Magnetic resonance imaging with dual scanning for disturbance reduction

Description

[0001] The present invention relates to a method for operating a magnetic resonance imaging system, a magnetic resonance imaging system and a computer product.

[0002] Magnetic resonance imaging (MRI) systems are imaging devices that use a strong external magnetic field to align the nuclear spins of a sample and then excite them to precession around the desired orientation using an alternating magnetic field. This precession, or the return of the spins from this excited state to a lower-energy state, in turn generates an alternating magnetic field that can be detected by receiving antennas.

[0003] Magnetic gradient fields can be used to imprint a spatial coding on the signals, which subsequently allows the received signal to be assigned to a volume element of the object under investigation. The received signal can then be evaluated, for example, to provide a three-dimensional imaging representation of the object. Local receiving antennas, so-called local coils, can be used as receiving antennas. These can be positioned directly on the object under investigation to achieve a better signal-to-noise ratio (SNR). Alternatively, the receiving antennas can be located in the vicinity of the object or, for example, integrated into a patient's examination table.

[0004] The magnetic resonance (MR) signals received for imaging are extremely weak, so that with known MRI systems, shielding against external interference signals is necessary to achieve a sufficient signal-to-noise ratio (SNR). This is primarily achieved by installing elaborate shielded enclosures to reduce interfering emissions. This leads to considerable costs and structural limitations due to the space requirements.

[0005] Document WO 2019 / 068687 A2 describes a magnetic resonance imaging (MRI) scanner with active noise suppression and a corresponding procedure. This procedure includes a first receiving antenna for acquiring a magnetic resonance signal from a patient and a second receiving antenna for acquiring an interference signal. A receiver connected to the receiving antennas is designed to suppress the interference signal received by the second receiving antenna within the MRI signal received by the first. To achieve this, the interference signal is determined during the MRI sequences for signal acquisition, utilizing time intervals in which no MRI signal is expected for imaging. An interference suppression controller can then combine the signals from the first and second receiving coils with a weighted ratio to minimize the energy of the interference signal in the combined signal.

[0006] Since these segments vary in length and timing depending on the MRI sequence used, the interference suppression procedure must be individually adapted to each MRI sequence, resulting in increased effort. Furthermore, depending on the MRI sequence, the available segments for determining the interference signal may not be long enough to reliably suppress its influence.

[0007] Document US 2018 / 0143272 A discloses a method for noise suppression in a magnetic resonance imaging (MRI) system with a receiving antenna. The method comprises the step of acquiring MRI data containing a noise component from the receiving antenna and noise data characteristic of noise signals in the vicinity of the MRI system. A compensation factor is determined based on the noise data and an MRI signal restricted to the boundary regions of k-space. The noise component of the MRI data is estimated by multiplying the noise signal by the compensation factor, and corrected MRI data is obtained by subtracting the estimated noise component from the MRI data.

[0008] Document US 2017 / 0108569 A1 describes a magnetic resonance imaging (MRI) system for acquiring MRI data from an image acquisition area. MRI data for imaging are acquired using active excitation by a radio frequency pulse. Simultaneously, noise data are acquired with at least one noise detection antenna. Calibration MRI data are acquired with deactivated excitation, and reference noise data are acquired simultaneously using the noise detection antenna. A noise calibration is then calculated using the reference noise data and the calibration MRI data.

[0009] Document EP 3723037 A1 discloses a medical data processing device comprising a first processing unit. The first processing unit determines an interference signal intensity from initial data acquired during a first scan. A second processing unit determines an interference suppression intensity for an interference reduction process based on the interference signal intensity and the difference between an image acquisition condition for the first scan and an image acquisition condition for a second scan, applying the interference reduction process to the second data acquired during the second scan.

[0010] Document EP 3470868 A1 discloses a magnetic resonance system for acquiring a series of magnetic resonance data that provide a quantitative representation of the relaxation time of a test subject. The magnetic data are acquired using sequences that include pauses during which interference signals are detected. No radio frequency excitation occurs during these pauses.

[0011] Against this background, it is an object of the present invention to provide an improved concept for an MRI system or for a method for operating such a system, which reduces the effort required for shielding external interference signals and at the same time enables high effectiveness of interference reduction, particularly with minimal adaptation effort.

