Decoupling of multiple channels of an MRI RF coil array

Patent metadata

Field	Value
Publication number	US-9229076-B2
Application number	US-201113697797-A
Country	US
Kind code	B2
Filing date	Apr 26, 2011
Priority date	May 27, 2010
Publication date	Jan 5, 2016
Grant date	Jan 5, 2016

Abstract

A radio-frequency coil assembly ( 18 ), for use in a magnetic resonance imaging system ( 10 ), includes a plurality of coil elements ( 18 n ). The coil elements ( 18 n ) are connected to a decoupling network ( 40 ) which includes a plurality of decoupling elements ( 40 n,x ) connected (via transmission lines) to pairs of coil elements ( 18 n , 18 x ) at corresponding ports ( 64 n ,64 x ) from which the coil can be fed. The decoupling elements ( 40 n,x ) compensate for mutual coupling between pairs of corresponding coil elements. An inductive coupling loop ( 51 n ), with a constant or adjustable mutual inductance, inductively couples the associated coil element ( 18 n ) to the corresponding decoupling network port ( 64 n ). Transmission lines ( 52 n ) electrically connect each inductive coupling loop ( 51 n ) to the decoupling network ( 40 ) at the corresponding port ( 64 n ). Each transmission line ( 52 n ) has an electrical length of kλ/2 where k=0, 1, 2, 3 . . . and λ is a wavelength of the excited and/or received resonance signals inside the transmission line.

First claim

The invention claimed is:

1. A radio-frequency coil assembly, comprising:
a plurality of N coil elements which transmits radio-frequency signals into an examination region to excite magnetic resonance and/or to receive induced magnetic resonance signals therefrom;
a decoupling network of up to Σ i=1 N-1 i=N(N−1)/2 decoupling elements, each decoupling element electrically decoupling a pair of corresponding coil elements;
inductive coupling loops which inductively couple the corresponding coil elements to corresponding decoupling network ports; and
transmission lines which electrically connect each inductive coupling loop to the corresponding decoupling network port located at the decoupling network, the transmission line having an electrical distance of kλ/2 where k=0, 1, 2, 3 . . . and λ is the wavelength of the excited and/or received magnetic resonance signals inside the transmission line.

2. The radio-frequency coil assembly according to claim 1 , wherein the value of k, the characteristic impedance, and a type of the transmission lines varies from channel to channel.

3. The radio-frequency coil assembly according to claim 2 , wherein the transmission lines include at least one of a coaxial cable, twisted pair cable, micro-strip, coplanar waveguide, strip-line, waveguide, equivalent lumped element circuit, or any combination thereof.

4. The radio-frequency coil assembly according to claim 1 , wherein each decoupling element is a reactive element with a reactance based on the mutual coupling between the pair of coil elements.

5. The radio-frequency coil assembly according to claim 1 , wherein one or more inductive coupling loops include at least one adjustable circuit which, when adjusted, matches an impedance of the coil element to the decoupling network port which than can be used for feeding the corresponding element.

6. The radio-frequency coil assembly according to claim 1 , wherein the inductive coupling loop includes a pair of conductors arranged to form a figure-eight loop, at least one loop including at least one reactive element.

7. The radio-frequency coil assembly according to claim 1 , wherein each adjustable inductive element is adjustable by at least one of rotation, deformation, and translation of at least one of the inductors or an insert defining the mutual flux.

8. A magnetic resonance imaging system, comprising:
a magnet which generates a static magnetic field in an examination region;
a radio-frequency coil assembly according to claim 1 which excites magnetic resonance in selected dipoles of a subject in the examination region, and receives a magnetic resonance signal therefrom;
a radio-frequency transmitter which causes the radio-frequency coil assembly to generate magnetic resonance excitation and manipulation pulses; and
a radio-frequency receiver which receives the generated magnetic resonance signals from the radio-frequency coil assembly.

9. The magnetic resonance imaging system according to claim 8 , further including:
a decoupling processor or computer routine which controls the radio-frequency transmitter to send test signals to a selected decoupling network port;
at least one of directional couplers, magnetic field probes, and signal sensors which determine impedance mismatch at corresponding feeding ports and/or which measure a degree of mutual coupling between pairs of corresponding coil elements according to the sent test signals.

10. The magnetic resonance imaging system according to claim 9 , further including:
a tuning/matching processor or computer routine which controls actuators to adjust one or more of the inductive coupling loops and/or to control adjustable reactances of corresponding reactive elements to adjust the inductive coupling with the corresponding coil element and the impedance at the corresponding decoupling network port.

11. The magnetic resonance imaging system according to claim 8 , further including:
a display unit which displays the measured impedance mismatch and/or the measured degree of mutual coupling.

12. The magnetic resonance imaging system according to claim 8 , wherein the decoupling network with corresponding inductive coupling loops and a transmission lines are combined with existing decoupling methods, such as inductive decoupling, ladder networks, or impedance inversion.

13. A method for generating radio-frequency fields, comprising:
transmitting radio-frequency signals into an examination region with a plurality of coil elements to induce magnetic resonance and/or receive induced magnetic resonance signals therefrom;
inductively coupling a corresponding coil element to a corresponding decoupling network port with an inductive coupling loop;
compensating for mutual coupling between pairs of coil elements with decoupling elements connected with corresponding ports, the decoupling elements being electrically connected to the adjustable inductive elements by transmission lines which have an electrical length of kλ/2 where k=0, 1, 2, 3 . . . and λ is a wavelength of the excited and/or received resonance signals inside the transmission lines.

14. The method according to claim 13 , wherein one or more transmission lines are realized by, at least partly, a lumped-element transmission line with equivalent circuit elements such as capacitors and/or inductors.

15. The method according to claim 13 , wherein each adjustable inductive element includes a loop coil or a pair of conductors arranged to form a figure-eight loop, at least one loop including at least one reactive element.

16. The method according to claim 13 , wherein each inductive coupling is adjustable by at least one of rotation, translation, and deformation of at least one of the inductors or an insert defining the mutual flux.

17. The method according to claim 13 , further including:
generating a static magnetic field in an examination region;
with the radio-frequency coil elements, at least one of:
(1) generating magnetic resonance excitation and manipulation pulses or inducing magnetic resonance in selected dipoles of a subject in the examination region; or
(2) receiving the generated magnetic resonance signals from the imaging region.

18. The method according to claim 17 , further including:
controlling radio-frequency transmitters to send test signals to selected decoupling network ports;
measuring the impedance mismatch at the corresponding feeding ports and/or measuring the mutual coupling between pairs of corresponding coil elements;
monitoring signals received by selected other coil elements;
controlling actuators to adjust one or more of the inductive coupling loops and/or controlling adjustable reactances of corresponding reactive elements to adjust the inductive coupling between corresponding coil elements and the impedance at the corresponding feeding ports according to the measured impedance mismatch; and
controlling adjustable reactances of the decoupling elements to adjust the mutual couple between corresponding coil elements according to the measured degree of mutual coupling.

19. The method according to claim 18 , further including:
displaying the measured impedance mismatch and/or the degree of mutual coupling.

20. The method according to claim 17 , wherein the decoupling network with corresponding inductive coupling loops and transmission lines is combined with an existing decoupling method, such as inductive decoupling, ladder networks, or impedance inversion or the like.

Assignees

• Findeklee Christian
• Koninkl Philips Nv

Inventors

• Findeklee Christian

Classifications

• G01R33/3642 Primary

  Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification · CPC title

• G01R33/3415

  comprising arrays of sub-coils {, i.e. phased-array coils with flexible receiver channels} · CPC title

• G01R33/365

  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 title