SILENT AND THIN RF BODY COIL

• US 20090128150A1
• Filed: 06/13/2007
• Published: 05/21/2009
• Est. Priority Date: 06/15/2006
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Tuithof, Hans, Ham, Kees
• Granted Patent: US 8,022,706 B2
• Time in Patent Office: Days
• US Class Current: 324/318
• CPC Class Codes: G01R 33/34076 Birdcage coils
• CPC Class Codes: G01R 33/3453 Transverse electromagnetic [TEM] coils
• CPC Class Codes: G01R 33/3854 means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems
• CPC Class Codes: G01R 33/422 of the radio frequency field
• CPC Class Codes: G01R 33/565 Correction of image distortions, e.g. due to magnetic field inhomogeneities
• CPC Class Codes: G01R 33/56509 due to motion, displacement or flow, e.g. gradient moment nulling G01R33/567 takes precedence
• 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 imaging subject (16) is disposed in an examination region (12) for examination. A cover (18) is disposed around the examination region (12). Magnetic field gradient coils (30) impose selected magnetic field gradients on a main magnetic field (B₀) within the examination region (12). A radio frequency (RF) coil (36) generates radio frequency excitation pulses in the examination region (12), the radio frequency coil (36) including a plurality of coil elements (38₁, 38₂, 38₃) disposed on the cover (18) distally from the examination region (12). A radio frequency (RF) screen (40) associated with the coil elements (38₁, 38₂, 38₃) shields the coil elements (38₁, 38₂, 38₃) and is disposed about the gradient coils (30) such that the coil elements (38₁, 38₂, 38₃) are mechanically decoupled from the RF screen (40) and substantially acoustically isolated from the RF screen (40) and gradient coils (30).

Claims

1. A magnetic resonance imaging apparatus comprising:

an examination region in which an imaging subject is disposed for examination;

a cover around the examination region;

magnetic field gradient coils that impose selected magnetic field gradients on a main magnetic field within the examination region;

a radio frequency (RF) coil for generating radio frequency excitation pulses in the examination region, the radio frequency coil including a plurality of coil elements disposed on the cover distally from the examination region; and

a radio frequency (RF) screen associated with the coil elements, which radio frequency screen shields the coil elements and is disposed about the gradient coils such that the coil elements are mechanically decoupled from the RF screen and substantially acoustically isolated from the RF screen and gradient coils.

2. The apparatus as set forth in claim 1, further including:

a compensating processor which determines compensating signals to compensate for distortion of signals in each individual coil element due to at least one of (a) an interference of the imaging subject with the coils and (b) vibrational interference between the RF screen and gradient coils; and

a transmitting system, which creates RF pulses in accordance with the determined compensating signals and transmits the corrected RF pulses to corresponding coil elements.

3. The apparatus as set forth in claim 1, further including:

a compensating processor which determines compensation for RF signals in the RF coil due to changes in a physical relationship between the RF coil and the RF screen.

4. The apparatus as set forth in claim 3, further including:

a waveform generating device which controls an RF transmitting system in accordance with the determined compensation to create compensated RF pulses for each of the coil elements to generate RF fields with selected characteristics.

5. The apparatus as set forth in claim 3, further including:

a plurality of pickup coils for measuring RF signals induced in the coil elements, the compensating processor determining the compensation in accordance with an error between the measured RF signals and required RF signals.

6. The apparatus as set forth in claim 5, further including a plurality of transmitters connected to the plurality of coil elements and wherein the compensating processor includes:

an adjusted signal determining device which compares the measured signals and the required signals and determines an adjusted signal for each of the transmitters.

7. The apparatus as set forth in claim 5, further including a plurality of receivers connected to the plurality of coil elements and the compensating processor includes:

an adjusted signal determining device which compares the measured signals and the required signals and determines an adjusted signal for each of the receivers.

8. The apparatus as set forth in claim 3, further including:

gradient coil controllers coupled to the gradient coils which superimpose selected magnetic field gradient waveforms on the main magnetic field.

9. The apparatus as set forth in claim 8, further including:

a correction table from which correction parameters are withdrawn to compensate for mechanical interference between the RF screen and the RF coil during activation of the gradient coil.

10. The apparatus as set forth in claim 9, further including:

a waveform generating device which controls a transmitting system to create RF pulses in accordance with the correction parameters and transmit the corrected RF pulses to each of the coil elements.

11. A magnetic resonance method comprising:

mechanically coupling individual coil segments adjacently one another on a bore cover distally from an examination region and proximately to gradient coils;

shielding the coil segments with a radio frequency (RF) screen which is mechanically decoupled from the coil segments and mechanically coupled to the gradient coils; and

covering a scanner bore with the bore cover and the coupled coil segments.

12. The method as set forth in claim 11, further including:

generating a substantially spatially and temporally constant magnetic field in the examination region which is defined by the bore cover;

imposing selected magnetic field gradients on the main magnetic field within the examination region with the gradient coils; and

conducting a magnetic resonance sequence including applying RF pulses to and receiving resonance signals with the coil segments.

13. The method as set forth in claim 11, further including:

compensating RF signals of each individual coil segment to compensate for changes in RF coupling between the RF coil segments and the RF screen caused by relative displacement between the RF screen and at least one of the RF coil segments.

14. The method as set forth in claim 11, further including:

creating RF pulses;

applying the created RF pulses to the coil segments;

sensing RF pulses transmitted by the RF coil segments; and

altering the created RF pulses in accordance with a difference between the sensed RF pulses and required RF pulses with a feedback compensation loop.

15. The method as set forth in claim 11, further including:

creating RF pulses;

applying the created RF pulses to the coil segments;

sensing RF pulses transmitted by the RF coil segments;

determining a difference between the sensed RF pulses and required RF pulses;

receiving magnetic resonance signals; and

altering the received magnetic resonance signals in accordance with the determined difference.

16. The method as set forth in claim 11, further including:

determining compensation corrections for RF signals in each individual coil segment due to activation of a mechanical relationship between the RF screen and the coil segments during actuation of the gradient coils.

17. The method as set forth in claim 16, wherein the step of determining compensation corrections includes:

superimposing selected magnetic field gradient waveforms on a main magnetic field with the gradient coils;

measuring a change in each coil segment during application of the gradient;

determining correction parameters which compensate for the measured change; and

storing the correction parameters in a correction table.

18. The method as set forth in claim 17, further including one of:

creating RF pulses in accordance with the correction parameters, and

applying the corrected RF pulses to each of the coil segments; and

receiving magnetic resonance signals, and

applying the correction parameters to the received magnetic resonance signals.

19. A magnetic resonance scanner constructed by the steps of claim 11.

20. A magnetic resonance apparatus comprising:

a main magnetic, which generates a main field through an examination region;

magnetic field gradient coils that impose selected magnetic field gradients on the main magnetic field within the examination region;

an RF coil;

a radio frequency (RF) screen associated with the RF coil, which radio frequency screen shields the RF coil, and is disposed about the gradient coils such that the RF coil is mechanically decoupled from the RF screen and substantially acoustically isolated from the RF screen and the gradient coils; and

a compensating processor, which compensates for at least induced changes in RF fields due to at least one of (a) a mechanical interference between the RF screen and the RF coil attributable to the gradient coils vibrations or (b) a patient interaction with the RF coil.