METHOD AND DEVICE FOR PROVIDING AN ANTENNA MATRIX FOR TRANSMITTING AND / OR RECEIVING HIGH-FREQUENCY SIGNALS FROM A MAGNETIC RESONANCE RECORDING

Description

[0001] The invention relates to a method for providing an antenna matrix or an antenna array for emitting high-frequency pulses to influence nuclear spin precession in a high-field magnetic resonance tomograph and / or receiving magnetic resonance signals of nuclear spin precession.

[0002] Magnetic resonance imaging (MRI) scanners are imaging devices that use a strong external magnetic field to align the nuclear spins of a sample and then stimulate them to precess around this alignment using an alternating magnetic field. The precession, or return of the spins from this excited state to a lower-energy state, in turn generates an alternating magnetic field that is received by antennas.

[0003] Using magnetic gradient fields, a spatial coding is imprinted on the signals, which subsequently allows the received signal to be assigned to a volume element. The received signal is then evaluated, and a three-dimensional imaging representation of the object under investigation is generated. Local receiving antennas, so-called local coils, are preferably used to receive the signal; these are positioned directly next to the object under investigation to achieve a better signal-to-noise ratio.

[0004] In magnetic resonance imaging (MRI) scanners with higher magnetic fields, for example 3 Tesla or greater, especially 7 Tesla, achieving a homogeneous field strength of the alternating magnetic field and consequently homogeneous excitation with a body coil is difficult due to the higher Larmor frequency and the associated shorter wavelengths and resulting interference. Therefore, a multitude of local transmitting antennas with at least partially independent control are used.

[0005] These antennas can be arranged in a matrix or array. The matrix often has more antenna elements than transmission channels. Which antenna elements are activated depends on a variety of factors, such as the patient and / or the arrangement of the antenna matrix.

[0006] The article by Zhipeng Cao et al, Magn Reson Med 83:2331-2342, 2020 reveals a method for designing a head coil array for parallel excitation in MRI.

[0007] It is therefore an object of the present invention to simplify and improve the use of an antenna matrix with a plurality of transmission channels.

[0008] This problem is solved by a method according to claim 1.

[0009] The method according to the invention is designed to provide an antenna matrix for image acquisition using magnetic resonance imaging (MRI). The antenna matrix can be used either to emit radio frequency pulses to influence nuclear spin precession in a high-field MRI scanner, or to receive magnetic resonance signals of the nuclear spin precession that are influenced by these radio frequency pulses. According to the invention, the antenna matrix is ​​provided in a design process. The radio frequency pulse can be used to excite the nuclear spin precession or to influence the nuclear spins within different sequences. Due to the time-reversibility of electromagnetic propagation, the antenna matrix determined by the method according to the invention is suitable for both transmission and reception.

[0010] The method includes a step to determine a plurality N of distinct predetermined positions distributed over a predetermined volume. "Distributed" here means that each point within the predetermined volume is no further than a maximum predetermined distance from one of the predetermined positions. The predetermined distance can be, for example, less than four, three, or two times the cube root of the predetermined volume. The distance can also be greater than one-quarter, one-third, or one-half of the cube root of the predetermined volume. In other words, the positions are essentially uniformly distributed over the volume.The predetermined volume can be defined, for example, by structural support elements such as a shell or frame of a local coil like a head coil, knee coil, spine coil, or other local coils, or by structural elements of the magnetic resonance imaging (MRI) scanner such as the patient tunnel or patient table. The predetermined volume can also vary during different examinations, for example, if it is defined by a flexible local coil. The flexible local coil can be placed or wound around the patient or limb.

[0011] Preferably, the positions are located on a surface that encloses the volume. In this context, a surface can also be a shell or a shell of the volume. This can be in or on a shell of a rigid local coil or inside a flexible local coil that is positioned around the patient for image acquisition. The predetermined positions are preferably distributed substantially uniformly over the surface. The spacing of the positions can, for example, be limited by an interval whose upper limit is two, five, or ten times a grid constant assuming uniform coverage with a square grid of N grid points, and whose lower limit is half, one-fifth, or one-tenth of the grid constant.

[0012] However, it is also conceivable that the positions are staggered in depth, i.e., arranged in the same direction at varying distances from the region to be captured. This is possible, for example, if a flexible local coil is arranged overlapping around the patient. Alternatively, a local coil could be used in which the positions are arranged in multiple shells or a grid at varying distances from the region to be captured, in order to provide different phase angles.

