Wireless signal transmission in magnetic resonance systems

Abstract

A method is described for the wireless signal transmission of a measurement signal and/or a control signal between two functional components of a MR system. The measurement signal and/or the control signal is encoded into a RF transmit signal with a predefined orbital angular momentum and this RF transmit signal is transmitted between transmit antenna arrangements of the functional components. In addition, the embodiments relate to a local coil and an orbital angular momentum transmit unit with which the method may be carried out, and also a MR system that has a local coil and an orbital angular momentum transmit unit of this type.

Claims

1. A method for a wireless signal transmission of a measurement signal or a control signal between two functional components of a magnetic resonance (MR) system, the method comprising: encoding, by an orbital angular momentum encoding unit of the MR system, the measurement signal, the control signal, or the measurement signal and the control signal into a radio-frequency (RFS transmit signal with a predefined orbital angular momentum rendering the RF transmit signal distinguishable from other RF signals within a same frequency range; transmitting the RF transmit signal between transmit antenna arrangements of the two functional components of the MR system; and decoding, by the orbital angular momentum encoding unit, the RF transmit signal.

2. The method as claimed in claim 1, wherein one of the two functional components comprises a local coil and a second of the two functional components comprises a local coil interface on a device site of the MR system, and wherein the measurement signal comprises a MR signal.

3. The method as claimed in claim 1, wherein RF transmit signals with different orbital angular momentum are superposed in a multiplex method.

4. The method as claimed in claim 1, wherein the RF transmit signal is in a frequency range above 1 GHz.

5. The method as claimed in claim 1, wherein the RF transmit signal is in a frequency range of 2 GHz with a frequency bandwidth of ±15 MHz.

6. The method as claimed in claim 1, wherein the RF transmit signal is generated by an antenna array.

7. The method as claimed in claim 6, wherein the antenna array comprises turnstile antennas, tripole antennas, or the turnstile antennas and the tripole antennas.

8. The method as claimed in claim 1, wherein the RF transmit signal is received and decoded by an antenna array.

9. The method as claimed in claim 8, wherein field values are measured for decoding RF transmit signals with different orbital angular momenta at different times at different angular positions of the antenna array, and a signal value of individual RF transmit signals at the respective time is calculated based on the field values.

10. The method as claimed in claim 1, wherein a Fourier transform is used to decode the RF transmit signal.

11. A method for a wireless signal transmission of a measurement signal or a control signal between two functional components of a magnetic resonance (MR) system, the method comprising: encoding the measurement signal, the control signal, or the measurement signal and the control signal into a radio-frequency (RF) transmit signal with a predefined orbital angular momentum, wherein the orbital angular momentum is impressed on the RF transmit signal by a phase plate; and transmitting the RF transmit signal between transmit antenna arrangements of the two functional components of the MR system.

12. A local coil comprising: a magnetic resonance (MR) antenna arrangement; and an orbital angular momentum transmit unit comprising: a local coil transmit antenna arrangement configured to receive and transmit a radio-frequency (RF) signal having an orbital angular momentum; an orbital angular momentum encoding unit configured to encode measurement signals and/or control signals onto a RF transmit signal rendering the RF transmit signal distinguishable from other RF signals within a same frequency range, and decode signals from the RF transmit signal.

13. An orbital angular momentum transmit unit comprising: an antenna array for receiving and transmitting a radio-frequency (RF) transmit signal, wherein the antenna array is a polar coordinate grid; and an orbital angular momentum encoding unit for encoding, decoding, or encoding and decoding the RF transmit signal.

14. The orbital angular momentum transmit unit as claimed in claim 13, wherein the orbital angular momentum encoding unit encodes, decodes, or encodes and decodes the RF transmit signal by a Fourier transform.

15. The orbital angular momentum transmit unit as claimed in claim 13, wherein the antenna array comprises turnstile antennas, tripole antennas, or the turnstile antennas and the tripole antennas.

16. A magnetic resonance (MR) system comprising: a local coil comprising: (1) a MR antenna arrangement; and (2) an orbital angular momentum transmit unit comprising: (a) a local coil transmit antenna arrangement configured to receive and transmit a radio-frequency (RF) transmit signal having an orbital angular momentum; and (b) an orbital angular momentum encoding unit configured to encode measurement signals and/or control signals onto the RF transmit signal rendering the RF transmit signal distinguishable from other RF signals within a same frequency range, and decode signals from the RF transmit signal; and an additional orbital angular momentum transmit unit comprising: (1) a transmit antenna arrangement; and (2) an orbital angular momentum encoding unit for encoding, decoding, or encoding and decoding the RF transmit signal.

