Antenna system for NMR and MRI apparatus

• US 5,903,150 A
• Filed: 08/20/1997
• Issued: 05/11/1999
• Est. Priority Date: 06/03/1996
• Status: Expired due to Term

• Current Assignee: Samuel Roznitsky
• Original Assignee: Samuel Roznitsky
• Inventors: Roznitsky, Samuel
• Primary Examiner(s): Arana, Louis M.
• Application Number:
  US08/915,205
• Time in Patent Office: 629 Days
• Field of Search: 324/318, 324/322, 324/314, 324/307, 324/309, 324/300
• US Class Current: 324/318
• CPC Class Codes: G01R 33/3657 Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil

Abstract

An antenna system, for use in an NMR or MRI apparatus which includes a radio frequency (RF) signal transmitter and a radio frequency (RF) signal receiver, includes at least first and second electromagnetically coupled circuits, the first circuit comprising a first inductance producing a first electromagnetic field flux vector, and the second circuit comprising a second inductance producing a second electromagnetic field flux vector having a component which interacts with a component of the first electromagnetic field flux vector. A switch system has a first switching position for coupling the first circuit to an output of the RF signal transmitter and preventing a damaging level of signal from the second circuit from being fed to an input of said RF signal receiver, and a second switching position for permitting an RF signal from the second circuit to be fed to an input of the RF signal receiver and decoupling the first circuit from the output of the RF signal transmitter. The antenna produces an electromagnetic field flux enclosing an examination object therewithin, to irradiate the examination object, when the switch system is in the first switching position. An electromagnetic field flux produced by a signal emitted by the examination object'"'"'s relaxing nuclei is picked up by the antenna system and is fed to the RF signal receiver via the second circuit, when the switch system is in the second switching position. An array antenna system capable of producing a useful variety of electromagnetic field shapes and coverages may be made up of a combination of antenna elements.

Claims

1. An antenna system for use in a nuclear magnetic resonance or magnetic resonance imaging apparatus which includes a radio frequency (RF) signal transmitter and a radio frequency (RF) signal receiver, the antenna system comprising:

at least first and second electromagnetically coupled circuits;

said first circuit comprising a first inductance producing a first electromagnetic field flux vector;

said second circuit comprising a second inductance producing a second electromagnetic field flux vector;

said first and second inductances being electromagnetically coupled such that the first electromagnetic field flux vector has a component interacting with a component of the second electromagnetic field flux vector; and

a switch system coupled to said first circuit and to said second circuit, said switch system having;

a first switching position for coupling said first circuit to an output of said RF signal transmitter and for preventing a damaging level of signal from said second circuit from being fed to an input of said RF signal receiver, and

a second switching position for permitting an RF signal from said second circuit to be fed to an input of said RF signal receiver and for decoupling said first circuit from the output of said RF signal transmitter;

and wherein;

said antenna system produces an electromagnetic field flux enclosing an examination object therewithin, which electromagnetic field flux is used to irradiate the examination object, when said switch system is in the first switching position; and

an electromagnetic field flux produced by a signal emitted by the examination object'"'"'s relaxing nuclei is picked up by said electromagnetically coupled inductances and is fed to said RF signal receiver via said second circuit, when said switch system is in the second switching position.

2. The antenna system of claim 1, wherein:

said first circuit comprises at least a first capacitance connected in parallel with said first inductance, and comprising together with said first inductance the first circuit, and wherein at least said first capacitance is used for frequency tuning of the antenna system at least during transmission; and

said switch system includes at least one first switching element coupling said first circuit to said RF signal transmitter output in said first switching position and decoupling said first circuit from said RF signal transmitter output in said second switching position.

3. The antenna system of claim 2, wherein said first capacitance comprises a variable capacitor element.

4. The antenna system of claim 2, wherein:

said second circuit comprises;

a variable capacitance element, coupled for frequency tuning of the antenna circuitry;

a second capacitance; and

an auxiliary inductance for roughly matching an impedance of said second capacitance;

said second capacitance, said variable capacitance element and said auxiliary inductance being coupled together and being further coupled to said second inductance; and

said switch system includes a second switching element coupled to selectively short out at least said variable capacitance element and said RF receiver input, and for electrically removing at least said variable capacitance element and said RF receiver input from said second circuit, in said first switching position, and said second switching element being electrically open and having substantially no electrical effect in said second switching position.