[0013] According to the invention, the method is part of a design process for a local coil, and the volume is a virtual volume. The predetermined volume can, for example, comprise the maximum volume to be occupied by the local coil or antenna matrix. Within the predetermined volume, the positions can form a virtual grid within the volume, for example, a cubic, hexagonal, or radially symmetrical grid. Preferably, grid points that are occupied by the patient or examination object in a typical application position of the antenna matrix or local coil are excluded from the predetermined positions.

[0014] The spacing between the positions is preferably greater than 1%, 5%, 10%, 25%, or 50% of a wavelength to be transmitted or received by the antenna matrix. The wavelength is defined as the wavelength of a radio signal in air at a frequency determined by the Larmor frequency of the nuclear spin precession in the static magnetic field B0 of the magnetic resonance imaging scanner.

[0015] In one step of the process, a distribution of a plurality of antenna elements across the predetermined positions is determined. The plurality of antennas is less than or equal to the number of positions. Preferably, the plurality of antennas is greater than the number of available transmit and receive channels.

[0016] In the simplest case of a design process, every predetermined position can be occupied by an antenna element.

[0017] In contrast, with a variable local coil such as a flexible local coil, the distribution is preferably determined by the arrangement of the antenna elements within the flexible local coil and the arrangement of the flexible local coil on the object under investigation.

[0018] In one step of the method according to the invention, a high-frequency pulse, or a high-frequency pulse and a gradient pulse, for influencing the nuclear spins in the magnetic resonance imaging (MRI) scanner by emitting the high-frequency pulse is determined by solving an optimization problem via the distribution of antenna elements. The high-frequency pulse can, for example, be an excitation pulse for the nuclear spins or a pulse to "flip" the nuclear spins. The gradient pulse can be a predetermined gradient pulse, e.g., for slice coding. For example, the boundary condition can be a predetermined flip angle to be achieved for the nuclear spins to be imaged in the B0 magnetic field. By means of a Bloch simulation of the achieved flip angles, the flip angles can first be determined in a linear optimization procedure, and then the distribution of the transmitted field strengths of the individual antenna elements can be optimized to the smallest possible variation using a least-squares-root method.Another boundary condition could, for example, be a maximum SAR exposure. Determining the optimized radiofrequency pulse can be done by controlling the magnetic resonance imaging scanner or by another dedicated processor. Boundary conditions and parameters to be optimized are also specified below in relation to the dependent claims.

[0019] In a further step of the process, the distribution of predetermined positions is reduced. To this end, one or more positions are removed from the predetermined positions that were previously considered when determining the optimized high-frequency pulse, depending on the determined high-frequency pulse. This means they are no longer considered in subsequent steps. In particular, it is conceivable that the process is applied iteratively, and that the removed positions are no longer considered when determining the high-frequency pulse, but only the remaining positions.

[0020] The high-frequency pulse preferably has a component for each position, and is therefore multidimensional. Preferably, each component has an amplitude and / or power, which, during the determination process, is supplied as an amplitude or power to an antenna element arranged at that position. This can also be a dependent quantity. It is also conceivable that the antenna element is only virtual, i.e., only considered in a calculation when determining the high-frequency pulse at the predetermined position.

[0021] The reduction or cancellation is performed depending on the detected high-frequency pulse. Preferably, the reduction depends on a component of the high-frequency pulse that is associated with the position or an antenna element located at that position. Preferably, positions whose contribution to the high-frequency pulse is small are reduced, for example, the power supplied by the detected high-frequency pulse. However, it is also conceivable that the detected high-frequency pulse is considered in a broader sense during the reduction, in particular not only locally by a component associated with the position to be cancelled. For example, as explained below in relation to the dependent claims, it is also conceivable that components of the detected high-frequency pulse are considered for positions that are adjacent to the position to be reduced.

[0022] In a further step of the method according to the invention, a termination criterion is checked, for example by the control of the magnetic resonance imaging scanner or the dedicated processor. The termination criterion can, for example, be a property of a magnetic and / or electric high-frequency field generated by the detected high-frequency pulse with antenna elements arranged at the remaining, uncrossed positions.

[0023] However, as explained below in relation to the subclaims, it can also depend on the number of remaining positions or the geometry of these positions.

[0024] If the termination criterion is not met, the procedure continues by determining the high-frequency pulse determined under a boundary condition in an optimization procedure with the reduced number of positions resulting from the deletion.

