MR coil arrangement with multiple dipole antennas and connecting elements with blocking circuits

Description

[0001] The present invention relates to a coil arrangement for use as a transmitting and / or receiving coil in an MRI system, in particular an MRI and / or MRS system, comprising a dipole antenna arrangement with several dipole antennas connected to one another via connecting elements, wherein the connecting elements are configured to be switched from an electrically connecting to an electrically disconnecting state, and vice versa, and the arrangement is such that, in the electrically connecting state of the connecting elements, the dipole antennas form at least a portion of a preferably cylindrical volume coil and / or a conductor loop arrangement of the coil arrangement comprising at least one conductor loop, in particular a flat conductor loop arrangement. Furthermore, the invention relates to an MRI system, in particular an MRI and / or MRS system, with such a coil arrangement. The invention also relates to the use of such a coil arrangement.

[0002] Magnetic resonance imaging, or MRI, has been used in medical diagnostics for many years. MRI is an imaging technique used to visualize the structure and function of tissues and organs in the form of cross-sectional images. MRI is based on the principles of nuclear magnetic resonance (NMR), particularly gradient NMR, and is therefore also known as nuclear magnetic resonance tomography. The term NMR is synonymous with magnetic resonance (MR). The abbreviation MRS stands for magnetic resonance spectroscopy. An MR system typically comprises a magnet, preferably superconducting, with a coil arrangement, for example, cylindrical, designed and / or configured to generate a static, preferably homogeneous, magnetic field B0, which is preferably oriented along the axis of the cylindrical coil arrangement.Within a central opening of the magnet is a high-frequency coil array surrounding a receiving chamber. During an MRI scan, the medium under investigation, in particular a person or body part, such as a person's head, is positioned within this chamber to physically interact with the high-frequency coil array. The high-frequency coil array can be configured for both transmitting and receiving, or as a dedicated transmitting or receiving coil array. The following description of the operating principles refers to individual nuclear spins. This represents the classical description of quantum mechanical processes. By exposing the medium under investigation to the magnetic field B₀, the nuclear spins of the atomic nuclei of the medium are aligned in the direction of the magnetic field B₀; that is, they undergo longitudinal magnetization in the direction of the magnetic field B₀.Using the high-frequency coil arrangement, a high-frequency excitation pulse is generated in the form of a time-limited, high-frequency alternating electromagnetic field. The medium under investigation is exposed to this field, causing specific atomic nuclei to be excited by the high-frequency alternating electromagnetic field. For this purpose, the high-frequency alternating electromagnetic field has a frequency that resonates with the Lamor frequency fL of the atomic nuclei to be excited. The Lamor frequency fL is given by the following formula: . f L = γB 0 / 2 π

[0003] Here, γ is the gyromagnetic constant, which is constant for a given type of nucleus. B0 is the static magnetic field.

[0004] Excitation of atomic nuclei means that the magnetization of the nuclear spins is deflected from the direction of the B₀ field, i.e., from the equilibrium position, meaning it is tilted away from the direction of the B₀ field. Thus, the longitudinal magnetization of the nuclear spins is at least partially converted into a transverse magnetization that precesses around the direction of the B₀ field. Here, the nuclear spins precess at their Lamor frequency. This precessing transverse magnetization ultimately induces a high-frequency alternating voltage in a combined high-frequency transmitting and receiving coil arrangement or a dedicated high-frequency receiving coil arrangement, the frequency of which corresponds, in particular, to the Lamor frequency of the excited atomic nuclei to be observed or detected. The amplitude of the induced alternating voltage indicates the strength of the transverse magnetization.Magnetic resonance imaging (MRI) is used to generate and display cross-sectional images of the spatial distribution of transverse magnetization and / or resonance spectra. This requires assigning the classical NMR signals to specific spatial regions of the medium under investigation, i.e., performing spatial encoding. In MRI, this is achieved using time-varying magnetic gradient fields generated by gradient coils positioned within the opening of the B0 field magnet.

[0005] In conventional MRI, imaging is based on the detection of <H nuclei, i.e., hydrogen nuclei. Clinical MRI imaging is typically performed with a B0 in the range of approximately 0.1 to 3.0 T. However, higher magnetic field strengths are increasingly being used, particularly in research. Ultra-high-field MRI (UHF MRI), which operates with a B0 ≥ 7 T, allows for the efficient detection of other atomic nuclei besides <H nuclei, known as X nuclei. Here, "X" represents any atomic nucleus with nuclear spin other than <H. Examples of X nuclei include, in particular, nuclei such as <P and <Na, which play an important role in physiological processes. X nuclei, due to their significantly lower concentration compared to 1< H nuclei and their physical properties, usually provide a much weaker signal than 1< H nuclei, whose signal is also referred to as the proton signal.However, with UHF-MRI, a comparatively high signal-to-noise ratio, a comparatively high phase contrast and a comparatively high spectral resolution can be achieved, especially for the X nuclei.

[0006] The aim is therefore to create a high-frequency coil array suitable for a so-called 1< H / X nucleus application, i.e., capable of exciting and / or detecting or observing various atomic nuclei. The coil array must thus be sensitive to both 1< H nuclei and at least one X nucleus. Specifically, the coil array must be able to emit or receive, on the one hand, a high-frequency alternating electromagnetic field resonant with the Lamor frequency fL of 1< H nuclei, and on the other hand, a high-frequency alternating electromagnetic field resonant with the Lamor frequency fL of a selected type of X nucleus. The coil array is then doubly tuned, namely to two resonant frequencies, and / or doubly resonant.

[0007] Different methods for tuning antennas or coil arrangements with antennas to specific frequencies have been known for a long time.

