Metal resistant MR imaging

Patent metadata

Field	Value
Publication number	US-10203394-B2
Application number	US-201414762591-A
Country	US
Kind code	B2
Filing date	Jan 6, 2014
Priority date	Jan 25, 2013
Publication date	Feb 12, 2019
Grant date	Feb 12, 2019

Abstract

The invention relates to a method of MR imaging near metal parts using SEMAC. It is an object of the invention to provide an improved MR imaging technique that is sufficiently fast and robust against susceptibility effects. The invention proposes to apply a weaker slice-selection magnetic field gradient (Gslice) for reduction of ripple-artefacts near metal parts or to apply undersampling in the slice-selection direction of the SEMAC sequence or to apply both these aspects. According to one aspect of the invention, a sparsity constraint is used to make the reconstruction of the undersampled MR images more stable. Moreover, the invention relates to a MR device (1) and to a computer program to be run on a MR device (1).

First claim

The invention claimed is:

1. A method of magnetic resonance imaging of at least a portion of a body placed within the examination volume of a magnetic resonance device, the method comprising the steps of:
subjecting the portion of the body to an imaging sequence of radio frequency pulses and a plurality of switched magnetic field gradients generated by a plurality of gradient coils of the magnetic resonance device, the imaging sequence comprising:
at least one slice-selective or slab-selective excitation radio frequency pulse, generated by at least one radio frequency coil of the magnetic resonance device, radiated toward the portion of the body in the presence of a magnetic field gradient in a slice-selection or slab-selection direction for exciting magnetic resonance within a slice or slab,
one or more refocusing radio frequency pulses, generated by the at least one radio frequency coil, radiated toward the portion of the body temporally subsequent to the excitation radio frequency pulse for generating spin echo signals, and
a switched phase-encoding magnetic field gradient in the slice-selection direction for phase-encoding of the spin echo signals,
acquiring phase-encoded spin echo signals from a plurality of spatially adjacent slices or slabs, by at least one radio frequency coil configured to receive magnetic resonance signals, wherein the thickness of the slices or slabs is selected such that spatially adjacent slices or slabs overlap at least partially in the slice-selection or slab-selection direction, and
reconstructing, by a reconstruction unit of the magnetic resonance device, a magnetic resonance image from the acquired phase-encoded spin echo signals using a sparsity constraint,
wherein a slice or slab image is reconstructed for each slice or slab, and
wherein image values of the magnetic resonance image are computed by combining image values from slice or slab images of different slices or slabs.

2. The method of claim 1 , wherein the sparsity constraint is derived from a spatial excitation profile of the excitation radio frequency pulse.

3. The method of claim 1 , wherein the spatial excitation profile is derived from a B 0 map indicating the spatial distribution of the main magnetic field B 0 .

4. The method of claim 1 , wherein the reconstruction of the magnetic resonance image is iterative, wherein the sparsity constraint is derived in an earlier iteration of the reconstruction of the magnetic resonance image and applied in a later iteration of the reconstruction of the magnetic resonance image.

5. The method of claim 1 , wherein the phase-encoded spin echo signals are acquired from each slice or slab with undersampling in the slice-selection or slab-selection direction.

6. The method of claim 1 , wherein spatially adjacent slices or slabs overlap in the slice-selection or slab-selection direction by at least 10.

7. The method of claim 1 , wherein the phase-encoded spin echo signals are acquired in the presence of a view-angle-tilting magnetic field gradient in the slice-selection or slab-selection direction.

8. The method of claim 1 , wherein the spin echo signals are acquired by parallel signal acquisition via at least two radio frequency coils having different spatial sensitivity profiles within the examination volume.

9. The method of claim 1 , wherein the reconstruction of the slice images is performed by at least one of parallel image reconstruction algorithm selected from a group consisting of: SENSE, SMASH, GRAPPA, and Compressed Sensing.

10. The method of claim 1 , wherein spatially adjacent slices or slabs overlap in the slice-selection or slab-selection direction by at least 30%.

11. The method of claim 1 , wherein spatially adjacent slices or slabs overlap in the slice-selection or slab-selection direction by at least 50%.

12. The method of claim 1 , wherein spatially adjacent slices or slabs overlap in the slice-selection or slab-selection direction by at least 10%.

13. The method of claim 1 , wherein the phase-encoded spin echo signals are acquired in the presence of a view-angle-tilting magnetic field gradient in the slice-selection or slab-selection direction.

14. The method of claim 1 , wherein the spin echo signals are acquired by parallel signal acquisition via at least two radio frequency coils having different spatial sensitivity profiles within the examination volume.

15. The method of claim 1 , wherein the reconstruction of the slice images is performed by at least one parallel image reconstruction algorithm selected from a group consisting of: SENSE, SMASH, GRAPPA, and Compressed Sensing.

16. A method of magnetic resonance imaging of at least a portion of a body placed within the examination volume of a magnetic resonance device, the method comprising the steps of:
subjecting the portion of the body to an imaging sequence of radio frequency pulses and a plurality of switched magnetic field gradients generated by a plurality of gradient coils of the magnetic resonance device, the imaging sequence comprising:
at least one slice-selective or slab-selective excitation radio frequency pulse, generated by at least one radio frequency coil of the magnetic resonance device, radiated toward the portion of the body in the presence of a magnetic field gradient in a slice-selective or slab-selection direction for exciting magnetic resonance within a slice or slab,
one or more refocusing radio frequency pulses, generated by the at least one radio frequency coil, radiated toward the portion of the body temporally subsequent to the excitation radio frequency pulse for generating spin echo signals, and
a switched phase-encoding magnetic field gradient in the slice-selection direction (z) for phase-encoding of the spin echo signals,
acquiring phase-encoded spin echo signals from a plurality of spatially adjacent slices or slabs by at least one radio frequency coil configured to receive magnetic resonance signals, and
reconstructing, by a reconstruction unit of the magnetic resonance device, a magnetic resonance image from the acquired phase-encoded spin echo signals using a sparsity constraint, wherein a slice or slab image is reconstructed for each slice or slab, and wherein image values of the magnetic resonance image are computed by combining image values from slice or slab images of different slices or slabs.

17. A magnetic resonance device comprising at least one main magnet coil for generating a uniform, steady magnetic field within an examination volume, a plurality of gradient coils for generating a plurality of switched magnetic field gradients in different spatial directions within the examination volume, at least one radio frequency coil for generating a plurality radio frequency pulses within the examination volume, at least one radio frequency coil for receiving magnetic resonance signals from at least a portion of a body of a patient positioned in the examination volume, a control unit for controlling the temporal succession of a plurality of radio frequency pulses and a plurality of switched magnetic field gradients, and a reconstruction unit for reconstructing magnetic resonance images from the received magnetic resonance signals, wherein the magnetic resonance device is configured to perform a method of magnetic resonance imaging, the method comprising:
subjecting the portion of the body to an imaging sequence of radio frequency pulses and a plurality of switched magnetic field gradients generated by the plurality of gradient coils, the imaging sequence comprising:
at least one slice-selective or slab-selective excitation radio fre

Assignees

• Philips Gmbh
• Koninklijke Philips Nv

Inventors

• Jurrissen Michel Paul Jurriaan
• Den Harder Johan Michiel
• Blume Ulrike Andrea
• De Weerdt Elwin
• Van Ijperen Gerrit Hendrik

Classifications

• G01R33/288

  Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room · CPC title

• G01R33/445 Primary

  MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging · CPC title

• G01R33/5659 Primary

  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

• G01R33/5611

  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

• G01R33/5615

  Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] · CPC title