Local coil system including an energy reception antenna for inductively receiving energy for the local coil system

Abstract

A local coil system for detecting magnetic resonance (MR) signals in a magnetic resonance tomography (MRT) device includes an energy reception antenna for inductively receiving energy for the local coil system from a magnetic field changing over time with an energy transmission frequency. The energy reception antenna includes a conductor loop running in loop-like fashion from a first loop connection to a second loop connection. At least one path filter that blocks for harmonic frequencies of the energy transmission frequency is arranged over the course of the energy reception path, and/or at least one path filter that blocks for harmonic frequencies of the energy transmission frequency is arranged over the course of an energy reception path leading from the loop connections to a rectifier.

Claims

1. A local coil system for detecting magnetic resonance (MR) signals in a magnetic resonance tomography (MRT) device, the local coil system comprising: an energy reception antenna operable for inductively receiving energy for the local coil system from a magnetic field changing over time with an energy transmission frequency, wherein the energy reception antenna comprises a conductor loop running in loop-like fashion from a first loop connection to a second loop connection, wherein at least one conductor loop filter that blocks a MR frequency of the MR signals to be detected is arranged over a course of the conductor loop, wherein the at least one conductor loop filter comprises a plurality of conductor loop filters arranged over the course of the conductor loop with a maximum mutual spacing of a quarter-wavelength corresponding to the MR frequency.

2. The local coil system of claim 1, wherein the conductor loop of the energy reception antenna frames an arrangement of one or more MR reception antennas of the local coil system, the arrangement being operable for receiving the MR signals.

3. The local coil system of claim 2, wherein the at least one conductor loop filter has a bandpass characteristic operable for allowing passage of the energy transmission frequency.

4. The local coil system of claim 1, wherein the at least one conductor loop filter has a bandpass characteristic operable for allowing passage of the energy transmission frequency.

5. The local coil system of claim 1, further comprising: an energy reception path that leads from conductor loop connectors of the energy reception antenna to a rectifier of the local coil system; and at least one path filter arranged over a course of the energy reception path, the at least one path filter being operable to block harmonic frequencies of the energy transmission frequency.

6. The local coil system of claim 5, wherein the at least one path filter has a low-pass characteristic.

7. The local coil system of claim 6, further comprising a matching network configured for impedance conversion provided over the course of the energy reception path.

8. The local coil system of claim 7, wherein the energy reception path is configured such that, with respect to a current flowing through the conductor loop of the energy reception antenna during energy reception, blocking of a DC component is provided.

9. The local coil system of claim 7, wherein the rectifier is configured such that a current flows at a rectifier input for both half-cycles.

10. The local coil system of claim 6, wherein the rectifier is configured such that a current flows at a rectifier input for both half-cycles.

11. The local coil system of claim 5, wherein the energy reception path is configured such that, with respect to a current flowing through the conductor loop of the energy reception antenna during energy reception, blocking of a DC component is provided.

12. The local coil system of claim 11, wherein the rectifier is configured such that a current flows at a rectifier input for both half-cycles.

13. The local coil system of claim 5, wherein the rectifier is configured such that a current flows at a rectifier input for both half-cycles.

14. The local coil system of claim 6, wherein the energy reception path is configured such that, with respect to a current flowing through the conductor loop of the energy reception antenna during energy reception, blocking of a DC component is provided.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic illustration of one embodiment of a local coil arrangement of a local coil system, and a conductor loop of an energy reception antenna of the local coil system;

(2) FIG. 2 shows an example of a configuration of a conductor loop filter that may be used for the energy reception antenna shown in FIG. 1;

(3) FIG. 3 shows an exemplary embodiment of the components of a local coil system for energy reception;

(4) FIG. 4 shows one embodiment of a local coil system; and

(5) FIG. 5 shows another embodiment of a local coil system.

DETAILED DESCRIPTION

(6) FIG. 1 illustrates one embodiment of an energy reception antenna 10 for use in a local coil system (not illustrated as a whole) for detecting MR signals in an MRT device. The energy reception antenna 10 serves to inductively receive energy for local electronics of the local coil system from a magnetic field changing over time with an energy transmission frequency. The energy reception antenna 10 includes a conductor loop 12 that runs in the form of a loop from a first loop connection 1 to a second loop connection 1′.

