Method for measuring eddy current fields in a magnetic resonance device, magnetic resonance device, computer program and electronically readable data carrier

Patent metadata

Field	Value
Publication number	US-11275143-B2
Application number	US-202016907598-A
Country	US
Kind code	B2
Filing date	Jun 22, 2020
Priority date	Jun 24, 2019
Publication date	Mar 15, 2022
Grant date	Mar 15, 2022

Abstract

Systems and methods for measuring eddy current fields occurring as a result of gradient pulses in a magnetic resonance sequence at a point in time during the magnetic resonance sequence in relation to at least one direction of pulse effect. At least the parts of the magnetic resonance sequence comprising the gradient pulses relating to the at least one direction of pulse effect are performed as a preparation sequence up until the point in time followed directly by a measurement sequence in which first measurement data is recorded. The preparation sequence is played out again with the same, directly consecutive measurement sequence without the gradient pulses relating to the at least one direction of pulse effect or with gradient pulses having an inverted sign relating to the at least one direction of pulse effect. Second measurement data is recorded. Using a joint evaluation of the first and second measurement data at least one variable characterizing the eddy current field generated by the eddy currents of the gradient pulses in the at least one direction of pulse effect is determined.

First claim

The invention claimed is:

1. A method for measuring eddy current fields occurring as a result of gradient pulses in an actual magnetic resonance sequence at a point in time during the actual magnetic resonance sequence in relation to at least one direction of pulse effect, the method comprising:
performing a preparation sequence up until the point in time, the preparation sequence comprising at least parts of the actual magnetic resonance sequence comprising gradient pulses relating to the at least one direction of pulse effect;
recording first measurement data during a measurement sequence that directly follows the preparation sequence;
repeating the preparation sequence and the measurement sequence without the gradient pulses relating to the at least one direction of pulse effect or only with gradient pulses relating to the at least one direction of pulse effect that include an inverted sign relating to the at least one direction of pulse effect;
recording second measurement data; and
determining, based on the first measurement data and the second measurement data, at least one variable characterizing the eddy current field generated by eddy currents of the gradient pulses in the at least one direction of pulse effect.

2. The method of claim 1 , wherein the point in time is selected as a point in time of output of a radio frequency pulse of the actual magnetic resonance sequence or as a point in time of measurement of k-space center.

3. The method of claim 2 , wherein the point in time of output of a radio frequency pulse is a preparation pulse.

4. The method of claim 1 , wherein the preparation sequence and the measurement sequence are repeated after a waiting period during which the eddy currents decay.

5. The method of claim 1 , wherein before each measurement sequence the preparation sequence or elements thereof are performed two or more times.

6. The method of claim 1 , wherein the measurement sequence is a gradient echo sequence.

7. The method of claim 1 , wherein the measurement sequence measures in a spatially resolved manner in at least one spatial direction.

8. The method of claim 1 , wherein the measurement sequence samples just one part of k-space to be sampled, and the first and second measurement data is recorded for all parts of the k-space to be sampled in two or more recording sections.

9. The method of claim 1 , wherein determining comprises:
evaluating a phase, an amplitude, or the phase and amplitude of the measurement data to determine the at least one variable.

10. The method of claim 1 , wherein the preparation sequence and the measurement sequence are programmed in an object-oriented manner and a combination of preparation sequence and measurement sequence is generated as a complete sequence from a base class describing the actual magnetic resonance sequence.

11. The method of claim 10 , wherein a base class is also used for the measurement sequence, wherein the complete sequence is generated using multiple inheritance from both base classes.

12. The method of claim 1 , wherein the at least one variable is determined successively for at least one of a plurality of different points in time, directions of pulse effect, or parameterizations of the actual magnetic resonance sequence.

13. The method of claim 1 , wherein the at least one variable is determined to parameterize at least one compensation measure for the eddy current field.

14. A magnetic resonance device comprising:
a control device configured to measure eddy current fields occurring as a result of gradient pulses in an actual magnetic resonance sequence at a point in time during the actual magnetic resonance sequence in relation to at least one direction of pulse effect, the control device comprising at least one processor and at least one storage device, the at least one processor configured to:
perform a preparation sequence up until the point in time, the preparation sequence comprising at least parts of the actual magnetic resonance sequence comprising gradient pulses relating to the at least one direction of pulse effect;
record first measurement data during a measurement sequence that directly follows the preparation sequence;
repeat the preparation sequence and the measurement sequence without the gradient pulses relating to the at least one direction of pulse effect or only with gradient pulses relating to the at least one direction of pulse effect that include an inverted sign relating to the at least one direction of pulse effect;
record second measurement data; and
determine, based on the first and second measurement data, at least one variable characterizing an eddy current field generated by eddy currents of the gradient pulses in the at least one direction of pulse effect.

15. A non-transitory computer implemented storage medium that stores machine-readable instructions executable by at least one processor for measuring eddy current fields occurring as a result of gradient pulses in an actual magnetic resonance sequence at a point in time during the actual magnetic resonance sequence in relation to at least one direction of pulse effect, the machine-readable instructions comprising:
performing a preparation sequence up until the point in time, the preparation sequence comprising at least parts of the actual magnetic resonance sequence comprising the gradient pulses relating to the at least one direction of pulse effect;
recording first measurement data during a measurement sequence that directly follows the preparation sequence;
repeating the preparation sequence and the measurement sequence without the gradient pulses relating to the at least one direction of pulse effect or only with gradient pulses relating to the at least one direction of pulse effect that include an inverted sign relating to the at least one direction of pulse effect;
recording second measurement data; and
determining, based on the first and second measurement data, at least one variable characterizing an eddy current field generated by eddy currents of the gradient pulses in the at least one direction of pulse effect.

16. The non-transitory computer implemented storage medium of claim 15 , wherein the point in time is selected as a point in time of output of a radio frequency pulse of the actual magnetic resonance sequence or as a point in time of measurement of k-space center.

17. The non-transitory computer implemented storage medium of claim 15 , wherein the point in time of output of a radio frequency pulse is a preparation pulse.

18. The non-transitory computer implemented storage medium of claim 15 , wherein the preparation sequence and the measurement sequence are repeated after a waiting period during which the eddy currents decay.

19. The non-transitory computer implemented storage medium of claim 15 , wherein before each measurement sequence the preparation sequence is performed two or more times.

20. The non-transitory computer implemented storage medium of claim 15 , wherein the measurement sequence is a gradient echo sequence.

Assignees

• Siemens Healthcare Gmbh

Inventors

• Köhler Michael

Classifications

• G01R33/543

  Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription (G01R33/546 takes precedence) · CPC title

• G01R33/56572

  caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/24

  for measuring direction or magnitude of magnetic fields or magnetic flux · CPC title

• G01R33/56518 Primary

  due to eddy currents, e.g. caused by switching of the gradient magnetic field · CPC title