[0012] This problem is solved here by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0013] The improved concept is based on the idea of ​​performing two different MR scans to generate MR data that at least partially represent an object and, depending on the different MR data, to determine a noise component that represents the influence of an external source of interference.

[0014] According to the improved concept, a method for operating an MRI system is described. A first MR scan to image an object is performed, in particular using the MRI system, to generate initial MR data representing the object. The first MR scan is performed according to a first k-space scanning scheme, and during the first MR scan, at least one first excitation pulse is emitted in the direction of the object, in particular using at least one transmitting antenna of the MRI system, according to a first pulse sequence. A second MR scan, different from the first, is performed, in particular using the MRI system, to generate second MR data different from the first.Depending on the second set of MR data, a processing unit, in particular a processing unit of the MRI system, determines a noise component that represents the influence of at least one external source of interference, specifically the influence of this external source on the first set of MR data. Using this processing unit, an MR image is generated based on the first set of MR data and the noise component.

[0015] During the first MR scan, at least one excitation pulse is applied, causing the object's nuclear spins to precess around the alignment axis according to the static magnetic field. Their resonance then generates MR signals that can be detected by one or more receiving antennas of the MRI system to produce the first MR data. These initial MR data are affected by at least one external source of interference, meaning that the interference component is present in the first MR data.

[0016] Similarly, during the second MR acquisition, second excitation pulses are switched to obtain corresponding MR signals and generate the second MR data. In this case, the second MR acquisition is performed differently from the first. In other unclaimed embodiments, no excitation pulse is switched during the second MR acquisition, so that only the influence of the external interference source is represented by the second MR data.

[0017] It should be noted that neither the first nor the second MR acquisition necessarily constitutes a complete MR image, meaning that the first and second MR data alone are not necessarily sufficient to generate the MR image, particularly a spatial image. Specifically, the entire k-space region required for imaging is not necessarily scanned during the first and / or second MR acquisition. Rather, further first and / or second MR acquisitions may be necessary to achieve a complete scan for the required imaging. However, it is also possible that a complete scan is achieved with the first MR acquisition alone.

[0018] A pulse sequence is characterized here and in the following by one or more time parameters, for example, an echo time (TE) and / or a repetition time (TR). Additional parameters may also contribute to the definition of a pulse sequence.

[0019] In this and subsequent texts, a k-space sampling scheme can be understood as a scheme that specifies which points or regions in k-space are sampled and in what order. A k-space sampling scheme can be, for example, a Cartesian k-space sampling scheme, a radial k-space sampling scheme, a helical k-space sampling scheme, and so on.

[0020] The interference component can include not only the influence of at least one external interference source but also the influence of thermal noise.

[0021] The MR image, which is generated depending on the initial MR data and the noise component, corresponds in particular to a noise-reduced k-space image or a spatial image.

[0022] The interference component can be determined, for example, depending on the second MR data and independently of the first MR data. Alternatively, the interference component can be generated or determined depending on both the first and second MR data.

[0023] Within the scope of the present invention, the distinction between the second and first MR scan is understood to mean that parameters are used for the second MR scan that differ from corresponding parameters used for the first MR scan. For example, the second MR scan can be performed according to a second k-space scanning scheme that differs from the first k-space scanning scheme. A second excitation pulse is emitted towards the object during the second MR scan according to a second pulse sequence, wherein the second pulse sequence differs from the first pulse sequence and / or wherein the at least one second excitation pulse differs from the at least one first excitation pulse.

[0024] The at least one external source of interference is, in particular, at least one essentially static source of interference. This can be understood to mean that the influence of the at least one external source of interference does not change, or does not change substantially, from the first MRI scan to the second. In particular, "static source of interference" does not necessarily mean that the effect of the static source of interference remains permanently unchanged. The closer the first and second MRI scans are to each other, the less noticeable any temporal change in the influence or effect of the at least one external source of interference becomes.

[0025] According to a method according to the improved concept, the second MR scan is performed according to a second k-space scanning scheme that differs from the first k-space scanning scheme.

[0026] According to the invention, during the second MR scan, at least one second excitation pulse, according to a second pulse sequence, is emitted towards the object, particularly by means of the at least one transmitting antenna. The second MR data set then also depicts the object. The second pulse sequence can be identical to the first pulse sequence or different from the first pulse sequence.