[0008] Thus, US2,229,865 reveals a two-band dipole antenna, or a double-resonant dipole antenna, whose electrical length can be varied by means of resonant circuits. The dipole antenna generates the double resonance by limiting standing waves between the resonant elements. In contrast, the entire length of the dipole antenna generates its natural standing wave current. The higher resonance therefore only uses a portion of the physical conductor structure. The required length of the dipole antenna for use in the detection of X nuclei is, for example, approximately 125 cm for 31< P nuclei at B 0 = 7 T and approximately 187 cm for 23< Na nuclei at B 0 = 7 T. The use of a monofrequency dipole or monopole antenna array for the detection of 1H nuclei is described by AJE Raaijmakers et al. in the paper "Design of a radiative surface coil array element at 7T: the single-side adapted dipole antenna", Magn. Reson. Med. Off. J. Soc. Magn. Reson. Med. Soc.Magn. Reson. Med., Vol. 66, No. 5, pp. 1488-1497, Nov. 2011, and by Hong Suk-Min, Park Joshua Haekyun, Woo Myung-Kyun, Kim Young-Bo, and Cho Zang-Hee in the article "New design concept of monopole antenna array for UHF 7T MRI", Magn. Reson. Med., Vol. 71, No. 5, pp. 1944-1952, July 2013. The required length of a dipole antenna is, for example, approximately 50 cm for 1< H nuclei at B 0 = 7 T or approximately 37 cm for 1< H nuclei at B 0 = 9.4 T. This length is close to a dimension suitable for head examinations and offers a relatively large penetration depth and more symmetrical MRI-relevant field component patterns compared to arrangements of conductor loops. However, due to the relatively large length required for the detection of X nuclei, the previously known two-band dipole antennas are not suitable for use in MRI examinations of the head, for example.

[0009] Furthermore, coil arrangements are known that include or consist of a so-called volume coil. An example of a volume coil is the Alderman-Grant coil. This was described by D.W. Alderman and D.M. Grant in the article "An efficient decoupler coil design which reduces heating in conductive samples in superconducting spectrometers," J. Magn. Reson. 1969, Vol. 36, No. 3, pp. 447-451, Dec. 1979. It is capable of generating a relatively homogeneous magnetic field and is well-suited for high field strengths. The Alderman-Grant coil consists of two or four rods, each connected at its end by an end ring. Its operating principle is based on the use of symmetrical striplines and is derived from the concept of the "Slotted Tube Resonator" (Schneider and Dullenkopf, 1977). Another example of a volume coil is the so-called birdcage coil, in particular a four- to eight-foot birdcage coil, which may also include rings and rods.

[0010] For example, JR Fitzsimmons, BL Beck, and H. Ralph Brooker describe a concentric arrangement of two physically separate birdcage coils in their article "Double resonant quadrature birdcage," Magn. Reson. Med., Vol. 30, No. 1, pp. 107-114, Spring 1993, and AM Hudson, W. Köckenberger, and RW Bowtell describe a similar arrangement in their article "Dual resonant birdcage coils for 1H detected 13C microscopic imaging at 11.7T," Magma NYN, Vol. 10, No. 2, pp. 61-68, June 2000. In these arrangements, one birdcage coil is tuned to a < 1H core resonance frequency, and the other is tuned to an < X core resonance frequency. However, these coil arrangements have the disadvantage that they exhibit a significantly reduced signal-to-noise ratio for the upper resonant frequency compared to their monofrequency implementations.

[0011] Double-resonant or double-tuned birdcage coils are also known. These are described by Y. Duan, BS Peterson, F. Liu, TR Brown, TS Ibrahim, and A. Kangarlu in the article "Computational and experimental optimization of a double-tuned 1H / 31P four-ring birdcage head coil for MRS at 3T", J. Magn. Reson. Imaging, Vol. 29, No. 1, pp. 13-22, Spring 2009, and by J. Murphyboesch, R. Srinivasan, L. Carvajal, and TR Brown in the article "Two Configurations of the Four-Ring Birdcage Coil for 1H Imaging and 1H-Decoupled 31P Spectroscopy of the Human Head", J. Magn. Reson. In B, Vol. 103, No. 2, pp. 103-114, Spring 1994, a double-resonant birdcage coil, more precisely a 4-ring birdcage coil formed by doubling the end rings, is described. Another double-resonant birdcage coil is described by GB Matson, P. Vermathen, and TC Hill in the article "A practical double-tuned 1H / 31P quadrature birdcage headcoil optimized for 31P operation", Magn.Reson. Med., Vol. 42, No. 1, pp. 173-182, Spring 1999. In the latter birdcage coil, 1< H-blocking circles are applied alternately, i.e., on every second rod.

[0012] When the aforementioned double-resonant birdcage coils are used in MRI, particularly RF-MRI, the capacitance values ​​required for tuning, especially fine-tuning, to the two resonant frequencies are very small. This is partly due to the high inductance of the birdcage coil. For example, an 8-step high-pass birdcage coil with a diameter of 26 cm and a length of 20 cm requires a capacitance of 2 pF. A 16-step low-pass birdcage coil with the same diameter and length requires 0.36 pF of capacitance. At 300 MHz, the capacitance values ​​required for tuning are approximately 0.5 pF. The aforementioned capacitance values ​​are within the range of typical stray capacitances and / or parasitic capacitances. A calculation method for the capacitances in a birdcage coil is described by C.-L. Chin, C.M. Collins, S. Li, B.J. Dardzinski, and MB.Smith described this in the article "BirdcageBuilder: Design of Specified-Geometry Birdcage Coils with Desired Current Pattern and Resonant Frequency", Concepts Magn. Reson., Vol. 15, No. 2, pp. 156-163, June 2002. Therefore, tuning the previously known double-resonant birdcage coils is extremely difficult.

[0013] Furthermore, US patent 5,462,055 discloses a coil arrangement for use in a combined MRI / hyperthermia system. The coil arrangement comprises a dipole antenna array with multiple dipole antennas interconnected by connecting elements. These connecting elements are designed to switch between an electrically connecting and an electrically disconnecting state, and vice versa. Specifically, the connecting elements are implemented as transistor circuits, each comprising a transistor that is switched by applying appropriate control signals provided by a controller. In the electrically connecting state, the dipole antennas form part of a cylindrical volume coil within the coil arrangement. By switching the connecting elements between the two states, the coil arrangement can provide either MRI excitation energy or hyperthermia energy.More precisely, the volume coil is used for proton imaging, while the dipole antennas are used for hyperthermia excitation. In the coil arrangement of US 5,462,055, switching the connecting elements between the electrically connecting and electrically disconnecting states is relatively complex, especially because additional control equipment is required.

[0014] Document US 2010 / 0253333 A1 discloses a dual-tuned volume coil adapted to provide an end-ring mode.

[0015] Document US 5,202,635 discloses a radio frequency volume resonator for magnetic resonance imaging.

