COIL ARRANGEMENT, MR SYSTEM, IN PARTICULAR MRI AND/OR MRS SYSTEM, WITH SUCH A COIL ARRANGEMENT AND USE OF SUCH A COIL ARRANGEMENT

Abstract

A coil assembly for use as a transmission and/or receiving coil in an MR system comprises a dipole antenna assembly with multiple dipole antennas. Connection elements are converted from an electrically conductive state to an electrically non-conductive state. In the electrically conductive state, the dipole antennas form a cylindrical volume coil and/or a conductor loop assembly, in particular a flat conductor loop assembly. The connection elements comprise blocking circuits which automatically block when a high-frequency alternating voltage with a frequency corresponding to the blocking frequency of the connection element blocking circuits is applied to the coil assembly.

Claims

1. Coil arrangement (1) for use as a transmitter and/or reception coil in an MR system, in particular an MRI and/or MRS system, which coil arrangement (1) comprises a dipole antenna arrangement (2) with a plurality of dipole antennas (2a-d) connected to one another via connecting elements (3a-h), the connecting elements (3a-h) being designed to be transferred from an electrically connecting state to an electrically disconnecting state, and vice versa, and the arrangement being made in such a manner that the dipole antennas (2a-d) in the electrically connecting state of the connecting elements (3a-h) form at least a part of a preferably cylindrical volume coil and/or a conductor loop arrangement, in particular a flat conductor loop arrangement, of the coil arrangement (1) comprising at least one conductor loop (20a-c), wherein the connecting elements (3a-h) comprise connecting element blocking circuits (4a-h), which automatically block when a high-frequency AC voltage having a frequency corresponding to the blocking frequency of the connecting element blocking circuits (4a-h) is applied to the coil arrangement (1).

2. Coil arrangement (1) according to claim 1, wherein the coil arrangement (1) is designed in such a way that the dipole antennas (2a-d) can radiate and/or receive a high-frequency electromagnetic alternating field with a first frequency, in particular corresponding to the blocking frequency, when the connecting elements (3a-h) are in the electrically disconnecting state, and in that the volume coil resulting in the electrically connecting state of the connecting elements (3ah) and/or each conductor loop (20a-c) of the conductor loop arrangement resulting in the electrically connecting state of the connecting elements (3a-h) can radiate and/or receive a high-frequency, electromagnetic alternating field with a second frequency different from the first.

3. Coil arrangement (1) according to claim 2, wherein the first frequency is a 1H-core resonant frequency and the second frequency is an X-core resonant frequency, in particular a 31P-core or 23Na-core resonant frequency.

4. Coil arrangement (1) according to claim 1, wherein the dipole antennas (2a-d) each comprise a rod-shaped base element (8a-d), at the axially opposite ends of which a conductor path segment (9a-h), in particular in the form of a ring segment, adjoins respectively, the axial ends of the rod-shaped base element (8a-d) adjoining the respective conductor path segment (9a-h) in particular centrally, and the conductor path segments (9a-h) of the dipole antennas (2a-d) preferably being of the same size, in particular having the same arc length.

5. Coil arrangement (1) according to claim 4, wherein the rod-shaped base elements (8a-d) of the dipole antennas (2a-d) are arranged at least substantially parallel to one another and/or the rod-shaped base elements (8a-d) of the dipole antennas (2a-d) are arranged uniformly spaced apart from one another in the circumferential direction of the volume coil or in the longitudinal direction of the conductor loop arrangement and/or the length of the rod-shaped base elements (8ad) of the dipole antennas (2a-d), the height of the volume coil or the width of the conductor loop arrangement is in the range from 25 to 30 cm, in particular is 25 cm or 28 cm.

6. Coil arrangement (1) according to claim 4, wherein the conductor path segments (9a-h) of the dipole antennas (2a-d) are connected to one another via the connecting elements (3a-h) to form two conductor paths (9), in particular two annularly closed conductor paths (9), and in particular the number of connecting elements (3a-h) per conductor path (9) is less by one than the number of dipole antennas (2a-d) or corresponds to the number of dipole antennas (2a-d), and/or the diameter of the annularly closed conductor paths (9) or of the volume coil is in the range from 25 to 30 cm, in particular is 26 cm.