[0027] Since, according to the aforementioned method according to the invention, the second k-space sampling scheme differs from the first k-space sampling scheme, the first MR data also differ from the second MR data. However, the influence of the external interference source is approximately the same for both the first and second MR data. Because the k-space sampling schemes differ, but the influence of the interference source is not significant, the effects of the external interference source, in the form of the interference component, can be determined by correlating the first and second MR data with each other. In particular, the interference component is determined in such embodiments as a function of the first and second MR data.

[0028] Such a method according to the invention also has the advantage that the second MR data can also be used to generate the MR image, so that the additional time spent on the second MR recording can be used even more efficiently.

[0029] According to the inventive method of claim 1, the first and second pulse sequences differ from each other. Within the framework of this inventive method, the first pulse sequence is defined by a first set of time parameters, and the second pulse sequence is defined by a second set of time parameters that differs from the first set of time parameters.

[0030] The first set of time parameters includes a first echo time and / or a first repetition time. The second pulse sequence accordingly includes a second echo time and a second repetition time. The first and second echo times differ from each other and / or the first and second repetition times differ from each other.

[0031] According to the invention, a first ratio of the first echo time to the first repetition time differs from a second ratio of the second echo time to the second repetition time. Thus, different contrasts are achieved for the first and second MR acquisitions. As a result, the MR signal components of the first and second MR data correlate even less with each other, allowing for even better extraction of the noise component, particularly through correlation of the first and second MR data.

[0032] The MR image is generated depending on the first MR data and depending on the second MR data.

[0033] This allows for higher accuracy of the resulting MR image while simultaneously reducing the influence of external sources of interference.

[0034] The improved concept thus generates different MR data sets—namely, the first MR data sets and the second MR data sets—in separate MR acquisitions. Since the effect of the external interference sources remains unchanged, or at least substantially unchanged, the influence of at least one interference source on the first MR data sets is approximately equal to its influence on the second MR data sets. Depending on the configuration of the second MR acquisition, the interference component can therefore be determined, for example, by correlating the first MR data sets with the second MR data sets or based solely on the second MR data sets. This determined interference component can then be at least partially removed from the first and / or second MR data sets to generate the MR image and thus compensate for the influence of at least one external interference source. The removal or reduction of the interference component can be performed in spatial space, k-space, or a hybrid space.However, the removal or reduction of the interference component can also be carried out partly in k-space and partly in local space, and so on.

[0035] Because the improved concept determines the interference component in situ for the specific interference environment currently present, particularly effective suppression of the influence of external interference sources is possible. Specifically, the improved concept eliminates the need to exploit specific time periods during MR acquisitions, especially during the first MR acquisition, when no MR signal is expected. Therefore, the improved concept is universally applicable to a wide variety of initial k-space scan schemes and / or initial pulse sequences.

[0036] Finally, the improved concept eliminates the need for shielding enclosures to block external interference, or allows for simpler enclosure designs, saving space and / or costs. Another advantage of the improved concept is that additional receiving antennas for dedicated interference measurement are no longer required. This further reduces space and costs.

[0037] According to at least one embodiment, a signal decomposition algorithm is performed by the computing unit, depending on the first MR data and the second MR data, in order to determine the noise component.

[0038] The signal decomposition algorithm may, for example, include a principal component analysis (PCA) algorithm or an independent component analysis (ICA) algorithm.

[0039] According to at least one embodiment, which is not part of the present invention, the second MR scan is performed according to the first k-space scanning scheme, and specifically not according to the second k-space scanning scheme. During the second MR scan, no excitation pulse is emitted in the direction of the object, particularly by means of the at least one transmitting antenna.

[0040] In embodiments not part of the present invention, the MR image is generated independently of the second MR data. In this case, the second MR data does not represent the object. The second MR image serves only to detect the interference component in such embodiments.

[0041] However, such designs have the advantage that the noise component can be determined independently of the first MR data. Since no excitation pulse is emitted during the second acquisition, no MR signal is expected from the object, so the second MR data reproduce the noise component with particular accuracy.

[0042] According to the method of claim 2, the first k-space sampling scheme corresponds to a Cartesian sampling scheme and the second k-space sampling scheme corresponds to a radial sampling scheme or a spiral sampling scheme or a Wave-CAIPIRINHA sampling scheme.

