Radio Frequency (RF) Receiver System Using Active Decoupling

Abstract

For a radio frequency (RF) receiver system 1 for use in a magnetic resonance imaging system, a solution is created for compensating for residual coupling of RF receiver coil elements 2 in the RF receiver system 1. This is achieved by an RF receiver system for use in a magnetic resonance imaging system, the RF receiver system 1 comprising at least two simultaneously used RF receiver coil elements 2, the RF receiver coil elements 2 comprising a signal generator 3 for providing a compensation signal and an excitation path 4, the excitation path 4 being configured to couple the compensation signal to the RF receiver coil elements 2 in order to reduce the residual coupling in the RF receiver system 1 by the compensation signal coupled to the RF receiver coil elements 2. The invention also relates to a magnetic resonance imaging system, a method for active decoupling of the RF receiver system 1 of a magnetic resonance imaging system, a software package for a magnetic resonance imaging system, a software package for upgrading a magnetic resonance imaging system, and a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method as recited in the claims.

Description

[Technical Field]

[0001] The present invention relates to the field of magnetic resonance (MR) imaging. In particular, the present invention relates to a radio frequency (RF) receiver system using active decoupling. The present invention also relates to an MR imaging system, a method for active decoupling of an RF receiver system, a software package for a magnetic resonance imaging system, a software package for upgrading a magnetic resonance imaging system, and a computer program product. [Background technology]

[0002] Array coils have been used in magnetic resonance imaging (MRI) for decades to improve both image quality (signal-to-noise ratio (SNR)) and speed (e.g., by accelerated imaging, e.g., via sensitivity encoding SensE). These techniques require decoupled coil elements, at least to some extent. The most common technique for decoupling is to use a precisely defined overlap of adjacent coil elements to null shared magnetic flux.

[0003] Modern coils with high channel counts generally suffer from residual coupling, which cannot be compensated for by traditional decoupling methods such as overlapping elements. This is primarily due to non-adjacent elements. Especially in high-field applications, coupling also depends on the patient load, which cannot be compensated for by fixed overlap. Until now, residual coupling was considered a given because its impact on image quality was too small to justify countermeasures.

[0004] However, thin and flexible coil arrays are now being developed and manufactured, which significantly increases the demand for compensating for residual coupling. In this type of array, the coil elements are closer to the tissue, and because of their flexibility and foldability, the coil coupling varies over a wide range, making it impossible to cancel the coil coupling by typical static means such as overlaps, transformers, or shared capacitors. Therefore, new means are needed to compensate for residual coupling over a wide, individually adjustable range.

[0005] U.S. Patent Application US2018 / 023978 discloses a magnetic resonance imaging system including a circuit for an RF receiver coil that uses GaN FETs to couple and decouple the receive electronics from the RF coil. In particular, an active decoupling circuit is provided to reduce inductive coupling between radio frequency coils in a multi-coil transmit / receive system. A feedback circuit is provided to couple a negative magnetic flux into the RF receiver coil, which mitigates the inductive coupling effect to nearby coils. This known feedback circuit simply feeds back the output of the RF receiver coil to generate a negative magnetic flux in the same RF receiver coil. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a radio frequency (RF) receiver system in which residual coupling can be actively compensated. [Means for solving the problem]

[0007] According to the present invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set out in the subclaims.

[0008] Therefore, according to the present invention, there is provided an RF receiver system for use in a magnetic resonance imaging system, the RF receiver system comprising at least two simultaneously used RF receiver coil elements, each RF receiver coil element comprising a signal generator for providing a compensation signal and an excitation path, the excitation path being configured to couple the compensation signal to the RF receiver coil element in order to reduce residual coupling in the RF receiver system due to the compensation signal being coupled to the RF receiver coil element.

[0009] The essential idea is therefore to compensate for the coupling by means of a compensation signal coupled to each single RF receiver coil by an excitation path. In other words, it is proposed to supply the coil elements of the RF receiver system with an active decoupling signal generated from a linear combination of all the RF receiver coil elements in order to decouple the coil elements. The term "RF receiver coil element" in the context of the present invention refers to a single physical receiving unit, such as a loop, or to one mode of a complex resonator, such as the mode of a birdcage resonator.

[0010] The RF receiver channels communicate with each other via a transverse communication circuit, and for each RF receiver coil element (2), its compensation signal depends on the output of one or more respective other RF receiver coil elements (2) of the RF receiver system, and for each RF receiver coil element, the transverse communication circuit is configured to provide the compensation signal to a respective excitation path. The transverse communication circuit is configured as a high-speed bidirectional data bus that provides correspondence between the RF receiver coil elements. The transverse communication circuit is coupled to a host that further processes the received signals from the RF receiver coil elements. Alternatively, the transverse communication circuit is configured to directly combine the controllers in the RF signal channels from the RF receiver channels to a common controller responsible for several RF receiver coils via their respective excitation path elements to be decoupled. According to a preferred embodiment of the present invention, the excitation path includes a loop element for coupling the compensation signal to the RF receiver coil element. The loop element facilitates coupling magnetic flux to the coil elements.