17. The MR system as claimed in claim 16, wherein the transmit antenna arrangement of the local coil or the additional orbital angular momentum transmit unit comprises turnstile antennas, tripole antennas, or the turnstile antennas and the tripole antennas for receiving and transmitting the RF transmit signal, wherein the turnstile antennas, the tripole antennas, or the turnstile antennas and the tripole antennas are arranged in an antenna array.

18. The MR system as claimed in claim 16, wherein the orbital angular momentum encoding unit of the orbital angular momentum transmit unit of the local coil or the additional orbital angular momentum transmit unit encodes, decodes, or encodes and decodes the RF transmit signal by a Fourier transform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a schematic representation of an embodiment of a generation of an electromagnetic wave with orbital angular momentum l=1 through a phase plate.

(2) FIG. 2 depicts a schematic representation of an embodiment of a MR system.

(3) FIG. 3 depicts a schematic representation of a first embodiment of a local coil and a local coil interface.

(4) FIG. 4 depicts a detailed view of a horn antenna of the local coil according to FIG. 3.

(5) FIG. 5 depicts a schematic representation of a first embodiment of an antenna array.

(6) FIG. 6 depicts embodiments of an electrical field distribution perpendicular to the direction of propagation for different RF transmit signals having orbital angular momenta.

(7) FIG. 7 depicts a schematic representation of a second embodiment of an antenna array.

(8) FIG. 8 depicts a detailed view of a turnstile antenna of the antenna array according to FIG. 5 or FIG. 7.

(9) FIG. 9 depicts a detailed view of an embodiment of a tripole antenna for use in an antenna array analogous to FIG. 5 or FIG. 7.

(10) FIG. 10 depicts a schematic representation of a second embodiment of a local coil and a local coil interface.

DETAILED DESCRIPTION

(11) FIG. 1 depicts an electromagnetic wave RF with an orbital angular momentum l=1 in the right-hand part of the illustration that propagates helically in the direction of a virtual propagation axis A. It is evident that the energy density decreases substantially in the center of the direction of propagation A. The number of helices of the wave is directly proportional to the orbital angular momentum I. As depicted in FIG. 1, the electromagnetic wave RF having an orbital angular momentum is generated, in particular, from a linear-polarized electromagnetic wave LEM arriving from the left. This wave runs through a circular phase plate 21 that, coiled around a coil axis at the azimuthal angle Φ, has an increasing thickness, where the thickness is in each case constant along a radius. The coil axis runs parallel to the direction of propagation. Depending on the frequency range in which the RF transmit signal is to be modulated, a suitable material and the suitable maximum density D (e.g., measured at the strongest point of the phase plate 21) may be selected in advance for the phase plate 21. The thickness is defined as D=λ.sub.m/4, where λ.sub.m refers to the wavelength in the selected material according to:

(12) $\begin{array}{cc}{\lambda }_m=\frac{{\lambda }_0}{\sqrt{{\mu }_r.Math.{\mathrm{.Math.}}_r}}.& \left(1\right)\end{array}$

(13) Here, λ.sub.0 is the wavelength of the signal in air or in a vacuum (e.g., approx. 1 dm at 3 GHz), μ.sub.r is the magnetic permeability (e.g., approx. 10) and ∈.sub.r is the dielectric constant of the material of the phase plate 21. The phase plate 21 may include metal oxide with a high dielectric constant ∈.sub.r, (e.g., aluminum oxide with ∈.sub.r=9 or titanium dioxide with E.sub.r=100).

(14) The impressed orbital angular momentum may be defined through a selection of the pitch d (e.g., the maximum thickness difference following a rotation of the coil) of the phase plate 21.

(15) FIG. 2 depicts an overview to explain the individual components of the MR system 10. Given that, due to the large data volumes, the system may be usable for transmitting MR signals (e.g., raw data) from a local coil 1 to a local coil interface 3 (e.g., as part of a MR signal processing device 12), it is assumed below, as an example, that the one functional component 1 is a local coil 1 and the other functional component is the local coil interface 3. However, this does not exclude the use of the embodiments on other functional components as well.