[0016] Against this background, the present invention is based on the objective of providing a coil arrangement of the type mentioned at the outset, which is designed in such a way that it can be adjusted and operated with less effort compared to the previously known coil arrangements.

[0017] This problem is solved according to the invention by a coil system according to claim 1. The connecting elements comprise connecting element blocking circuits that automatically block when a high-frequency alternating voltage with a frequency corresponding to the blocking frequency of the connecting element blocking circuits is applied to the coil arrangement. The connecting element blocking circuits remain blocked as long as the high-frequency alternating voltage of the blocking frequency is applied to the coil arrangement. The high-frequency alternating voltage can also be a high-frequency alternating voltage induced in the coil arrangement.

[0018] The invention is based on the concept of providing the connecting elements of a coil assembly with connecting element blocking circuits that automatically block when a high-frequency alternating voltage with a frequency corresponding to the blocking frequency of the connecting element blocking circuits is applied to the coil assembly, but otherwise do not block, or at least not completely. The blocking frequency is the frequency that cannot pass through the respective connecting element blocking circuit. When the connecting element blocking circuits are blocked, the connecting elements are in their electrically isolated state, meaning that the dipole antennas are electrically isolated from each other.The volume coil and / or conductor loop arrangement, when the connecting elements are electrically connected, is—when the resonant circuits are blocked—effectively separated into individual dipole antennas, which can operate independently of one another. A coil comprises at least one conductor loop; in the simplest case, it is a conductor loop. The conductor loop arrangement, especially if it is flat, can be used, for example, in the examination of a spine. A coil arrangement with a flat conductor loop can be called a surface coil arrangement. The volume coil can be, in particular, an Alderman-Grant or Birdcage coil.Because the coil arrangement according to the invention uses connecting element blocking circuits to automatically connect or disconnect the dipole antennas electrically in a frequency-dependent manner, the coil arrangement according to the invention can be tuned and operated with less effort compared to previously known coil arrangements and does not require control of the connecting element blocking circuits. In contrast to active switches, which establish or disconnect connections in the time domain, the use of frequency-selective blocking circuits also advantageously enables the use of the coil arrangement described here in so-called decoupling experiments using the Kern-Overhauser effect.

[0019] According to the invention, the coil arrangement is configured such that, in the electrically disconnected state of the connecting elements, the dipole antennas radiate and / or receive a high-frequency alternating electromagnetic field with a first frequency, in particular corresponding to the blocking frequency, and that, in the electrically connected state of the connecting elements, the resulting volume coil and / or each conductor loop of the conductor loop arrangement resulting in the electrically connected state of the connecting elements radiates and / or receives a high-frequency alternating electromagnetic field with a second frequency different from the first. In particular, this constitutes a doubly tuned coil arrangement.The coil arrangement according to the invention makes it possible, particularly in high-field MRI, to use capacitors with capacitance values ​​that are significantly larger and therefore much more readily achievable than those known from the prior art for fine-tuning the first and second emission frequencies. Furthermore, coils with significantly easier-to-achieve inductance values ​​can be used. The first frequency can be a < 1H core resonance frequency, meaning that the high-frequency alternating electromagnetic field radiated and / or received by the dipole antennas and / or a corresponding high-frequency alternating electrical voltage induced in the coil arrangement is in resonance with the Lamor frequency of the < 1H cores for a specific B< 0 field. In this case, standing waves are formed between the connecting element resonant circuits or within the individual dipole antennas for < 1H imaging.The second frequency can be an X-nucleus resonance frequency, in particular a 31 < P-nucleus or 23 < Na-nucleus resonance frequency. This means that the high-frequency alternating electromagnetic field radiated and / or received by the volume coil or each conductor loop of the conductor loop arrangement, and / or a corresponding high-frequency alternating electrical voltage induced in the coil arrangement, is in resonance with the Lamor frequency of a specific X-nucleus for a specific B₀ field. The X-nucleus resonance frequency thus corresponds to the Lamor frequency of the X-nuclei. The conductor loops can therefore each act as antennas for the X-nucleus resonance frequency. By electrically disconnecting or connecting the dipole antennas, the coil arrangement can thus provide different electrical configurations for the two resonance frequencies, both of which can be advantageously used for MRI examinations.The coil arrangement according to the invention is sensitive to two MRI cores without significant losses and, in particular, does not require the use of lossy components. Therefore, compared to previously known coil arrangements, this arrangement exhibits... a high The system exhibits a sensitivity comparable to monofrequency arrangements, resulting in a high signal-to-noise ratio (SNR) and high efficiency for both resonant frequencies, i.e., when recording both cores. The connecting element blocking circuits are preferably so-called 1< H connecting element blocking circuits, or simply 1< H blocking circuits, whose blocking frequency corresponds to a 1< H core resonant frequency.

[0020] Generally, the homogeneity of X-cores improves with the number of dipole antennas used. However, the number of dipole antennas is limited because beyond a certain number, the coupling of the dipole antennas in 1<H operation becomes too high to be used effectively. A number of four to eight, and especially four or eight, dipole antennas has proven advantageous.

[0021] Advantageously, the dipole antennas each comprise a rod-shaped base element, at the axially opposite ends of which a conductor segment, particularly annular, is attached. The axial ends of the rod-shaped base element connect, in particular, centrally to the respective conductor segment. Preferably, the conductor segments of the dipole antennas are of the same size. In the case of annular conductor segments, they have, in particular, the same arc length. The rod-shaped base elements of the dipole antennas can be arranged at least substantially parallel to each other. Advantageously, the rod-shaped base elements of the dipole antennas are arranged at uniform intervals from each other in the circumferential direction of the volume coil or in the longitudinal direction of the conductor loop arrangement.The length of the rod-shaped base elements of the dipole antennas, the height of the volume coil, or the width of the conductor loop arrangement can be in the range of 25 to 30 cm, particularly for measurements on the human head, and especially 25 cm or 28 cm. Preferably, the length of the dipole antenna is matched to the blocking frequency of the connecting element blocking circuits. Measures for varying the physical length of dipole antennas, e.g., by incorporating concentrated components, are known to those skilled in the art and are described, among other places, in G. Janzen, "Short Antennas. Design and Calculation of Shortened Transmitting and Receiving Antennas", Kosmos Verlags GmbH, June 1989, ISBN: 978-3440054697.