[0011] Alternatively, according to another preferred embodiment, the excitation path is realized by a coupling circuit configured to couple the compensation signal to the RF receiver coil elements, the coupling circuit comprising at least one lumped element or transmission line for coupling the compensation signal to the RF receiver coil elements.

[0012] According to a preferred embodiment, each RF receiver coil element comprises a matching network and the coupling circuit is incorporated into the matching network of the RF receiver coil element.

[0013] According to another preferred embodiment of the invention, the RF receiver coil element comprises a digital receive chain for digitization of the signals received by the RF receiver coil element. A digital receive chain with digitization performed directly on the RF receiver coil allows for easy decoupling of the RF receiver coil element.

[0014] According to one embodiment of the present invention, the digital receive chain of each RF receiver coil is equipped with a controller, and the controllers are connected by a high-speed bidirectional data bus. The existing controllers of the RF coils can be used to perform the necessary calculations for decoupling. The high-speed bidirectional data bus between the controllers of the different RF receiver coils ensures fast and easy data exchange.

[0015] In one embodiment of the present invention, the RF receiver system includes a digital-to-analog converter (DAC) for each RF receiver coil element, the DAC configured to generate a compensation signal.

[0016] According to one embodiment of the present invention, the RF receiver coil is a flexible and / or foldable and / or arbitrarily shaped RF receiver coil. The present invention relates to all kinds of array receiver coils, but especially in the case of flexible coils with strong patient coupling, adaptation to load changes can be taken into account with the proposed RF receiver system.

[0017] The invention further relates to a magnetic resonance imaging system comprising the RF receiver system previously described.

[0018] The present invention also provides a method for active decoupling of an RF receiver system, the method comprising: providing an RF receiver system as previously described; generating a compensation signal by a signal generator of each RF receiver coil element; Compensation signal through excitation path

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[0019] According to another embodiment of the present invention, the combined complex signal vector

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[0020] According to a preferred embodiment, each RF receiver coil element comprises a digital receive chain for digitizing the signals received by the RF receiver coil element, the digital receive chain of each RF receiver coil element comprising a controller, which assigns a vector

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[0021] The present invention further provides a method for active decoupling of a radio frequency (RF) receiver system, the method comprising: Combined complex signal vector

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[0022] The present invention also relates to a software package for a magnetic resonance imaging system, the software package including instructions for controlling an RF receiver system in accordance with the method previously described.

[0023] The invention further relates to a software package for upgrading a magnetic resonance imaging system, the software package including instructions for controlling an RF receiver system according to the method previously described.

[0024] Finally, the invention relates to a computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the methods described above, i.e. the computer program product of the invention comprises instructions which, when executed by a computer, cause the computer to carry out the steps of the methods defined in claims 11 to 13.

[0025] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, but such embodiments do not necessarily represent the full scope of the invention, and reference is therefore made to the claims and this specification for interpreting the scope of the invention. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram illustrating a schematic of a radio frequency (RF) receiver system with an RF receiver coil element and three excitation paths, according to an embodiment of the present invention. [Figure 2]FIG. 1 illustrates a flowchart of a method for active decoupling of a radio frequency (RF) receiver system, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 schematically illustrates an RF receiver system 1 having three RF receiver coil elements 2 and three excitation paths 4 according to an embodiment of the present invention. Each of the RF receiver coil elements 2 is equipped with an analog matching / detuning / preamplifier section 6 followed by an analog / digital chip 7. The excitation path 4 of each RF receiver coil element 2 is sketched in FIG. 1 by a small coupling loop 5 for coupling magnetic flux into the RF receiver coil element 2. Alternatively, a coupling circuit comprising at least one lumped element or transmission line for coupling a compensation signal into the RF receiver coil element may also be incorporated, for example, into the matching network. Furthermore, each RF receiver coil element 2 of the RF receiver system 1 comprises a signal generator 10 for providing a compensation signal. In one embodiment of the present invention, the signal generator 10 is a digital-to-analog converter (DAC). It is provided that each RF receiver coil element 2 comprises a digital receive chain 8 for digitizing signals received by the RF receiver coil element 2. This is particularly advantageous because the digital receive chain 8 of each RF receiver coil element 2 can be equipped with a controller 11, and the controllers 11 of the different RF receiver coil elements 2 are connected between each other and to a host 12 by a high-speed bidirectional data bus 13. The host 12 further processes the received and digitized signals from the RF receiver coil elements 2. In one embodiment of the present invention, the controllers 11 may even be directly combined with a common controller, or one controller 11 may be responsible for several elements. The controllers 11 of the RF receiver coil elements 2 may not only be for controlling the RF receiver coil elements 2, but may also be used to calculate compensation for coupling of the RF receiver coil elements 2 in the RF receiver system 1.