(16) Here, the MR system 10 includes a patient table 11 with which a patient P may be introduced into a patient tunnel 14 of a scanner 13 of the MR system 10. A local coil 1 is located at an area of the patient P to be examined. In the operation of the MR system 10, the local coil 1 receives MR signals (e.g., raw data). In addition, the local coil 1 includes an orbital angular momentum transmit unit 2 that serves to encode the MR signals into a radio frequency signal HF (e.g., RF transmit signal) and transmit the radio frequency signal HF to a local coil interface 3. Here, the local coil interface 3 is designed as a component of a signal processing device 15 that is in turn a part of a control device 12 of the MR system 10. The RF transmit signal RF is received and decoded in the local coil interface 3 and the raw data are further processed in the signal processing device 15 or image data are reconstructed therefrom. The control device 12 and the scanner 13 of the MR system 10 may be constructed in a conventional manner and have all the components of a conventional MR system 10. In particular, the scanner 13 may have a basic magnetic field system, a gradient coil arrangement, an integrated whole-body coil to transmit RF pulses and/or to receive MR signals, etc.

(17) FIG. 3 depicts a schematic representation of a first example embodiment of a local coil 1 and a local coil interface 3, of the type that may be used in the MR system 10 according to FIG. 2. This representation serves to explain the arrangement of the components involved in the signal transmission method. The local coil 1 includes a MR antenna element arrangement 7, an amplifier arrangement 8, a modulator arrangement 9, and the orbital angular momentum transmit unit 2 also depicted in FIG. 2.

(18) Here, the antenna element arrangement 7 includes a plurality of antenna conductor loops 7a, 7b, . . . , 7n. A dedicated amplifier 8a, 8b, . . . , 8n of the amplifier arrangement 8 is assigned to each of the antenna conductor loops 7a, 7b, . . . , 7n, wherein the amplifiers 8a, 8b, . . . , 8n preamplify in a conventional manner the MR signals received by the antenna conductor loops 7a, 7b, . . . , 7n. Each of the amplifiers 8a, 8b, . . . , 8n is connected on the output side to a modulator 9a, 9b, . . . , 9n of the modulator arrangement 9.

(19) Different embodiments are possible for the modulators 9a, 9b, . . . , 9n. On the one hand, this may involve analog modulators, which modulate the MR signal in a conventional manner, for example, through a frequency modulation, onto a carrier signal. Alternatively, digital modulators may also be used, in which the amplified MR signals are digitized in an ADC and encoded into the carrier signal. A RF signal with a frequency in the GHz range may be used as the carrier signal, (e.g., with a carrier frequency of 2 GHz), and the modulation bandwidth is ±15 MHz. The modulated carrier signal, (which includes the information of the MR signals and may be regarded as the measurement signal f.sub.MRI that includes the MR signal), is intended to be transmitted from the local coil 1 to the local coil interface 3.

(20) Prior to the transmission, the measurement signal f.sub.MRI is further processed in the orbital angular momentum transmit unit 2. The orbital angular momentum transmit unit 2 includes an orbital angular momentum encoding unit 5 and a local coil transmit antenna arrangement 4. In the local coil 1 according to FIG. 3, the local coil transmit antenna arrangement 4 has a plurality of horn antennas 4a, 4b, 4c, 4d, 4e that are explained in more detail later, in each case with a phase plate 21.

(21) The measurement signals f.sub.MRI supplied by the modulator arrangement 9 are encoded in the orbital angular momentum encoding unit 5 according to a predefined algorithm, for example, hardwired or programmed into the orbital angular momentum encoding unit 5.

(22) The algorithm may provide a one-to-one assignment between an individual antenna conductor loop 7a, 7b, . . . , 7n of the MR antenna element arrangement 7 and an individual horn antenna 4a, 4b, 4c, 4d, 4e of the local coil transmit antenna arrangement 4. In certain embodiments, a more complex algorithm may also be used in the orbital angular momentum encoding unit 5. For example, the signals of a plurality of conductor coils of the MR antenna element arrangement 7 may be encoded onto a signal fed to an individual horn antenna 4a, 4b, 4c, 4d, 4e of the local coil transmit antenna arrangement 4 and may be transmitted by the latter. For example, modes may thus be formed in a known manner through combination of different MR signals, or a multiplexing may be achieved, (e.g., a time division multiplexing and/or a frequency division multiplexing), particularly if the modulators operate at different carrier frequencies.

(23) Following the encoding of the RF signals in the orbital angular momentum encoding unit 5, the RF signals are transmitted using the horn antennas 4a, 4b, 4c, 4d, 4e of the local coil transmit antenna arrangement 4 in the form of RF transmit signals HF.sub.−2, HF.sub.−1, HF.sub.0, HF.sub.+1, HF.sub.+2, which in each case have different orbital angular momenta. A detailed representation of a horn antenna 4a of the antenna arrangement 4 is depicted as an example in FIG. 4.