5. The antenna circuitry of claim 4, wherein said variable capacitance element comprises at least one varactor.

6. The antenna system of claim 4, wherein said first capacitance comprises a variable capacitor element.

7. The antenna system of claim 1, wherein:

said second circuit comprises;

a variable capacitance element, coupled for frequency tuning of the antenna circuitry;

a second capacitance; and

an auxiliary inductance for roughly matching an impedance of said second capacitance;

said second capacitance, said variable capacitance element and said auxiliary inductance being coupled together and being further coupled to said second inductance; and

said switch system includes a second switching element coupled to selectively short out at least said variable capacitance element and said RF receiver input, and for electrically removing at least said variable capacitance element and said RF receiver input from said second circuit, in said first switching position, and said second switching element being electrically open and having substantially no electrical effect in said second switching position.

8. The antenna circuitry of claim 7, wherein said variable capacitance element comprises at least one varactor.

9. The antenna system of claim 7, wherein said first circuit comprises a capacitor element connected to said first inductance.

10. The antenna system of claim 7, wherein said second capacitance, said variable capacitance element and said auxiliary inductance are connected in a series connection.

11. The antenna system of claim 10, wherein said series connection is serially connected with said second inductance.

12. The antenna system of claim 7, wherein said auxiliary inductance is connected in series with a switch device, the series connection being connected in parallel with said second capacitance.

13. The antenna system of claim 1, wherein said switch system comprises:

at least a first pair of opposite polarity, parallel connected, diodes coupled to an output of said RF signal transmitter; and

at least a second pair of opposite polarity, parallel connected, diodes coupled across an input of said RF signal receiver.

14. The antenna system of claim 1, further comprising a resistance coupled to an output of said RF signal transmitter.

15. The antenna system of claim 1, wherein:

said second circuit comprises;

a variable capacitance element, coupled for frequency tuning of the antenna circuitry;

a second capacitance; and

said second capacitance and said variable capacitance element being connected to said second inductance; and

said switch system includes a second switching element coupled to selectively short out at least said variable capacitance element and said RF receiver input, and for electrically removing at least said variable capacitance element and said RF receiver input from said second circuit, in said first switching position, and said second switching element being electrically open and having substantially no electrical effect in said second switching position.

16. The antenna circuitry of claim 15, wherein said variable capacitance element comprises a varactor.

17. The antenna system of claim 15, wherein said first circuit comprises a capacitor element connected to said first inductance.

18. The antenna system of claim 1, wherein:

said second circuit comprises;

a variable capacitance element, coupled for frequency tuning of the antenna circuitry;

said variable capacitance element being coupled to said second inductance; and

said switch system includes a second switching element coupled to selectively short out at least said variable capacitance element and said RF receiver input, and for electrically removing said variable capacitance element and said RF receiver input from said second circuit, in said first switching position, and said second switching element being electrically open and having substantially no electrical effect in said second switching position.

19. The antenna circuitry of claim 18, wherein said variable capacitance element comprises a varactor.

20. The antenna system of claim 18, wherein said first circuit comprises a capacitor element connected to said first inductance.

27. The antenna system of claim 1, wherein:

at least one of the first and second circuits is electromagnetically coupled to at least one third circuit which includes at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductance so as to contribute to an electromagnetic field flux enclosing the examination object.

28. The antenna system of claim 27, comprising a plurality of said third circuits electromagnetically coupled to at least some of said first and second circuits and each other.

29. The antenna system of claim 1, comprising:

a plurality of first circuits, each first circuit including an inductance, each first circuit being coupled to said signal transmitter through said switch system;

and wherein said first circuits are electromagnetically coupled to said second circuit.

30. The antenna system of claim 29, wherein said first circuits are electromagnetically coupled together.

31. The antenna system of claim 29, comprising:

a plurality of second circuits, each second circuit including an inductance, each second circuit being coupled to said receiver through said switch system;

and wherein said second circuits are electromagnetically coupled to said first circuits.

32. The antenna system of claim 31, wherein said second circuits are electromagnetically coupled together.

33. The antenna system of claim 32, wherein said first circuits are electromagnetically coupled together.

34. The antenna system of claim 1, comprising:

a plurality of second circuits, each second circuit including an inductance, each second circuit being coupled to said receiver through said switch system;

and wherein said second circuits are electromagnetically coupled to said first circuit.