(7) The magnetic field changing over time (e.g., rotating field rotating with the energy transmission frequency) induces an AC voltage UE provided at the loop connections 1, 1′. Using the AC voltage, after rectification, an energy store (capacitor) of the local coil system may be charged or recharged. This rectification and energy storage will be described in more detail further below with reference to FIG. 3.

(8) FIG. 1 illustrates the conductor loop 12 with only one turn. The profile of the conductor loop 12 may also form a plurality of turns.

(9) A plurality of filters (e.g., two filters 14-1 and 14-2), referred to below as conductor loop filters, are arranged over the course of the conductor loop 12. The plurality of filters each block for the MR frequency (e.g., 123 MHz +/−1 MHz) of the MR signals to be picked up by a local coil arrangement 16 (e.g., corresponding to the nuclear spin responses).

(10) This advantageously suppresses energy withdrawal by the energy reception antenna 10 from the magnetic field that changes over time with the MR frequency of the excited nuclear spins. The magnetic field is to be detected by the local coil arrangement 16 provided for this purpose in the form of the MR signals.

(11) Correspondingly, influencing of the MR signal detection performed by the arrangement 16 owing to the additional energy reception performed by the energy reception antenna 10 is reduced.

(12) In the example illustrated, the conductor loop 12 frames the local coil arrangement 16. The local coil arrangement is formed from a flat arrangement of 9 partially overlapping local coils (“loops”), in the example illustrated. The tap of the MR signals at the individual local coils of the local coil arrangement 16 is not illustrated in FIG. 1, for reasons of simplicity.

(13) In the example illustrated, the conductor loops of the local coil arrangement 16 and the conductor loop 12 of the energy reception antenna 10 are in a common plane, with the result that the arrangement shown in FIG. 1 may easily be accommodated in a flat “local coil mat” or the like. In a manner known, such a local coil mat may be curved, with the result that, correspondingly, the arrangement illustrated in FIG. 1 may likewise overall have such a curvature.

(14) In one embodiment, the framed local coil arrangement has, as does, for example, the local coil arrangement 16 illustrated, a polygonal contour (e.g., rectangular or square). The conductor loop, following this contour, likewise has a polygonal profile (e.g., octagonal).

(15) The profile of the conductor loop 12 may have a length (e.g., >1 m) that is often greater than a wavelength corresponding to the MR frequency (e.g., the wave propagation at the MR frequency on the conductor loop 12). For example, a plurality of conductor loop filters, such as the filters 14-1, 14-2 illustrated, may be arranged distributed over the length of the conductor loop 12. For example, all of the conductor sections between these filters or between the loop connections 1, 1′ and the respectively adjacent one of the filters correspond to a quarter-wavelength.

(16) FIG. 2 shows a simple and particularly effective configuration of the conductor loop filters 14-1, 14-2, in the exemplary embodiment illustrated. There is a parallel circuit of a capacitance and an inductance that forms a bandstop configured such that the MR frequency (e.g., of the order of magnitude of approximately 100 MHz) is blocked.

(17) As an alternative to a bandstop, at a deviation from the example illustrated, for example, a conductor loop filter with a bandpass characteristic may also be used, with the energy transmission frequency (e.g., of the order of magnitude of a few MHz) being in the passband thereof.

(18) FIG. 3 illustrates, for greater understanding of the present embodiments, components of a local coil system LS using a block circuit diagram illustrating an energy reception chain, via which the supply energy is received and passed on up to an energy store (e.g., capacitor).

(19) The left-hand part of the figure illustrates an energy reception antenna 10 configured as described with reference to FIGS. 1 and 2, for example, again including a conductor loop 12 with conductor loop filters 14-1, 14-2 arranged over the course of the conductor loop between conductor loop connections 1, 1′. An impedance Z1 results at the output of the energy reception antenna 10.