(24) The horn antenna 4a has a waveguide 22 and a horn 23, so that a RF transmit signal incoming via the waveguide 22 is radiated by the horn 23. A phase plate 21, already explained above in connection with FIG. 1, which has a maximum thickness D and a pitch d, is disposed in the horn 23. RF signals fed via the waveguide 22 to the phase plate 21 are provided by the phase plate 21 with an orbital angular momentum, so that a RF transmit signal having an orbital angular momentum is transmitted via the horn 23 of the horn antenna 4a, as depicted in FIG. 1.

(25) The use of phase plates 21 with different pitches d in the different horn antennas 4a, 4b, 4c, 4d, 4e offers the possibility of using a plurality of transmit channels at the same frequency of the RF transmit signal, where an orbital angular momentum is uniquely allocated to each of the transmit channels. For example, the horn antenna 4a may transmit a RF transmit signal HF.sub.+2 having an orbital angular momentum l=2, the horn antenna 4b may transmit a RF transmit signal HF.sub.+1 having an orbital angular momentum l=1, the horn antenna 4c may transmit a RF transmit signal HF.sub.0 having an orbital angular momentum l=0, the horn antenna 4d may transmit a RF transmit signal HF.sub.−1 having an orbital angular momentum l=−1 and the horn antenna 4e may transmit a RF transmit signal HF.sub.−2 having an orbital angular momentum l=−2.

(26) The RF transmit signals HF.sub.−2, HF.sub.−1, HF.sub.0, HF.sub.+1, HF.sub.+2 transmitted in parallel by the horn antennas 4a, 4b, 4c, 4d, 4e are spatially superposed on one another (symbolized in FIG. 3 by the bracket) and may be received in the local coil interface 3 as a superposed RF transmit signal (or mixed RF transmit signal) using an antenna array 6. The superposed RF transmit signal is processed, (e.g., decoded once more), with an orbital angular momentum encoding unit 5 of the MR signal processing device 12.

(27) FIG. 5 depicts a first embodiment of an antenna array 6. In this antenna array 6, a total of 33 individual turnstile antennas 40 are disposed according to a polar coordinate grid. An example of a turnstile antenna of this type is depicted in FIG. 8. The turnstile antenna 40 has a structural form with a conductor 41 that runs in a conductor plane along the outer contours of a cross. The four connections 42 of the turnstile antennas 40 pass on the inner corners of the cross shape in each case perpendicular to the conductor plane. The direction and strength of the electrical field at the location of the antenna 40, e.g., the local field vector that may be used as a field value, as described below, to determine the angular momentum of the received RF transmit signal, may be measured with a turnstile antenna 40 of this type.

(28) One of the turnstile antennas 40 is located in the center point of the antenna array 6, and four turnstile antennas 40 out of the other turnstile antennas 40 are arranged in each case at equal distances from one another on eight (imaginary) beams or “spokes” running radially outward, which in turn are disposed at equal angular distances from one another.

(29) The antenna array 6 according to FIG. 5 enables the reception and decoding of individual RF transmit signals HF.sub.−2, HF.sub.−1, HF.sub.0, HF.sub.+1, HF.sub.+2 with different orbital angular momenta, irrespective of whether they are measured separately in time or as a superposed or mixed RF transmit signal. To do this, antenna measurement values, (e.g., field values of the electrical field at the time concerned), are measured at different times t, in each case simultaneously at different angular positions θ of the antenna array 6. The signal value for the individual RF transmit signals at the respective time t may then be calculated on the basis of these antenna measurement values.

(30) The principle underlying this procedure is explained with reference to FIG. 6. FIG. 6 depicts, from left to right, the different field distributions of the electrical field vectors of electromagnetic signals with the orbital angular momenta 1=0, l=1, l=2, and l=4, in each case in a cross section selected perpendicular to the direction of propagation A. In each case, the strength of the electrical field vector is depicted locally by a vector arrow, where the arrow direction represents the local alignment of the electrical field vector and the length of the vector arrows represents the amount of the electrical field. These figures indicate how the relative local spatial alignment of the electrical field vector changes due to the angular momentum. In the field with the angular momentum l=0 (left image), the local field vector is located with a rotation along the circle drawn as a dotted line at a given time parallel at all locations (here, for example, upward). In the field with the angular momentum l=1 (second image from the left), the field direction changes with a rotation around the center point every 180°, in the field with the angular momentum l=2 (second image from the right) every 90°, and in the field with the angular momentum I=4 (right image) every 45°.