[0022] According to a further embodiment, the conductor track segments of the dipole antennas are connected to each other via the connecting elements, forming two conductor tracks, in particular two ring-shaped closed conductor tracks. Especially in the case of two ring-shaped closed conductor tracks, the number of connecting elements per conductor track can correspond to the number of dipole antennas. Particularly in the case of a flat conductor loop arrangement, the number of connecting elements per conductor track is preferably one less than the number of dipole antennas. The diameter of the ring-shaped closed conductor tracks or the volume coil can be in the range of 25 to 30 cm, and in particular 26 cm, especially for measurements on the human head.

[0023] According to a further advantageous embodiment, at least one of the connecting element blocking circuits comprises a connecting element coil and a connecting element capacitor connected in parallel. The connecting element coil preferably has an inductance in the range of 38 to 41 nH, particularly preferably in the range of 39 to 40 nH, and especially 39 nH or 40 nH. The connecting element capacitor preferably has a capacitance in the range of 6 to 8 pF, particularly 6.8 pF. At least one connecting element can comprise a second connecting element capacitor connected in series with the connecting element blocking circuit. The second connecting element capacitor preferably has a capacitance in the range of 5 to 50 pF, particularly preferably in the range of 8.2 to 40 pF, and especially 8.2 pF or 40 pF.Advantageously, the second connecting element capacitor is designed, in particular, to have a suitable capacitance for tuning the coil assembly to the second frequency, especially for fine-tuning. A capacitance value for the second connecting element capacitor in the aforementioned order of magnitude is easily achievable, which contributes to the fact that the coil assembly can be tuned with relatively little effort. The aforementioned capacitance and inductance values ​​are particularly advantageous when the coil assembly is used as part of an MR system that includes a magnet designed to generate a magnetic field B0 of 7 T.

[0024] In a preferred embodiment, the rod-shaped base elements of the dipole antennas are each split in the middle to form two poles of the respective dipole antenna. Advantageously, the rod-shaped base elements of the dipole antennas are each provided with a connection device for connecting to an AC power supply and / or receiving device, which comprises electrical connection elements connected to the two poles of the dipole antenna. Preferably, the rod-shaped base elements are each provided with the connection device in their middle section.An H-core signal can be fed into each of the electrical connection elements of the connection devices. In particular, each dipole antenna can be supplied with a high-frequency alternating voltage, the frequency of which preferably corresponds to an H-core resonant frequency, to cause the dipole antennas to radiate a high-frequency alternating electromagnetic field at the H-core resonant frequency. If the frequency of the supplied high-frequency alternating voltage corresponds to the blocking frequency of the connection element's blocking circuits, an alternating current corresponding to the supplied high-frequency alternating voltage is isolated on the respective dipole antenna. A high-frequency alternating voltage induced in the coil arrangement can also be tapped and / or received via the electrical connection elements of the connection devices.

[0025] The coil arrangement can be configured such that 1< H-core signals and / or X-core signals can be fed in and / or tapped via the electrical connection elements of at least one connection device, in particular all connection devices. The term "1< H-core signals" includes both a high-frequency alternating voltage fed into the coil arrangement, the frequency of which corresponds to the 1< H-core resonant frequency, and a high-frequency alternating voltage tapped from the coil arrangement, induced in the coil arrangement by excited 1< H-cores, the frequency of which corresponds in particular to the 1< H-core resonant frequency.The term "X-core signals" includes both a high-frequency alternating voltage fed into the coil arrangement, the frequency of which differs from the H-core resonant frequency and preferably corresponds to an X-core resonant frequency, and a high-frequency alternating electrical voltage tapped from the coil arrangement, induced in the coil arrangement due to excited X-cores, the frequency of which in particular corresponds to the X-core resonant frequency.

[0026] The coil arrangement is advantageously designed to allow operation in 4-channel and / or 2-channel quadrature mode. In 4-channel quadrature mode, the X-core signal or the 1H-core signal is fed in / tapped at four connection points, whereas in 2-channel quadrature mode, the X-core signal or the 1H-core signal is fed in / tapped at two connection points. Quadrature mode enables the generation of a circular polarized field. By generating a circular field polarization, the required transmit power is reduced and the received SNR is increased compared to linear field polarization.

[0027] According to a preferred embodiment, the coil arrangement is designed such that X-core signals can be fed in and / or tapped via the electrical connection elements of a pair of two adjacent connection devices, in particular adjacent in the circumferential direction of the volume coil, of a total of four connection devices.The coil arrangement can be configured such that the resulting volume coil and / or conductor loop arrangement, when the connecting elements are electrically connected, can be supplied via the two adjacent connection devices in quadrature mode with a high-frequency alternating voltage whose frequency differs from the H-core resonant frequency and preferably corresponds to an X-core resonant frequency, in order to cause the volume coil or each conductor loop of the conductor loop arrangement to radiate a high-frequency alternating electromagnetic field with an X-core resonant frequency. The two adjacent connection devices can be controlled with signals that are phase-shifted by 90 degrees.In the case of a feed to four connection devices, which is known in MRI as a "four port drive" and also enables the generation of a circularly polarized field distribution, the phase relationship between the feed signals is preferably 0 -90 -180 -270 degrees.

[0028] If a conductor loop arrangement results in the electrically connecting state of the connecting elements, an input and / or a tap of 1< H-core signals and / or X-core signals can also take place at the free ends of the two conductor tracks.

[0029] A dipole capacitor can be provided in the center of a dipole antenna between the two poles, and this capacitor is particularly useful as part of the connection device. The term "dipole capacitor" is used here solely to distinguish it from other capacitors, and the prefix "dipole-" has no functional significance. The dipole capacitor preferably has a capacitance of 0 pF. However, dipole capacitors can also have capacitance values ​​other than 0 pF to achieve improved impedance matching, particularly with a connected transmission line. Advantageously, the dipole capacitor is designed, and in particular has a suitable capacitance, to tune the coil arrangement to the first frequency, especially to fine-tune it.

