data space, enabling faster identification and correction.

[0304] In a further sub-step S43, the controller 23 separates the interference signal from the magnetic resonance data. This is possible, for example, if, by performing the segmentation, it is possible, based on other additional information about the patient and the position or a pre-scan, to determine regions in image space where no magnetic resonance signals from nuclear spins are expected. Signals present in these regions in image space are then correlated with interference.

[0305] In a further sub-step S44 , the interference signal is transformed back into the original data space, for example, by performing a Fourier transformation.

[0306] Then, in a further sub-step S45, parameters for interference suppression can be determined based on the interference signal in the raw data space, separated from the useful signal and inversely transformed, for example as phase and amplitude for destructive interference in the receiver based on the signals of the first and second receive antennas. It is also conceivable to combine the inverse transformation step with the parameter determination, since the frequency and phase in the raw data space are associated with the position in the image space.

[0307] Figure 10 A flow chart of another sub-aspect of the method according to the invention for interference suppression, which determines a transfer function between the first and second receiving antennas 60 and one or more additional calibration elements 86 , is schematically shown.

[0308] In sub-step S80, a transfer function is determined between the first receiving antenna and calibration element 86. To this end, it is conceivable that, under the coordination of controller 23, the interference suppression controller transmits a signal via calibration element 86, which is received and analyzed by the first receiving antenna. This signal is preferably encoded using a pseudorandom sequence or in some other manner, so that receiver 70 can easily determine the correlation between the transmitted signal and the received signal.

[0309] In sub-step S82, the transfer function between the first receiving antenna and the calibration element 86 is determined in the same manner. To this end, it is conceivable that, under the coordination of the controller 23, the interference suppression controller sends a signal via the calibration element 86, the second receiving antenna 60 receives the signal, and the receiver 70 analyzes the signal.

[0310] However, due to the reversibility of the propagation of electromagnetic fields, it is also possible for a signal to be transmitted by the first and second receiving antennas 62 and received by the calibration element 86 .

[0311] In another sub-step S82, at least one parameter for receiving interference cancellation is set based on the measured transfer function so that the portion of the interference signal received by the receiver 70 via the first receiving antenna that is received from the second receiving antenna 60 is reduced. For example, the transfer function can be used to determine how, and in particular with what amplitude and phase shift, the interference signal reaches the input of the receiver 70 from the direction of the calibration element 86 via the first and second receiving antennas 60. Thus, for example, an additional phase shift can be set in the receiver 70 so that the signals from the first and second receiving antennas are destructively superimposed in the receiver and interference is suppressed. As another parameter, an amplitude gain can be set so that interference signals are canceled at a point in space. In the case of multiple first and second receiving antennas 60, more parameters or parameter pairs are adjusted accordingly, which can be performed, for example, using a linear optimization method such as LSR.

[0312] exist Figure 11 1 shows the interaction of multiple magnetic resonance tomography systems 1 according to the present invention. Here, a control unit 20 of a first magnetic resonance tomography system 1 receives signals from a second magnetic resonance tomography system 101 via an interface. The control unit 21 is designed to synchronize image acquisition based on the signals received from the second magnetic resonance tomography system via the interface.

[0313] exist Figure 11 , multiple possible embodiments are shown. On the one hand, the interface can be a LAN interface 26, via which the magnetic resonance tomography apparatus 1 is signal-connected to the second magnetic resonance tomography apparatus 101. However, all other interfaces for exchanging information are also conceivable, such as Wi-Fi, WAN, or serial or parallel point-to-point connections.

[0314] In one embodiment, it is conceivable that the second magnetic resonance tomography system 101 transmits a message regarding the planned image acquisition using a signal. This message may, for example, indicate that the second magnetic resonance tomography system 101 will transmit an excitation pulse of duration d at a specific time t and at a frequency f. The control unit 20 of the first magnetic resonance tomography system 1 then synchronizes its own image acquisition based on this information.

[0315] One possibility is that the control unit 20 synchronizes its excitation pulses so that they occur at the same time, since due to the extremely high field strengths required for excitation, the excitation pulses of adjacent magnetic resonance tomographs do not interfere with each other due to the attenuation already provided by the design of the magnetic resonance tomograph.