[0043] According to the improved concept, an MRI system is also described, comprising a scanner unit configured to perform a first MR scan to image an object according to a first k-space scanning scheme, in order to generate initial MR data representing the object. During the first MR scan, at least one initial excitation pulse is emitted in the direction of the object, in particular by means of one or more transmitting antennas of the MRI system, according to a first pulse sequence. The scanner unit is configured to perform a second MR scan, distinct from the first, to generate second MR data. The MRI system also includes a processing unit configured to determine, based on the second MR data, a noise component representing the influence of at least one external noise source, and to generate an MR image based on the first MR data and the noise component.

[0044] The scanner unit can, for example, include a magnet unit. The magnet unit can include a field magnet for generating a static magnetic field, as well as one or more gradient coils for generating time-dependent magnetic field gradients, particularly in the three different spatial directions. The scanner unit also includes, for example, a radio frequency unit for generating the at least one excitation pulse by means of the at least one transmitting antenna. The at least one transmitting antenna can also be part of the scanner unit. A control unit of the scanner unit can control or supply the aforementioned components accordingly in order to perform the MR scans as described.

[0045] Further embodiments of the MRI system according to the improved concept follow directly from the various configurations of the method according to the improved concept, and vice versa. In particular, an MRI system according to the improved concept is configured to perform a method according to the improved concept or performs such a method.

[0046] According to the improved concept, a computer program with commands is also specified. When the commands or the computer program are executed by an MRI system according to the improved concept, the commands cause the MRI system to perform a procedure according to the improved concept.

[0047] According to the improved concept, a computer-readable storage medium is also specified, which stores the computer program according to the improved concept.

[0048] The computer program and the computer-readable storage medium can each be referred to as computer program products with the commands.

[0049] The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the figure description and / or shown in the figures alone, are usable not only in the combinations specified but also in other combinations without departing from the scope of the invention as defined by the claims. Embodiments and combinations of features that do not exhibit all the features of an originally formulated independent claim and / or that go beyond or deviate from the combinations of features set forth in the cross-references of the claims are also to be considered disclosed. However, the scope of protection of the invention is determined by the claims.

[0050] The figures show: FIG 1 a schematic representation of an exemplary embodiment of an MRI system according to the improved concept; FIG 2 a flowchart of an exemplary embodiment of a method according to the improved concept; FIG 3 schematic k-space representations of the effects of an external disturbance; and FIG 4 schematic spatial representations of the effects of an external disturbance.

[0051] FIG 1 shows a schematic representation of an exemplary embodiment of an MRI system 1 according to the improved concept.

[0052] The MRI system 1 comprises a magnet unit 10 with a field magnet 11, which generates a static magnetic field for aligning the nuclear spins of a sample, for example, a patient 100, within an examination or acquisition area. The patient 100 may, for example, be positioned on a patient table 30. The acquisition area is characterized by an extremely homogeneous static magnetic field, with the homogeneity relating in particular to the magnetic field strength or its magnitude. The acquisition area is, for example, nearly spherical and positioned within a patient tunnel 16, which extends longitudinally 2 through the magnet unit 10. The field magnet 11 may, for example, be a superconducting magnet capable of providing magnetic fields with a magnetic flux density of up to 3 T or more.For lower field strengths, however, permanent magnets or electromagnets with normally conducting coils can also be used.

[0053] Furthermore, the magnet unit 10 includes gradient coils 12, which are designed to superimpose location-dependent magnetic fields in the three spatial directions onto the static magnetic field in order to spatially differentiate the captured imaging areas within the recording area. The gradient coils 12 can, for example, be designed as coils made of normally conducting wires, which can generate fields or field gradients that are orthogonal to each other within the recording area.

[0054] The magnetic unit 10 can, for example, include a body coil 14 as a transmitting antenna, which is designed to radiate a high-frequency signal supplied via a signal line into the examination area. In some embodiments, the body coil 14 can also be used to receive resonance signals emitted by the patient 100 and transmit them via a signal line.

[0055] The MRI system 1 has a control unit 20 that can supply the magnet unit 10 with various signals for the gradient coils 12 and the body coil 14 and can evaluate the received signals. The control unit 20 can, for example, have a gradient controller 21 designed to supply the gradient coils 12 with variable currents via supply lines, which can provide the desired gradient fields in the examination area in a time-coordinated manner.

