Method and magnetic resonance apparatus for echo planar imaging with data entry into k-space along a zigzag trajectory

Patent metadata

Field	Value
Publication number	US-9739857-B2
Application number	US-201414154364-A
Country	US
Kind code	B2
Filing date	Jan 14, 2014
Priority date	Jan 14, 2013
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

In a method and apparatus for echo planar magnetic resonance (MR) imaging sequence of phase encoding gradient fields and a sequence of readout gradient fields are applied in order to produce a well-defined zigzag-type trajectory for entering raw data into k-space. Zigzag-type trajectories can be achieved that have flanks without curvature, or without significant curvature. Cartesian methods for image reconstruction of parallel MR imaging are applied to echo planar MR imaging with such zigzag-type trajectories.

First claim

We claim as our invention:

1. A method for echo planar magnetic resonance (MR) imaging, comprising:
operating an MR data acquisition unit, in which a subject is situated, to acquire MR raw data from the subject in an echo planar MR imaging sequence including, in said echo planar MR imaging sequence, radiating a radio-frequency (RF) pulse that produces a transverse magnetization of nuclear spins in the subject, said transverse magnetization of said nuclear spins exhibiting a phase;
operating said MR data acquisition unit in said echo planar MR imaging sequence to also apply a sequence of readout gradient fields configured with alternating positive and negative values, and to apply a sequence of phase encoding gradient fields configured to have only positive values that vary as a function of time and that continuously increase the phase of the transverse magnetization as a function of time, or to have only negative values that vary as a function of time and that continuously decrease the phase of the transverse magnetization as a function of time, wherein applying said sequence of readout gradient fields and applying said sequence of phase encoding gradient fields produces a zigzag-type trajectory for entering MR raw data into an electronic memory organized as k-space;
operating said MR data acquisition unit in said echo planar MR imaging sequence to acquire said MR raw data representing gradient echoes resulting from said transverse magnetization, while applying said sequence of readout gradient fields and said sequence of phase encoding gradient fields, and entering the acquired MR raw data into k-space along said zigzag-type trajectory; and
via a processor having access to said memory, making the MR raw data in k-space available in electronic form as a data file.

2. A method as claimed in claim 1 comprising operating said MR data acquisition unit in said echo planar MR imaging sequence with said sequence of readout gradients and said sequence of phase encoding gradients synchronized in time to give said zigzag-type trajectory substantially linear flanks.

3. A method as claimed in claim 1 comprising:
operating said MR data acquisition unit in said echo planar MR imaging sequence to apply said sequence of readout gradient fields configured to have values described by a first time-dependent function;
operating said MR data acquisition unit in said echo planar MR imaging sequence to apply said sequence of phase encoding gradient fields configured to have values described by a second time-dependent function that equals an absolute value of said first time-dependent function, multiplied by a scaling factor.

4. A method as claimed in claim 1 , comprising:
operating said MR data acquisition unit in said echo planar MR imaging sequence with said sequence of readout gradient fields configured to have values described by a sinusoidal-type time-dependent function; and
operating said MR data acquisition unit in said echo planar MR imaging sequence with said sequence of phase encoding gradient fields configured to have values described by an absolute value of said sinusoidal-type time-dependent function, multiplied by a scaling factor.

5. A method as claimed in claim 1 comprising operating said MR data acquisition unit in said echo planar MR imaging sequence with at least one of said sequence of readout gradient fields or said sequence of phase encoding gradient fields configured to give a density of data points of said MR raw data along said zigzag-type trajectory periodically varying values.

6. A method as claimed in claim 5 comprising operating said MR data acquisition unit in said echo planar MR imaging sequence with said at least one of said sequence of readout gradients and said sequence of phase encoding gradients configured to give said density higher values for larger distances along a readout direction of k-space, with respect to a center of k-space, than for smaller distances along said readout direction of k-space.

7. A method as claimed in claim 1 comprising:
operating said MR data acquisition unit in said echo planar MR imaging sequence with said sequence of readout gradient fields and said sequence of phase encoding gradient fields synchronized in time to cause at least one of: maximum values of said phase encoding gradient fields to be coincident with extreme values of said readout gradient fields, or zero crossings of said phase encoding gradient fields to be coincident with zero crossing of said readout gradient fields.

8. A method for echo planar magnetic resonance (MR) imaging, comprising:
operating an MR data acquisition unit, in which a subject is situated, to acquire MR raw data from the subject in an echo planar MR imaging sequence including, in said echo planar MR imaging sequence, radiating a radio-frequency (RF) pulse that produces a transverse magnetization of nuclear spins in the subject, said transverse magnetization of said nuclear spins exhibiting a phase;
operating said MR data acquisition unit in said echo planar MR imaging sequence to also apply a sequence of readout gradient fields configured with alternating positive and negative values, and to apply a sequence of phase encoding gradient fields configured to have only positive values that continuously increase the phase of the transverse magnetization as a function of time, or to have only negative values that continuously decrease the phase of the transverse magnetization as a function of time, wherein applying said sequence of readout gradient fields and applying said sequence of phase encoding gradient fields produces a zigzag-type trajectory for entering MR raw data into an electronic memory organized as k-space;
operating said MR data acquisition unit in said echo planar MR imaging sequence to acquire said MR raw data, via multiple receiver coils of said MR data acquisition unit, representing gradient echoes resulting from said transverse magnetization, while applying said sequence of readout gradient fields and said sequence of phase encoding gradient fields, and entering the acquired MR raw data into k-space along said zigzag-type trajectory, said zigzag-type trajectory in k-space exhibiting a first class of flanks that have positive values of said readout gradient fields and a second class of flanks that have negative values of the readout gradient fields; and
from a processor, accessing said MR raw data in said electronic memory and applying a parallel MR image reconstruction algorithm to said MR raw data to obtain a data file representing an MR image of the subject, and making said data file available at an output of the processor in electronic form.

9. A method as claimed in claim 8 wherein k-space represents a spatial frequency domain, said method comprising:
in said processor, applying said reconstruction algorithm to said MR raw data in the spatial frequency domain represented by k-space, and reconstructing a plurality of reconstructed data points in said spatial frequency domain from a plurality of data points of said MR raw data in k-space that are situated on neighboring flanks of a same class of said flanks.

10. A method as claimed in claim 9 comprising:
reconstructing a reconstructed flank from said plurality of reconstructed data points, said reconstructed flank belonging to the same class as the flanks in which said plurality of MR raw data points are situated in k-space.

11. A method as claimed in claim 9 comprising, in said processor, executing said reconstruction algorithm using at least one reconstruction kernel having a predetermined dimension in k-space.

12. A method as claimed in claim 11 comprising determining said at least one reconstruction kernel by:
operati

Assignees

• Porter David Andrew
• Heidemann Robin
• Siemens Ag
• Max-Planck-Gesellschaft Zur Foerderung Der Wss E V

Inventors

• Porter David Andrew
• Heidemann Robin

Classifications

• G01R33/4818 Primary

  MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space · 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

• G01R33/5616

  using gradient refocusing, e.g. EPI · CPC title

• G01R33/4824 Primary

  using a non-Cartesian trajectory · CPC title