Wireless local transmit coils and array with controllable load

Patent metadata

Field	Value
Publication number	US-9488705-B2
Application number	US-201214233274-A
Country	US
Kind code	B2
Filing date	Jul 5, 2012
Priority date	Jul 20, 2011
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

A local radio frequency (RF) transmitting coil ( 26 ) of a magnetic resonance imaging system ( 5 ) has a plurality of coil elements ( 100 ). Each coil element ( 100 ) has an adjustable load ( 62 ) which is adjusted by a control unit ( 60 ) to adjust a transmitted B 1 field distribution. The load can be adjusted to shim for a uniform B 1 field distribution. Non-uniform B 1 field distributions can be selected to perform magnetic resonance sequences that use such B 1 field distributions, such as parallel imaging. The B 1 field distribution can be changed during the magnetic resonance sequence to track a moving region of interest, time division multiplex parallel imaging, and the like.

First claim

Having thus described the preferred embodiments, the invention is now claimed to be:

1. A magnetic resonance system comprising:
a main magnet which generates a static (B 0 ) magnetic field in an examination region;
magnetic field gradient coil which superimposes time varying magnetic field gradients on the B 0 in selected directions within the examination region;
a whole body radio frequency coil which generates radio frequency (B 1 ) pulses; and
a local radio frequency coil inductively coupled to the whole body radio frequency coil, the inductively coupled local radio frequency coil for a magnetic resonance system comprising:
a plurality of radio frequency coil elements each including an adjustable load, the load having at least one of an adjustable capacitance, resistance or impedance; and
a control unit which includes:
a load controller which controls adjustments of the load; and
a communications interface connected to the load controller which communicates between the load controller and an off-coil controller.

2. The system according to claim 1 , wherein each radio frequency coil element further includes:
a measuring device connected to the control unit, the measuring device measuring current on the radio frequency coil element; and wherein the load controller compares the measured current with a selected current and adjusts at least one of the capacitance, resistance, and impedance of the load accordingly.

3. The system according to claim 2 , wherein the load controller compares the measured current with a selected current and adjusts at least one of the capacitance, resistance, and impedance of the load accordingly.

4. The system according to claim 1 , wherein the load controller compares at least one of a measured frequency and phase of a transmitted radio frequency signal to at least one of a selected frequency and phase.

5. The system according to claim 1 , wherein each radio frequency coil element is connected with a different control unit to be individually controlled.

6. The system according to claim 1 further including:
a local power source which harvests power from the magnetic resonance system.

7. The system according to claim 1 , wherein the communications interface connects wirelessly with the control.

8. The system according to claim 1 , wherein the communications interface connects to the control with a fiber optic cable.

9. The system according to claim 1 , wherein the coil element includes at least one of: a loop coil, and a transverse electromagnetic (TEM) array.

10. The system according to claim 1 , wherein the control unit further includes:
a computer memory connected the load controller which stores at least one of:
adjustment configurations for the loads, and
software which controls operation of the load controller.

11. A magnetic resonance system comprising:
a main magnet which generates a static (B 0 ) magnetic field in an examination region;
magnetic field gradient coil which superimposes time varying magnetic field gradients on the B 0 in selected directions within the examination region;
a whole body radio frequency coil which generates radio frequency (B 1 ) pulses; and
the local radio frequency coil according to claim 1 inductively coupled to the whole body radio frequency coil.

12. A magnetic resonance method comprising:
a) positioning a subject and a local transmit coil inductively coupled to a whole body coil of a magnetic resonance scanner in an examination region of the magnetic resonance scanner;
b) determining a B 1 field distribution for each coil element of the local transmit coil;
c) adjusting a load in each coil element of the local transmit coil to adjust the B 1 field distribution for each coil element;
d) performing a magnetic resonance sequence using the local transmit coil.

13. The method according to claim 12 wherein the local transmit coilis inductively coupled with the whole body coil and performing the imaging sequence includes transmitting with the whole body coil and the local transmit coil concurrently.

14. The method according to claim 12 , further including:
e) transmitting a radio frequency signal into the examination region;
f) measuring at least one of a frequency, an amplitude, and a phase of the transmitted signal;
g) adjusting the load of one or more of the coil elements based on a deviation between the measured and a preselected current, frequency, amplitude, and/or phase;
h) repeating steps e)-g) for one or more of the coil elements.

15. The method according to claim 14 comprising:
iteratively repeating step h) until the B 1 field in the examination region is substantially uniform.

16. The method according to claim 12 , further including:
measuring a current on each coil element; and
adjusting the load based on the measured current.

17. The method according to claim 12 further including:
before performing each magnetic resonance sequence, adjusting the loads to produce one or more selected non-uniform B 1 field distributions during the magnetic resonance sequence.

18. The method according to claim 12 further including:
during the magnetic resonance sequence and/or during the magnetic resonance excitation, adjusting the loads to change the B 1 field distribution in the examination region.

19. The method according to claim 18 wherein the loads are changed to apply a series of parallel imaging B 1 field distributions sequentially to achieve a time division multiplex sensitivity encoding.

20. A non-transient computer readable medium carrying software which controls one or more processors to perform the method according to claim 12 .

Assignees

• Reykowski Arne
• Koninklijke Philips Nv

Inventors

• Reykowski Arne

Classifications

• G01R33/3642

  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

• G01R33/3692

  involving signal transmission without using electrically conductive connections, e.g. wireless communication or optical communication of the MR signal or an auxiliary signal other than the MR signal · CPC title

• G01R33/3628 Primary

  Tuning/matching of the transmit/receive coil · CPC title

• G01R33/36 Primary

  Electrical details, e.g. matching or coupling of the coil to the receiver · CPC title

• G01R33/5612

  Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels · CPC title