7. Coil arrangement (1) according to claim 1, wherein at least one of the connecting element blocking circuits (4a-h) comprises a connecting element coil (5a-h) and a connecting element capacitor (6a-h), which are connected in parallel, wherein the connecting element coil (5a-h) preferably has an inductance in the range from 38 to 41 nH, particularly preferably in the range from 39 to 40 nH, in particular of 39 nH or 40 nH, and/or the connecting element capacitor (6a-h) preferably has a capacitance in the range from 6 to 8 pF, in particular of 6.8 pF.

8. Coil arrangement (1) according to claim 7, wherein at least one connecting element (3a-h) comprises a second connecting element capacitor (7a-h) which is connected in series with the connecting element blocking circuit (4a-h), the second connecting element capacitor (7a-h) preferably having a capacitance in the range from 5 to 50 pF, in particular preferably in the range from 8.2 to 40 pF, in particular of 8.2 pF or 40 pF.

9. Coil arrangement (1) according to claim 2, wherein the second connecting element capacitor (7a-h) is designed, in particular has a suitable capacitance, to tune, in particular fine-tune, the coil arrangement (1) to the second frequency.

10. Coil arrangement (1) according to claim 4, wherein the rod-shaped base elements (8a-d) of the dipole antennas (2a-d) are each preferably separated centrally to form two poles of the respective dipole antenna (2a-d).

11. Coil arrangement (1) according to claim 10, wherein the rod-shaped base elements (8a-d) of the dipole antennas (2a-d) are each provided with a junction device (11a-d) for connection to an AC voltage supply and/or scanning device, which comprises electrical junction elements (12a-d) connected to the two poles of the dipole antenna (2a-d).

12. Coil arrangement (1) according to claim 3, wherein the coil arrangement (1) is designed in such a way that a feed and/or a tap of 1H-core signals and/or X-core signals can take place via the electrical junction elements (12a-d) of at least one junction device (11a-d), in particular of all junction devices (11a-d).

13. Coil arrangement (1) according to claim 1, wherein the coil arrangement (1) is designed in such a way that it can be operated in a 4-channel and/or 2-channel quadrature mode.

14. Coil arrangement (1) according to claim 12, wherein the coil arrangement (1) is designed in such a way that a feed and/or a tap of X-core signals can take place via the electrical junction elements (12a-d) of a pair of two adjacent, in particular adjacent in the circumferential direction of the volume coil, junction devices (11a-d) of, in particular, a total of four junction devices (11a-d).

15. Coil arrangement (1) according to claim 14, wherein the coil arrangement (1) is designed in such a way that the volume coil and/or conductor loop arrangement resulting in the electrically connecting state of the connecting elements (3a-h) can be fed via the two adjacent junction devices (11a-d) in quadrature mode with a high-frequency AC voltage, whose frequency differs from the 1H-core resonant frequency and preferably corresponds to an X-core resonant frequency in order to cause the volume coil or each conductor loop (20a-c) of the conductor loop arrangement to radiate a high-frequency alternating electromagnetic field having an X-core resonant frequency.

16. Coil arrangement (1) according to claim 10, wherein a dipole capacitor (13a-d) is provided in the center of a dipole antenna (2a-d) between the two poles, which dipole capacitor (13a-d) is in particular part of the junction device (11a-d), the dipole capacitor (13a-d) preferably having a capacitance of 0 pF.

17. Coil arrangement (1) according to claim 2, wherein the dipole capacitor (13a-d) is designed, in particular has a suitable capacitance, to tune, in particular fine-tune, the coil arrangement (1) to the first frequency.

18. Coil arrangement (1) according to claim 10, wherein a coupling element (14a-d) is provided, in particular connected in parallel with the dipole capacitor (13a-d), which is electrically connected to and bridges the two poles of the dipole antenna (2a-d), and the coupling element (14a-d) is designed to be transferred from an electrically connecting state to an electrically disconnecting state, and vice versa, the coupling element (14a-d) preferably being part of the junction device (11a-d).

19. Coil arrangement (1) according to claim 18, wherein the coupling element (14a-d) comprises a coupling element blocking circuit (15a-d), which automatically blocks when a high-frequency AC voltage with a frequency corresponding to the blocking frequency of the coupling element blocking circuit (15a-d) is applied to the coil arrangement (1), in particular to the electrical junction elements (12a-d) of the junction device (11a-d) of the corresponding dipole antenna (2a-d), wherein the blocking frequency of the coupling element blocking circuit (15a-d) corresponds in particular to the first frequency.

