Transmit profile control in MRI

1. A magnetic resonance imaging apparatus, comprising:

a main magnet to generate a substantially uniform main B 0 magnetic field through an examination region; and

a radio frequency coil system to:

produce a prespecified B 1 magnetic field within the examination region to selectively excite magnetic resonances in at least a portion of a subject within the examination region, the radio frequency coil system including:

a first coil layer comprising a first coil array to generate a primary B 1 I magnetic field; and

a second coil layer comprising a second coil array to generate a secondary B 1 II magnetic field, the second coil array being disposed substantially parallel to the first coil layer with a defined air gap in a radial direction,

the first and second coil arrays being coupled and cooperating to:

manipulate the primary B 1 I magnetic field with the secondary B 1 II magnetic field to selectively produce the prespecified B 1 magnetic field; and

acquire image data based on the magnetic resonances, wherein the image data is used to reconstruct an image representation of the at least a portion of the subject; and

a memory to store the image data.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein the first and second coil arrays cooperate to reduce inhomogeneities in the B 1 magnetic field caused by the subject in the examination region.

3. The magnetic resonance imaging apparatus according to claim 1 , wherein the first coil array includes at least one of:

a birdcage coil;

surface coils;

a saddle coil; or

volumetric transmit coils.

4. The magnetic resonance imaging apparatus according to claim 1 , wherein the second coil array includes at least one of a surface coil or stripline coils.

5. The magnetic resonance imaging apparatus according to claim 4 , wherein the surface coil of the second coil array includes at least one of:

overlapped loop coils;

touching loop coils;

gapped loop coils; or

stripline coils.

6. The magnetic resonance imaging apparatus according to claim 1 , wherein the second coil array includes at least one of:

a head coil; or

a body coil.

7. The magnetic resonance imaging apparatus according to claim 1 , wherein the second coil array includes:

multiple coil arrays extending in an axial direction.

8. The magnetic resonance imaging apparatus according to claim 1 , wherein the second coil layer further includes:

second coil layers disposed with a defined air gap and substantially parallel one another and the first coil layer in the radial direction.

9. The magnetic resonance imaging apparatus according to claim 1 , wherein the second coil array includes:

coils distributed along an axial direction for a specific radio frequency magnetic field behavior.

10. A magnetic resonance imaging method, comprising:

generating, at a main magnet, a substantially uniform main B 0 magnetic field through an examination region;

generating a primary B 1 I magnetic field at a first radio frequency coil array disposed in a first coil layer, wherein the first radio frequency coil array is actively driven;

generating a secondary B 1 II magnetic field with a second radio frequency coil array disposed in a second coil layer, wherein the second radio frequency coil array is a passive radio frequency coil array; and

manipulating the primary B 1 I magnetic field with the secondary B 1 II magnetic field to generate a prespecified B 1 magnetic field within the examination region and to selectively excite magnetic resonances in at least a portion of a subject in the examination region;

acquiring image data based on the magnetic resonances excited in the at least a portion of the subject; and

processing the image data at a processor to reconstruct an image representation of the at least a portion of the subject from the image data for display.

11. The magnetic resonance imaging method according to claim 10 , wherein the first radio frequency coil array includes at least one of a birdcage coil, a surface coil, or a saddle coil, and wherein the second radio frequency coil array includes a surface coil.

12. The magnetic resonance imaging method according to claim 11 , wherein the surface coil of the second coil array includes at least one of:

overlapped loop coils,

touching loop coils,

gapped loop coils, or

stripline coils.

13. The magnetic resonance imaging method according to claim 11 , wherein the second coil array includes:

multiple coil arrays extending in an axial direction.

14. The magnetic resonance imaging method according to claim 11 , wherein the second coil array includes:

second coil arrays disposed with a defined air gap and substantially parallel one another and the first coil array in the radial direction.

15. The magnetic resonance imaging method according to claim 11 , wherein the second coil array includes:

coils distributed along an axial direction for a specific magnetic field behavior.

16. The magnetic resonance imaging method according to claim 10 , wherein generating the prespecified B 1 magnetic field includes at least one of:

reducing inhomogeneities in the B 1 magnetic field caused by a subject disposed in the examination region; or generating a non-uniform localized B 1 magnetic field.

17. A magnetic resonance imaging scanner for performing the method of claim 10 .

18. A radio frequency coil arrangement for a magnetic resonance imaging apparatus having a main magnet that generates a substantially uniform main B 0 magnetic field through an examination region, the radio frequency coil arrangement comprising:

a first coil layer including a first coil array to generate a primary B 1 I magnetic field; and

a second coil layer including a second coil array to generate a secondary B 1 II magnetic field, the second coil layer being disposed substantially parallel to the first coil layer with a defined air gap in a radial direction, the first and second coil arrays being coupled and cooperating to:

manipulate the primary B 1 I magnetic field with the secondary B 1 II magnetic field to selectively produce a prespecified B 1 magnetic field within an examination region; and

selectively excite magnetic resonances in at least a portion of a subject within the examination region; and

acquire image data based on the magnetic resonances for storage in a memory, wherein the image data is used to reconstruct an image representation of the at least a portion of the subject.

19. The radio frequency coil arrangement according to claim 18 , wherein the first and second coil arrays cooperate to selectively produce at least one of a uniform B 1 magnetic field or a non-uniform B 1 magnetic field within the examination region.

20. The radio frequency coil arrangement according to claim 18 , wherein the first coil array includes at least one of a birdcage coil, surface coils, volumetric coils or a saddle coil, and the second coil array includes at least one of a surface coil or stripline coils.

21. The radio frequency coil arrangement according to claim 18 , wherein the surface coil of the second coil array includes at least one of:

overlapped loop coils,

touching loop coils,

gapped loop coils, or

stripline coils.

22. The radio frequency coil arrangement according to claim 18 , wherein the second coil array includes:

multiple second coil arrays extending in an axial direction.

23. The radio frequency coil arrangement according to claim 18 , wherein the second coil layer includes:

second coil layers each including at least one second coil array, the second coil layers each being disposed with a defined air gap and substantially parallel one another and the first coil layer in the radial direction.