[0025] If the termination criterion is met, in a further step the antenna matrix with antenna elements is provided according to the distribution over the predetermined volume in the positions distributed.

[0026] According to the invention, this is achieved by manufacturing a local coil with a corresponding antenna matrix, wherein the determined, unpainted positions are occupied with antenna elements in a manufacturing process.

[0027] However, in a variant not covered by the claims, it is also conceivable that, in the case of a configurable antenna matrix, the control system of the magnetic resonance imaging scanner provides the antenna elements at the uncrossed or remaining positions by activating them through a setting, e.g., by connecting them to receivers and / or transmitters or receiver channels and / or transmitter channels via a switching matrix in order to transmit and / or receive signals.

[0028] The method according to the invention advantageously allows an antenna matrix to be adapted to different boundary conditions while simultaneously reducing the number of required transmit and receive channels.

[0029] Further advantageous embodiments are specified in the following dependent claims.

[0030] In a preferred embodiment of the method according to the invention, the determined high-frequency pulse is emitted via the provided antenna matrix during image acquisition with the magnetic resonance tomograph.

[0031] In one possible embodiment of the method according to the invention, the method further includes the step of receiving a magnetic resonance signal with the provided antenna matrix.

[0032] By optimizing under a boundary condition, improved imaging is advantageously achieved with a limited number of transmit and / or receive channels.

[0033] In one conceivable embodiment of the method according to the invention, the antenna elements are electrical and / or magnetic antenna elements. These can be, for example, electrical monopoles, dipoles, striplines, or magnetic antenna coils.

[0034] Advantageously, the method according to the invention can provide antenna matrices for different frequency ranges.

[0035] In one possible embodiment of the method according to the invention, the optimization problem to be solved is to achieve a predetermined strength or homogeneity of the alternating magnetic field B1 in a predetermined target volume. For example, a minimum requirement can be to achieve a homogeneity of excitation of the nuclear spins by the alternating magnetic field B1 or a field strength that must not be exceeded.

[0036] By optimizing the parameter, for example, optimizing homogeneity can advantageously reduce shadowing in the image or improve patient safety by reliably adhering to limit values.

[0037] In one possible embodiment of the method according to the invention, the boundary condition in the optimization process is a maximum permissible coupling of adjacent antenna elements. A minimum distance between two antenna elements is also conceivable. Alternatively, it could be a limit value for the current or voltage of the high-frequency pulse through an antenna element. Another possibility is a limit value for the field strength or power density of the interaction between the high-frequency pulse and the provided antenna matrix.

[0038] A lower coupling advantageously improves the images obtained, while adhering to the limit values ​​increases the safety in the operation of the magnetic resonance tomograph.

[0039] In one conceivable embodiment of the method according to the invention, the reduction step involves reducing or removing the antenna elements depending on the voltage, current, or high-frequency power assigned to each antenna element by the high-frequency pulse. For example, the antenna elements with the lowest assigned voltages, currents, and / or high-frequency powers can be removed.

[0040] Advantageously, by considering the voltage, currents, and / or radio frequency power, antenna elements that contribute little to the measured alternating magnetic field B1 can be identified and eliminated. Due to the reversibility of Maxwell's laws, this applies equally to the receiving case, where the antenna elements with the smallest contribution during transmission also contribute the smallest share to the received signal.

[0041] In one possible embodiment of the method according to the invention, the dependence on voltage, current, or radio frequency power is a minimum power threshold that must not be undercut. This can, for example, be a minimum power radiated by the respective antenna element. The threshold can, for example, be less than 1 W, 5 W, or 10 W.

[0042] The threshold value allows for efficient filtering out of positions that are of little importance for generating the alternating magnetic field.

[0043] In one conceivable embodiment of the method according to the invention, the reduction step is made dependent on a current, voltage, or high-frequency power of a neighboring antenna element during the predetermined high-frequency pulse, as assigned by the determined high-frequency pulse. A neighboring antenna element is, for example, a real antenna element or a position for a virtual antenna element located at a position adjacent to the position for which a decision regarding occupancy or activation is to be made. Neighboring elements can be those with the smallest distance, or, in a grid or matrix, adjacent control points. It is also conceivable that neighbors beyond the nearest are considered neighboring within the meaning of the invention. A virtual antenna element is conceivable if, during the provision or...The construction of a local coil matrix is ​​merely a simulation of possible positions. However, it is also conceivable that with a real antenna, for example with a flexible local coil or antenna matrix, adjacent positions or antenna elements are created by the arrangement on the patient, as the matrix overlaps due to winding.