[0030] According to a further embodiment, a coupling element is provided, in particular connected in parallel to the dipole capacitor, which is electrically connected to and bridges the two poles of the dipole antenna. The coupling element is designed to switch from an electrically connecting to an electrically disconnecting state, and vice versa. The coupling element is preferably part of the connection device. Preferably, the coupling element includes a coupling element blocking circuit that automatically blocks when a high-frequency alternating voltage with a frequency corresponding to the blocking frequency of the coupling element blocking circuit is applied to or induced in the coil arrangement, in particular to the electrical connection elements of the connection device of the corresponding dipole antenna. The blocking frequency of the coupling element blocking circuit corresponds in particular to the first frequency.The blocking frequencies of the connecting element blocking circuits and the coupling element blocking circuits preferably coincide. The coupling element blocking circuit remains active as long as the high-frequency AC voltage of the blocking frequency is applied to the coil assembly.

[0031] Advantageously, at least one of the coupling element blocking circuits comprises a coupling element coil and a coupling element capacitor connected in parallel. The coupling element coil preferably has an inductance in the range of 38 to 41 nH, particularly preferably in the range of 39 to 40 nH, especially 39 nH or 40 nH. The coupling element capacitor preferably has a capacitance in the range of 6 to 8 pF, particularly 6.8 pF. At least one coupling element can comprise a second coupling element capacitor connected in series with the coupling element blocking circuit of the first coupling element. The second coupling element capacitor preferably has a capacitance in the range of 20 to 110 pF, particularly preferably in the range of 33 to 100 pF, especially 33 pF, 95 pF, or 100 pF.Advantageously, the second coupling element capacitor is designed, in particular having a suitable capacitance, to tune the coil arrangement to the second frequency, especially to fine-tune it, and / or to trigger a short circuit at the second frequency. A capacitance value of the coupling element capacitor and the second coupling element capacitor in the aforementioned order of magnitude is easily achievable, which contributes to the tuning of the coil arrangement with relatively little effort. The aforementioned capacitance and inductance values ​​are particularly advantageous when the coil arrangement is used as part of an MR system that includes a magnet configured to generate a B0 of 7T.

[0032] A further embodiment of the invention is characterized in that the axial ends of the rod-shaped base element of at least one dipole antenna are connected to the respective conductor segment of the dipole antenna via an interposed terminal capacitor. The terminal capacitor preferably has a capacitance in the range of 10 to 40 pF, particularly preferably in the range of 18 to 32 pF, and especially 18 pF or 32 pF. Advantageously, the terminal capacitor is designed to have a suitable capacitance for tuning the coil arrangement to the second frequency, particularly for fine-tuning. The terminal capacitors thus provide an additional degree of freedom for tuning, especially when other capacitors, which are also preferably provided for tuning, are already determined by boundary conditions.

[0033] Preferably, the coil arrangement is tuned, in particular by means of the second connecting element capacitors and / or the second coupling element capacitors and / or the dipole capacitors and / or the connection point capacitors, such that each dipole antenna, in the electrically isolating state of the connecting elements and in particular the coupling elements, can radiate and / or receive a high-frequency alternating electromagnetic field with a 1 < H-core resonant frequency, and the resulting volume coil and / or each conductor loop of the conductor loop arrangement, in the electrically connecting state of the connecting elements and in particular the coupling elements, can radiate and / or receive a high-frequency alternating electromagnetic field with an X-core resonant frequency.

[0034] Table 1 below lists advantageous capacitance and inductance values ​​for the electrical components of a connection device for a 1< H / 31< P tuning at B 0 = 7T. The corresponding capacitance and inductance values ​​for a 1< H / 23< Na tuning at B 0 = 7T are given in parentheses. Here, 1< H / 31< P tuning refers to tuning to the 1< H core resonant frequency of 300 MHz and the 31< P core resonant frequency of 120 MHz as the X core resonant frequency at B 0 = 7T. 1< H / 23< Na tuning accordingly stands for a tuning to the 1< H core resonance frequency of 300 MHz and the 23< Na core resonance frequency of 78.82 MHz as the X core resonance frequency at B 0 =7T. Table 1: Coupling element coil inductance [nH] Coupling element capacitor capacitance [pF] Dipole capacitor capacitance [pF] Second coupling element capacitor capacitance [pF] 40 6,8 0 33 or 100 (39) (6,8) (0) (33 or 95)

[0035] If the dipole antenna arrangement comprises four dipole antennas, the second coupling element capacitors of the coupling elements of the connection devices of two adjacent dipole antennas, in particular two dipole antennas adjacent in the circumferential direction of the volume coil, can each have the same capacitance, preferably 33 pF, and the second coupling element capacitors of the two remaining dipole antennas can also have the same capacitance, preferably 100 pF, particularly for 1< H / 31< P tuning, or 95 pF, particularly for 1< H / 23< Na tuning at B 0 = 7T. Preferably, the two connection devices whose coupling element capacitors have a capacitance of 33 pF are two connection devices that are not used for injecting / tapping an X-core signal.

[0036] In Table 2 below, advantageous capacitance and inductance values ​​of the electrical components of a connecting element are listed for the above-described 1< H / 31< P tuning or in parentheses for the above-described 1< H / 23< Na tuning. Table 2: Connecting element coil inductance [nH] Connecting element capacitor capacitance [pF] Second connecting element capacitor capacitance [pF] 40 (39) 6,8 (6,8) 8,2 (40)

[0037] The terminal capacitors can have a capacitance of 18 pF for the 1< H / 31< P tuning and a capacitance of 32 pF for the 1< H / 23< Na tuning.

[0038] If a conductor loop arrangement results in the electrically connected state of the connecting elements, and in particular the coupling elements, each conductor loop of the conductor loop arrangement can be formed by at least parts of two adjacent dipole antennas. The conductor loop arrangement preferably comprises several conductor loops, in particular three conductor loops. At least a part of a dipole antenna, in particular, if present, at least its rod-shaped base element and preferably, if present, two terminal capacitors thereof, can form a part of two adjacent conductor loops. In this case, two conductor loops then practically "share" at least a part of a dipole antenna, in particular, if present, the rod-shaped base element and the two terminal capacitors thereof.If at least part of a dipole antenna forms part of two adjacent conductor loops, the capacitance values ​​of the connecting element capacitors and / or the second connecting element capacitors and / or the coupling element capacitors and / or the second coupling element capacitors and / or the dipole capacitors and / or the terminal capacitors and / or other capacitors within the conductor loop arrangement are preferably selected such that adjacent conductor loops are preferably capacitively decoupled. The determination of the capacitance values ​​required for decoupling adjacent conductor loops is described by A.L. Perrier, D. Grenier, N. Ravel, P. Litaudon, and O. Beuf in the article "Capacitive approach to restore decoupling between channels for four-element MR coil array," ELECTRONICS LETTERS, June 20, 2013, Vol. 49, No. 13.

