Method of characterizing

Patent metadata

Field	Value
Publication number	US-9575146-B2
Application number	US-201113882293-A
Country	US
Kind code	B2
Filing date	Oct 26, 2011
Priority date	Nov 2, 2010
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

The invention relates to a method of characterizing the RF transmit chain of a magnetic resonance imaging scanner ( 1 ) using a local transmit/receive coil system ( 204; 210 ), comprising a first local NMR probe and a first local magnetic resonance coil, the first NMR probe being spatially located in immediate neighborhood to the first coil, a local receive coil system ( 206; 208 ), comprising a second local NMR probe and a second local magnetic resonance coil, the second NMR probe being spatially located in immediate neighborhood to the second coil, wherein the transmit chain comprises an external MR coil ( 9; 11; 12; 13 ), the method comprising: determining with the first magnetic resonance coil, a first MR signal phase evolution of the local RF transmit field generated by MR excitation of the first probe using the first magnetic resonance coil by measuring the RF response of the first probe upon said excitation, determining with the second magnetic resonance coil a second MR signal phase evolution of the local RF transmit field generated by MR excitation of the second probe using the external MR coil ( 9; 11; 12; 13 ) by measuring the RF response of the second probe upon said excitation, calculating a phase offset between the first and second MR signal phase evolution.

First claim

The invention claimed is:

1. A method of characterizing a radio frequency (RF) transmit chain of a magnetic resonance imaging scanner comprising:
a local transmit/receive coil system comprising a first probe and a first magnetic resonance coil, the first probe being spatially located in an immediate neighborhood of the first magnetic resonance coil,
a local receive coil system comprising a second probe and a second magnetic resonance coil, the second probe being spatially located in an immediate neighborhood of the second magnetic resonance coil,
wherein the RF transmit chain comprises an external magnetic resonance (MR) coil, the method comprising:
generating, with the first magnetic resonance coil, an MR excitation of the first probe;
measuring, with the first magnetic resonance coil, the RF response of the first probe to the MR excitation;
determining a first MR signal phase evolution of a first local RF transmit field from the RF response measured by the first magnetic resonance coil;
generating, with the external MR coil, an MR excitation of the second probe;
measuring, with the second magnetic resonance coil, the RF response of the second probe to the MR excitation;
determining a second MR signal phase evolution of a second local RF transmit field from the RF response measured by the second magnetic resonance coil; and
calculating a phase offset between the first MR signal phase evolution and the second MR signal phase evolution that characterizes the RF transmit chain.

2. The method of claim 1 , wherein the excitations of the first and second probes are performed simultaneously.

3. The method of claim 1 , wherein nuclei excited using the first local RF transmit field differ from nuclei excited using the second local RF transmit field.

4. The method of claim 1 , wherein:
the excitations of the first and second probes are performed sequentially, and
the method further comprises monitoring timings of the excitations of the first and second probes and aligning the first and second MR signal phase evolutions using the excitation timings.

5. The method of claim 1 , further comprising adjusting an RF frequency of the RF transmit chain for compensation of the phase offset.

6. The method of claim 1 , wherein from the RF responses of the first and second probes, a level of electromagnetic coupling is derived between each of the first and second magnetic resonance coils and an object to be examined, each of the levels of electromagnetic coupling is compared to a pre-set threshold, the first magnetic resonance coil is deactivated when its level of coupling with the object exceeds the pre-set threshold, and the second magnetic resonance coil is deactivated when its level of coupling with the object exceeds the pre-set threshold.

7. The method of claim 1 , wherein from the RF responses of the first and second probes, a level of electromagnetic coupling is derived for the first or second magnetic resonance coil when the respective one of the first and second magnetic resonance coils is deactivated.

8. The method of claim 6 , wherein:
a magnetic resonance imaging sequence is applied which includes RF excitation pulses, and
RF responses of the first and second probes o said RF excitation is measured.

9. The method of claim 1 , wherein the first probe and the second probe are commonly provided as one single probe.

10. The method of claim 1 , wherein the first coil and the second coil are commonly provided as one single RF coil.

11. The method of claim 1 , wherein the characterization of the RF transmit chain is performed using an MR calibration sequence prior to the execution of an imaging sequence.

12. The method of claim 1 , wherein the external MR coil comprises a parallel transmit coil.

13. The method of claim 1 , wherein the first coil and second coil are
spatially located in an immediate neighborhood of each other, or
partially separated from each other, wherein
the method further comprises virtually relating the first coil and second coil to each other.

14. An arrangement for characterizing the RF transmit chain of a magnetic resonance imaging scanner, the arrangement comprising:
a local transmit/receive coil system, comprising a first local NMR probe and a first local magnetic resonance coil, the first NMR probe being spatially located in immediate neighborhood to the first coil,
a local receive coil system, comprising a second local NMR probe and a second local magnetic resonance coil, the second NMR probe being spatially located in immediate neighborhood to the second coil,
wherein the transmit chain comprises an external MR coil, the arrangement being adapted for:
determining a first MR signal phase evolution of the local RF transmit field generated by MR excitation of the first probe using the first magnetic resonance coil by measuring the RF response of the first probe upon said excitation, the measurement being performed using the first magnetic resonance coil,
determining a second MR signal phase evolution of the local RF transmit field generated by MR excitation of the second probe using the external MR coil by measuring the RF response of the second probe upon said excitation, the measurement being performed using the second magnetic resonance coil,
providing the characterization of the RF transmit chain phase error by calculating a phase offset between the first MR signal phase evolution and the second MR signal phase evolution.

15. The arrangement of claim 14 , wherein the excitations of the first and second probes are performed simultaneously.

16. The arrangement of claim 14 , wherein:
the excitations of the first and second probes are performed sequentially, and
the arrangement is further adapted for monitoring timings of the excitations of the first and second probes and aligning the first and second MR signal phase evolutions using the excitation timings.

17. The arrangement of claim 14 , wherein the arrangement is further adapted for adjusting an RF frequency of the RF transmit chain for compensation of the phase offset.

18. The arrangement of claim 14 , wherein the arrangement is further adapted for deriving, from the RF responses of the first and second probes, a level of electromagnetic coupling between each of the first and second magnetic resonance coils and an object to be examined, comparing each of the levels of electromagnetic coupling to a pre-set threshold, deactivating the first magnetic resonance coil when its level of coupling with the object exceeds the pre-set threshold, and deactivating the second magnetic resonance coil when its level of coupling with the object exceeds the pre-set threshold.

19. The arrangement of claim 14 , wherein the arrangement is further adapted for deriving, from the RF responses of the first and second probes, a level of electromagnetic coupling for the first or second magnetic resonance coil when the respective one of the first and second magnetic resonance coils is deactivated.

20. The arrangement of claim 14 , wherein the first probe and the second probe are commonly provided as one single probe.

Assignees

• Van Den Brink Johan
• Graesslin Ingmar
• Krueger Sascha
• Weiss Steffen
• Vernickel Peter
• Koninl Philips Electronics Nv

Inventors

• Van Den Brink Johan
• Graesslin Ingmar
• Krueger Sascha
• Weiss Steffen
• Vernickel Peter

Classifications

• G01R33/36 Primary

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

• G01R33/246 Primary

  Spatial mapping of the RF magnetic field B1 · CPC title

• G01R33/583

  Calibration of signal excitation or detection systems, e.g. for optimal RF excitation power or frequency (G01R33/246 takes precedence) · CPC title

• G01R33/44

  using nuclear magnetic resonance [NMR] (G01R33/24, G01R33/62 take precedence) · CPC title

• G01R33/5612

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