MR antenna with compensation for variable distance to shield

Patent metadata

Field	Value
Publication number	US-9829549-B2
Application number	US-201313890128-A
Country	US
Kind code	B2
Filing date	May 8, 2013
Priority date	May 9, 2012
Publication date	Nov 28, 2017
Grant date	Nov 28, 2017

Abstract

A whole-body coil for a magnetic resonance tomography device includes one or more compensation capacitors between a high-frequency antenna and an RF shield. The one or more compensation capacitors each have variable capacitance caused by a variation in a distance of the RF shield to the high-frequency antenna.

First claim

The invention claimed is:

1. A whole-body coil for a magnetic resonance tomography device, the whole-body coil comprising:
one or more compensation capacitors between a high-frequency antenna and an RF shield,
wherein each of the one or more compensation capacitors has a variable capacitance caused by a variation in a distance of the RF shield to the high-frequency antenna,
wherein the RF shield is arranged on a gradient coil, mounted on the gradient coil, fixed to the gradient coil, or a combination thereof, and
wherein the distance of the RF shield to the high-frequency antenna varies during expansion of the gradient coil.

2. The whole-body coil as claimed in claim 1 , wherein the one or more compensation capacitors are each configured as a plate capacitor.

3. The whole-body coil as claimed in claim 1 , wherein the one or more compensation capacitors are each configured as a plate capacitor,
wherein plates of the plate capacitor have a distance to one another, the distance in each case being variable by expansion of the gradient coil, by distance variation of the distance of the RF shield to an element of the high-frequency antenna, or a combination thereof.

4. The whole-body coil as claimed in claim 1 , wherein the one or more compensation capacitors comprise a plurality of compensation capacitors,
wherein each compensation capacitor of the plurality of compensation capacitors has a number of varying capacitances with a number of varying distances, in a plurality of regions, from a gradient coil that is expandable as a result of heating to the high-frequency antenna.

5. The whole-body coil as claimed in claim 1 , wherein the capacitance of each compensation capacitor of the one or more compensation capacitors is variable only based on a distance variation of the distance of the RF shield to an element of the high-frequency antenna.

6. The whole-body coil as claimed in claim 1 , wherein a compensation capacitor of the one or more compensation capacitors is configured so that, when the distance from an element of the high-frequency antenna to the RF shield increases, the capacitance of the compensation capacitor is reduced to the extent that any increase in inductance is compensated for in full or in part.

7. The whole-body coil as claimed in claim 1 , wherein only a part of an entire resonance capacitor of the high-frequency antenna is configured in the form of the one or more compensation capacitors.

8. The whole-body coil as claimed in claim 1 , wherein each of the one or more compensation capacitors has a capacitive plate attached to, connected to, or attached and connected to an element of the high-frequency antenna, a capacitive plate attached to, connected to, or attached and connected to the RF shield or a gradient system, or a combination thereof.

9. The whole-body coil as claimed in claim 1 , wherein each of the one or more compensation capacitors has a capacitive plate attached to an element of the high-frequency antenna, the capacitive plate being attached more closely to the RF shield than to the high-frequency antenna or more closely to the high-frequency antenna than to the RF shield.

10. The whole-body coil as claimed in claim 1 , wherein the one or more compensation capacitors are located less remotely from the RF shield than elements of the high-frequency antenna by a factor or a reciprocal value, the factor corresponding to the capacitance of the one or more compensation capacitors as a proportion of the entire resonance capacitance of the radio frequency shield, the high-frequency antenna, or the radio frequency shield and the high-frequency antenna.

11. The whole-body coil as claimed in claim 1 , wherein in a magnetic resonance tomography device in the form of a TEM resonator, the resonance capacitance of the RF shield, the high-frequency antenna, or the RF shield and the high-frequency antenna is located between ends of rods and a surface of the RF shield, a voltage on capacitors between rods and ferrule segments is equal to a voltage on the one or more compensation capacitors, or a combination thereof.

12. The whole-body coil as claimed in claim 1 , wherein in a magnetic resonance tomography device in the form of a birdcage, the one or more compensation capacitors are configured as a series capacitance that is introduced into current flow in rods, in ferrules, or in the rods and in the ferrules.

13. The whole-body coil as claimed in claim 1 , wherein the high-frequency antenna is a multichannel controllable HF antenna,
wherein in the multichannel controllable HF antenna, voltages on the one or more compensation capacitors depend on a selected transmit mode, and
wherein for each transmit mode, energies of a sum of all involved capacitances, distances, surfaces of the one or more compensation capacitors, or a combination thereof is dimensioned so that each transmit mode is separately compensated for.

14. The whole-body coil as claimed in claim 1 , wherein a distance of the RF shield to the high-frequency transmitting antenna, a distance between plates of a compensation capacitor of the one or more compensation capacitors, or a combination thereof is variable in each case by one to three percent.

15. The whole-body coil as claimed in claim 1 , wherein the one or more compensation capacitors comprise at least two compensation capacitors, the at least two compensation capacitors being provided for each linearly polarized subsystem of the HF antenna.

16. The whole-body coil as claimed in claim 1 , wherein a maximum of one compensation capacitor of the one or more compensation capacitors is available for each ferrule segment of a plurality of ferrule segments of a birdcage antenna of the magnetic resonance tomography device.

17. A magnetic resonance tomography device comprising:
a whole-body coil comprising:
one or more compensation capacitors between a high-frequency antenna and an RF shield,

wherein each of the one or more compensation capacitors has a variable capacitance caused by a variation in a distance of the RF shield to the high-frequency antenna,
wherein the RF shield is arranged on a gradient coil, mounted on the gradient coil, fixed to the gradient coil, or a combination thereof, and
wherein the distance of the RF shield to the high-frequency antenna varies during expansion of the gradient coil.

18. The whole-body coil as claimed in claim 17 , wherein the one or more compensation capacitors are each configured as a plate capacitor.

19. A whole-body coil for a magnetic resonance tomography device, the whole-body coil comprising:
one or more compensation capacitors between a high-frequency antenna and an RF shield,
wherein each of the one or more compensation capacitors has a variable capacitance caused by a variation in a distance of the RF shield to the high-frequency antenna,
wherein the one or more compensation capacitors comprise a plurality of compensation capacitors, and
wherein each compensation capacitor of the plurality of compensation capacitors has a number of varying capacitances with a number of varying distances, in a plurality of regions, from a gradient coil that is expandable as a result of heating to the high-frequency antenna.

20. A whole-body coil for a magnetic resonance tomography device, the whole-body coil comprising:
one or more compensation capacitors between a high-frequency antenna and an RF shield,
wherein each of the one or more compensation capacitors has a variable capacitance caused by a variation in a distance of the RF shield to the high-fr

Assignees

• Eberler Ludwig
• Nistler Jürgen
• Vester Markus
• Siemens Ag

Inventors

• Eberler Ludwig
• Nistler Jürgen
• Vester Markus

Classifications

• G01R33/56341

  Diffusion imaging · CPC title

• G01R33/34092 Primary

  RF coils specially adapted for NMR spectrometers · CPC title

• G01R33/4806

  Functional imaging of brain activation · CPC title

• G01R33/34076

  Birdcage coils · CPC title

• G01R33/34046 Primary

  Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils · CPC title