[0039] It is understood that the coil arrangement according to the invention may be suitable for use as a transmitting and / or receiving coil in a UHF MRI system.

[0040] The aforementioned problem is also solved according to the invention by an MR system, in particular an MRI, preferably a high-field / ultra-high-field MRI, and / or an MRS, preferably a high-field / ultra-high-field MRS system with the coil arrangement described above according to the invention.

[0041] The MR system preferably comprises a magnet, in particular a superconducting magnet, configured to generate a static, preferably homogeneous, magnetic field B0, wherein B0 is preferably 7T. The coil arrangement can be located within a central opening of the magnet. The coil arrangement can surround a receiving chamber in which a medium to be examined is or can be arranged during an MR examination.

[0042] Furthermore, the invention relates to the use of the previously described coil arrangement according to the invention as a high-frequency transmitting and / or receiving 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.

[0043] Further features and advantages of the present invention will become clear from the following description of an embodiment of a coil arrangement according to the present invention with reference to the accompanying drawing. This includes: Figure 1 is a schematic perspective view of a coil arrangement according to an embodiment of the present invention; Figure 2 is a kind of exploded view of the coil arrangement. Figure 1 , in which the dipole antennas are shown separately; Figure 3 a circuit diagram of the coil arrangement of the Figure 1Figure 4 shows a frequency spectrum of the input reflection factor illustrating the two resonant frequencies to which the coil arrangement according to the invention is tuned; Figure 5 shows 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 1 < H-core resonant frequency of 300 MHz; and Figure 6 shows 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 birdcage coil at the 31 < P-core resonant frequency of 120 MHz.

[0044] The Figure 1 Figure 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 connected to each other via eight connecting elements 3a-h. Figure 2 Figure 1 shows an 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 switch from an electrically connecting to an electrically disconnecting state, and vice versa. The arrangement is recognizably such that, in the electrically connecting state of the connecting elements 3a-h, the dipole antennas 2a-d form a cylindrical volume coil.

[0045] The connecting elements 3a-h each comprise a connecting element blocking circuit 4a-h, which automatically blocks when a high-frequency alternating voltage with 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 is located in the Figure 3The circuit diagram of the coil arrangement 1 shown can be seen. The connecting element blocking circuits 4a-h each comprise a connecting element coil 5a-h and a connecting element capacitor 6a-h, which are connected in parallel. In addition, each 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.

[0046] The dipole antennas 2a-d each have a rod-shaped base element 8a-d, at the axially opposite ends of which a ring-shaped conductor segment 9a-h is attached. The axial ends of the rod-shaped base element 8a-d are connected centrally to the respective conductor segment 9a-h via a connecting capacitor 10a-h. The rod-shaped base elements 8a-d of the dipole antennas 2a-d are arranged parallel to each other and uniformly spaced from one another in the circumferential direction of the volume coil. The conductor segments 9a-h are of the same size, more precisely, they have the same arc length. Furthermore, the ring-shaped conductor segments 9a-h are connected to each other via connecting elements 3a-h, forming two ring-shaped closed conductor tracks 9. Thus, four connecting elements 3a-h are arranged in each conductor track 9.

[0047] The rod-shaped base elements 8a-d of the dipole antennas 2a-d are each split in the middle to form two poles of the respective dipole antenna 2a-d. Furthermore, each rod-shaped base element 8a-d is provided in its central section with a connection device 11a-d for connection to an AC power supply and receiving device (not shown). The connection device 11a-d comprises electrical connection elements 12a-d connected to the two poles of the dipole antenna 2a-d. The connection device 11a-d also includes a dipole capacitor 13a-d, which is located in the middle of the dipole antenna 2a-d between the two poles. In addition, the connection device 11a-d includes 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 four coupling elements 14a-d are each designed to be converted from an electrically connecting state to an electrically separating state, and vice versa.

[0048] For this purpose, the coupling elements 14a-d each comprise a coupling element blocking circuit 15a-d, which includes 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 alternating voltage with 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. Furthermore, the coupling elements 14a-d each comprise a second coupling element capacitor 18a-d, which is connected in series with the coupling element blocking circuit 15a-d.

[0049] The cylindrical volume coil formed when the connecting elements 3a-h are electrically connected is an Alderman-Grant type volume coil with two end rings, here the ring-shaped closed conductor tracks 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 and has a diameter of 26 cm. In the Figure 1 and 2 A spherical phantom 19 is shown within the coil arrangement 1. This represents a body part to be examined, in particular a human or animal head.

[0050] The following table briefly describes the electrical components of the four connection devices 11a-d and lists their values. Connection setup Coupling element coil 16a-d Coupling element capacitor 17a-d Dipole capacitor 13a-d Second coupling element capacitor 18a-d Description Value (nH) Description Value (pF) Description Value (pF) Description Value (pF) 11a Coil 16a for 1< H-coupling element blocking circuit 15a 40 Capacitor 17a for 1< H-coupling element blocking circuit 15a 6,8 Capacitor 13a for dipole matching 0 Capacitor 18a for tuning, which triggers a short circuit at the X-core frequency. 33 11b Coil 16b for 1< H-coupling element blocking circuit 15b 40 Capacitor 17b for 1< H-coupling element blocking circuit 15b 6,8 Capacitor 13b for dipole matching 0 Capacitor 18b for tuning, which triggers a short circuit at the X-core frequency. 33 11c Coil 16c for 1< H-coupling element blocking circuit 15c 40 Capacitor 17c for 1< H-coupling element blocking circuit 15c 6,8 Capacitor 13c for dipole matching 0 Capacitor 18c for X-Kem matching 100 11d Coil 16d for 1< H-coupling element blocking circuit 15d 40 Capacitor 17d for 1< H-coupling element blocking circuit 15d 6,8 Capacitor 13d for dipole matching 0 Capacitor 18d for X-Kem matching 100