20. Coil arrangement (1) according to claim 19, wherein at least one of the coupling element blocking circuits (15a-d) comprises a coupling element coil (16a-d) and a coupling element capacitor (17a-d), which are connected in parallel, wherein the coupling element coil (16a-d) preferably has an inductance in the range from 38 to 41 nH, particularly preferably in the range from 39 to 40 nH, in particular of 39 nH or 40 nH, and/or the coupling element capacitor (17a-d) preferably has a capacitance in the range from 6 to 8 pF, in particular of 6.8 pF.

21. Coil arrangement (1) according to claim 20, wherein at least one coupling element (14a-d) comprises a second coupling element capacitor (18a-d) which is connected in series with the coupling element blocking circuit (15a-d) of the coupling element (14a-d), the second coupling element capacitor (18a-d) preferably having a capacitance in the range from 20 to 110 pF, in particular preferably in the range from 33 to 100 pF, in particular of 33 pF, 95 pF or 100 pF.

22. Coil arrangement (1) according to claim 2, wherein the second coupling element capacitor (18a-d) is designed, in particular has a suitable capacitance, to tune, in particular fine-tune, the coil arrangement (1) to the second frequency and/or to trigger a short circuit at the second frequency.

23. Coil arrangement (1) according to claim 21, wherein the dipole antenna arrangement (2) comprises four dipole antennas (2a-d), wherein the second coupling element capacitors (18a-d) of the coupling elements (14a-d) of the junction devices (11a-d) of two adjacent dipole antennas (2a-d), in particular of two dipole antennas (2a-d) adjacent in the circumferential direction of the volume coil, each have an equal capacitance of in particular 33 pF, and the second coupling element capacitors (17a-d) of the two remaining dipole antennas (2a-d) likewise have an equal capacitance of in particular 95 pF or 100 pF.

24. Coil arrangement (1) according to claim 4, wherein the axial ends of the rod-shaped base element (8a-d) of at least one dipole antenna (2a-d) each connect to the respective conductor path segment (9a-h) of the dipole antenna (2a-d) with the interposition of a junction point capacitor (10a-h), the junction point capacitor (10a-h) preferably having a capacitance in the range from 10 to 40 pF, particularly preferably in the range from 18 to 32 pF, in particular of 18 pF or 32 pF.

25. Coil arrangement (1) according to claim 2, wherein the junction point capacitor (10a-h) is designed, in particular has a suitable capacitance, to tune, in particular fine-tune, the coil arrangement (1) to the second frequency.

26. Coil arrangement (1) according to claim 3, wherein the coil arrangement (1) is tuned, in particular by means of the second connecting element capacitors (7a-h) and/or the second coupling element capacitors (18a-d) and/or the dipole capacitors (13a-d) and/or the junction point capacitors (10a-h) such, that each dipole antenna (2a-d) in the electrically disconnecting state of the connecting elements (3a-h) and in particular of the coupling elements (14a-d) can radiate and/or receive a high-frequency electromagnetic alternating field with a 1H-core resonant frequency, and the volume coil resulting in the electrically connecting state of the connecting elements (3a-h) and in particular of the coupling elements (14a-d) and/or each conductor loop (20a-c) of the conductor loop arrangement resulting in the electrically connecting state of the connecting elements (3ah) and in particular of the coupling elements (14a-d) can radiate and/or receive a high-frequency electromagnetic alternating field with an X-core resonant frequency.

27. Coil arrangement (1) according to claim 1, wherein each conductor loop (20a-c) of the conductor loop arrangement resulting in the electrically connecting state of the connecting elements (3a-h) and in particular of the coupling elements (14a-d) is formed at least by parts of two adjacent dipole antennas (2a-d).

28. Coil arrangement (1) according to claim 27, wherein at least a part of a dipole antenna (2a-d), in particular, if present, at least its rod-shaped base element (8a-d), forms part of two adjacent conductor loops (20a-c) and preferably the capacitance values of the connecting element capacitors (6a-h) and/or of the second connecting element capacitors (7a-h) and/or of the coupling element capacitors (17a-d) and/or of the second coupling element capacitors (18a-d) and/or of the dipole capacitors (13a-d) and/or of the junction point capacitors (10a-h) and/or of further capacitors within the conductor loop arrangement are selected in such a manner that adjacent conductor loops (20a-c) are decoupled.

29. MR system, in particular MM, preferably high-field/ultrahigh-field MM, and/or MRS, high-field/ultra-high-field MRS system, having a coil arrangement (1) according to claim 1.