[0056] The control unit 20 can also include a high-frequency unit 22, which is designed to generate high-frequency pulses or excitation pulses with predefined time profiles, amplitudes, and spectral power distribution to excite magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be used. The excitation pulses can be radiated into the patient 100 via the body coil 14 or via one or more local transmitting antennas. The control unit 20 can also include a controller 23, which can communicate with the gradient controller 21 and the high-frequency unit 22 via a signal bus 25.

[0057] Optionally, a local coil 50 can be arranged in the immediate vicinity of the patient 100, for example on the patient 100 or in the patient bed 30, which can be connected to the high-frequency unit 22 via a connecting cable 33. Depending on the configuration, the local coil 50 can serve as a receiving antenna alternatively or additionally to the body coil 14.

[0058] The receiving antennas 14, 50, for example, are in signal communication with a computing unit 70, which is, for example, part of a receiver of the control unit 20. The computing unit 70 can, for example, include a programmable logic unit, such as a field-programmable gate array (FPGA), or a digital signal processor (DSP).

[0059] The functionality of the MRI system 1 is explained in more detail below with reference to exemplary embodiments of a method for operating an MRI system according to the improved concept, in particular with reference to the figures. FIG 2 bis FIG 4 .

[0060] In FIG 2 The diagram shows a schematic flowchart of an exemplary embodiment of a method according to the improved concept.

[0061] In step S1, an initial MR scan of patient 100 is performed using the MRI system 1. This initial MR scan generates the first MR data. The first MR scan is performed according to an initial k-space scanning scheme. To visualize patient 100 using the initial MR data, excitation pulses are emitted during the first MR scan according to an initial pulse sequence, specifically via the body coil 14.

[0062] In step S2, a second MR scan, different from the first, is performed using MRI system 1 to generate a second set of MR data. In step S3, the processing unit 70 determines a noise component representing the influence of at least one external source of interference (not shown). This noise component is determined based on both the second set of MR data and the first set of MR data. In step S4, the processing unit 70 generates an MR image based on the first set of MR data, the noise component, and the second set of MR data.

[0063] In various embodiments, the first MR scan can, for example, be performed according to a first coding using a Cartesian k-space scan.

[0064] The second MRI scan is also used to visualize patient 100, thus improving the final MRI image quality and utilizing the doubled scan time more efficiently. During the second MRI scan, at least one second excitation pulse is emitted, specifically according to a second pulse sequence. The second MRI scan is performed according to a second k-space scan scheme, which differs from the first k-space scan scheme.

[0065] The less correlated the two coding strategies are for the first and second MR acquisitions, the more the resulting MR signals will differ. For example, combinations with Wave-Caipirinha coding are conceivable, which can contribute to improved image quality in the final image reconstruction.

[0066] Both the first and second MR data sets contain contributions from MR signals originating from patient 100. The noise component correlates between the first and second MR data sets and can be adjusted using appropriate methods.

[0067] Signal decomposition algorithms, such as PCA or ICA algorithms, can be extracted. For example, all local coil channels from both coding strategies can be analyzed together to determine the common noise component from the uncorrelated MR signal codings. This noise component can then be removed from both the first and second MR data sets.

[0068] Since both the first and second MR data sets now contain MR signal components, they can be combined in a single reconstruction process to generate the MR image. This improves the overall image quality and the signal-to-noise ratio. Furthermore, variations in external interference between individual acquisitions can be suppressed even further.

[0069] For example, the final MR image can be expressed by X = X₁ + α*X₂, where X₁ and X₂ correspond to the spatial images reconstructed based on the first and second MR data, respectively, which are varied to minimize a cost function K. α represents a constant weighting factor. The cost function K can, for example, be given by K = K X 1 , X 2 = S 1 − T 1 X 1 + α * S 2 − T 2 X 2 + α ′ * X 1 − X 2 .

[0070] Here, S1 and S2 represent the first and second MR data, respectively, cleaned using the signal decomposition algorithm, and T1 and T2 represent the respective inverse reconstruction kernels, which in the simplest case can be given by a Fourier transform. α' represents a further weighting factor to suppress differences between the two encodings more effectively, if necessary.

