Minimization of effects of concomitant fields in multi echo imaging

Patent metadata

Field	Value
Publication number	US-11474184-B2
Application number	US-202016891689-A
Country	US
Kind code	B2
Filing date	Jun 3, 2020
Priority date	Jun 3, 2019
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

The present disclosure relates to operating an MR system in which MR signals of an object under examination are acquired in an examining region using a multi echo imaging sequence, in which an RF excitation pulse and a plurality of RF refocusing pulses are applied. The techniques include determining a first accumulated phase of a magnetization in the object under examination. Then, a second accumulated phase of the magnetization in the object under examination is determined due to concomitant magnetic fields occurring between a second pair of consecutive RF pulses. Finally, it is determined whether a deviation from the predefined relationship is larger than a threshold and, if this is the case, a measure is applied in view of the fact that the deviation is larger than the threshold.

First claim

What is claimed is:

1. A method for operating a magnetic resonance (MR) system, comprising:
acquiring, in an imaging region using a multi echo imaging sequence in which (i) an RF excitation pulse, and (ii) a plurality of RF refocusing pulses are applied as a plurality of applied RF pulses, MR signals of an object under examination;
determining a first accumulated phase of a magnetization in the object under examination due to concomitant magnetic fields occurring between a first pair of consecutive RF pulses of the plurality of applied RF pulses with respect to spatial locations within a currently-selected field of view (FoV) within the imaging region that is used to perform the multi spin echo imaging sequence;
determining a second accumulated phase of the magnetization in the object under examination due to concomitant magnetic fields occurring between a second pair of consecutive RF pulses of the plurality of applied RF pulses in the currently-selected FoV, the first accumulated phase and the second accumulated phase having a predetermined relationship with respect to one another; and
when a deviation from the predetermined relationship between the first accumulated phase and the second accumulated phase exceeds a threshold value, increasing a time between the plurality of RF refocusing pulses, and
wherein the first accumulated phase and the second accumulated phase in the object under examination are a result of a magnetization in the object under examination that forms a stimulated echo having a different amount of accumulated phase than a magnetization in the object under examination that forms a spin echo.

2. The method according to claim 1 , further comprising:
when the deviation from the predetermined relationship exceeds the threshold value,
informing a user of the MR system that the deviation exceeding the threshold value has occurred.

3. The method according to claim 1 , comprising:
determining the first and second accumulated phases in a plurality of locations within the imaging region; and
executing the one or more actions when the deviation exceeds the threshold value for each of the plurality of locations.

4. The method according to claim 1 , wherein the first accumulated phase and the second accumulated phase are determined without considering gradients applied in a phase encoding direction.

5. The method according to claim 1 , wherein the first accumulated phase and the second accumulated phase are determined using gradients applied in a readout direction and a slice selection direction.

6. The method according to claim 1 , wherein the first accumulated phase and the second accumulated phase are determined in at least one of the following locations:
in a central location of the currently-selected FoV that is used in the multi spin echo sequence; and
in a plurality of points located on an edge of the currently-selected FoV that is used in the multi spin echo sequence.

7. The method according to claim 1 , wherein the threshold value is a predetermined, fixed value.

8. The method according to claim 1 , wherein the threshold is determined based on current operating conditions at which the multi spin echo sequence is acquired.

9. The method according to claim 1 , wherein the first accumulated phase is determined between the RF excitation pulse and a first refocusing pulse, and
wherein the second accumulated phase is determined between 2 consecutive RF refocusing pulses.

10. The method according to claim 9 , wherein the predetermined relationship indicates that the first accumulated phase is half of second accumulated phase, which is calculated by evaluating:
∫ t0 t1 BC ( t ) dt= ½∫ t1 t2 BC ( t ) dt= . . . = ½∫ tn-1 tn BC ( t ) dt , and

wherein the first accumulated phase and the second accumulated phase are determined by evaluating:
Φ c ( t 0, t 1)=γ∫ t0 t1 BC ( t ) dt , with the concomitant fields BC:

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Assignees

• Siemens Healthcare Gmbh

Inventors

• Ferguson George William
• Koehler Michael
• Von Deuster Constantin

Classifications

• G01R33/56581 Primary

  due to Maxwell fields, i.e. concomitant fields · CPC title

• 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

• G01R33/5617

  using RF refocusing, e.g. RARE · CPC title

• G01R33/56545 Primary

  caused by finite or discrete sampling, e.g. Gibbs ringing, truncation artefacts, phase aliasing artefacts · CPC title