30. Use of a coil arrangement (1) according to claim 1 as a high-frequency transmitter and/or reception coil in magnetic resonance imaging, in particular high-field/ultra-high-field magnetic resonance imaging and/or magnetic resonance spectroscopy, in particular high-field/ultra-high-field magnetic resonance spectroscopy.

Description

[0041] Further features and advantages of the present invention will become apparent from the following description of an embodiment of a coil arrangement according to the present invention, with reference to the accompanying drawing. Therein is:

[0042] FIG. 1 a schematic perspective view of a coil arrangement according to an embodiment of the present invention;

[0043] FIG. 2 a kind of exploded view of the coil arrangement of FIG. 1, in which the dipole antennas are shown separated;

[0044] FIG. 3 a circuit diagram of the coil arrangement of FIG. 1;

[0045] FIG. 4 a frequency spectrum of the input reflection coefficient illustrating the two resonant frequencies to which the coil arrangement according to the invention is tuned;

[0046] FIG. 5 a graphical representation of the safe transmission efficiency of the coil arrangement according to the invention compared with the safe transmission efficiency of a simply tuned 8-channel loop arrangement at the .sup.1H core resonant frequency of 300 MHz; and

[0047] FIG. 6 a graphical representation of the safe transmission efficiency of the coil arrangement of the invention compared with the safe transmission efficiency of a single-tuned birdcage coil at the .sup.31P core resonant frequency of 120 MHz.

[0048] FIG. 1 shows a schematic view of a coil arrangement 1 according to an embodiment of the present invention. The coil arrangement 1 comprises a dipole antenna arrangement 2 with four dipole antennas 2a-d, which are interconnected by eight connecting elements 3a-h. FIG. 2 shows a kind of exploded view of the coil arrangement 1, in which the dipole antennas 2a-d are shown separately. The connecting elements 3a-h are designed to be transferred from an electrically connecting to an electrically disconnecting state, and vice versa. The arrangement is recognizably made such that the dipole antennas 2a-d form a cylindrical volume coil in the electrically connecting state of the connecting elements 3a-h.

[0049] The connecting elements 3a-h each comprise a connecting element blocking circuit 4a-h which automatically blocks when a high-frequency AC voltage having a frequency corresponding to the blocking frequency of the connecting element blocking circuits 4a-h is applied to and/or induced in the coil arrangement 1. This can be seen in the circuit diagram of the coil arrangement 1 shown in FIG. 3. The connecting element blocking circuits 4a-h each comprise a connecting element coil 5ah and a connecting element capacitor 6a-h, which are connected in parallel. In addition, each connecting element 3a-h includes a second connecting element capacitor 7a-h connected in series with the connecting element blocking circuit 4a-h.

[0050] The dipole antennas 2a-d each have a rod-shaped base element 8a-d, at the axially opposite ends of which a ring-segment-like conductor path segment 9a-h adjoins, respectively. The axial ends of the rod-shaped base element 8a-d adjoin to the center of the respective conductor path segment 9a-h with the interposition of a junction point capacitor 10a-h. The rod-shaped base elements 8a-d of the dipole antennas 2a-d are arranged parallel to each other and evenly spaced from each other in the circumferential direction of the volume coil. The conductor loop segments 9a-h are of the same size, or more precisely, have the same arc length. Moreover, the ring-segment-like conductor path segments 9a-h are connected to each other via the connecting elements 3a-h to form two conductor paths 9 closed in a ring shape. Thus, four connecting elements 3a-h are arranged in each conductor path 9.

[0051] The rod-shaped base elements 8a-d of the dipole antennas 2a-d are each separated centrally to form two poles of the respective dipole antenna 2a-d. In addition, the rod-shaped base elements 8a-d are each provided in their central section with a junction device 11a-d for connection to an AC voltage supply and receiving device not shown. The junction device 11a-d comprises electrical junction elements 12a-d connected to the two poles of the dipole antenna 2a-d. Furthermore, the junction device 11a-d comprises a dipole capacitor 13a-d provided at the center of the dipole antenna 2a-d between the two poles. Furthermore, the junction device 11a-d comprises a coupling element 14a-d connected in parallel to the dipole capacitor 13a-d, which is electrically connected to the two poles of the dipole antenna 2a-d and bridges them. The total of four coupling elements 14a-d are each designed to be transferred from an electrically connecting state to an electrically disconnecting state, and vice versa. For this purpose, the coupling elements 14a-d each include a coupling element blocking circuit 15a-d having a coupling element coil 16a-d and a coupling element capacitor 17a-d connected in parallel. The coupling element blocking circuits 15a-d automatically block when a high-frequency AC voltage having a frequency corresponding to the blocking frequency of the coupling element blocking circuits 15a-d is applied to and/or induced in the coil arrangement 1. Further, the coupling elements 14a-d each include a second coupling element capacitor 18a-d connected in series with the coupling element blocking circuit 15a-d.

