Parallel multi-slice MR imaging with suppression of side band artefacts

Patent metadata

Field	Value
Publication number	US-10401461-B2
Application number	US-201615544899-A
Country	US
Kind code	B2
Filing date	Jan 25, 2016
Priority date	Jan 27, 2015
Publication date	Sep 3, 2019
Grant date	Sep 3, 2019

Abstract

An object ( 10 ) placed in an examination volume of a MR device ( 1 ) is subject to an imaging sequence including multi-slice RF pulses for simultaneously exciting two or more spatially separate image slices. MR signals are received in parallel via a set of RF coils ( 11, 12, 13 ) having different spatial sensitivity profiles within the examination volume. An MR image is reconstructed for each image slice from the acquired MR signals. MR signal contributions from the different image slices are separated on the basis of the spatial sensitivity profiles of the RF coils ( 11, 12, 13 ). Side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, are suppressed in the reconstructed MR images on the basis of the spatial sensitivity profiles of the RF coils ( 11, 12, 13 ).

First claim

The invention claimed is:

1. A method of magnetic resonance (MR) imaging of an object placed in an examination volume of a MR device, the method comprising:
subjecting the object to an imaging sequence comprising multi-slice RF pulses for simultaneously exciting two or more spatially separate image slices,
acquiring MR signals, wherein the MR signals are received in parallel via a set of RF coils having different spatial sensitivity profiles within the examination volume, and
reconstructing a MR image for each of the two or more image slices from the acquired MR signals, wherein MR signal contributions from the two or more image slices are separated on the basis of the spatial sensitivity profiles of the RF coils, and wherein the MR signal contributions from the two or more image slices are separated from the side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, wherein the MR signal contributions from the image slices are separated from the side-band artifacts by using a signal model of the acquired MR signals, which signal model includes signal contributions from (i) the image slices and (ii) regions excited by the one or more side-bands of the multi-slice RF pulses, wherein the side-band artifacts are determined by solving a set of linear equations including iteratively adjusting relative signal contributions from (i) and (ii) of the acquired signals, and wherein the separated side-band artifacts are suppressed in the reconstructed MR images on the basis of the spatial sensitivity profiles of the RF coils.

2. A non-transitory computer-readable medium carrying instructions configured to be run on a magnetic resonance (MR) device to control the MR device to:
generate an imaging sequence comprising multi-slice RF pulses for simultaneously exciting two or more spatially separate image slices,
acquire MR signals, and
reconstruct an MR image for each image slice from the acquired MR signals, wherein MR signal contributions from the different image slices are separated on the basis of the spatial sensitivity profiles of a set of RF coils, and wherein the MR signal contributions from the image slices are separated from the side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, wherein the regions excited by the side-bands of the multi-slice RF pulses are regions where the side-band frequencies, namely the higher order harmonics of the fundamental frequency of the multi-slice RF pulses, are in resonance in the presence of a slice-selection magnetic field gradient of the imaging sequence and the separated side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, are suppressed in the reconstructed MR images on the basis of the spatial sensitivity profiles of the RF coils.

3. A magnetic resonance imaging (MRI) device comprising:
at least one main magnet coil configured to generate a static magnetic field within an examination volume;
a plurality of gradient coils configured to generate switched magnetic field gradients in a plurality of spatial directions within the examination volume;
a set of radio frequency (RF) coils having different spatial sensitivity profiles;
a controller configured to control the gradient coils and the set of RF coils to generate succession of multi-slice RF pulses and switched magnetic field gradients in a subject in the examination volume to simultaneously excite two or more spatially separate slices images with multi-slice RF pulses and receive MR signals in parallel with the set of RF coils from the subject in the examination volume; and
a reconstruction processor configured to reconstruct an MR image for each of the separate image slices from the received MR signals including:
separating MR signal contributions from the plurality of image slices on the basis of the spatial sensitivity profiles of the set of RF coils,
separating MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, wherein the MR signal contributions from the regions excited by the one or more side bands include higher order harmonics of a fundamental frequency of the multi-slice RF pulses which are in resonance in the presence of a slice-selection magnetic field gradient of the imaging sequence,
suppressing separate side-band artifacts from the regions excited by the one or more sidebands in the reconstructed MR images using the spatial sensitivity profiles of the RF coils.

4. The method of claim 1 , wherein the MR signal contributions from the image slices are separated from the side-band artifacts without taking prior information about the excitation spectra of the multi-slice RF pulses into account.

5. The method of claim 1 , wherein determining the relative signal contributions includes determining a ratio.

6. The method of claim 1 , wherein the regions excited by the side-bands of the multi-slice RF pulses are the locations where the side-band frequencies, namely the higher order harmonics of the fundamental frequency of the multi-slice RF pulses, are in resonance in the presence of a slice-selection magnetic field gradient of the imaging sequence.

7. The method of claim 1 , wherein the multi-slice RF pulses are phase-modulated, wherein the phase-modulation comprises a varying phase shift, such that a phase cycle is applied to the MR signals of each image slice.

8. The method of claim 7 , wherein the phase shift is linearly incremented from phase-encoding step to phase-encoding step.

9. The method of claim 1 , wherein the MR signals are acquired with undersampling in the in-plane direction of the image slices, wherein the MR images are reconstructed using a parallel image reconstruction algorithm, like SENSE, SMASH or GRAPPA.

10. A magnetic resonance (MR) device for carrying out the method claimed in claim 6 , wherein the MR device includes at least one main magnet coil for generating a uniform, static magnetic field within an examination volume, a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume, a set of RF coils having different spatial sensitivity profiles, a control unit for controlling the temporal succession of RF pulses and switched magnetic field gradients, and a reconstruction unit, wherein the MR device is arranged to perform the following steps:
subjecting the object to an imaging sequence comprising multi-slice RF pulses for simultaneously exciting two or more spatially separate image slices,
acquiring MR signals, wherein the MR signals are received in parallel via a set of RF coils having different spatial sensitivity profiles within the examination volume, and
reconstructing a MR image for each image slice from the acquired MR signals, wherein MR signal contributions from the different image slices are separated on the basis of the spatial sensitivity profiles of the RF coils, and the MR signal contributions from the image slices are separated from the side-band artifacts, namely MR signal contributions from regions excited by one or more side-bands of the multi-slice RF pulses, wherein the regions excited by the side-bands of the multi-slice RF pulses are the regions where the side-band frequencies, namely the higher order harmonics of the fundamental frequency of the multi-slice RF pulses, are in resonance in the presence of a slice-selection magnetic field gradient of the imaging sequence and the separated side-band artifacts are suppressed in the reconstructed MR images on the basis of the spatial sensitivity profiles of the RF coils.

Assignees

• Koninklijke Philips Nv

Inventors

• Chen Zhaolin
• Fuderer Miha

Classifications

• G01R33/4835 Primary

  of multiple slices · CPC title

• G01R33/483

  with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy · CPC title

• G01R33/56

  Image enhancement or correction, e.g. subtraction or averaging techniques {, e.g. improvement of signal-to-noise ratio and resolution} · CPC title

• G01R33/565

  Correction of image distortions, e.g. due to magnetic field inhomogeneities · CPC title

• G01R33/5611

  Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE (structural details of arrays of sub-coils G01R33/3415) · CPC title