(20) The local coil system LS also includes an energy reception path 20 that is connected on the input side to the conductor loop connections 1, 1′ and leads on the output side, via connections 3, 3′, to a rectifier 30 of the local coil system LS.

(21) A smoothing and storage capacitor Cgl to be charged with the received energy is arranged at the output of the rectifier 30, with local coil electronics being supplied from the smoothing and storage capacitor. The local coil electronics are symbolized by a load resistor RL in FIG. 3.

(22) The energy reception path 20 in the example illustrated is formed from a matching network 22 and a filter network, referred to below as path filter 24.

(23) The conductor loop filter 14-1, 14-2 arranged over the course of the conductor loop 12 prevent, to a relatively large degree, energy being removed from the MR signal field (and/or MR excitation field) by the energy reception antenna 10. Such a withdrawal of energy takes place unimpeded, however, at the energy transmission frequency of the magnetic field provided for energy transmission.

(24) The matching network 22 in the example illustrated is arranged so as to directly follow the energy reception antenna 10 along the energy reception path 20 and serves the purpose of converting the output impedance Z1 inherent to the energy reception antenna 10 to give a desired impedance Z2 (e.g., taking into consideration the rectifier properties). The desired impedance Z2 is then present at the output of the matching network 22 (e.g., connections 2, 2′). In the case of the impedance conversion of Z1 to give Z2 thus realized, in the example illustrated, consideration should further be given to the fact that the impedance Z2 is converted to give an impedance Z3 (e.g., at the connections 3, 3′) by the downstream filter network 24.

(25) The matching network 22 is formed with particularly low losses from the capacitors CS1, CP and CS2 with the circuitry illustrated (e.g., the capacitors CS1 and CS2 form impedances integrated in the current flow path in series on the input side or on the output side, whereas the capacitor CP represents an impedance which connects the two path lines and is connected to a node between the capacitors CS1, CS2).

(26) The matching network 22 or the impedances used for this (e.g., the capacitors CS1, CS2 and CP) are, in accordance with a more specific configuration variant, configured for an impedance conversion (e.g., from Z1 to Z2) that does not result in optimum energy withdrawal from the energy transmission magnetic field, but provides a certain “mismatching” or relatively weak coupling of the antenna 10 to the transmission path 20.

(27) This may be very advantageous, for example, for implementing simultaneous and uniform energy supply given the presence of a plurality of further energy reception antennas (not illustrated in the figures).

(28) These further energy reception antennas that may be provided may be configured as has already been described for the antenna 10 and may be used for separately supplying energy to other parts of the local electronics.

(29) For example, a plurality of energy reception antennas of the local coil system may each be used for separate supply of electrical energy to multiply provided parts of the local electronics (e.g., preamplifiers, analog-to-digital converters, modulators, etc.) that are each assigned to that MR local coil arrangement in the vicinity of which the respective energy reception antenna is arranged (e.g., is framed by the respective energy reception antenna).

(30) In the example illustrated, the matching network 22, owing to the use of the capacitors CS1 and CS2 integrated in series, also has a further advantageous functionality that includes providing blocking of the DC component with respect to a current flowing through the conductor loop 12 during energy reception.

(31) If such a DC component blocking is not already realized by a suitable configuration of the conductor loop filter(s), this may advantageously be provided, for example, by the matching network 22 of the type illustrated. The DC component suppression advantageously avoids the generation of an extremely disadvantageous DC magnetic field in the system environment of interest, for example, through the conductor loop 12. Such a DC magnetic field may disadvantageously impair, for example, the spatial resolution provided in the MRT examination using the gradient fields. In the energy reception path 20 illustrated, for example, the capacitor CS1 already effects such decoupling of DC voltage components in order to thus prevent retrospective interaction with the MR imaging.

(32) The path filter 24 arranged downstream of the matching network 22 in the example illustrated is used for blocking harmonic frequencies of the energy transmission frequency. In the example illustrated, this is in the form of a fifth-order low-pass filter in order to achieve a particularly steep edge of the low-pass characteristic at a specific limit frequency, which may be selected to be just, in relative terms (e.g., less than 5%), above the energy transmission frequency to which passage is allowed (e.g., 5 MHz), for example.