[0052] The cylindrical volume coil resulting in the electrically connecting state of the coupling elements 3a-h is an Alderman-Grant type volume coil with two end rings, here the ring-shaped closed conductor paths 9, and four webs, here the rod-shaped base elements 8a-d of the dipole antennas 2a-d. The coil arrangement 1 is 28 cm long in the present case and has a diameter of 26 cm in the present case. FIGS. 1 and 2 show a spherical phantom 19 within the coil arrangement 1. This is representative of a body part to be examined, in particular a human or animal head to be examined.

[0053] In the following table, the electrical components of the four junction devices 11a-d are briefly described again and their values are listed.

TABLE-US-00003 Second Coupling element Coupling element Dipole- coupling element coil 16a-d capacitor 17a-d capacitor 13a-d capacitor 18a-d Junction Value Value Value Value device Description (nH) Description (pF) Description (pF) Description (pF) 11a Coil 40 Capacitor 6.8 Capacitor 0 Capacitor 18a 33 16a for 17a for 13a for for tuning that .sup.1H coupling .sup.1H coupling dipole triggers short- element element tuning circuit at X- blocking blocking core frequency circuit 15a circuit 15a 11b Coil 40 Capacitor 6.8 Capacitor 0 Capacitor 18b 33 16b for 17b for 13b for for tuning that .sup.1H coupling .sup.1H coupling dipole triggers short- element element tuning circuit at X- blocking blocking core frequency circuit 15b circuit 15b 11c Coil 40 Capacitor 6.8 Capacitor 0 Capacitor 18c 100 16c for 17c for 13c for for X-core .sup.1H coupling .sup.1H coupling dipole tuning element element tuning blocking blocking circuit 15c circuit 15c 11d Coil 40 Capacitor 6.8 Capacitor 0 Capacitor 18d 100 16d for 17d for 13d for for X-core .sup.1H coupling .sup.1H coupling dipole tuning element element tuning blocking blocking circuit 15d circuit 15d

[0054] In the following table the electrical components of the eight connecting elements 3a-h are again briefly described and their values are listed.

TABLE-US-00004 Connecting element Connecting element Second connecting coil 5a-h capacitor 6a-h element capacitor 7a-h Connecting Value Value Value elements Description (nH) Description (pF) Description (pF) 3a Coil 5a for 40 Capacitor 6a for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4a circuit 4a 3b Coil 5b for 40 Capacitor 6b for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4b circuit 4b 3c Coil 5c for 40 Capacitor 6c for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4c circuit 4c 3d Coil 5d for 40 Capacitor 6d for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4d circuit 4d 3e Coil 5e for 40 Capacitor 6e for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4e circuit 4e 3f Coil 5f for 40 Capacitor 6f for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4f circuit 4f 3g Coil 5g for 40 Capacitor 6g for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4g circuit 4g 3h Coil 5h for 40 Capacitor 6h for 6.8 Tuning for 8.2 .sup.1H-Connecting .sup.1H-Connecting X-cores element element blocking blocking circuit 4h circuit 4h

[0055] FIG. 4 shows a frequency spectrum of the input reflection coefficient of the coil arrangement 1 according to the invention, which is tuned by the capacitance and inductance values listed in the above tables. The junction point capacitors 10ah and, in particular, also the connecting element coils 5a-h and the coupling element coils 16a-d also contribute to the tuning. In the present case, the capacitance of the junction point capacitors 10a-h is 18 pF each. It can be seen that the coil system is doubly tuned at B.sub.0=7 T, namely to the .sup.1H-core resonant frequency of 300 MHz and to an X-core resonant frequency, namely the .sup.31P-core resonant frequency of 120 MHz.