[0028] FIG. 2 shows a flowchart of a method for active decoupling of an RF receiver system 1 according to one embodiment of the present invention. The method begins in step 200, in which an RF receiver system 1 is provided. The RF receiver system 1 comprises at least two simultaneously used RF receiver coil elements 2. The term "coil element" can also include system-integrated coils. Thus, in one embodiment of the present invention, the RF receiver coil elements can also be system-integrated coils, such as body coils and / or local receiver coils. The present invention can also be used to combine such system-integrated coils. Each RF receiver coil element 2 comprises a signal generator 10 for providing a compensation signal. The RF receiver coil element 2 further comprises an excitation path 4, which is configured to couple (input) the compensation signal to the RF receiver coil element 2. The excitation path 4 can comprise, for example, a small coupling loop 5 for coupling magnetic flux into the RF receiver coil 2, as sketched in FIG. 1 . In step 210, a compensation signal is generated by the signal generator 10 of each RF receiver coil element 2. In step 220, the compensation signal generated by the signal generator 10 is coupled to the corresponding RF receiver coil element 2 by the excitation path 4. At the same time, the combined complex signal vector

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[0029] While the present invention has been shown and described in detail in the drawings and the foregoing description, such examples and descriptions are to be considered illustrative or exemplary, and not restrictive, and the present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. Moreover, for the sake of clarity, not all elements in the drawings have been labeled with reference signs. Appendix 1: 1. A radio frequency (RF) receiver system for use in a magnetic resonance imaging system, the RF receiver system comprising: two or more simultaneously used RF receiver coil elements and two or more RF signal channels, each RF receiver coil element coupled to a respective RF signal channel; each RF receiver coil element comprising a signal generator for providing a compensation signal and an excitation path, the excitation path coupling the compensation signal to the RF receiver coil element to reduce residual coupling in the RF receiver system with the compensation signal coupled to the RF receiver coil element; the RF receiver channels communicate with each other by transverse communication circuits; An RF receiver system in which, for each RF receiver coil element, its compensation signal depends on the output of one or more respective other RF receiver coil elements of the RF receiver system, and for each RF receiver coil element, the transverse communication circuitry provides the compensation signal to a respective one of the excitation paths. Appendix 2: 2. The RF receiver system of claim 1, wherein, for each RF receiver coil element, the respective transverse communication circuit generates a decoupled signal from a linear combination of all RF receiver coil elements to the RF receiver coil element of the RF receiver system. Appendix 3: 2. The RF receiver system of claim 1, wherein the excitation path comprises a loop element for coupling the compensation signal to the RF receiver coil element. Appendix 4: 2. The RF receiver system of claim 1, wherein the excitation path is realized by a coupling circuit that couples the compensation signal to the RF receiver coil element, the coupling circuit comprising at least one lumped element or transmission line for coupling the compensation signal to the RF receiver coil element. Appendix 5: 4. The RF receiver system of claim 3, wherein each RF receiver coil element comprises a matching network, and the coupling circuit is incorporated into the matching network of the RF receiver coil element. Appendix 6: 6. The RF receiver system of claim 1, wherein for each RF receiver coil element, the RF receiver channel is configured as a digital receive chain for digitizing the signal received by the RF receiver coil element. Appendix 7: 7. The RF receiver system of claim 6, wherein the digital receive chain of each RF receiver coil element includes a controller, and the controllers are connected to each other by a high-speed bidirectional data bus. Note 8: 8. The RF receiver system of any one of claims 1 to 7, wherein the RF receiver system comprises a digital-to-analog converter (DAC) for each RF receiver coil, the DAC generating the compensation signal. Appendix 9: 9. The RF receiver system of any one of claims 1 to 8, wherein the RF receiver coil element is a flexible and / or foldable and / or arbitrarily shaped RF receiver coil. Appendix 10: 10. A magnetic resonance imaging system comprising an RF receiver system according to any one of claims 1 to 9. Note 11: 1. A method for active decoupling of a radio frequency (RF) receiver system, the method comprising: providing an RF receiver system according to any one of claims 1 to 9; generating a compensation signal by a signal generator of each RF receiver coil element; The compensation signal is