[0316] In contrast, the reception of magnetic resonance signals from the examination volume or patient 100 is more sensitive to interference. Because this is attenuated by more than 100 dB relative to the excitation pulse, even with shielding, the excitation pulses of adjacent magnetic resonance tomography scanners 101 can interfere with the reception of MR signals. Therefore, the control unit 20 of the magnetic resonance tomography scanner 1 can plan and execute image acquisition so that it does not occur simultaneously with the excitation pulses of the second magnetic resonance tomography scanner 101. For example, the control unit 20 can set its own excitation pulses and the associated readout sequence so that the receive window of the first magnetic resonance tomography scanner 1 does not coincide with the excitation pulses of the second magnetic resonance tomography scanner 101.

[0317] The opposite is also possible, that is, the second magnetic resonance tomography system 101 sends information about the planned reception. This message can, for example, indicate that the second magnetic resonance tomography system 101 is to record MR signals at a specific time t and at a frequency f for a duration d. The first magnetic resonance tomography system 1 can then set its own transmission process so that, within the time window specified in the message, no transmission occurs, at least in the frequency band that includes the frequency f and the bandwidth specified in the message.

[0318] Finally, combined messages are conceivable in which the sending and receiving processes between the first magnetic resonance tomography device 1 and the second magnetic resonance tomography device 101 are coordinated with each other, preferably so that the image acquisition devices can be implemented with the shortest possible delay by performing interleaving operations.

[0319] But in Figure 11In another embodiment shown in FIG, it is also conceivable that the signal is the radio wave of the excitation pulse itself, and the interface is, for example, a local coil 50 with a high-frequency unit 22. In this case, reception is preferably performed also at or precisely during a time when the first magnetic resonance tomography system 1 itself is not recording MR signals. The control unit 20 can detect from the excitation pulse that the second magnetic resonance tomography system 101 has just transmitted an excitation pulse and subsequently plan the acquisition of magnetic resonance signals. It is then conceivable, for example, that the first magnetic resonance tomography system 1 itself does not transmit an excitation pulse for a certain period of time. The first magnetic resonance tomography system 1 can also use the excitation pulse of the second magnetic resonance tomography system 101 as a trigger pulse and transmit its own excitation pulse almost synchronously, since there is typically a pause between the excitation pulse and the reception of magnetic resonance signals when no reception is taking place and therefore no mutual interference is possible.

[0320] Whether the issuance of an excitation pulse is detected directly from the electromagnetic field of a received pulse or via a message via a data interface, it is also conceivable that the control unit 20 changes the frequency of the next excitation pulse based on the signal. In magnetic resonance tomography, individual slices are distinguished in frequency by gradient fields superimposed in the z-direction along the direction of the B0 field, typically along the z-axis 2. For example, the control unit 20 can change the scanning order of the individual slices so that the first magnetic resonance tomography system 1 and the second magnetic resonance tomography system 101 acquire slices at different center frequencies, thereby avoiding crosstalk or mutual influence by using different frequencies. An additional degree of freedom that the control unit 20 can utilize is the position of the patient 100 on the movable patient couch 30 relative to the center of symmetry of the field magnet 10. By slightly moving the patient 100 along the z-axis, the Larmor frequency of the slice changes due to the different position relative to the z gradient field. That is, due to the relative movement of the patient along the z-axis, the first magnetic resonance tomography scanner 1 can also acquire the same slice in the body of the patient 100 at different frequencies, thereby avoiding mutual influence with the second magnetic resonance tomography scanner 101 .

[0321] 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 magnetic resonance tomography apparatus, wherein: The magnetic resonance tomography device (1) comprises: a patient tunnel (16); a first receiving antenna for receiving a magnetic resonance signal from a patient (100) in the patient tunnel (16); and a second receiving antenna (60) for receiving a signal having a Larmor frequency of the magnetic resonance signal. and a receiver (70), wherein the second receiving antenna (60) is arranged outside or near the opening of the patient tunnel (16), wherein the receiver (70) is signal-connected to the first receiving antenna and the second receiving antenna (60), and the receiver (70) is designed to suppress interference signals received by the second receiving antenna (60) in the magnetic resonance signals received by the first receiving antenna, wherein the magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses using an ISM filter, wherein the ISM filter (223) is designed to suppress signals outside the ISM band.

2. A magnetic resonance tomography apparatus, wherein: The magnetic resonance tomography device (1) comprises: a patient tunnel (16); a first receiving antenna for receiving magnetic resonance signals from a patient (100) in the patient tunnel (16); and a second receiving antenna (60) for receiving signals near the Larmor frequency of the magnetic resonance signals. and a receiver (70), wherein the second receiving antenna (60) is arranged outside or near the opening of the patient tunnel (16), wherein the receiver (70) is signal-connected to the first receiving antenna and the second receiving antenna (60), and the receiver (70) is designed to suppress broadband interference signals in the magnetic resonance signal received by the first receiving antenna, which are received by the second receiving antenna (60) outside the frequency range of the magnetic resonance signal, wherein the magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses, and the transmission path has an ISM filter (223), wherein the ISM filter (223) is designed to suppress signals outside the ISM band.

3. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography apparatus (1) is designed to receive magnetic resonance signals having a Larmor frequency in an industrial frequency band.

4. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography system comprises a transmitting antenna for emitting excitation pulses, wherein the magnetic resonance tomography system (1) comprises a nonlinear component for detuning the transmitting antenna, wherein the nonlinear component is arranged in an area of ​​the magnetic resonance tomography system that is shielded from high frequencies by a patient tunnel, wherein the ISM filter (223) is arranged between the nonlinear component and the transmitting antenna.

5. The magnetic resonance tomography system according to claim 1 or 2, comprising a high-frequency unit (22), wherein: The radio-frequency unit (22) has a predistorter (221) which is designed to predistort an excitation pulse for exciting nuclear spins so that the signal portion of the emitted excitation pulse outside the ISM band is reduced compared to a non-predistorted excitation pulse.

6. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The cut-off frequency of radio waves propagating in the patient tunnel (16) is greater than the Larmor frequency of the magnetic resonance tomography apparatus (1).

7. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography device (1) has a waveguide (260) surrounding the magnetic resonance tomography device (1), wherein the waveguide (260) has a cutoff frequency that is greater than the Larmor frequency of the magnetic resonance tomography device (1).

8. The magnetic resonance tomography apparatus according to claim 7, wherein: The waveguide (260) has an electrically conductive connection (262) to the patient tunnel (16).

9. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The second receiving antenna (60) is arranged on the opening of the patient tunnel (16) or on the patient bed (30).

10. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The second receiving antenna (60) has an omnidirectional receiving characteristic.

11. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography apparatus (1) has a plurality of second receiving antennas (60), and the receiver (70) is designed to suppress interference signals in magnetic resonance signals based on reception signals of the plurality of second receiving antennas (60).

12. The magnetic resonance tomography apparatus according to claim 11, wherein: The plurality of second receiving antennas (60) are arranged in a symmetrical manner with respect to the patient tunnel (16).

13. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The receiver (70) has an autocorrelation device, and the autocorrelation device is designed to determine the signal portion of the magnetic resonance signal received by the first receiving antenna that is received by the second receiving antenna (60).

14. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The receiver (70) has an estimation device, and the estimation device is designed to estimate the signal portion of the magnetic resonance signal received by the first receiving antenna that is received by the second receiving antenna (60).

15. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography device (1) has an interference suppression transmitter (80) and an interference suppression antenna (81), wherein the interference suppression antenna (81) is arranged at a certain distance from the patient tunnel (16), wherein the interference suppression transmitter (80) is designed to output a signal within the frequency range of the excitation pulse of the magnetic resonance tomography device (1) via the interference suppression antenna (81) based on a transmission interference cancellation parameter, so that the field strength of the excitation pulse is reduced by destructive interference in a predetermined area of ​​the environment of the magnetic resonance tomography device (1).

16. The magnetic resonance tomography apparatus according to claim 15, wherein: The magnetic resonance tomography device (1) has a calibration element (86) in the environment of the magnetic resonance tomography device (1) and an interference suppression controller (84), wherein the interference suppression controller (84) is designed to, with the help of the calibration element (86), detect the field strength within the frequency range of the excitation pulse at the position of the calibration element (86), and set the transmission interference elimination parameter based on the detected field strength so that the field strength of the excitation pulse is reduced in the predetermined environment of the calibration element (86).

17. The magnetic resonance tomography apparatus according to claim 15, wherein: The interference suppression transmitter (80) is designed to generate signals for one or more interference suppression antennas (81) by performing phase shifting and / or amplitude adjustment according to one or more transmit interference cancellation parameters.

18. The magnetic resonance tomography apparatus according to claim 15, wherein: The interference suppression antenna (81) has a high-frequency power amplifier.

19. The magnetic resonance tomography apparatus according to claim 1 or 2, wherein: The magnetic resonance tomography device (1) has a calibration element (86) located in the environment of the magnetic resonance tomography device (1), wherein the receiver (70) is designed to measure a first transfer function between the first receiving antenna and the calibration element (86), and a second transfer function between the second receiving antenna (60) and the calibration element (86), and to set one or more interference cancellation parameters based on the measured first transfer function and the second transfer function, so that the interference signal received by the second receiving antenna (60) in the magnetic resonance signal received by the first receiving antenna is reduced.