[0051] The following table briefly describes the electrical components of the eight connecting elements 3a-h and lists their values. Connecting elements Connecting element coil 5a-h Connecting element capacitor 6a-h Second connecting element capacitor 7a-h Description Value (nH) Description Value (pF) Description Value (pF) 3a Coil 5a for 1< H-connecting element blocking circuit 4a 40 Capacitor 6a for 1< H-connecting element blocking circuit 4a 6,8 Vote for X cores 8,2 3b Coil 5b for 1< H-connecting element blocking circuit 4b 40 Capacitor 6b for 1< H-connecting element blocking circuit 4b 6,8 Vote for X cores 8,2 3c Coil 5c for 1< H-connecting element blocking circuit 4c 40 Capacitor 6c for 1< H-connecting element blocking circuit 4c 6,8 Vote for X cores 8,2 3d Coil 5d for 1< H-connecting element blocking circuit 4d 40 Capacitor 6d for 1< H-connecting element blocking circuit 4d 6,8 Vote for X cores 8,2 3e Coil 5e for 1< H-connecting element blocking circuit 4e 40 Capacitor 6e for 1< H-connecting element blocking circuit 4e 6,8 Vote for X cores 8,2 3f Coil 5f for 1< H-connecting element blocking circuit 4f 40 Capacitor 6f for 1< H-connecting element blocking circuit 4f 6,8 Vote for X cores 8,2 3g Coil 5g for 1< H-connector blocking circuit 4g 40 Capacitor 6g for 1< H-connecting element blocking circuit 4g 6,8 Vote for X cores 8,2 3h Coil 5h for 1< H-connecting element blocking circuit 4h 40 Capacitor 6h for 1< H-connecting element blocking circuit 4h 6,8 Vote for X cores 8,2

[0052] In Figure 4Figure 1 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 preceding tables. The terminal capacitors 10a-h and, in particular, the connecting element coils 5a-h and the coupling element coils 16a-d also contribute to the tuning. In this case, the capacitance of the terminal capacitors 10a-h is 18 pF each. It can be seen that the coil system is doubly tuned at B0 = 7T, namely to the H-core resonant frequency of 300 MHz and to an X-core resonant frequency, namely the P-core resonant frequency of 120 MHz.

[0053] When the inventive coil arrangement 1, tuned in the manner described above, is used in an MRI system with B0 = 7 T, the dipole antennas 2a-d are each supplied with a high-frequency alternating voltage via the electrical connection elements 12a-d of their connection devices 11a-d in a first operating mode of the MRI system. The phase relationship between the supply signals applied to the four connection devices 11a-d can be, for example, 0, 90, 180, or 270 degrees. The frequency of the high-frequency alternating voltage corresponds to a common blocking frequency of the connecting element blocking circuits 4a-h and the coupling element blocking circuits 15a-d. This common blocking frequency corresponds to the H-core resonance frequency.Subsequently, the connecting element blocking circuits 4a-h and the coupling element blocking circuits 15a-d automatically close, thereby switching the connecting elements 3a-h and the coupling elements 14a-d into their electrically isolated state. In the electrically isolated state, each dipole antenna 2a-d radiates a high-frequency alternating electromagnetic field with the 1< H-core resonance frequency of 300 MHz. Later, a high-frequency alternating electrical voltage induced by excited 1< H-cores in the coil arrangement 1 is tapped at the connection devices 11a-d.

[0054] In a second operating mode of the MRI system, the coil assembly 1 is supplied with a high-frequency alternating voltage via the electrical connection elements 12c and 12d of the two connection devices 11c and 11d adjacent to the volume coil in a quadrature operation, whereby the connection devices 11c and 11d are driven with signals phase-shifted by 90 degrees. The frequency of the high-frequency alternating voltage differs from the common blocking frequency. Thus, the connecting elements 3a-h and the coupling elements 14a-d are in their electrically connecting state. Subsequently, the volume coil, in its electrically connecting state, emits a high-frequency alternating electromagnetic field with the P-core resonance frequency of 120 MHz. Later, an alternating electrical voltage induced by excited 31< P-cores in the coil arrangement 1 is tapped at the connection devices 11c and 11d.The coil arrangement 1 described above according to the invention was used as a high-frequency coil in an MRI system.

[0055] The electromagnetic field distribution in the head of a subject was first simulated, assuming the excitation and subsequent detection of 1H nuclei. With B0 = 7 T, the 1H nucleus resonance frequency, or 1H nucleus Larmor frequency, was 300 MHz. The same MRI examination was then performed again using a comparison setup. This setup employed an 8-channel coil arrangement as the high-frequency coil, tuned only to the 1H nucleus resonance frequency. Specifically, in the comparison setup, eight conductor loops were placed around the subject's head. This simply tuned 8-channel arrangement provided a virtually optimal comparison measurement for a 1H examination. The resulting MRI images, both when using the coil arrangement according to the invention and when using the comparison setup, are shown in Figure 5The data is presented in the form of a matrix. The left column contains the cross-sectional images for the comparison setup, and the right column contains the cross-sectional images for the coil arrangement 1 according to the invention. The top row shows the cross-sectional images in the sagittal plane, and the bottom row shows the cross-sectional images in the frontal or coronal plane. Specifically, a comparison of the reliable transmission efficiency of both MRI examinations is shown. Here, the reliable transmission efficiency is defined as the amplitude of the circularly polarized high-frequency excitation field divided by the maximum specific absorption rate B1 + √(SAR). The comparison shows that the reliable transmission efficiency when using the coil arrangement 1 according to the invention has a mean value of 0.48. μT / w about the subject's brain and the virtually optimal safe transmission efficiency when using the comparison setup with a mean value of 0.51 μT / w They resemble each other, although the coil arrangement 1 according to the invention is a doubly tuned or doubly resonant coil arrangement. This indicates only a small loss.

