RF coil assembly and method for practicing magnetization transfer on magnetic resonance imaging and spectroscopy systems

• US 7,508,212 B2
• Filed: 08/20/2007
• Issued: 03/24/2009
• Est. Priority Date: 03/22/2007
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Fain, Sean B., Holmes, James H., Grist, Thomas M., Erickson, Matthew G., Kurpad, Krishna N.
• Primary Examiner(s): Arana; Louis M
• Application Number:
  US11/841,201
• Publication Number:
  US 20080231281A1
• Time in Patent Office: 582 Days
• Field of Search: 324/318, 324/322
• US Class Current: 324/318
• CPC Class Codes: G01R 33/345 of waveguide type G01R33/343 takes precedence
• CPC Class Codes: G01R 33/3453 Transverse electromagnetic [TEM] coils
• CPC Class Codes: G01R 33/3635 Multi-frequency operation
• CPC Class Codes: G01R 33/365 Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array
• CPC Class Codes: G01R 33/3678 involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field
• CPC Class Codes: G01R 33/3685 Means for reducing sheath currents, e.g. RF traps, baluns
• CPC Class Codes: G01R 33/5601 involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
• CPC Class Codes: G01R 33/5605 by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE]
• CPC Class Codes: G01R 33/5659 caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field G01R33/56509, G01R33/56518, G01R33/56536 take precedence

Abstract

An RF coil assembly for an MRI system includes a resonator formed by a cylindrical shield and pairs of opposing conductive legs disposed symmetrically around a central axis and extending the axial length of the shield. One set of conductive leg pairs is tuned to operate at the Larmor frequency of ¹³C and another set is tuned to operate at the Larmor frequency of ¹H. Drive circuitry operates the RF coil assembly to produce ¹H spin magnetization which is transferred to ¹³C magnetization by the nuclear overhauser effect and to acquire MR data from the ¹³C spins. Multinuclear measurements can be made simultaneously at different Larmor frequencies.

Claims

1. A magnetic resonance imaging (MRI) system for acquiring magnetic resonance data from one spin species using magnetization transfer from another spin species having a different Larmor frequency, the combination comprising:

a resonator having a cylindrical shield formed around a central axis and having plurality of pairs of opposing conductive legs arranged symmetrically around the central axis with the pairs of opposing conductive legs being divided into a first set and a second set, each conductive leg extending from one end of the cylindrical shield to another end of the cylindrical shield;

means for tuning each conductive leg in the first set to the Larmor frequency of the first spin species;

means for tuning each conductive leg in the second set to the Larmor frequency of the second spin species;

first drive circuitry connected to each pair of opposing conductive legs in the first set and being operable to establish substantially equal and opposite current flow in opposing conductive legs at the Larmor frequency of the first spin species;

second drive circuitry connected to each pair of opposing conductive legs in the second set and being operable to establish substantially equal and opposite current flow in opposing conductive legs at the Larmor frequency of the second spin species; and

means for directing the first drive circuit to excite the first spin species and thereby transfer magnetization to the second spin species and for directing the second drive circuit to excite the second spin species and acquire a magnetic resonance signal from the same.

2. The system as recited in claim 1, wherein the first and second means for tuning include termination stubs, each termination stub is connected to one end of a respective conductive leg in series.

3. The system as recited in claim 2, wherein each of the termination stubs for the first means for tuning has a length that combined with a half length of a respective conductive leg is approximately equal to n₁λ

₁/4, where λ

₁ is a wavelength corresponding to the first Larmor frequency, and n₁ is an odd integer if the termination stub is open circuited, and n₁ is an even integer if the termination stub is short circuited, and further wherein each of the termination stubs for the second means for tuning has a length that combined with a half length of a respective conductive leg is approximately equal to n₂λ

₂/4, where λ

₂ is a wavelength corresponding to the second Larmor frequency, and n₂ is an odd integer if the termination stub is open circuited, and n₂ is an even integer if the termination stub is short circuited.

4. The system as recited in claim 2, wherein each of the termination stubs for the first means for tuning are open circuited at a distal end thereof and each has a length that combined with a half length of a respective conductive leg is approximately equal to n₁λ

₁/4, where λ

₁ is a wavelength corresponding to the first Larmor frequency and n₁ is an odd integer, and further wherein each of the termination stubs for the second means for tuning are short circuited at a distal end thereof and each has a length that combined with a half length of a respective conductive leg is approximately equal to λ

₂, where λ

₂ is a wavelength corresponding to the second Larmor frequency.

5. The system as recited in claim 1 in which the first spin species is hydrogen (¹H) and the second spin species is carbon (¹³C).

6. The MRI system as recited in claim 1 in which the means for directing the first and second drive circuits includes a pulse sequencer programmed to perform a prescribed pulse sequence.

7. The MRI system as recited in claim 6 in which the prescribed pulse sequence is a magnetization transverse type pulse sequence.

8. The MRI system as recited in claim 6 in which the prescribed pulse sequence is an INEPT pulse sequence and readout simultaneously acquires images of ¹H and ¹³C nuclei.

9. The MRI system as recited in claim 1 in which the first spin species is hyperpolarized.

10. The MRI system as recited in claim 9 in which the hyperpolarized first spin species is ¹³C.