(31) With a simultaneous measurement of the electrical field vector at different points with different angles (e.g., on a circular path around the center point or on a spiral-shaped path), as is possible, for example, with the antenna array 6 according to FIG. 5, the obtained field values in total also contain the information indicating the angular momentum that the received electromagnetic signal had.

(32) For the further mathematical explanation of the procedure, the signal, (e.g., the electrical field vector E(θ,t)), which may be received along a circular path K, is depicted in the following formula as a function of the azimuthal angular positions θ.

(33) The electrical field vector E(θ,t) varies with the time t, but, for the sake of simplicity, only values at an individual measurement time are considered below, and therefore only the symbol E(θ) is used below for the electrical field vector. This electrical field vector E(θ) of the superposed RF transmit signal measured by the antenna array 6 along a spoke r is given in dependence on the angular position θ by:

(34) $\begin{array}{cc}E\left(\theta \right)=E_0+\underset{l=1}{\overset{\infty }{.Math.}}{E}_1\sin \left(l.Math.\theta \right)& \left(2\right)\end{array}$

(35) Here, E.sub.0 is the mean field strength of all field vectors E(θ) measured at the different angular positions θ:

(36) $\begin{array}{cc}{E}_0=\begin{array}{c}\mathrm{avg}\\ \theta \end{array}\left[E\left(\theta \right)\right]={\int }_0^{2\pi }E\left(\theta \right)d\theta & \left(3\right)\end{array}$

(37) The field strength E.sub.1 (e.g., for a time t) of the component of a RF transmit signal with the angular momentum I within the received mixed RF transmit signal may be determined from these values by a discrete Fourier transform or Fourier decomposition as follows:

(38) $\begin{array}{cc}\begin{array}{c}{E}_1=\begin{array}{c}\mathrm{avg}\\ \theta \end{array}\left[\left(E\left(\theta \right)-E_0\right)\sin \left(l.Math.\theta \right)\right]={\int }_0^{2\pi }\left(E\left(\theta \right)-E_0\right)\sin \left(l.Math.\theta \right)d\theta \\ ={\int }_0^{2\pi }\underset{k=1}{\overset{N}{.Math.}}{E}_k\sin \left(k.Math.\theta \right)\sin \left(l.Math.\theta \right)d\theta \end{array}& \left(4\right)\end{array}$

(39) Equation (3) therefore corresponds to an integration, weighted with the weighting factor e.sup.(−i/l), of the complex field vector along a rotation (e.g., integration path) around the beam axis, e.g., the axis of the direction of propagation of the wave. Here, l represents the different angular momentum states, N is the maximum number of the various different angular momentum states l, and k is a control variable that similarly represents the different angular momentum states within the Fourier decomposition. The maximum number N of the different angular momentum states I of the RF transmit signal distinguishable or decodable by an antenna array of this type is in fact limited by the number M of antenna elements or possible different measurement points along a rotation around the beam axis according to N<M/2. An equation system is obtained by Equation (3) for each specific measurement at a time t, from which the target field vector E.sub.1 of the RF transmit signal with the angular momentum state I may ultimately be calculated from the electrical field vectors E(θ) measured by the antenna array 6. Interestingly, it suffices in each case only to determine one value E(θ) for a sufficient number of angular positions θ (e.g., double the number of the maximum possible angular momentum states l). It may suffice to measure the signal of an antenna element along a spoke r. In this respect, it would also suffice to construct an antenna array that has only one circle of antenna elements. In the embodiment according to FIG. 5, all antenna elements located on a spoke r may advantageously be combined initially to form a common field vector E(θ), which is then incorporated into the above calculation. For example, a mean value of the measurement values along a spoke may be formed. This has the advantage that the signal is measured redundantly. The antenna element located in the center serves primarily to acquire RF transmit signals with the angular momentum l=0.

(40) A second example embodiment of an antenna array is depicted in FIG. 7. The antenna array 6 according to FIG. 7 includes 7×7 antenna elements 40 in an even grid in a Cartesian coordinate arrangement. Field values may also be determined herewith depending on the angle θ , e.g., on a circle around the center point of the antenna array 6 in order to receive and decrypt the RF transmit signals having an orbital angular momentum with the method described above (e.g., by Equations (1) to (3)). If necessary, (virtual) field values lying between the individual antenna elements 40 may also be interpolated here from the antenna measurement values measured on the antenna elements 40. The individual antenna elements 40 may again be designed here also as turnstile antennas 40, as depicted in FIG. 8.