20. The magnetic resonance tomography apparatus according to claim 1 or 2, comprising: a control unit (20) for controlling image acquisition; and an interface connected to the control unit (20) by signals, wherein: The control unit (20) is designed to synchronize image acquisition in dependence on a signal received from a second magnetic resonance tomography device (101) via the interface.

21. The magnetic resonance tomography apparatus according to claim 1 or 2, comprising: a control unit (20) for controlling image acquisition; and an interface connected to the control unit (20) by signals, wherein: The control unit is designed to send a signal containing information about an upcoming image acquisition to a second magnetic resonance tomography device (101).

22. The magnetic resonance tomography apparatus according to claim 20, wherein: The interface is designed for data exchange, wherein the control unit (20) is designed to synchronize image acquisition with a second magnetic resonance tomography device (101) by means of information exchange via the interface.

23. The magnetic resonance tomography apparatus according to claim 21, wherein: The signal contains information about the time and / or frequency of the transmission process.

24. The magnetic resonance tomography apparatus according to claim 21, wherein: The signal contains information about the time and / or frequency of the reception process.

25. A method for operating a magnetic resonance tomography device (1), wherein: The magnetic resonance tomography device (1) comprises: a patient tunnel (16); a first receiving antenna for receiving a magnetic resonance signal from a patient (100) in the patient tunnel (16); and a second receiving antenna (60) for receiving a signal having a Larmor frequency of the magnetic resonance signal. and a receiver (70), wherein the second receiving antenna (60) is arranged outside the patient tunnel (16) or near the opening of the patient tunnel (16), wherein the magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses, the transmission path having an ISM filter (223), wherein the ISM filter (223) is designed to suppress signals outside the ISM band, and wherein the method comprises the following steps: (S10) the receiver (70) receives an interference signal via the second receiving antenna (60); (S20) the receiver (70) receives a magnetic resonance signal via the first receiving antenna; (S30) the receiver (70) processes the magnetic resonance signal in correlation with the interference signal to form a received signal, wherein the correlation depends on a parameter; (S40) The receiver (70) sets parameters so that the interference signal portion in the received signal is reduced.

26. A method for operating a magnetic resonance tomography device (1), wherein: The magnetic resonance tomography device (1) comprises: a patient tunnel (16); a first receiving antenna for receiving magnetic resonance signals from a patient (100) in the patient tunnel (16); and a second receiving antenna (60) for receiving signals near the Larmor frequency of the magnetic resonance signals. and a receiver (70), wherein the second receiving antenna (60) is arranged outside the patient tunnel (16) or near the opening of the patient tunnel (16), wherein the magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses, the transmission path having an ISM filter (223), wherein the ISM filter (223) is designed to suppress signals outside the ISM band, and wherein the method comprises the following steps: (S10) the receiver (70) receives a frequency portion of an interference signal near the Larmor frequency via the second receiving antenna (60); (S20) the receiver (70) receives a magnetic resonance signal via the first receiving antenna; (S30) the receiver (70) processes the magnetic resonance signal in correlation with the frequency component of the interference signal to form a received signal, wherein the correlation depends on a parameter; (S40) The receiver (70) sets parameters so that the interference signal portion in the received signal is reduced.

27. The method according to claim 25 or 26, wherein The step (S40) of setting parameters has a step (S41) of averaging over time by averaging over time based on the interference signal.

28. The method according to claim 25 or 26, wherein The step of receiving an interference signal ( S10 ) is performed during a time period in which a sequence of magnetic resonance signals for imaging is not received.

29. A method for operating a magnetic resonance tomography apparatus (1) according to claim 19, wherein: The method comprises the following steps: (S80) measuring a transfer function between the first receiving antenna and the calibration element (86); (S81) measuring a transfer function between the second receiving antenna (60) and the calibration element (86); (S82) Setting interference cancellation parameters based on the measured transfer function so that the portion of the interference signal received by the second receiving antenna (60) in the signal received by the receiver (70) via the first receiving antenna is reduced.

30. The method of claim 25, 26 or 29, wherein The receiver (70) has a memory, and the method has a storing step (S25), in which the receiver (70) stores the interference signal and the magnetic resonance signal in the memory, Therein, the processing step ( S30 ) is performed with a delay relative to the reception of the interference signal and / or the magnetic resonance signal.

31. The method of claim 25, 26 or 29, wherein: The receiver (70) has an autocorrelation device, and in the step (S40) of setting parameters, the autocorrelation device determines an interference signal portion in the magnetic resonance signal and sets parameters according to the determined interference signal portion.

