Measurement of a gradient field in an MRT system

Patent metadata

Field	Value
Publication number	US-12429541-B2
Application number	US-202318127644-A
Country	US
Kind code	B2
Filing date	Mar 28, 2023
Priority date	Mar 29, 2022
Publication date	Sep 30, 2025
Grant date	Sep 30, 2025

Abstract

In a method for measuring a gradient field in a magnetic resonance tomography (MRT) system, a first slice is excited by a first radio frequency (RF) pulse being emitted and by a first slice selection gradient being switched at least partly at the same time as the first RF pulse. A second slice is excited by a second RF pulse being emitted and by a second slice selection gradient being switched at least partly at the same time as the second RF pulse. The second slice intersects with the first slice in an intersection region. After the excitation of the second slice, a readout gradient is switched, and an MR signal emitted from the intersection region is acquired. Depending on the MR signal, a disruption variable is computed, which determines a deviation of a temporal course of an amplitude of the readout gradient from a predetermined required course.

First claim

The invention claimed is:

1. A method for measuring a gradient field in an imaging region of a magnetic resonance tomography (MRT) system, the method comprising:
exciting a first slice in a test object that is located in the imaging region;
after the exciting of the first slice, exciting a second slice in the test object, wherein the second slice intersects with the first slice in an intersection region;
after the exciting of the second slice, switching a readout gradient and acquiring a magnetic resonance (MR) signal emitted from the intersection region;
after the exciting of the second slice and before the switching of the readout gradient, exciting a third slice in the test object, wherein the third slice, the second slice, and the first slice intersect with one another in the intersection region; and
depending on the MR signal, computing a disruption variable that determines a deviation of a temporal course of an amplitude of the readout gradient from a predetermined required course for the readout gradient.

2. The method of claim 1 , wherein the disruption variable is computed as a variable independent of the predetermined required course.

3. The method of claim 1 , wherein exciting the first slice comprises exciting the first slice by a first radio frequency (RF) pulse being emitted into the imaging region and a first slice selection gradient being switched at least partly at a same time as the first RF pulse, and
wherein a first flip angle resulting from the first RF pulse lies between 60° and 120°, lies between 80° and 100°, or is equal to 90°.

4. The method of claim 3 , further comprising:
exciting a further first slice in the test object;
after the exciting of the further first slice, exciting a further second slice in the test object, wherein the further second slice intersects with the further first slice in a further intersection region;
after the exciting of the further second slice, depending on the predetermined required course, switching a further readout gradient, and acquiring a further MR signal emitted from the further intersection region,
wherein computing the disruption variable comprises computing the disruption variable depending on the MR signal and the further MR signal.

5. The method of claim 4 , wherein the disruption variable is computed depending on a phase difference between the MR signal and the further MR signal.

6. The method of claim 5 , wherein the disruption variable is computed as a time-dependent function e(t) based on the relationship

ϕ
˙

(
t
)

/

(

2
⁢
π
⁢
d
⁢
γ

)

=

G
s

(
t
)

-

∫
0
t

e
⁡
(
τ
)

⁢

G
^

s

(
τ
)

⁢
d
⁢
τ

wherein t refers to a time, G s refers to the predetermined required course, Ġ s refers to a first temporal derivation of the predetermined required course, {dot over (ϕ)} refers to a first temporal derivation of the phase difference, γ refers to a gyromagnetic ratio, and d refers to a spatial distance between the intersection region and the further intersection region.

7. The method of claim 6 , wherein an approach is chosen for the disruption variable in accordance with which the disruption variable is defined by a plurality of parameters independent of one another, and respective values for the plurality of parameters independent of one another are computed by a fit method.

8. The method of claim 4 , wherein the further first slice is equal to the first slice, and the further second slice is parallel to the second slice; or
wherein the further second slice is equal to the second slice, and the further first slice is parallel to the first slice.

9. The method of claim 1 , wherein the third slice is at right angles to the first slice and at right angles to the second slice.

10. The method of claim 1 , wherein exciting the second slice comprises exciting the second slice by a second RF pulse being emitted into the imaging region and by a second slice selection gradient being switched at least partly at a same time as the second RF pulse,
wherein a second flip angle resulting from the second RF pulse lies between 60° and 120°, lies between 80° and 100°, or is equal to 90°,
wherein exciting the third slice comprises exciting the third slice by a third RF pulse being emitted into the imaging region and by a third slice selection gradient being switched at least partly at a same time as the third RF pulse, and
wherein a third flip angle resulting from the third RF pulse lies between 60° and 120°, lies between 80° and 100°, or is equal to 90°.

11. The method of claim 3 , wherein exciting the second slice comprises exciting the second slice by a second RF pulse being emitted into the imaging region and by a second slice selection gradient being switched at least partly at a same time as the second RF pulse, and
wherein a second flip angle resulting from the second RF pulse lies between 150° and 210°, lies between 170° and 190°, or is equal to 180°.

12. A method for magnetic resonance tomography (MRT) using an MRT system, the method comprising:
measuring a gradient field in an imaging region of the MRT system, the measuring comprising:
exciting a first slice in a test object that is located in the imaging region;
after the exciting of the first slice, exciting a second slice in the test object, wherein the second slice intersects with the first slice in an intersection region;
after the exciting of the second slice, switching a readout gradient and acquiring a magnetic resonance (MR) signal emitted from the intersection region;
after the exciting of the second slice and before the switching of the readout gradient, exciting a third slice in the test object, wherein the third slice, the second slice, and the first slice intersect with one another in the intersection region; and
depending on the MR signal, computing a disruption variable that determines a deviation of a temporal course of an amplitude of the readout gradient from a predetermined required course for the readout gradient; and

creating at least one MR image depending on the disruption variable.

13. The method of claim 12 , further comprising:
creating MR data th

Assignees

• Siemens Healthineers Ag

Inventors

• Köhler Michael

Classifications

• 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

• G01R33/56518

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

• G01R33/385 Primary

  using gradient magnetic field coils · CPC title

• G01R33/243 Primary

  Spatial mapping of the polarizing magnetic field · CPC title