35. The antenna system of claim 34, wherein said second circuits are electromagnetically coupled together.

36. The antenna system of claim 29, wherein:

at least one of the plurality of first circuits is electromagnetically coupled to said second circuit with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

37. The antenna system of claim 36, wherein said first circuits are electromagnetically coupled together.

38. The antenna system of claim 31, wherein:

the plurality of first circuits are electromagnetically coupled to said plurality of second circuits with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

39. The antenna system of claim 38, wherein said first circuits are electromagnetically coupled together.

40. The antenna system of claim 39, wherein said second circuits are electromagnetically coupled together.

41. The antenna system of claim 38, wherein said second circuits are electromagnetically coupled together.

42. The antenna system of claim 34, wherein:

at least one of the plurality of second circuits is electromagnetically coupled to said first circuit with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

43. The antenna system of claim 42, wherein said second circuits are electromagnetically coupled together.

21. A method of operating an antenna system in a nuclear magnetic resonance or magnetic resonance imaging apparatus which includes a radio frequency (RF) signal transmitter and a radio frequency (RF) signal receiver, the method comprising:

providing at least first and second electromagnetically coupled circuits;

said first circuit comprising a first inductance producing a first electromagnetic field flux vector;

said second circuit comprising a second inductance producing a second electromagnetic field flux vector;

causing said first and second inductances to be electromagnetically coupled such that the first electromagnetic field flux vector has a component interacting with a component of the second electromagnetic field flux vector; and

switching said first circuit and said second circuit with a switch system such that;

when said switch system is in a first switching position, said first circuit is coupled to an output of said RF signal transmitter, and a damaging level of signal from said second circuit is prevented from being fed to an input of said RF signal receiver, and

when said switch system is in a second switching position, an RF signal from said second circuit is fed to an input of said RF signal receiver and said first circuit is decoupled from an output of said RF signal transmitter; and

wherein;

said antenna system produces an electromagnetic field flux enclosing an examination object therewithin, which electromagnetic field flux is used to irradiate the examination object, when said switch system is in the first switching position; and

an electromagnetic field flux produced by a signal emitted by the examination object'"'"'s relaxing nuclei is picked up by said electromagnetically coupled inductances and is fed to said RF signal receiver via said second circuit, when said switch system is in the second switching position.

22. The method of claim 21, wherein:

the frequency response and the electromagnetic field flux of said antenna system is set independently and separately in the first and second switching positions.

23. The method of claim 21, wherein the antenna system is positioned at any angle orthogonal to a static magnetic field of the apparatus.

24. The method of claim 21, comprising maintaining said antenna system tuned to the object'"'"'s Larmor frequency when said switch system is in said first switching position.

25. The method of claim 21, comprising detuning said second circuit from the object'"'"'s Larmor frequency when said switch system is in said first switching position.

26. The method of claim 21, wherein said antenna system is tuned to the object'"'"'s Larmor frequency when said switch system is in said second switching position.

44. The method of claim 21, comprising:

providing at least one third circuit which includes at least a third inductance;

at least one of said first and second circuits being electromagnetically coupled to said at least one third circuit; and

said at least one third circuit being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

45. The method of claim 21, comprising:

providing a plurality of said third circuits electromagnetically coupled to said at least some of said first and second circuits and to each other.

46. The method of claim 21, comprising:

providing a plurality of first circuits, each first circuit including an inductance, and each first circuit being coupled to said signal transmitter through said switch system;

and wherein said first circuits are electromagnetically coupled to said second circuit.

47. The method of claim 46, wherein said first circuits are electromagnetically coupled together.

48. The method of claim 46, comprising:

providing a plurality of second circuits, each second circuit including an inductance, and each second circuit being coupled to said receiver through said switch system;

and wherein said second circuits are electromagnetically coupled to said first circuits.

49. The method of claim 48, wherein said second circuits are electromagnetically coupled together.

50. The method of claim 49, wherein said first circuits are electromagnetically coupled together.

51. The method of claim 21, comprising:

providing a plurality of second circuits, each second circuit including an inductance, and each second circuit being coupled to said receiver through said switch system;

and wherein said second circuits are electromagnetically coupled to said first circuit.

52. The method of claim 51, wherein said second circuits are electromagnetically coupled together.

53. The method of claim 46, comprising:

electromagnetically coupling at least one of the plurality of first circuits to said second circuit with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

54. The method of claim 53, wherein said first circuits are electromagnetically coupled together.

55. The method of claim 48, comprising:

electromagnetically coupling at least one of the plurality of first circuits to plurality of said second circuits with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductance so as to contribute to an electromagnetic field flux enclosing the examination object.

