Quadrature surface coils for magnetic resonance imaging

• US 4,918,388 A
• Filed: 08/19/1988
• Issued: 04/17/1990
• Est. Priority Date: 08/14/1985
• Status: Expired due to Term

• Current Assignee: Picker International, Inc. (Marconi Holdings Company Limited)
• Original Assignee: Picker International, Inc. (Marconi Holdings Company Limited)
• Inventors: Mehdizadeh, Mehrdad, Molyneaux, David A., Holland, G. Neil
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/234,278
• Time in Patent Office: 606 Days
• Field of Search: 324/307, 324/309, 324/318, 324/322, 335/299, 128/653, 336/228, 336/232
• US Class Current: 324/322
• 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 33/34046 Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
• CPC Class Codes: G01R 33/341 comprising surface coils
• CPC Class Codes: G01R 33/3628 Tuning/matching of the transmit/receive coil
• CPC Class Codes: G01R 33/3678 involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field

Abstract

A thin dielectric sheet (36) has a first or loop coil (30) defined on one surface thereof and a second or Helmholtz coil (32) defined on an obverse surface thereof. The dielectric sheet and associated coils may be laid flat (FIG. 3) or bent to match a selected curved surface of the subject (FIGS. 6-8). The first and second coils are arranged symmetrically about an axis or plane of symmetry (34). The first coil has an associated magnetic field along a y-axis and the second coil has an associated magnetic field along the x-axis. Circuits (40 and (42) tune the first and second magnetic resonance coils to a preselected magnetic resonance frequency. Magnetic resonance signals of the selected frequency received by one of the coils are phase shifted 90° by a phase shifting circuit (50) and combined with the unphase shifted signals from the other coil by a combining circuit (52). The combined signals are amplified (54) and conveyed to electronic image processing circuitry (E) of a magnetic resonance scanner.

Claims

1. A magnetic resonance imaging apparatus comprising:

a main magnetic field means for providing a magnetic field through an examination region;

a magnetic resonance excitation means for exciting magnetic resonance of nuclei of a subject in the examination region;

a thin quadrature coil for quadrature detecting magnetic resonance signals from the excited nuclei of the subject including;

a thin dielectric layer;

a thin loop coil fixedly mounted on one surface of the thin dielectric layer;

a thin Helmholtz coil fixedly mounted on an obverse surface of the thin dielectric layer; and

,

processing means for processing the quadrature detected magnetic resonance signals into an image representation.

2. The apparatus as set forth in claim 1 wherein the loop coil has an associated magnetic field along a first axis;

and,

the Helmholtz coil has an associated magnetic field along a second axis, the loop and Helmholtz coils being disposed along generally parallel surfaces and the first and second axes being generally orthogonal.

3. The apparatus as set forth in claim 1 wherein the thin dielectric layer is curved to conform to a surface portion of the subject.

4. The apparatus as set forth in claim 2 wherein the loop and Helmholtz coils are symmetric about a common axis of symmetry.

5. A magnetic resonance imaging apparatus comprising:

a main magnetic field means for providing a magnetic field through an examination region;

a magnetic resonance excitation means for exciting magnetic resonance of nuclei of a subject in the examination region;

first and second coils lying on parallel surfaces for quadrature detecting magnetic resonance signals from the excited nuclei of the subject, the first coil being a loop coil and the second coil being a Helmholtz;

pair coil; and

,

processing means for processing the quadrature detected magnetic resonance signals into an image representation.

6. A flat coil assembly for quadrature detecting magnetic resonance signals, the coil assembly comprising:

a first, coil disposed along a first plane with its associated magnetic field generally transverse to the first plane; and

,

a Helmholtz coil disposed along a second plane, the first and second planes being disposed parallel and contiguous to each other, the Helmholtz coil having an associated magnetic field that lies substantially orthogonal to the first magnetic fields, such that the first and second coils quadrature detect magnetic resonance signals.

7. The coil assembly as set forth in claim 6 wherein the first and second coils are symmetric about a plane of symmetry which is perpendicular to the first and second planes.

8. The coil assembly as set forth in claim 7 wherein the first coil is a loop coil.

9. A quadrature coil assembly comprising:

a dielectric sheet;

a first coil having an associated magnetic field along a first axis, the first coil being mounted to the dielectric sheet; and

,

a Helmholtz coil having an associated magnetic filed along a second axis, the second coil being mounted to the dielectric sheet and the second axis being substantially orthogonal to the first axis for quadrature coil operation.

10. The coil assembly as set forth in claim 9 wherein the dielectric sheet is curved to conform to a surface portion of an object being examined.

11. The coil assembly as set forth in claim 9 wherein the first and Helmholtz coils are mounted to opposite faces of the dielectric sheet.

12. The coil assembly as set forth in claim 11 wherein the first and Helmholtz coils are constructed of thin foil.

13. A coil assembly comprising:

a first coil having an associated magnetic field along a first axis;

a second coil having an associated magnetic field along a second axis, the first and second coils being mounted closely adjacent and such that the first and second axes are substantially orthogonal;

a phase shift circuit operatively connected with one of the first and second coils for phase shifting received signals by 90°

;

a combining means for combining the phase shifted signal from one coil with the signal from the other coil;

a cable for connecting the combining means with a radio frequency receiver; and

,

a matching means for matching the impedance of the cable.

14. A coil assembly comprising:

a first coil associated with a magnetic field along a first axis;

a second coil associated with a magnetic field along a second axis, the first and second coils being tuned to a preselected magnetic resonance frequency the first and second coils being mounted closely adjacent and such that the first and second axes are substantially orthogonal;

a decoupling means for selectively detuning the first and second coils from the preselected magnetic resonance frequency

a phase shift circuit operatively connected with one of the first and second coils for phase shifting received signals by 90°

; and

,

a combining mean for combining the phase shifted signal from one coil with the signal from other coil.

15. A coil assembly comprising:

a first coil associated with a magnetic field along a first axis;

a second coil associated with a magnetic field along a second axis, the first and second coils being mounted closely adjacent and such that the first and second axes are substantially orthogonal;

a first phase shifting circuit associated with the first coil for phase shifting received signals by 90°

;

a second 90°

phase shifting circuit associated with the second coil;

a combining means for combining the phase shifted signal from one coil with the signal from the other coil; and

,

a switching means for selectively switching one of the 90°

phase shift circuits between its associated coil and the combining means for connecting the other coil directly with the combining means.

16. A coil assembly comprising:

a first coil associated with a magnetic field along a first axis;

a second coil extending in generally a semi-ellipse and associated with a magnetic field along a second axis, the first and second coils being mounted closely adjacent and such that the first and second axes are substantially orthogonal, whereby the coil assembly is contoured generally in accordance with a patient'"'"'s neck;

a phase shift circuit operatively connected with one of the first and second coils for phase shifting received signals by 90°

; and

,

a combining means for combining the phase shifted signal from one coil with the signal from the other coil.

17. A coil assembly comprising:

a first coil associated with a magnetic field along a first axis;

a second coil associated with a magnetic field along a second axis, the second coil includes two coil portions which are disposed at generally at 45°

angle relative to each other, the first and second coils being mounted closely adjacent and such that the first and second axes are substantially orthogonal;

a phase shift circuit operatively connected with one of the first and second coils for phase shifting received signals by 90°

; and

,

a combining means for combining the phase shifted signal from one coil with the signal from the other coil.