[0056] When the coil arrangement 1 according to the invention, which is doubly tuned in the manner described above, is used in an MRI system with B.sub.0=7 T, the dipole antennas 2a-d are each supplied with a high-frequency alternating voltage via the electrical junction elements 12a-d of their junction devices 11a-d in a first operating mode of the MRI system. Here, the phase relationship between the feed signals applied to the four junction devices 11a-d may be, for example, 0-90-180 270 degrees. The frequency of the high-frequency AC voltage corresponds to a common blocking frequency of the connecting element blocking circuits 4a-h and the coupling element blocking circuits 15a-d. Here, the common blocking frequency corresponds to the .sup.1H core resonance frequency. Thereupon, the connecting element blocking circuits 4a-h and the coupling element blocking circuits 15a-d automatically block, thereby transferring the connecting elements 3a-h and the coupling elements 14a-d to their electrically disconnecting state. In the electrically disconnecting state, each dipole antenna 2a-d radiates a high-frequency alternating electromagnetic field with the .sup.1H-core resonant frequency of 300 MHz. Later, a high-frequency alternating electric voltage induced due to excited .sup.1H nuclei in the coil arrangement 1 is tapped at the junction devices 11a-d.

[0057] In a second operating mode of the MRI system, the coil arrangement 1 is supplied with a high-frequency AC voltage via the electrical junction elements 12c and 12d of the two junction devices 11c and 11d adjacent to each other in the circumferential direction of the volume coil in a quadrature mode, wherein the junction devices 11c and 11d are driven with signals phase-shifted by 90 degrees. Here, the frequency of the high-frequency AC voltage is different from the common blocking frequency. Thus, the connecting elements 3a-h and the coupling elements 14a-d are in their electrically connecting state. Thereupon, the volume coil resulting in the electrically connecting state radiates a high-frequency alternating electromagnetic field with the .sup.31P core resonance frequency of 120 MHz. Later, an AC electric voltage induced due to excited .sup.31P cores in the coil arrangement 1 is tapped at the junction devices 11c and 11d.

[0058] The coil arrangement 1 according to the invention described above was used as a high-frequency coil in an MRI system.

[0059] The electromagnetic field distribution in the head of a subject was first simulated in the case where the .sup.1H nuclei were excited and subsequently detected. With B.sub.0=7 T, the .sup.1H-nucleus resonance frequency and .sup.1H-nucleus Lamor frequency, respectively, were 300 MHz. The same MRI study was performed again with a comparison arrangement using an 8-channel coil arrangement tuned only to the .sup.1H-nucleus resonant frequency as the high-frequency coil. Specifically, in the comparison arrangement, eight conductor loops were placed around the subject's head. The simply tuned 8-channel arrangement provided a quasi-optimal comparison measurement for a .sup.1H examination. The resulting MRI sectional images using both the coil arrangement 1 according to the invention and the comparison arrangement are shown in FIG. 5 in matrix form. In the left column are the sectional images for the comparison arrangement and in the right column are the sectional images for the coil arrangement 1 according to the invention. The top row shows the sectional views in the sagittal plane and the bottom row shows the sectional views in the frontal or coronal plane. Specifically, a comparison of the safe transmission efficiency of both MRI examinations is shown. Here, the safe transmission efficiency is defined as the amplitude of the circularly polarized radiofrequency excitation field divided by the maximum specific absorption rate B.sub.1.sup.+/sqrt(SAR). The comparison shows that the safe transmission efficiency using the coil arrangement 1 according to the invention with a mean value of 0.48 μT/√{square root over (w)} over the brain of the test person and the safe transmission efficiency using the comparison arrangement with a mean value of 0.51 μT/√{square root over (w)}, which can be regarded as quasi-optimal, are similar, although the coil arrangement 1 according to the invention is a double-tuned or double-resonant coil arrangement. This indicates only a small loss.

[0060] In addition, a simulation of the field distribution in the head of a subject was carried out in which the .sup.31P nuclei were excited and subsequently detected. With B.sub.0=7 T, the .sup.31P-nucleus resonance frequency and .sup.31P-nucleus Lamor frequency, respectively, were 120 MHz. The same MRI study was performed again with a comparison setup using a birdcage coil as the high-frequency coil, which was tuned only to the .sup.31P-core resonant frequency. The single-tuned birdcage coil provided a quasi-optimal comparison measurement for a .sup.31P examination. The resulting MRI sectional images using both the coil arrangement 1 according to the invention and the comparison arrangement are shown in FIG. 6 in matrix form. In the right column are the sectional images for the coil arrangement 1 according to the invention and in the left column are the sectional images for the comparison arrangement. The top row shows the sectional views in the sagittal plane and the bottom row shows the sectional views in the frontal or coronal plane. The presented comparison of the safe transmission efficiency of both MRI examinations shows that the safe transmission efficiency when using the coil arrangement 1 according to the invention with a mean value of 1.09 μT/√{square root over (w)} over the brain of the subject and the safe transmission efficiency when using the comparison arrangement with a mean value of 1.00 μT/√{square root over (w)}, which can be regarded as quasi-optimal, are similar, although the coil arrangement 1 according to the invention is a double-tuned or double-resonant coil arrangement. This indicates only a small loss.

