Resonator system

• US 7,193,418 B2
• Filed: 06/13/2005
• Issued: 03/20/2007
• Est. Priority Date: 07/23/2004
• Status: Active Grant

• Current Assignee: Bruker Switzerland AG (Bruker Corporation)
• Original Assignee: Bruker Biospin AG (Bruker Corporation)
• Inventors: Freytag, Nicolas
• Primary Examiner(s): Shrivastav; Brij B.
• Application Number:
  US11/150,197
• Publication Number:
  US 20060017440A1
• Time in Patent Office: 645 Days
• Field of Search: 324/318, 324/319, 324/433, 324/309, 324/307, 324/300, 324/322, 600/410, 600422-425
• US Class Current: 324/318
• CPC Class Codes: G01R 33/34007 Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
• CPC Class Codes: G01R 33/34023 Superconducting RF coils
• CPC Class Codes: G01R 33/34046 Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
• CPC Class Codes: G01R 33/34061 Helmholtz coils
• CPC Class Codes: G01R 33/34076 Birdcage coils
• CPC Class Codes: G01R 33/34092 RF coils specially adapted for NMR spectrometers

Abstract

A resonator system for generating a radio frequency (RF) magnetic field in a volume under investigation of a magnetic resonance (MR) arrangement, comprises a number N of individual resonators (2) which surround the volume under investigation and which are each disposed on a flat dielectric substrate (1) around a z-axis, wherein the individual resonators (2) have windows (8) through each of which one individual RF field is generated in the volume under investigation in single operation of the individual resonators (2) and, through cooperation among the individual resonators (2), a useful RF field (7) is generated in the volume under investigation, wherein a remote RF field (6) is asymptotically generated far outside of the resonator system, and the spatial distribution of the useful RF field (7) is substantially mirror-symmetrical relative to a first plane A which contains the z-axis, and that of the asymptotic remote RF field (6) is substantially mirror-symmetrical relative to a second plane B which contains the z-axis, the useful RF field (7) extending substantially parallel to the first plane A in the volume under investigation, wherein the number of individual resonators (2) is N>4 and wherein, during operation of the resonator system at at least one point in time, the substrate plane of at least one individual resonator (2) subtends an angle of more than 40° with respect to the direction of the useful RF field (7) in the volume under investigation, and at least one further individual resonator (2) subtends an angle of less than 40° with respect to the direction of the useful RF field (7) in the volume under investigation, is characterized in that the first plane A is not rotated about the z-axis relative to the second plane B or is rotated by less than 360°/(N+1). The inventive resonator system realizes a resonator system with improved field homogeneity and full quadrature suitability, high quality factor and large efficiency using straightforward constructional measures.

Claims

1. A resonator system for generating a radio frequency (RF) magnetic field in a volume under investigation of a magnetic resonance (MR) apparatus, the resonator system comprising:

a number N of individual flat resonators containing superconducting materials, surrounding volume under investigation, and each being disposed on a flat dielectric substrate about and parallel to a z-axis, each individual resonator having a window through which one individual RF field is generated in the volume under investigation in single operation of the respective individual resonator, said individual resonators cooperating to generate a useful RF field in the volume under investigation, said resonators also generating an asymptotic, remote RF field far outside of the resonator system, wherein a spatial configuration of said individual resonators as well as a dependence of said useful RF field are substantially mirror-symmetrical relative to a first plane A which contains the z-axis, and a spatial distribution of said asymptotic remote RF field is also substantially mirror-symmetrical relative to said first plane A, said useful RF field extending substantially parallel to said first plane A in the volume under investigation, wherein said individual resonators only have 2-fold rotational symmetry about the z-axis, all substrate planes of said individual resonators differing within a partial region defined and subdivided by said first plane A, wherein a number of individual resonators N>

4 and, during operation of the resonator system, a substrate plane of at least one individual resonator subtends an angle of more than 40°

with respect to a direction of said useful RF field in the volume under investigation.

2. The resonator system of claim 1, wherein said individual resonators are exclusively produced from superconducting material except for said dielectric substrates and an optional normally conducting metallic quench protection layer.

3. The resonator system of claim 1, wherein said individual resonators are disposed on surfaces of a polyhedron.

4. The resonator system of claim 1, wherein said individual resonators are disposed such that surface normals of said substrates have a tangential component.

5. The resonator system of claim 4, wherein said individual resonators are disposed radially outwardly like a star such that surface normals of said substrates are tangentially oriented.

6. The resonator system of claim 1, wherein said individual resonators comprise at least one of spiral resonators, resonators with distributed capacitances, resonators with localized capacitances, and double-sided resonators.

7. The resonator system of claim 1, wherein several individual resonators are disposed along the z-direction for active shielding of the generated RF magnetic field in the z-direction and/or wherein several individual resonators are nested in a radial direction in an xy-plane perpendicular to the z-direction for active shielding of the generated RF magnetic field.

8. The resonator system of claim 1, wherein several substrates are provided with one or more individual resonators and are stacked or nested in the z-direction and/or in a radial direction.