(41) The turnstile antennas 40 depicted in FIGS. 5, 7, and 8 have a compact structural form and may therefore be used if the antenna array may be aligned at least approximately perpendicular to the virtual propagation axis A of the electromagnetic wave to be received (see FIG. 1).

(42) Tripole antennas 50 may also be used in an antenna array 6 as an alternative to the turnstile antennas 40. FIG. 9 depicts a schematic representation of a possible tripole antenna 50. This involves a structural form in which six rod antennas may be used from the center point in the direction of the respective axes. Tripole antennas 50 may transmit and/or receive signals having an orbital angular momentum in any direction in relation to the propagation axis A.

(43) Exclusively turnstile antennas 40 or exclusively tripole antennas 50, but also turnstile antennas 40 and tripole antennas 50 may be used in the antenna arrays 6.

(44) Particularly with digital sampling units that are connected directly to each turnstile antenna 40 or tripole antenna 50, the local current two-dimensional or three-dimensional field vectors of the RF transmit signals may be measured coherently into the gigahertz range so that they may then be evaluated, for example with suitable software, in the manner described above.

(45) FIG. 10 depicts a schematic representation of a second example embodiment of a local coil 1 and a local coil interface 3. This second embodiment differs from the first embodiment according to FIG. 3 in that the local coil transmit antenna arrangement 4′ is designed as an antenna array 4′ along the lines of the antenna array with directional antenna elements (e.g., the turnstile antennas or tripole antennas already illustrated), as depicted, for example, in FIG. 5 or FIG. 7. Using the antenna array 4′, an individual RF transmit signal having an orbital angular momentum may be generated, e.g., a RF transmit signal with I=1. A superposed or mixed RF transmit signal may also be generated that includes a plurality of RF transmit signals HF.sub.−2, HF.sub.−1, HF.sub.0, HF.sub.+1, HF.sub.+2 having an orbital angular momentum, so that an orbital angular momentum multiplexing may thus be achieved, as is also possible with the antenna arrangement 4 with the individual horn antennas 4a, 4b, . . . , 4e. The fact that the superposed RF transmit signal is transmitted here directly is symbolized in FIG. 10 by the bracket on the antenna arrangement 4′ and the frames emanating therefrom, which includes the individual RF transmit signals HF.sub.−2, HF.sub.−1, HF.sub.0, HF.sub.+1, HF.sub.+2. To do this, the orbital angular momentum encoding unit 5 is designed so that it calculates the field vectors E(θ) in each case for the individual antenna elements depending on the angular positions θ of the respective antenna element in order to generate in total a RF transmit signal with the orbital angular momentum I via the parallel transmission of the fields of the individual antenna elements at the relevant time. Equation (3) may again be used to calculate the electrical field vectors E(θ) required for the transmission of an electrical (e.g., complex) field vector E.sub.1.

(46) Otherwise, the arrangement according to FIG. 10 corresponds in terms of its structure and function to the arrangement depicted in FIG. 3. The use of horn antennas has proven to be particularly advantageous if a carrier frequency above 10 GHz is used, and an antenna array may be used below 10 GHz. The use of an antenna array furthermore has the advantage that it is well suited for both transmitting and receiving the RF transmit signals having an orbital angular momentum.

(47) According to the example above, measurement signals f.sub.MRI, for example, were transmitted from a local coil 1 to the local coil interface 3 on the control device 12 of the MR system 10. The local coil interface 3 may also transmit a RF transmit signal, (e.g., a control signal), to the local coil transmit antenna arrangement 4′. The local coil transmit antenna arrangement 4′ receives this signal and via the signal, controls, for example, the particular antenna conductor loops 7a, 7b, . . . , 7n of the MR antenna element arrangement 7 that are to be activated.

(48) It is again noted that the methods and transmit devices described in detail above are merely example embodiments that may be modified by the person skilled in the art in the widest variety of ways without deviating from the scope of the invention. For the sake of completeness, it is also noted that the use of the indefinite article “a” or “an” does not exclude the possibility that the features concerned may also be present in multiple form. Similarly, the term “unit” does not exclude the possibility that said unit may also include a plurality of components that may, where appropriate, also be spatially distributed.

(49) It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

(50) While the present invention has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.