[0056] Furthermore, a simulation of the field distribution in the head of a subject was performed, in which the 31< P nuclei were excited and subsequently detected. With B 0 = 7 T, the 31< P nucleus resonance frequency, or 31< P nucleus Lamor frequency, was 120 MHz. The same MRI examination was repeated with a comparison setup using a birdcage coil as the radio frequency coil, tuned only to the 31< P nucleus resonance frequency. The simply tuned birdcage coil provided virtually an optimal comparison measurement for a 31< P examination. The resulting MRI images in both cases use The coil arrangement 1 according to the invention, as well as the comparison arrangement, are in Figure 6The data is presented in the form of a matrix. The right-hand column contains the cross-sectional images for the coil arrangement 1 according to the invention, and the left-hand column contains the cross-sectional images for the comparison arrangement. The top row shows the cross-sectional images in the sagittal plane, and the bottom row shows the cross-sectional images in the frontal or coronal plane. The comparison of the reliable transmission efficiency of both MRI examinations shows that the reliable transmission efficiency when using the coil arrangement 1 according to the invention has a mean value of 1.09. μT / w about the subject's brain and the virtually optimal safe transmission efficiency when using the comparison setup with a mean value of 1.00 μT / w They resemble each other, although the coil arrangement 1 according to the invention is a doubly tuned or doubly resonant coil arrangement. This indicates only a small loss.

[0057] In the previously described embodiment of a coil arrangement 1 according to the invention, a volume coil is formed in the electrically connected state of the connecting elements 3a-h and the coupling elements 14a-d. In an alternative embodiment, a flat conductor loop arrangement can be formed instead of a volume coil, which, for example, has a flat structure similar to the illustration of Figure 3The conductor loop arrangement can be configured as follows, but without the two connecting elements 3d and 3h. In this case, the conductor loop arrangement comprises three conductor loops 20a-c, each of which is formed by at least parts of two adjacent dipole antennas 2a-d. In the present example, a part of the dipole antenna 2b forms both a part of conductor loop 20a and a part of conductor loop 20b. Furthermore, a part of the dipole antenna 2c forms both a part of conductor loop 20b and a part of conductor loop 20c. More precisely, the conductor loop 20a is formed by the rod-shaped base element 8a, the two connection point capacitors 10a and 10e and each half of the conductor track segments 9a and 9e of the dipole antenna 2a, as well as the rod-shaped base element 8b, the two connection point capacitors 10b and 10f and each half of the conductor track segments 9b and 9f of the dipole antenna 2b.The conductor loop 20b is formed by the rod-shaped base element 8b, the two connection capacitors 10b and 10f, and half of each of the conductor segments 9b and 9f of the dipole antenna 2b, as well as by the rod-shaped base element 8c, the two connection capacitors 10c and 10g, and half of each of the conductor segments 9c and 9g of the dipole antenna 2c. Finally, the conductor loop 20c is formed by the rod-shaped base element 8c, the two connection capacitors 10c and 10g, and half of each of the conductor segments 9c and 9g of the dipole antenna 2c, as well as by the rod-shaped base element 8d, the two connection capacitors 10d and 10h, and half of each of the conductor 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 connection 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 connection point capacitors 10c and 10g of the dipole antenna 2c. The capacitance values ​​of all capacitors within the conductor loop arrangement are chosen such that adjacent conductor loops 20a-c are preferably capacitively decoupled.

[0058] In the case of a flat conductor loop arrangement, the two conductor tracks 2 are preferably straight and not ring-shaped. In a flat conductor loop arrangement, input and / or output of 1 < H-core and / or X-core signals can alternatively be made via the free ends 21a-d of the conductor tracks instead of the connection devices 11a-d. In the case of a flat conductor loop arrangement, the radiation and / or reception of the high-frequency alternating electromagnetic field at the X-core resonant frequency occurs via the individual conductor loops 20a-c. The radiation and / or reception of the high-frequency alternating electromagnetic field at the 1 < H-core resonant frequency occurs via the individual dipole antennas 2a-d. Reference symbol list

[0059] 1 Coil assembly 2 Dipole antenna assembly 2a-d Dipole antennas 3a-h Connecting elements 4a-h Connecting element-blocking circuit 5a-h Connecting element-coil 6a-h Connecting element-capacitor 7a-h Second connecting element-capacitor 8a-d Rod-shaped base element 9 Conductor 9a-h Conductor segment 10a-h Connection point-capacitor 11a-d Connection device 12a-d Connection element 13a-d Dipole capacitor 14a-d Coupling element 15a-d Coupling element-blocking circuit 16a-d Coupling element-coil 17a-d Coupling element-capacitor 18a-d Second coupling element-capacitor 19 Phantom 20a-c Conductor loop 21 Free end

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

2. Coil arrangement (1) according to claim 1, characterized in that 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.

3. Coil arrangement (1) according to claims 1 or 2, characterized in that 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 (9ah) of the dipole antennas (2a-d) preferably being of the same size, in particular having the same arc length, in particular, 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 (8a-d) 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, and / or 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.

4. Coil arrangement (1) according to any of the preceding claims, characterized in that at least one of the connecting element blocking circuits (4ah) 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.

5. Coil arrangement (1) according to claim 4, characterized in that 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.

6. Coil arrangement (1) according to claim 5, characterized in that 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.

7. Coil arrangement (1) according to claim3 or one of claims 4 to 6, if referred back to claim 3, characterized in that 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).

8. Coil arrangement (1) according to claim 7, characterized in that 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).

9. Coil arrangement (1) according to claim 2 and claim 8, characterized in that 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), preferably, 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), in particular, 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.

10. Coil arrangement (1) according to one of claims 7 to 9, characterized in that 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.

11. Coil arrangement (1) according to claim 10, characterized in that 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.

12. Coil arrangement (1) according to any one of claims 7 to 11, characterized in that 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), in particular, 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, preferably, 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, in particular, 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, preferably, 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, and / or that 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.

13. Coil arrangement (1) according to claim 3 or one of claims 4 to 12, if referred back to claim 3, characterized in that 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.

14. Coil arrangement (1) according to claim 13, characterized in that 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.

15. Coil arrangement (1) according to any of the preceding claims, if referred back to claim 2, characterized in that 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 (3a-h) 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, and / or that 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), preferably, 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 (1 0a-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.

16. MR system, in particular MRI, preferably high-field / ultra-high-field MRI, and / or MRS, high-field / ultra-high-field MRS system, having a coil arrangement (1) according to one of the preceding claims.

17. Use of a coil arrangement (1) according to any one of claims 1 to 15 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.