56. The method of claim 55, wherein said first circuits are electromagnetically coupled together.

57. The method of claim 56, wherein said second circuits aeelectromagnetically coupled together.

58. The method of claim 55, wherein said second circuits are electromagnetically coupled together.

59. The method of claim 51, comprising:

electromagnetically coupling at least one of the plurality of second circuits to said first circuit with at least one third circuit, the at least one third circuit including at least a third inductance;

said third inductance being electromagnetically coupled at least to adjacent inductances so as to contribute to an electromagnetic field flux enclosing the examination object.

60. The method of claim 59, wherein said second circuits are electromagnetically coupled together.

61. An antenna system for use in a nuclear magnetic resonance or magnetic resonance imaging apparatus which includes a radio frequency (RF) signal transmitter and a radio frequency (RF) signal receiver, the antenna system comprising:

at least one circuit, including an inductance, for producing an electromagnetic field flux vector; and

a switch system coupled to said at least one circuit, said switch system having;

a first switching position for coupling said at least one circuit to an output of said RF signal transmitter and for preventing a damaging level of signal from said at least one circuit from being fed to an input of said RF signal receiver, and

a second switching position for permitting an RF signal from said at least one circuit to be fed to an input of said RF signal receiver and for decoupling said at least one circuit from the output of said RF signal transmitter;

and wherein;

said antenna system produces an electromagnetic field flux enclosing an examination object therewithin, which electromagnetic field flux is used to irradiate the examination object, when said switch system is in the first switching position; and

an electromagnetic field flux produced by a signal emitted by the examination object'"'"'s relaxing nuclei is picked up by said at least one circuit and is fed to said RF signal receiver, when said switch system is in the second switching position.

62. The antenna system of claim 61, wherein:

said at least one circuit comprises at least a first capacitance connected in parallel with said inductance, and wherein at least said first capacitance is used for frequency tuning of the antenna system at least during transmission; and

said switch system includes at least one first switching element coupling said at least one circuit to said RF signal transmitter output in said first switching position and decoupling said at least one circuit from said RF signal transmitter output in said second switching position.

63. The antenna system of claim 62, wherein said first capacitance comprises a variable capacitor element.

64. The antenna system of claim 62, wherein:

said at least one circuit further comprises a second capacitance, said second capacitance comprising a variable capacitance element coupled to said inductance for frequency tuning at least during reception when said switch system is in the second switching position; and

said switch system includes a second switching element coupled to selectively effectively short out at least said variable capacitance element and said RF receiver input, and for thereby electrically removing at least said variable capacitance element and said RF receiver input from said at least one circuit when said switch system is in the first switching position, and said second switching element being electrically open and having substantially no electrical effect when said switch system is in said second switching position.

65. A method of operating an antenna system in a nuclear magnetic resonance or magnetic resonance imaging apparatus which includes a radio frequency (RF) signal transmitter and a radio frequency (RF) signal receiver, the method comprising:

providing at least one circuit including an inductance, for producing an electromagnetic field flux vector; and

switching said at least one circuit with a switch system such that;

when said switch system is in a first switching position, said at least one circuit is coupled to an output of said RF signal transmitter, and a damaging level of signal from said at least one circuit is prevented from being fed to an input of said RF signal receiver, and

when said switch system is in a second switching position, an RF signal from said at least one circuit is fed to an input of said RF signal receiver and said at least one circuit is decoupled from an output of said RF signal transmitter;

and wherein;

said antenna system produces an electromagnetic field flux enclosing an examination object therewithin, which electromagnetic field flux is used to irradiate the examination object, when said switch system is in the first switching position; and

an electromagnetic field flux produced by a signal emitted by the examination object'"'"'s relaxing nuclei is picked up by said at least one circuit and is fed to said RF signal receiver when said switch system is in the second switching position.

66. The method of claim 65, comprising frequency tuning the antenna system with a capacitance coupled to said inductance.

67. The method of claim 66, wherein said capacitance comprises a variable capacitance for frequency tuning the antenna system.

68. The method of claim 66, comprising maintaining said antenna system tuned to the object'"'"'s Larmor frequency when said switch system is in said first switching position.

69. The method of claim 66, wherein said antenna system is tuned to the object'"'"'s Larmor frequency when said switch system is in said second switching position.