Multiband RF/MRI pulse design for multichannel transmitter

Patent metadata

Field	Value
Publication number	US-10684337-B2
Application number	US-201414762093-A
Country	US
Kind code	B2
Filing date	Jan 24, 2014
Priority date	Jan 25, 2013
Publication date	Jun 16, 2020
Grant date	Jun 16, 2020

Abstract

A method for designing one or more multichannel, multiband radio frequency (“RF”) pulses for use with a magnetic resonance imaging (“MRI”) system is provided. The method includes determining a number of RF amplitude modulations and a number of RF phase modulations for each channel in a multichannel RF coil by minimizing an objective function that includes a complex-valued vector. The objective function also contains a system matrix that accounts for both a spatial sensitivity profile of each channel in the multichannel RF coil and a magnetic field map for each excitation band in the multiband RF pulse.

First claim

The invention claimed is:

1. A method for directing a magnetic resonance imaging (MRI) system to generate a multiband radio frequency (RF) pulse, the steps of the method comprising:
a) determining an RF amplitude modulation and an RF phase modulation for each channel in a multichannel RF coil by minimizing an objective function that includes:
a complex-valued vector containing the RF amplitude modulation and RF phase modulation; and
a system matrix that accounts for both a spatial sensitivity profile of each channel in the multichannel RF coil and a magnetic field map for each excitation band in the multiband RF pulse; and

b) directing the MRI system to generate at least one multiband RF pulse using the RF amplitude modulations and RF phase modulations determined in step a).

2. The method as recited in claim 1 , wherein step a) includes determining a different RF amplitude modulation and RF phase modulation for each channel in the multichannel RF coil.

3. The method as recited in claim 1 , wherein step b) includes transmitting multiband RF pulse waveforms using a single channel transmitter before splitting the multiband RF pulse waveforms into the multiple different channels of the multichannel RF coil, at which time each multiband RF pulse waveform is subjected to a channel-specific amplitude and phase change determined by the RF amplitude modulations and RF phase modulations determined in step a).

4. The method as recited in claim 1 , wherein step b) includes independently controlling each channel in the multichannel RF coil to generate a multiband RF pulse using the RF amplitude modulations and the RF phase modulation determined for that channel in step a).

5. The method as recited in claim 1 , wherein step a) includes:
a)i) selecting a multiband factor that defines a number of slices to be excited by each multiband RF pulse;
a)ii) determining a number of multiband RF pulses to be designed;
a)iii) defining a plurality of slabs to be excited based on the selected multiband factor and the determined number of multiband RF pulses; and
wherein step b) includes generating a plurality of multiband RF pulses, directing the MRI system to generate a plurality of multiband RF pulses using the RF amplitude modulations and RF phase modulations determined in step a), whereby the plurality of multiband RF pulses excite the plurality of slabs defined in step a)iii).

6. The method as recited in claim 1 , wherein step a) includes determining each RF amplitude modulation and each RF phase modulation using a single spoke trajectory in k-space.

7. The method as recited in claim 1 , wherein step a) includes determining an RF amplitude modulation and an RF phase modulation for each of a plurality of different spoke trajectories in k-space.

8. A method for directing a magnetic resonance imaging (MRI) system to generate a plurality of multiband radiofrequency (RF) pulses, the steps of the method comprising:
a) selecting a multiband factor that defines a number of slices to be excited by each multiband RF pulse;
b) determining a number of multiband RF pulses to be designed;
c) defining a plurality of slabs to be excited based on the selected multiband factor and the determined number of multiband RF pulses;
d) determining a number of RF amplitude modulations and a number of RF phase modulations for each channel in a multichannel RF coil by minimizing an objective function that includes:
a complex-valued vector that contains the RF amplitude modulation and the RF phase modulation for each multiband RF pulse; and
a system matrix that accounts for a spatial sensitivity profile of each channel in the multichannel RF coil, a magnetic field map for each excitation band in each multiband RF pulse, and a number of magnetic field gradients for each multiband RF pulse; and

e) directing the MRI system to generate a plurality of multiband RF pulses using the RF amplitude modulations and RF phase modulations determined in step d), whereby the plurality of multiband RF pulses excite the plurality of slabs defined in step c).

9. The method as recited in claim 8 , wherein step c) includes defining a spatial location for each slab and an order in which each slab is to be excited.

10. The method as recited in claim 9 , wherein step c) includes defining the order as an interleaved order.

11. The method as recited in claim 9 , wherein step c) further includes defining a spatial location for each of a plurality of slices located within each slab.

12. The method as recited in claim 10 , wherein the spatial locations for the plurality of slices are equally distributed in each slab.

13. A method for simultaneously exciting multiple different slice locations in a subject using a magnetic resonance imaging (MRI) system, the steps of the method comprising:
a) computing a multiband radio frequency (RF) pulse waveform to be applied to each channel in a multichannel RF coil;
b) simultaneously computing a transmit-channel specific RF magnitude modulation for each channel in the multichannel transmitter and computing a transmit-channel specific RF phase modulation for each channel in the multichannel transmitter by minimizing an objective function that includes:
a complex-valued vector that contains the transmit-channel specific RF amplitude modulation and the transmit-channel specific RF phase modulation for each transmit channel; and
a system matrix that accounts for a spatial sensitivity profile of each channel in the multichannel RF coil, a magnetic field map for each excitation band in each multiband RF pulse, and a magnetic field gradient for each multiband RF pulse;

c) directing the MRI system to generate an RF excitation field by, for each transmit channel, applying the transmit-channel magnitude and the transmit-channel phase for a given transmit channel to the computed multiband RF pulse waveform for the given transmit channel, thereby exciting spins in the multiple different slice locations in the subject.

14. The method as recited in claim 13 , wherein each transmit-channel specific RF magnitude modulation is a same global RF magnitude modulation, and each transmit-channel specific RF phase modulation is a same global RF phase modulation.

15. The method as recited in claim 13 , wherein the magnetic field gradient for each multiband RF pulse defines a same k-space trajectory.

16. The method as recited in claim 15 , wherein the same k-space trajectory is a spoke trajectory.

17. The method as recited in claim 13 , wherein the magnetic field gradient for each multiband RF pulse defines a different k-space trajectory.

Assignees

• Wu Xiaoping
• Van De Moortele Pierre Francois
• Schmitter Sebastian
• Ugurbil Kamil
• Auerbach Edward
• Univ Minnesota

Inventors

• Wu Xiaoping
• Van De Moortele Pierre-Francois
• Schmitter Sebastian
• Ugurbil Kamil
• Auerbach Edward

Classifications

• G01R33/4835 Primary

  of multiple slices · CPC title

• G01R33/3607

  RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal · CPC title

• G01R33/246

  Spatial mapping of the RF magnetic field B1 · CPC title

• 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

• A61B5/0042

  for the brain · CPC title