(33) With the path filter 24, it is advantageously possible for harmonics resulting during the rectification by the rectifier 30 to be impeded when returning to the energy reception antenna 10, with the result that emission of magnetic fields at the frequencies of the harmonics is thus advantageously avoided, which would be damaging for the MR signal reception.

(34) As a deviation from the exemplary embodiment illustrated, the matching network 22 for impedance conversion (and possibly, as implemented here, for DC component separation) and the path filter 24 in the form of a filter network for harmonic separation may also form one unit, in terms of circuitry.

(35) The rectifier 30 forming the termination of the energy transmission path 20 serves the purpose of making the energy received at the energy transmission frequency usable by virtue of rectification for charging and recharging the smoothing and storage capacitor Cgl.

(36) In one embodiment, a rectifier circuit, as is also illustrated in FIG. 3, in which a current flows at a rectifier input (e.g., connections 3, 3′) for both half-cycles of the supplied AC signal, is provided. In the case of the rectifier 30 illustrated, this is implemented by the use of two Schottky diodes D1 and D2, which are arranged in a so-called Villard or Greinacher circuit in order to charge the storage capacitor Cgl with voltage doubling.

(37) In addition, with the Villard or Greinacher circuit illustrated, the application of a relatively high voltage to a diode in the reverse direction of the diode in question is avoided, which likewise represents a considerable advantage (but may also be realized by other rectifier circuits than the specific Villard or Greinacher circuit illustrated).

(38) In the rectifier circuit shown in FIG. 3, by charging the capacitor CS2 integrated in this case in the matching network 22 via the diode D2 in one half-cycle and the capacitor Cgl via the diode D1 in the other half-cycle, the rectifier voltage is virtually doubled, and the reverse voltage at the diode D1 is limited.

(39) Instead of the diode D2, an inductance (e.g., inductor) may also be used. Should very low rectifier voltages be required, the diode losses (e.g., brought about by the forward voltage of D2) may be higher than if an inductor is used instead of the diode D2. During the time period in which the diode D1 is off, however, there is a much higher reverse voltage at the diode, which may result in rapid degradation or destruction of the diode. For this reason, as a deviation from the example shown in FIG. 3, a symmetric embodiment of the energy reception path 20 (cf., the exemplary embodiments shown in FIGS. 4 and 5) may be selected even if the number of components required for this is greater in comparison with the circuit shown in FIG. 3.

(40) The example shown in FIG. 3 has the advantage in terms of circuitry that the circuit blocks matching network 22, path filter 24 and rectifier 30 form an asymmetric or “single-ended” arrangement and therefore require fewer components than in the case of a symmetrical design.

(41) In each case, symmetrical configurations will be described below with reference to FIGS. 4 and 5.

(42) In the examples shown in FIGS. 4 and 5, in each case, the same reference symbols are used for functionally identical components. With respect to the way in which these examples function, whereby these examples differ substantially only in terms of their symmetrized design, reference is made to the preceding description.

(43) In the example shown in FIG. 4, as illustrated, a symmetrical energy reception antenna 10 and a symmetrizing energy reception path 20 are provided.

(44) In contrast, in the example shown in FIG. 5, as illustrated, a symmetrizing energy reception antenna 10 with a symmetrical energy reception path 20 is provided.

(45) In both embodiments, the filtering and rectification have a symmetrical form. The diodes D2 used in the respective rectifiers 30 may also be replaced by inductances (e.g., inductors).

(46) By way of summary, advantageously, a high degree of interference suppression with respect to the MR signal detection may be achieved with the local coil system according to one or more of the present embodiments, and the circuit arrangements explained by way of example here for forming an energy reception chain from the energy reception antenna to the energy storage capacitor. With the described configurations of the components of the energy reception path, a high degree of flexibility with respect to the voltage or current ranges desired on the output side and a high degree of efficiency of the energy transmission (e.g., with low losses) are enabled.

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

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