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[0030] 1 Radio Frequency (RF) Receiver System 2 RF receiver coil elements 4 Excitation path 5. Coupling Loop 6 Analog Matching / Detuning / Preamp Sections 7 Analog / Digital Chips 8 Digital Receive Chain 9 Analog-to-Digital Converter 10 Signal Generator / Digital-to-Analog Converter 11 Controller 12 hosts 13 Bidirectional Data Bus

Claims

1. 1. A radio frequency (RF) receiver system for use in a magnetic resonance imaging system, the RF receiver system comprising: two or more RF receiver coil elements and two or more RF signal channels, each RF receiver coil element coupled to a respective RF signal channel; each RF receiver coil element comprises a signal generator for providing a compensation signal and an excitation path, the excitation path configured to couple the compensation signal to the RF receiver coil element, and each RF receiver coil element configured to reduce residual coupling in the RF receiver system by the compensation signal coupled to the RF receiver coil element; two or more RF receiver channels communicating with each other by transversely coupled communication circuits; An RF receiver system in which, for each RF receiver coil element, its compensation signal depends on the output of one or more respective other RF receiver coil elements of the RF receiver system, and for each RF receiver coil element, the transversely coupled communication circuitry provides the compensation signal to a respective one of the excitation paths.

2. 2. The RF receiver system of claim 1, wherein for each RF receiver coil element, the respective communication circuit generates a decoupling signal from a linear combination of all RF receiver coil elements to the RF receiver coil element of the RF receiver system.

3. The RF receiver system of claim 1 , wherein the excitation path comprises a loop element for coupling the compensation signal to the RF receiver coil element.

4. 2. The RF receiver system of claim 1, wherein the excitation path is realized by a coupling circuit that couples the compensation signal to the RF receiver coil element, the coupling circuit comprising at least one lumped element or transmission line for coupling the compensation signal to the RF receiver coil element.

5. 5. The RF receiver system of claim 4, wherein each RF receiver coil element comprises a matching network, and the coupling circuit is incorporated into the matching network of the RF receiver coil element.

6. 6. The RF receiver system of claim 1, wherein for each RF receiver coil element, the RF receiver channel is configured as a digital receive chain for digitizing the compensation signal received by the RF receiver coil element.

7. 7. The RF receiver system of claim 6, wherein the digital receive chain of each RF receiver coil element comprises at least two controllers, the at least two controllers being connected to each other by a bidirectional data bus.

8. 8. The RF receiver system of claim 1, wherein the RF receiver system comprises a digital-to-analog converter (DAC) for each RF receiver coil, the DAC generating the compensation signal.

9. 9. The RF receiver system according to any one of claims 1 to 8, wherein the RF receiver coil element is a flexible and / or foldable and / or differently shaped RF receiver coil.

10. A magnetic resonance imaging system comprising an RF receiver system according to any one of claims 1 to 9.

11. 1. A method for active decoupling of a radio frequency (RF) receiver system, the method comprising: Providing an RF receiver system according to any one of claims 1 to 9; generating a compensation signal by a signal generator of each RF receiver coil element; The compensation signal is [0000] to the corresponding RF receiver coil elements, and all RF receiver coil elements combine to produce a combined complex signal vector [Equation 22] receiving a signal from the signal generator, wherein: [Equation 23] is a signal vector received at the RF receiver coil element without coupling; the combined complex signal vector [0000] and compensating for the coupling of A method comprising:

12. the combined complex signal vector [Equation 25] The step of compensating for the coupling of For each RF receiver coil element, the vector [Equation 26] by the corresponding row of a matrix B and applying the result to the received compensation signal of the RF receiver coil element via the excitation path, wherein B=A －１ −1, 1 being the identity matrix, each RF receiver coil element comprising a digital receive chain for digitizing the signal received by the RF receiver coil element, the digital receive chain of each RF receiver coil element comprising a controller, and the corresponding row of the matrix B is assigned to the vector [0000] The step of multiplying by is performed on the controller.

12. The method of claim 11, comprising:

13. Combined complex signal vector [0000] The combination of [0000] From the left, the inverse matrix A －１ 12. The method of claim 11, comprising the step of compensating by multiplying

14. 14. A computer program for a magnetic resonance imaging system, the computer program comprising instructions for controlling a radio frequency (RF) receiver system of the magnetic resonance imaging system according to the method of any one of claims 11 to 13.

15. 14. A computer program for upgrading a magnetic resonance imaging system, the computer program comprising instructions for controlling a radio frequency (RF) receiver system of the magnetic resonance imaging system according to the method of any one of claims 11 to 13.

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