[0071] In FIG 3 The influence of 17 external sources of interference in k-space for different coding strategies is schematically illustrated. The figure on the left in FIG 3 This corresponds, for example, to a Cartesian k-space scan, assuming, for instance, an external interference source with an approximately monofrequency radiation pattern. The influence 17 now manifests itself at the same position in each k-space row. In the right-hand figure of FIG 3 This is contrasted with a radial k-space sampling scheme. The influences of the external sources of interference are visible at different positions in k-space due to the different coding strategies.

[0072] In FIG 4 Figure 17' shows a simplified representation of the influences of another external source of interference for different coding strategies in spatial space. In the left figure of the FIG 4 A first coding strategy is used, while a second coding strategy is used on the right, in which the MR signals receive an additional frequency and phase shift, which the effects 17' of the external interference source, however, do not experience. An object 18, which is accordingly depicted in the two MR images, is therefore represented differently in the two spatial representations. The effects 17' of the external interference sources, however, are essentially the same in both spatial images.

[0073] As regarding FIG 3 and FIG 4 To illustrate with an example, the improved concept allows the correlating interference to be separated from the non-correlating MR signals.

[0074] As described, particularly with regard to the figures, the improved concept thus provides a way to reduce interference during the operation of an MRI system, thereby reducing the requirements for shielding devices and allowing for more reliable and effective suppression of interference.

[0075] Since MRI systems, according to the improved concept, do not require shielding cabins or require less elaborate shielding cabins, the costs of installation and, in particular, the relocation of a device to another location can be significantly reduced, as the installation is much less dependent on the building in which it is installed.

[0076] The local coils in the patient tunnel are decoupled from the environment by approximately 20 to 50 dB, as the patient tunnel acts as a cut-off waveguide, at least in systems with a static magnetic field of up to 3 T, thus suppressing wave propagation from the entrance to the patient tunnel to the local coil. The effectiveness of this suppression increases with decreasing frequency for a given patient tunnel diameter. However, the patient, whose tissue is slightly conductive, acts as a monopole antenna protruding from the patient tunnel, forming a coaxial structure together with the surrounding structures. This can lead to interference being picked up and directed to the local coil. Similar effects can be caused by the coil wiring extending from the patient tunnel. The improved design compensates for or attenuates these effects.

Claims

1. Method for operating a magnetic resonance tomography system (1), wherein - a first MR recording is performed so as to map an object (100) in order to generate first MR data that represents the object (100); - the first MR recording is performed in accordance with a first k-space scanning scheme and during the first MR recording at least one first excitation pulse is transmitted in accordance with a first pulse sequence in the direction of the object (100); - a second MR recording that is different from the first MR recording is performed in order to generate second MR data; - a noise component is determined in dependence upon the second MR data by means of a computing unit (70) and said noise component represents an influence of at least one external noise source; and - an MR image is generated by means of the computing unit (70) in dependence upon the first MR data and in dependence upon the noise component, wherein the second MR recording is performed in accordance with a second k-space scanning scheme that differs from the first k-space scanning scheme, - at least one second excitation pulse is transmitted in accordance with a second pulse sequence in the direction of the object during the second MR recording, wherein the second pulse sequence differs from the first pulse sequence; and - the second MR data represents the object (100); and wherein the MR image is generated in dependence upon the second MR data, characterised in that - the first pulse sequence is defined by a first time parameter set; - the second pulse sequence is defined by a second time parameter set that differs from the first time parameter set, wherein the first time parameter set contains a first echo time and / or a first repetition time and the second pulse sequence contains a second echo time and a second repetition time, wherein the first and the second echo time and / or the first and the second repetition time differ from one another, wherein a first ratio of the first echo time to the first repetition time differs from a second ratio of the second echo time to the second repetition time, so that different contrasts are realised for the first and second MR recording in each case.