9. The resonator system of claim 1, wherein at least one of said individual resonators has a resonance frequency which differs from that of other said individual resonators.

10. The resonator system of claim 1, wherein said individual resonators are inductively, and/or capacitively, and/or galvanically coupled.

11. A resonator system comprising a combination of the resonator system of claim 1, with a conventional normally conducting and/or superconducting individual resonators and/or resonator systems.

12. A method for adjusting eigen-resonances of individual resonators of the resonator system of claim 1, the method comprising the steps of:

a) designing a resonator system;

b) calculating currents I₀ that permit maximum field homogeneity in a volume under investigation for a given geometrical arrangement of individual resonators;

c) calculating a current distribution in the resonator system and a magnetic field in the volume under investigation for a desired resonance mode;

d) calculating average currents in conductor elements of individual resonators;

e) correcting the eigen-resonances of the individual resonators, wherein changes are substantially proportional to a respective deviation of the currents from the currents I₀ calculated in step b); and

f) repeating steps b) through e) until a homogeneity of a useful RF field in the volume under investigation is maximized.

13. A resonator system for generating a radio frequency (RF) magnetic field In a volume under investigation of a magnetic resonance (MR) apparatus, the resonator system comprising:

a number N of individual resonators which surround the volume under investigation and which are each disposed, about a z-axis, on a flat dielectric substrate, each individual resonator having a window through which one individual RF field is generated in the volume under investigation in single operation of the respective individual resonator, said individual resonators cooperating to generate a useful RF field in the volume under investigation, said resonators also generating an asymptotic, remote RF field far outside of the resonator system, wherein a spatial distribution of said useful RF field is substantially mirror-symmetrical relative to a first plane A which contains the z-axis, and a spatial distribution of said asymptotic remote RF field is substantially mirror-symmetrical relative to a second plane B which contains the z-axis, said useful RF field extending substantially parallel to said first plane A in the volume under investigation, wherein a number of individual resonators N>

4 and, at at least one point in time during operation of the resonator system, a substrate plane of at least one individual resonator subtends an angle of more than 40°

with respect to a direction of said useful RF field in the volume under investigation, wherein said first plane A is not rotated about the z-axis relative to said second plane B or is rotated about the z-axis relative to said second plane B by less than 360°

/(N+1) and wherein said individual resonators comprise at least one of spiral resonators, resonators with distributed capacitances, resonators with localized capacitances, and double-sided resonators.

14. The resonator system of claim 13, wherein said individual resonators contain superconducting material and/or are exclusively produced from superconducting material except for said dielectric substrates and an optional normally conducting metallic quench protection layer.

15. The resonator system of claim 13, wherein said number N of said individual resonators is N=2(i+2), or N=4(i+1), wherein i is a natural number.

16. The resonator system of claim 13, wherein said individual resonators are disposed in 2-fold, 4-fold or N-fold rotational symmetry about the z-axis.

17. The resonator system of claim 13, wherein at least one of said individual resonators has a resonance frequency which differs from that of other said individual resonators.

18. The resonator system of claim 17, wherein the resonator system has two linearly polarized modes with different frequencies.

19. The resonator system of claim 13, wherein said individual resonators are inductively, and/or capacitively, and/or galvanically coupled.

20. A resonator system for generating a radio frequency (RF) magnetic field in a volume under investigation of a magnetic resonance (MR) apparatus, the resonator system comprising:

a number N of individual resonators which surround the volume under investigation and which are each disposed, about a z-axis, on a flat dielectric substrate, each individual resonator having a window through which one individual RF field is generated in the volume under investigation in single operation of the respective individual resonator, said individual resonators cooperating to generate a useful RF field in the volume under investigation, said resonators also generating an asymptotic, remote RF field far outside of the resonator system, wherein a spatial distribution of said useful RF field is substantially mirror-symmetrical relative to a first plane A which contains the z-axis, and a spatial distribution of said asymptotic remote RF field is substantially mirror-symmetrical relative to a second plane B which contains the z-axis, said useful RF field extending substantially parallel to said first plane A in the volume under investigation, wherein a number of individual resonators N>

4 and, at at least one point in time during operation of the resonator system, a substrate plane of at least one individual resonator subtends an angle of more than 40°

with respect to a direction of said useful RF field in the volume under investigation, wherein said first plane A is not rotated about the z-axis relative to said second plane B or is rotated about the z-axis relative to said second plane B by less than 360°

/(N+1); and

a conventional normally conducting and/or superconducting individual resonators and/or resonator systems.

21. The resonator system of claim 20, wherein said individual resonators contain superconducting material and/or are exclusively produced from superconducting material except for said dielectric substrates and an optional normally conducting metallic quench protection layer.

22. The resonator system of claim 20, wherein said individual resonators or groups of said individual resonators are disposed in 2-fold, 4-fold or N-fold rotational symmetry about the z-axis.

23. The resonator system of claim 20, wherein said number N of said individual resonators is N=2(i+2) or N=4(i+1), wherein i is a natural number.

24. The resonator system of claim 20, wherein said individual resonators are inductively, and/or capacitively, and/or galvanically coupled.