[0044] By taking into account the currents, voltages and / or high-frequency power of adjacent positions or antenna elements assigned to the neighboring antenna element in the high-frequency pulse, redundancies can be advantageously identified and eliminated.

[0045] In one possible embodiment of the method according to the invention, the termination criterion relates to a maximum number of antenna elements. Preferably, a maximum number of active antenna elements should not be exceeded. This number can be predetermined, for example, by the maximum number of simultaneously available connection contacts or independent transmission channels.

[0046] The method according to the invention thus allows for effective optimization of the configuration for different magnetic resonance systems and / or arrangements.

[0047] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0048] They show: Fig. 1 a schematic representation of a magnetic resonance tomograph that is not within the scope of the claims; Fig. 2 a schematic representation of parts of the magnetic resonance tomograph in detail; Fig. 3 a schematic flowchart for an exemplary method according to the invention.

[0049] Fig. 1 Figure 1 shows a schematic representation of an embodiment of a magnetic resonance imaging scanner.

[0050] The magnet unit 10 includes a field magnet 11 that generates a static magnetic field B0 for aligning the nuclear spins of samples or the patient 100 within a recording area. The recording area is characterized by an extremely homogeneous static magnetic field B0, with the homogeneity referring in particular to the magnetic field strength or magnitude. The recording area is nearly spherical and arranged within a patient tunnel 16 that extends longitudinally 2 through the magnet unit 10. A patient bed 30 can be moved within the patient tunnel 16 by the traversing unit 36. The field magnet 11 is typically a superconducting magnet capable of generating magnetic fields with a magnetic flux density of up to 3 T, and even higher in the latest devices. However, for lower magnetic field strengths, permanent magnets or electromagnets with normal-conducting coils can also be used.Furthermore, the magnetic unit 10 includes gradient coils 12, which are designed to superimpose temporally and spatially variable magnetic fields in three spatial directions onto the magnetic field B0 in order to spatially differentiate the captured imaging areas in the investigation volume. The gradient coils 12 are typically coils made of normally conducting wires that can generate mutually orthogonal fields in the investigation volume.

[0051] The magnet unit 10 also has a body coil 14, which is designed to radiate a high-frequency signal supplied via a signal line into the examination volume and to receive 100 resonance signals emitted by the patient and to transmit them via a signal line.

[0052] A control unit 20 supplies the magnet unit 10 with the various signals for the gradient coils 12 and the body coil 14 and evaluates the received signals.

[0053] The control unit 20 thus has a gradient control 21 which is designed to supply the gradient coils 12 with variable currents via supply lines, which provide the desired gradient fields in the investigation volume in a time-coordinated manner.

[0054] Furthermore, the control unit 20 includes a high-frequency unit 22 designed to generate a high-frequency pulse with a predefined temporal profile, amplitude, and spectral power distribution to excite magnetic resonance of the nuclear spins in the patient 100. Pulse powers in the kilowatt range can be achieved. The excitation signals can be radiated into the patient 100 via the body coil 14 or via a local transmitting antenna.

[0055] A controller 23 communicates via a signal bus 25 with the gradient controller 21 and the high-frequency unit 22.

[0056] A local coil 50 is arranged on the patient 100, which receives a magnetic resonance signal from the body of the patient 100 and transmits it via a signal connection 33 to receivers of the high frequency unit 22.

[0057] In Fig. 2 Parts of the magnetic resonance imaging scanner are shown schematically in detail.

[0058] The local coil 50 comprises a plurality of antenna coils 51 as antenna elements, which are distributed as a matrix over the local coil 50 to cover a surface of the patient 100 for the excitation or influencing of nuclear spins by radio frequency pulses and / or the reception of an MR signal from the patient 100. The local coil 50 can, for example, be a flexible local coil that is wound around the patient or their limbs, so that the relative arrangement of the antenna coils 51 to each other can vary with each image acquisition, for example by overlapping layers of the flexible local coil.

