Loop-gap resonator for localized NMR imaging

• US 4,724,389 A
• Filed: 05/08/1985
• Issued: 02/09/1988
• Est. Priority Date: 05/08/1985
• Status: Expired due to Term

• Current Assignee: MCW Research Foundation Incorporated Milwaukee Wisconsin
• Original Assignee: Medical College of Wisconsin Incorporated
• Inventors: Jesmanowicz, Andrzej, Hyde, James S., Froncisz, Wojciech
• Primary Examiner(s): Levy, Stewart J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/731,923
• Time in Patent Office: 1,007 Days
• Field of Search: 324/318, 324/316, 324/322, 324/307, 324/309, 333/219, 333/227, 333/228, 333/235
• US Class Current: 324/318
• CPC Class Codes: G01R 33/343 of slotted-tube or loop-gap type

Abstract

A local probe for use in nuclear magnetic resonance imaging includes a pair of loop-gap resonators which are connected together and positioned adjacent a region of interest. FID signals produced in the region of interest induce signals in coupling loops mounted near each loop-gap resonator, and these connect to a transmission line leading to the receiver. Three embodiments are disclosed, one best suited for imaging appendages, a second best suited for imaging the head and neck, and a third best suited for the spine.

Claims

1. A local probe for use in nuclear magnetic resonance imaging, the combination comprising:

a first loop-gap resonator having a gap formed by a pair of spaced plates and a conductive loop which connects to the spaced plates and encircles a resonator axis;

a second loop-gap resonator having a second gap formed by a second pair of spaced plates and a second conductive loop which connects to the second plates and encircles a second resonator axis;

support means connected to the first and second loop-gap resonators for positioning said loop-gap resonators adjacent to one another;

connection means for electrically connecting each plate in the first loop-gap resonator to a respective plate in the second loop-gap resonator to suppress an unlinked resonant mode of the first and second loop-gap resonators; and

coupling means positioned adjacent to the first and second loop-gap resonators for coupling signals detected by the first and second loop-gap resonators out of the local probe.

2. The local probe as recited in claim 1 in which each loop-gap resonator is pivotally connected to the support means such that the loop-gap resonators may be oriented in a number of positions ranging from an axial pair orientation to a planar pair orientation.

3. The local probe as recited in claim 1 in which the support means includes adjustment means for changing the lateral spacing between the first and second loop-gap resonators.

4. The local probe as recited in claim 1 in which each loop-gap resonator includes a plurality of gaps.

5. The local probe as recited in claim 1 in which the connection means includes a pair of flexible, electrically insulated wires.

6. The local probe as recited in claim 5 in which a variable capacitor is connected across the wires and the capacitor may be adjusted to alter the resonant frequency of the loop-gap resonators.

7. The local probe as recited in claim 1 in which the first and second loop-gap resonators are substantially identical, and the coupling means comprises a pair of substantially identical coupler coils connected in series across a transmission line and mounted adjacent the respective first and second loop-gap resonators to produce a signal on the transmission line which is responsive to the magnetic field produced in a region of sensitivity located between the loop-gap resonators.

8. In an NMR scanner for producing images from FID signals emanating from a subject which is irradiated with an excitation field in the presence of a polarizing magnetic field, a local probe for receiving the FID signals emanating from a region of interest in the subjust, which comprises:

a pair of loop-gap resonators, each loop-gap resonator being placed adjacent to the region of interest;

connection means for electrically connecting the loop-gap resonators together at their respective gaps to suppress a resonance mode characterized by separate, unlinked magnetic flux paths in the two loop-gap resonators, and to support a resonance mode characterized by a magnetic flux path which links the two loop-gap resonators and which resonates at the frequency of the FID signals; and

conductive means positioned adjacent the pair of loop-gap resonators for receiving the FID signals emanating from the region of interest.

9. The local probe as recited in claim 8 in which the excitation field is circularly polarized and the loop-gap resonators are substantially identical and oriented as a planar pair.

10. The local probe as recited in claim 8 in which the conductor means is formed as a pair of coupler coils, with one coupler coil positioned adjacent each loop-gap resonator, and with both coupler coils connected in series across a transmission line.

11. The local probe as recited in claim 8 in which the loop-gap resonators are oriented as an axial pair with the region of interest disposed between the loop-gap resonators.

12. The local probe as recited in claim 8 in which the loop-gap resonators are fastened to support means that enables the position of the loop-gap resonators to be adjusted with respect to each other and to the region of interest.

13. In an NMR scanner for producing images from FID signals emanating from a subject which is irradiated with an excitation field in the presence of a polarizing magnetic field, a local probe for receiving the FID signals emanating from a region of interest in the subject, which comprises:

a pair of coupler coils;

support means connected to the coupler coils for positioning them adjacent to one another and adjacent to the region of interest in the subject;

a pair of loop-gap resonators connected to the support means, each loop-gap resonator being positioned adjacent to a respective one of the coupler coils and being tuned to resonate at the frequency of the FID signals produced in the region of interest;

a transmission line attached to the support means and leading to a receiver which processes the FID signals; and

connection means for electrically connecting each coupler coil to the transmission line and in series with each other such that FID signals emanating from the region of interest produce a corresponding electrical signal in the transmission line;

wherein the coupler coils are symmetrical such that signals induced in one coupler coil by the excitation field substantially cancels the signal induced in the other coupler coil by the same excitation field.

14. The local probe as recited in claim 13 in which the loop-gap resonators are substantially identical.

15. The local probe as recited in claim 13 in which each loop-gap resonator has a plurality of gaps.

16. In an NMR scanner for producing images from FID signals emanating from a subject which is irradiated with an excitation field in the presence of a polarizing magnetic field, a local probe for receiving the FID signals emanating from a region of interest in the subject, which comprises:

a first axial pair of loop-gap resonators placed adjacent to the region of interest;

a second axial pair of loop-gap resonators placed adjacent to the region of interest and spaced from the first axial pair of loop-gap resonators;

connection means for electrically connecting a loop-gap resonator in each of said axial pairs together to suppress an unlinked resonant mode and to thereby produce a relatively uniform sensitivity to FID signals emanating from the region of interest; and

coupling means positioned adjacent to the first and second axial pairs for coupling signals detected by the first and second axial pairs out of the local probe.

17. The local probe as recited in claim 16 in which each axial pair includes cross connections between the loop-gap resonators within each axial pair to suppress a linked resonant mode and to thereby unlink the loop-gap resonators in each axial pair.

18. The local probe as recited in claim 16 in which each axial pair of loop-gap resonators is positioned with respect to each other such that their area of uniform sensitivity is shaped to substantially correspond to the region of interest.

19. A local probe for use in nuclear magnetic resonance imaging, the combination comprising:

a pair of loop-gap resonator sections which are oriented as a planar pair about a common axis between the resonators; and

connection means for connecting corresponding capacitive elements in each loop-gap resonator section together;

wherein each loop-gap resonator section includes a loop having opposite ends which are tilted with respect to the common axis and are symmetrical about the common axis.

20. The local probe as recited in claim 19 in which each loop-gap resonator section is comprised of a pair of loop-gap resonator which are tilted with respect to the common axis such that each defines one of said opposite ends.