[0061] In the previously described embodiment of a coil arrangement 1 according to the invention, the electrically connecting state of the connecting elements 3a-h and the coupling elements 14a-d results in a volume coil. In an alternative embodiment, instead of a volume coil, a flat conductor loop arrangement may result, which may, for example, have a flat structure similar to the embodiment of FIG. 3, but without the two connecting elements 3d and 3h. In this case, the conductor loop arrangement comprises three conductor loops 20a-c, each formed by at least parts of two adjacent dipole antennas 2a-d. In the present example, a portion of dipole antenna 2b forms both a portion of conductor loop 20a and a portion of conductor loop 20b. Also, a portion of the dipole antenna 2c forms both a portion of the conductor loop 20b and a portion of the conductor loop 20c. More specifically, the conductor loop 20a is formed by the rod-shaped base element 8a, the two junction point capacitors 10a and 10e, and one half of each of the conductor path segments 9a and 9e of the dipole antenna 2a, and the rod-shaped base element 8b, the two junction point capacitors 10b and 10f, and one half of each of the conductor loop segments 9b and 9f of the dipole antenna 2b. The conductor loop 20b is formed by the rod-shaped base element 8b, the two junction point capacitors 10b and 10f, and one half of each of the conductor path segments 9b and 9f of the dipole antenna 2b, and the rod-shaped base element 8c, the two junction point capacitors 10c and 10g, and one half of each of the conductor path segments 9c and 9g of the dipole antenna 2c. Lastly, the conductor loop 20c is formed by the rod-shaped base element 8c, the two junction point capacitors 10c and 10g, and one half each of the conductor path segments 9c and 9g of the dipole antenna 2c, and the rod-shaped base element 8d, the two junction point capacitors 10d and 10h, and one half each of the conductor path segments 9d and 9h of the dipole antenna 2d. Thus, the conductor loops 20a and 20b “share” the rod-shaped base element 8b and the two junction point capacitors 10b and 10f of the dipole antenna 2b. The conductor loops 20b and 20c “share” the rod-shaped base element 8c and the two junction point capacitors 10c and 10g of the dipole antenna 2c. The capacitance values of all capacitors within the conductor loop arrangement are selected such that adjacent conductor loops 20a-c are preferably capacitively decoupled.

[0062] In the case of a flat conductor loop arrangement, the two conductor loops 2 are preferably straight and not ring-shaped. A feed and/or a tap of .sup.1H-core and/or X-core signals can take place via the free ends 21a-d of the conductor loops as an alternative to the junction devices 11a-d in the case of a flat conductor loop arrangement. In the case of a flat conductor loop arrangement, the radiation and/or reception of the high-frequency, electromagnetic alternating field with the X-core resonant frequency takes place via the individual conductor loops 20a-c. The radiation and/or the reception of the high-frequency, electromagnetic alternating field with the .sup.1H-core resonant frequency takes place via the individual dipole antennas 2a-d.

LIST OF REFERENCE SIGNS

[0063] 1 coil arrangement [0064] 2 dipole antenna arrangement [0065] 2a-d dipole antennas [0066] 3a-h connecting elements [0067] 4a-h connecting element blocking circuit [0068] 5a-h connecting element coil [0069] 6a-h connecting element capacitor [0070] 7a-h second connecting element capacitor [0071] 8a-d rod-shaped base element [0072] 9 conductor path [0073] 9a-h conductor path segment [0074] 10a-h junction point capacitor [0075] 11a-d junction device [0076] 12a-d junction element [0077] 13a-d dipole capacitor [0078] 14a-d coupling element [0079] 15a-d coupling element blocking circuit [0080] 16a-d coupling element coil [0081] 17a-d coupling element capacitor [0082] 18a-d second coupling element capacitor [0083] 19 phantom [0084] 20a-c conductor loop [0085] 21 free end