32. The method of claim 25, 26 or 29, wherein: The receiver (70) has an estimation device, and in the step (S40) of setting parameters, the estimation device determines an interference signal portion in the magnetic resonance signal and sets the parameters according to the determined interference signal portion.

33. The method of claim 25, 26 or 29, wherein: The step of setting parameters (S40) has the following sub-steps: (S42) transforming the received magnetic resonance signal into an image space; (S43) separating the interference signal from the magnetic resonance data; (S44) transforming the interference signal into the original data space; (S45) Determine parameters according to the interference signal in the transformed original data space.

34. The method according to claim 33, wherein The transforming step ( S42 ), the separating step ( S43 ), the inverse transforming step ( S44 ) and the parameter determining step ( S45 ) are performed according to the rows of the magnetic resonance signal data in the received raw data space.

35. The method of claim 25, 26 or 29, wherein: The receiver (70) monitors changes in the interference signal in a step (S50) and adjusts parameters in a step (S51) when there are changes.

36. The method of claim 25, 26 or 29, wherein: The receiver (70) stores the received first magnetic resonance signal in a memory in a step (S21); In one step (S22), the received second magnetic resonance signal is stored; and In a step ( S23 ), the received first magnetic resonance signal is compared with the received second magnetic resonance signal and, if there is a deviation attributable to external interference, interference suppression measures are performed.

37. The method according to claim 36, wherein The interference suppression measure is one of the following measures: discarding ( S60 ) the received first and / or second magnetic resonance signals, repeating acquisition of the first and / or second magnetic resonance signals or setting of parameters ( S40 ).

38. A method for operating a magnetic resonance tomography apparatus (1), wherein: The magnetic resonance tomography device (1) has a patient tunnel (16); a first receiving antenna for receiving magnetic resonance signals from a patient (100) in the patient tunnel (16); a second receiving antenna (60) for receiving a signal having a Larmor frequency of a magnetic resonance signal; and a receiver (70), wherein the second receiving antenna (60) is arranged outside the patient tunnel (16) or near the opening of the patient tunnel (16), wherein the magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses, the transmission path having an ISM filter (223), wherein the ISM filter (223) is designed to suppress signals outside the ISM band, and wherein the method comprises the following steps: (S10) the receiver (70) receives an interference signal via the second receiving antenna (60); (S20) the receiver (70) receives a magnetic resonance signal via the first receiving antenna; (S60) Discarding the magnetic resonance signal based on the interference signal received by the second receiving antenna (60).

39. A method for operating a magnetic resonance tomography apparatus (1) having a Larmor frequency in the ISM band, wherein: The magnetic resonance tomography device (1) has a transmission path for emitting excitation pulses, the transmission path having an ISM filter (223), wherein the ISM filter (223) is designed to suppress signals outside the ISM frequency band, wherein the method comprises the following steps: (S110) determining an excitation pulse for exciting nuclear spins in the examination object; (S120) issuing an excitation pulse; (S130) receiving magnetic resonance signals; (S140) determining a map of the distribution of nuclear spins in the examination object; In the step of determining the excitation pulse ( S110 ), the determination is performed based on a predetermined frequency boundary of the ISM band.

40. The method of claim 39, wherein The step of determining the excitation pulse (S110) has the following sub-steps: (S111) determining an excitation pulse for exciting nuclear spins in the slice of the examination object based on the relative position of the slice of the examination object with respect to the magnet unit (10), a predetermined gradient strength, a thickness of the slice, and a type of measurement; (S112) checking whether the determined excitation pulse is located within a predetermined frequency boundary of the ISM band; Repeating the determining step (S111) while changing pulse parameters, which in determining the excitation pulse have an influence on the spectral frequency distribution of the excitation pulse when the excitation pulse is not within predetermined frequency limits, or In step (S120), the determined excitation pulse is emitted.

41. The method according to claim 40, wherein The pulse parameter that influences the determination of the excitation pulse is one of the following parameters: the duration of the excitation pulse, the thickness of the slice, the relative position of the slices or the strength of the gradient.

42. The method of claim 40, wherein: The issuing step (S120) has the following sub-step (S121): before the step (S122) of emitting pulses, the relative position of the inspection object with respect to the magnet unit (10) is changed.

43. A computer-readable storage medium having electronically readable control information stored thereon, the electronically readable control information being designed to execute the method according to any one of claims 25 to 42 when the storage medium is used in a controller (23) of a magnetic resonance tomography device (1) according to any one of claims 1 to 24.

Images