Method and magnetic resonance system to acquire MR data and to determine a B1 magnetic field

Patent metadata

Field	Value
Publication number	US-9625546-B2
Application number	US-201414169556-A
Country	US
Kind code	B2
Filing date	Jan 31, 2014
Priority date	Feb 1, 2013
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

In a method to acquire magnetic resonance (MR) data within a volume segment with a magnetic resonance system, the MR data are repeatedly acquired with a sequence that includes radiating a first resonant RF pulse, radiating a second resonant RF pulse, applying a dephasing first gradient after the first resonant RF pulse and before the second resonant RF pulse, radiating a third resonant RF pulse after the second resonant RF pulse, applying a second gradient after the third RF pulse in order to refocus a stimulated echo of a magnetization component prepared by the first gradient, and read out MR data. At least one of the first gradient and/or the second gradient is/are different in a respective repetition of the sequence and an additional repetition of the sequence that directly follows the respective repetition.

First claim

We claim as our invention:

1. A method to acquire magnetic resonance (MR) data from a volume segment of a subject situated in an MR data acquisition unit, comprising:
operating the MR data acquisition unit to repeatedly, in a plurality of repetitions, expose the subject situated in the MR data acquisition unit to an MR data acquisition sequence;
in each repetition of said sequence, operating the MR data acquisition unit to radiate a first resonant radio-frequency (RF) pulse, radiate a second resonant RF pulse after radiating said first resonant RF pulse, apply a dephasing first gradient after radiating the first resonant RF pulse and before radiating the second resonant RF pulse, radiate a third resonant RF pulse after radiating the second resonant RF pulse, apply a second gradient after radiating the third RF resonant pulse, that refocuses a stimulated echo of a magnetization component in the subject prepared by the dephasing first gradient, and reading out MR data associated with the stimulated echo;
operating said MR data acquisition unit with a dissimilarity between a respective repetition, among said plurality of repetitions, and a next-successive repetition that directly follows said respective repetition, said dissimilarity being selected from the group consisting of (i) said first gradient in said respective repetition differing from said first gradient in said next-successive repetition, (ii) said second gradient in said respective repetition differing from said second gradient in said next-successive repetition, and (iii) both (i) and (ii); and
in a processor, collecting all MR data read out in said plurality of repetitions in a data file, and making said data file available in electronic form at an output of the processor.

2. A method as claimed in claim 1 wherein said volume segment comprises a slice and, in each repetition of said sequence, applying a slice selection gradient during said first resonant RF pulse and during said second resonant RF pulse and during said third resonant RF pulse.

3. A method as claimed in claim 1 wherein said volume segment is a three-dimensional volume segment, and exciting nuclear spins in an entirety of said three-dimensional volume segment with each of said first resonant RF pulse, said second resonant RF pulse and said third resonant RF pulse.

4. A method as claimed in claim 1 comprising, in each repetition of said sequence, applying a spoiler gradient, that rephases transverse components of magnetization in the volume segment, after radiating said second resonant RF pulse and before radiating said third resonant RF pulse.

5. A method as claimed in claim 1 comprising radiating each of said first resonant RF pulse and said second resonant RF pulse with a flip angle of 90°.

6. A method as claimed in claim 1 comprising, in each repetition of said sequence, radiating said third resonant RF pulse, applying said second gradient, and reading out said MR data multiple times.

7. A method to determine a B1 magnetic field within a volume segment of a subject situated in a magnetic resonance (MR) data acquisition unit, comprising:
operating the MR data acquisition unit to repeatedly, in a plurality of repetitions, expose the subject situated in the MR data acquisition unit to an MR data acquisition sequence;
in each repetition of said sequence, operating the MR data acquisition unit to radiate a first resonant radio-frequency (RF) pulse, radiate a second resonant RF pulse after radiating said first resonant RF pulse, apply a dephasing first gradient after radiating the first resonant RF pulse and before radiating the second resonant RF pulse, radiate a third resonant RF pulse after radiating the second resonant RF pulse, apply a second gradient after radiating the third RF resonant pulse, that refocuses a stimulated echo of a magnetization component in the subject prepared by the dephasing first gradient, and reading out MR data associated with the stimulated echo;
operating said MR data acquisition unit with a dissimilarity between a respective repetition, among said plurality of repetitions, and a next-successive repetition that directly follows said respective repetition, said dissimilarity being selected from the group consisting of (i) said first gradient in said respective repetition differing from said first gradient in said next-successive repetition, (ii) said second gradient in said respective repetition differing from said second gradient in said next-successive repetition, and (iii) both (i) and (ii);
operating said MR data acquisition unit to radiate a non-resonant RF pulse, after radiating said first resonant RF pulse and before radiating said second resonant RF pulse, in at least one of said respective repetition of said sequence and said next-successive repetition of said sequence, said non-resonant RF pulse producing a phase shift in said at least one repetition of said sequence in which said non-resonant RF pulse is radiated, relative to MR data read out in a repetition of said sequence in which said non-resonant RF pulse was not radiated;
in a processor, collecting all MR data read out in said plurality of repetitions in a data file and, in said processor, determining said phase shift from a difference of phase values of said MR data read out in said at least one of said sequences, and the phase values of MR data read out in said sequence in which said non-resonant RF pulse was not radiated;
in said processor, automatically determining an amplitude of a B1 magnetic field in said volume segment from said phase shift; and
emitting an electronic signal from an output of said processor, which represents said amplitude of said B1 magnetic field.

8. A method as claimed in claim 7 comprising operating said MR data acquisition unit to radiate said non-resonant RF pulse in each of said respective repetition of said sequence and said next-successive repetition of said sequence, and comprising radiating said non-resonant RF pulse in said respective repetition of said sequence with a first frequency, and radiating said non-resonant RF pulse in said next-successive repetition of said sequence with a second frequency that differs from said first frequency.

9. A method as claimed in claim 8 wherein said MR data acquisition unit has a system frequency, and radiating the respective non-resonant RF pulses in said respective repetition of said sequence and in said next-successive repetition of said sequence with one of said first frequency and said second frequency being above said system frequency, and the other of said first frequency and said second frequency being below said system frequency.

10. A method as claimed in claim 7 comprising operating said MR data acquisition unit to repeat said sequence three times, so that said plurality of repetitions consist of a first repetition, a second repetition and a third repetition;
operating said MR data acquisition unit to radiate said non-resonant RF pulse in each of said second repetition and said third repetition; and
operating said MR data acquisition unit to radiate said non-resonant RF pulse in said second repetition with a frequency that differs from a frequency of the non-resonant RF pulse radiated in said third repetition.

11. A method as claimed in claim 10 wherein said MR data acquisition unit comprises multiple transmission channels, and comprising:
radiating said non-resonant RF pulse in each of said respective repetition of said sequence and said next-successive repetition of said sequence, via a same set of said transmission channels, comprising at least one of said transmission channels, in both said respective repetition of said sequence and said next-successive repetition of said sequence; an

Assignees

• Koehler Michael
• Speckner Thorsten
• Siemens Ag

Inventors

• Koehler Michael
• Speckner Thorsten

Classifications

• G01R33/48 Primary

  NMR imaging systems · CPC title

• G01R33/246 Primary

  Spatial mapping of the RF magnetic field B1 · CPC title

• A61B5/055

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/54

  Signal processing systems, e.g. using pulse sequences {; Generation or control of pulse sequences; Operator console} · CPC title

• G01R33/443 Primary

  Assessment of an electric or a magnetic field, e.g. spatial mapping, determination of a B0 drift or dosimetry · CPC title