2. Method for operating a magnetic resonance tomography system (1), wherein - a first MR recording is performed so as to map an object (100) in order to generate first MR data that represents the object (100); - the first MR recording is performed in accordance with a first k-space scanning scheme and during the first MR recording at least one first excitation pulse is transmitted in accordance with a first pulse sequence in the direction of the object (100); - a second MR recording that is different from the first MR recording is performed in order to generate second MR data; - a noise component is determined in dependence upon the second MR data by means of a computing unit (70) and said noise component represents an influence of at least one external noise source; and - an MR image is generated by means of the computing unit (70) in dependence upon the first MR data and in dependence upon the noise component, wherein the second MR recording is performed in accordance with a second k-space scanning scheme that differs from the first k-space scanning scheme, - at least one second excitation pulse is transmitted in accordance with a second pulse sequence in the direction of the object during the second MR recording, wherein the second pulse sequence differs in particular from the first pulse sequence; and - the second MR data represents the object (100); and wherein the MR image is generated in dependence upon the second MR data, characterised in that - the first k-space scanning scheme corresponds to a Cartesian scanning scheme; and - the second k-space scanning scheme corresponds to a radial scanning scheme or a spiral scanning scheme or a wave CAIPIRINHA scanning scheme.

3. Method according to one of claims 1 or 2, wherein in dependence upon the first MR data and the second MR data a signal separation algorithm is implemented by means of the computing unit (70) in order to determine the noise component.

4. Method according to claim 3, wherein the signal separation algorithm contains an algorithm for principal component analysis or an algorithm for independent component analysis.

5. Magnetic resonance tomography system having a scanner unit (10, 20) that is configured so as to - perform a first MR recording so as to map an object (100) in accordance with a first k-space scanning scheme in order to generate first MR data that represents the object (100), wherein during the first MR recording at least one first excitation pulse is transmitted in accordance with a first pulse sequence in the direction of the object (100); and - perform a second MR recording that is different from the first MR recording in order to generate second MR data; and a computing unit (70) that is configured so as to - determine in dependence upon the second MR data a noise component that represents an influence of at least one external noise source; and - to generate an MR image in dependence upon the first MR data and the noise component, wherein the scanner unit is configured to perform the second MR recording in accordance with a second k-space scanning scheme that differs from the first k-space scanning scheme, wherein - the scanner unit is configured to transmit at least one second excitation pulse in accordance with a second pulse sequence in the direction of the object during the second MR recording, wherein the second pulse sequence differs from the first pulse sequence; and - the second MR data represents the object (100) and wherein the scanner unit is configured to generate the MR image in dependence upon the second MR data, characterised in that - the first pulse sequence is defined by a first time parameter set; - the second pulse sequence is defined by a second time parameter set that differs from the first time parameter set, wherein the first time parameter set contains a first echo time and / or a first repetition time and the second pulse sequence contains a second echo time and a second repetition time, wherein the first and the second echo time and / or the first and the second repetition time differ from one another, wherein a first ratio of the first echo time to the first repetition time differs from a second ratio of the second echo time to the second repetition time, so that different contrasts are realised for the first and second MR recording in each case.

6. Magnetic resonance tomography system having a scanner unit (10, 20) that is configured so as to - perform a first MR recording so as to map an object (100) in accordance with a first k-space scanning scheme in order to generate first MR data that represents the object (100), wherein during the first MR recording at least one first excitation pulse is transmitted in accordance with a first pulse sequence in the direction of the object (100); and - perform a second MR recording that is different from the first MR recording in order to generate second MR data; and a computing unit (70) that is configured so as to - determine in dependence upon the second MR data a noise component that represents an influence of at least one external noise source; and - to generate an MR image in dependence upon the first MR data and the noise component, wherein the scanner unit is configured to perform the second MR recording in accordance with a second k-space scanning scheme that differs from the first k-space scanning scheme, - the scanner unit is configured to transmit at least one second excitation pulse in accordance with a second pulse sequence in the direction of the object during the second MR recording, wherein the second pulse sequence differs in particular from the first pulse sequence; and - the second MR data represents the object (100) and wherein the scanner unit is configured to generate the MR image in dependence upon the second MR data, characterised in that - the first k-space scanning scheme corresponds to a Cartesian scanning scheme; and - the second k-space scanning scheme corresponds to a radial scanning scheme or a spiral scanning scheme or a wave CAIPIRINHA scanning scheme.

7. Computer program product having commands that, in the case of execution by a magnetic resonance tomography system (1) according to claim 5 or 6, prompt the magnetic resonance tomography system (1) to implement a method according to one of claims 1 to 4.