[0059] Due to this flexible configuration, the magnetic resonance imaging scanner 1, in one possible embodiment, has a switching matrix 60 designed to connect antenna coils 51 to transmitters and / or receivers of the radio frequency unit 22. Preferably, the switching matrix 60 has more connections for antenna coils 51 than connections for transmitters or receivers, so that a selection of antenna coils 51 can be connected to a transmitter or receiver. The selection is preferably made by the control unit according to the following. Fig. 3 The described method according to the invention is used. The control unit 23 then establishes the connection according to the selected option via the switching matrix 60, e.g., by means of a setting command. It is conceivable that the switching matrix 60 is configured as described in the inventive method. Fig. 2 The switching matrix 60 is shown in the high-frequency unit 22. However, it can also be located in the local coil 50, so that only one connection in the signal link 33 is required for the transmitters and receivers. This advantageously reduces the number of necessary connections between the local coil 50 and the high-frequency unit 22. This applies both to wired cables, where the cable thickness and the number of contacts can be reduced, and to wireless signal links 33, in order to reduce the bandwidth.

[0060] In one embodiment, it is conceivable that the arrangement of the antenna coils 51 in a local coil 50 is not variable during operation between image acquisitions, but is fixed, for example, by a rigid structure of the local coil 50.

[0061] In this embodiment, it is conceivable that the inventive method of the Fig. 3 The design of the local coil 50 is already carried out, and the distribution of the antenna elements or antenna coils 51 across the possible positions is determined according to the selection obtained using the method according to the invention. The local coil 50 can then be manufactured according to this distribution, so that only the number of antenna elements determined using the method according to the invention is arranged at the predetermined positions.

[0062] In Fig. 3A schematic flowchart of an embodiment of the method according to the invention is shown. Using the method according to the invention, an antenna matrix is ​​determined and provided. The provided antenna matrix is ​​designed to transmit high-frequency pulses to influence nuclear spin precession in a high-field magnetic resonance imaging (MRI) scanner and / or to receive magnetic resonance signals of the nuclear spin precession. The transmission and reception characteristics satisfy a predetermined criterion or boundary condition. The boundary condition can, for example, relate to the homogeneity of the generated B1 field or limit values ​​for field strengths or radio frequency power levels that must not be exceeded.

[0063] In step S10, a plurality N of different predetermined positions distributed over a predetermined volume is determined. The positions can, for example, be given by nodes of a virtual grid inscribed in a possible volume of the local coil.

[0064] In step S20, a distribution of a plurality of antenna elements across the predetermined positions is determined. In the simplest case, it can be stipulated that each position is assigned one antenna element. This can be the case, for example, with a flexible local coil. However, it is also conceivable that certain positions can be excluded based on geometric considerations, for example, because the spacing in the application-specific arrangement falls below a threshold value. It is also conceivable that the coupling of antenna coils 51 is measured using a test signal, and antenna coils whose coupling to their respective neighbor exceeds a threshold value are removed from the distribution.

[0065] In step S30, a high-frequency pulse is determined that is optimized for a specific boundary condition when transmitted via the distribution of antenna elements to influence the nuclear spins. The high-frequency pulse could, for example, be a pulse to excite the nuclear spins into precession. High-frequency pulses intended to effect a targeted change in the deflection angle, such as a 180° flip angle, are also conceivable, for instance, to refocus the phases in an echo spin sequence. The boundary condition could be, for example, maximum homogeneity of the generated alternating magnetic field or the excitation of the nuclear spins. A maximum or minimum value, or a total power of the high-frequency pulse, could also be specified. Due to the reversibility of the underlying Maxwell's laws, a boundary condition for transmission corresponds to a boundary condition for reception.For example, homogeneous excitation corresponds to homogeneous sensitivity.

[0066] Determining the high-frequency pulse in step S30 is preferably carried out using the control system 23 of the magnetic resonance imaging scanner 1, for example, with an optimization method such as LSR. However, with the antenna matrix design according to the invention, implementation on a dedicated computer is also conceivable. The antenna elements are then virtual antenna elements until they are implemented in the optimization method. In step S40, one or more antenna elements of the distribution are removed from the distribution, or the distribution is thereby reduced, depending on the determined high-frequency pulse. For example, it is conceivable that the antenna element(s) with the lowest radiated power at the determined high-frequency pulse is / are removed, since its contribution to the field is the smallest.

[0067] It is also possible that a lower or upper power threshold is set for the power of the high-frequency pulse of a respective antenna element, if this threshold is exceeded or fallen below, the respective antenna element is removed from the distribution.

[0068] It is also conceivable that, when removing the high-frequency pulse, values ​​for neighboring antenna elements are taken into account in addition to the values ​​determined for the respective antenna element. For example, the measured power of one antenna element might be lower than the measured power of a neighboring antenna element by a certain factor, such as 12 dB, 18 dB, 24 dB, or more. If there are significantly stronger emitting or receiving antenna elements in the vicinity, the intervening antenna element can be advantageously omitted or remain inactive.

