Method and system for controlling a magnetic resonance imaging system

Patent metadata

Field	Value
Publication number	US-11921180-B2
Application number	US-202117553433-A
Country	US
Kind code	B2
Filing date	Dec 16, 2021
Priority date	Dec 16, 2020
Publication date	Mar 5, 2024
Grant date	Mar 5, 2024

Abstract

A method for controlling a magnetic resonance imaging system, including: selecting a plurality of spatially non-selective initial RF-pulses each having a predefined pulse shape and a predefined frequency; determining a combined RF-pulse from the initial RF-pulses by choosing a time-offset comprising a relative application time-shift between the initial RF-pulses, wherein this time-offset is chosen such that the initial RF-pulses overlap; and including the combined RF pulse in a pulse sequence applied in a magnetic resonance imaging system.

First claim

The invention claimed is:

1. A method for controlling a magnetic resonance imaging system, comprising:
selecting a plurality of spatially non-selective initial radio frequency (RF)-pulses, each having a predefined pulse shape and a predefined frequency;
determining a combined RF-pulse from the plurality of spatially non-selective initial RF-pulses by determining a time-offset comprising a relative application time-shift and a phase-shift between the plurality of spatially non-selective initial RF-pulses,
wherein the time-offset is determined in accordance with the predefined pulse shape and the predefined frequency of the plurality of spatially non-selective initial RF-pulses such that the plurality of spatially non-selective initial RF-pulses overlap; and
including the combined RF pulse in a pulse sequence applied in the magnetic resonance imaging system.

2. The method according to claim 1 , wherein the plurality of spatially non-selective initial RF-pulses are designed for a spatially non-selective excitation of proton spins, for pulse sequences designed for magnetization transfer, a chemically selective saturation, or a chemical exchange saturation transfer.

3. The method according to claim 1 , wherein two of the plurality of spatially non-selective initial RF-pulses have a different frequency with separate, non-overlapping frequency bands, and the difference between the frequencies is more than 50 Hz.

4. The method according to claim 1 , wherein the time-offset is determined such that an absolute value of a maximum RF-intensity of the combined RF-pulse does not exceed a predefined maximum RF-intensity that is lower than a maximum RF-intensity of the magnetic resonance imaging system or an absolute value of a maximum RF-intensity of the plurality of spatially non-selective initial RF-pulses.

5. The method according to claim 1 , wherein the predefined pulse shape B1(t) of a number of the plurality of spatially non-selective initial RF-pulses with an amplitude A follows the formula:

B
1

⁡

(
t
)

=

A
⁢

e

-

(

t
-

t
0

)

2

/

σ
2

⁢

e
iΔΔω

⁢

⁢
or
⁢

⁢

B
1

⁡

(
t
)

=

A
⁢

⁢

sin
⁡

(

t
-

t
0

σ

)

⁢

σ

t
-

t
0

⁢

e
iΔωt

.

and wherein:
t represents time,
t 0 to represents a center of the plurality of spatially non-selective initial RF-pulses,
σ represents a temporal width parameter,
Δω represents a frequency offset, and
i represents an imaginary number √−1.

6. The method according to claim 1 , wherein the predefined pulse shape and/or a duration of a number of the plurality of spatially non-selective initial RF-pulses is identical, and a number of the plurality of spatially non-selective initial RF-pulses have different frequency offsets.

7. The method according to claim 1 , wherein two of the plurality of spatially non-selective initial RF-pulses are arranged such that there is a temporal overlap therebetween having a non-empty set of time points, and
wherein an RF-contribution of the two of the plurality of spatially non-selective initial RF-pulses is non-zero.

8. The method according to claim 1 , wherein the time-offset is determined such that a minimal temporal shift between two of the plurality of spatially non-selective initial RF-pulses is determined, with the steps:
a) providing predefined pulse shapes of the plurality of spatially non-selective initial RF-pulses;
b) providing a predefined minimal test-offset comprising a time-shift and a phase-shift with the value zero;
c) providing a predefined maximum RF-intensity of the combined RF-pulse;
d) calculating a summed RF-pulse of the plurality of spatially non-selective initial RF-pulses, where at least one of the plurality of spatially non-selective initial RF-pulses is temporally shifted with the test-offset; and
e) comparing an absolute value of the--a maximum RF-intensity of the summed RF-pulse with the predefined maximum RF-intensity of the combined RF-pulse,
when the absolute value of the maximum RF-intensity of the summed RF-pulse exceeds the predefined maximum RF-intensity of the combined RF-pulse, increasing the test-offset between the two of the plurality of spatially non-selective initial RF-pulses with a predefined temporal value and repeat steps d) to e), and
when the absolute value of the maximum RF-intensity of the summed RF-pulse does not exceed the predefined maximum RF-intensity of the combined RF-pulse, taking the summed RF-pulse as the combined RF-pulse,

wherein the steps are performed until the time-shift of the test-offset exceeds a length of the plurality of spatially non-selective initial RF-pulses such that the plurality of spatially non-selective initial RF-pulses no longer overlap.

9. The method according to claim 8 , wherein in the course of increasing the test-offset, the time-shift is increased by a predefined positive or negative shift, or a phase-shift is increased by a p

Assignees

• Siemens Healthcare Gmbh

Inventors

• Feiweier Thorsten
• Clifford Bryan
• Hilbert Tom

Classifications

• G01R33/543 Primary

  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

• G01R33/446 Primary

  Multifrequency selective RF pulses, e.g. multinuclear acquisition mode (spatially selective RF pulses G01R33/4833) · CPC title

• G01R33/4835

  of multiple slices · CPC title

• G01R33/5659

  caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/5605

  by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE] · CPC title