[0069] In a further step, S50, the controller 23 or the computer checks whether a termination criterion is met. If the termination criterion is met, the process is terminated with the subsequent steps. If the termination criterion is not met, a new high-frequency pulse is determined with the modified distribution under the boundary condition in step S30.

[0070] A termination criterion could be, for example, when the number of remaining antenna elements or positions in the distribution falls below a threshold. This threshold could be defined, for instance, by the number of available transmit or receive channels of magnetic resonance imaging (MRI) scanner 1. A homogeneity criterion, such as a maximum deviation in the excitation of the nuclear spins or the field strength, is also conceivable.

[0071] In another step S60, an antenna matrix with antenna elements is provided in positions distributed according to the distribution over the predetermined volume.

[0072] To provide the antenna matrix, it is also conceivable that spacers, e.g. in the form of cushions or pieces of foam, etc., are arranged on the antenna matrix to provide the predetermined position of the distribution.

[0073] According to the invention, the method is used in the construction or design of an antenna matrix, and the provision of the antenna matrix comprises the step of arranging antenna elements in a local coil according to the specified distribution.

[0074] In a possible embodiment of the method according to the invention, in step S70 the determined high-frequency pulse is further transmitted from the magnetic resonance tomograph 1 via the antenna matrix and / or in step S80 a magnetic resonance signal is received with the antenna matrix.

[0075] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived by the person skilled in the art without leaving the scope of protection of the invention as defined by the claims.

Claims

1. Method for providing an antenna matrix for transmitting high frequency pulses for influencing a nuclear spin precession in a high-field magnetic resonance tomography system and / or receiving magnetic resonance signals of the nuclear spin precession, wherein the provision takes place in a design process for the antenna matrix, wherein the method has the following steps: (S10) Determining a plurality N of different predetermined positions distributed over a predetermined volume; (S20) Determining a distribution of a plurality of antenna elements over the predetermined positions; (S30) Ascertaining a high frequency pulse or high frequency pulses and gradient pulses for influencing the nuclear spin precession by transmitting the high frequency pulse over the distribution of antenna elements, wherein the high frequency pulse is ascertained by means of solving an optimisation problem under a boundary condition; (S40) Reducing the distribution by eliminating an antenna element as a function of the ascertained high frequency pulse; (S50) Checking an abort criterion and continuing with the step of ascertaining a high frequency pulse (S30), if the abort criterion is not fulfilled; (S60) Providing the antenna matrix with antenna elements according to the distribution of positions distributed over the predetermined volume, characterised in that a local coil is manufactured with a corresponding antenna matrix, wherein the determined not-eliminated positions are populated with antenna elements during manufacture.

2. Method according to claim 1, wherein the method further has the step (S70) of transmitting the high frequency pulse and / or the step (S80) of receiving a magnetic resonance signal.

3. Method according to claim 1 or 2, wherein the antenna elements are electrical and / or magnetic antenna elements.

4. Method according to one of claims 1 to 3, wherein one objective of the optimisation problem is at least one of a magnetic and / or electrical field strength in a predetermined recording area, homogeneity of the magnetic and / or electrical field strength in the predetermined recording area, a predetermined distribution of the magnetic and / or electrical fields from a plurality of antenna elements.

5. Method according to one of claims 1 to 4, wherein the boundary condition is one of a maximum permissible coupling or minimal alternate distance between two antenna elements, a power or flow limit value for an antenna element or a SAR limit value.

6. Method according to one of the preceding claims, wherein in the reduction step (S40), the reduction in the antenna elements takes place as a function of a high frequency power and / or electrical voltage and / or electrical current assigned to the respective antenna element by the high frequency pulse.

7. Method according to claim 6, wherein the dependency on the high frequency power and / or electrical voltage and / or electrical current is a limit value not to be undercut.

8. Method according to claim 6, wherein the reduction step (S40) depends on a high frequency power and / or electrical voltage and / or electrical current assigned to an adjacent antenna element by the predetermined high frequency pulse.

9. Method according to one of the preceding claims, wherein the abort criterion relates to a maximum number of antenna elements.

10. Method according to claim 1, wherein the step (S60) of providing the antenna matrix with antenna elements according to the distribution of positions distributed over the predetermined volume has the step of positioning spacers between the patient and the antenna element in accordance with the distribution.