PARALLEL MRI WITH SPATIALLY MISREGISTERED SIGNAL

• US 20140361770A1
• Filed: 06/10/2013
• Published: 12/11/2014
• Est. Priority Date: 06/10/2013
• Status: Active Grant

• Current Assignee: Toshiba Medical Systems Corporation (Canon Inc.)
• Original Assignee: Toshiba Medical Systems Corporation (Canon Inc.), Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: DANNELS, WAYNE R.
• Granted Patent: US 10,534,060 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: G01R 33/34 Constructional details, e.g. resonators , specially adapted to MR
• CPC Class Codes: G01R 33/385 using gradient magnetic field coils
• CPC Class Codes: G01R 33/543 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 Class Codes: G01R 33/5611 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 Class Codes: G01R 33/5616 using gradient refocusing, e.g. EPI
• CPC Class Codes: G01R 33/56554 caused by acquiring plural, differently encoded echo signals after one RF excitation, e.g. correction for readout gradients of alternating polarity in EPI

Abstract

A magnetic resonance imaging (MRI) system, method and/or computer readable medium is configured to effect improved parallel MR imaging with reduced unfolding artifacts by using either or both of:

• • (a) an unfolded “intermediate” diagnostic image to create a more accurate mask for use in further processing raw image data for final unfolded diagnostic images; and/or
  • (b) an extension of coil sensitivity maps by replication (rather than curve-fitted extrapolation) for use in final unfolding of diagnostic images.

Claims

1. A magnetic resonance imaging (MRI) system for effecting parallel MR imaging with reduced unfolding artifacts, said MRI system comprising:

an MRI gantry including a static magnetic field coil, gradient magnetic field coils, at least one radio frequency (RF) coil configured to transmit RF signals into an imaging volume, and a plurality of RF receiver coils configured to receive nuclear magnetic resonance (NMR) RF signals from an object located in the imaging volume;

at least one digital data processing unit coupled to receive digital data from said plurality of RF receiver coils, said at least one digital data processing unit being configured to;

generate an extended coil sensitivity map corresponding to each of the plurality of receiving RF coils based upon prescan local sensitivity data provided from a preparation MRI scan (prescan) of the object, said prescan local sensitivity data being extended beyond a measured data boundary for processing of spatially misregistered MRI signals;

unfold MRI scan data provided from a diagnostic MRI scan of the object by parallel imaging matrix inversion using said extended coil sensitivity maps; and

output MR image data to a display or to storage in a non-transient digital data storage medium or to an outbound data transmission,

wherein, said at least one digital data processing unit has been further configured to effect either or both of;

(a) generation of said extended coil sensitivity maps by replicating measured local sensitivity map data beyond said measured data boundary; and

/or

(b) generation of a mask image for discriminating against spatially misregistered MRI signals located beyond a boundary of the object, by preliminarily unfolding diagnostic image data to define a boundary of said mask image which is thereafter used to mask diagnostic image data prior to unfolding into an output diagnostic MR image using parallel imaging matrix inversion.

2. The MRI system as in claim 1, wherein a direction of coil sensitivity map extension by replication is in a direction of MRI phase encoding of said diagnostic MRI scan.

3. The MRI system as in claim 1, wherein the at least one digital data processing unit is configured to:

(a) extend the coil sensitivity maps by replication in at least one direction, and

(b) generate a mask for the object based upon an unfolded intermediate copy of diagnostic image data; and

(c) thereafter unfold said diagnostic image data into an output diagnostic image based upon both the extended coil sensitivity maps and the generated mask.

4. The MRI system as in claim 1, wherein the at least one digital data processing unit is further configured to extend the coil sensitivity maps by replicating points selected from within an area defined by a detected edge corresponding to the object.

5. The MRI system as in claim 4, wherein the at least one digital data processing unit is further configured to extend the coil sensitivity maps to a desired field of view (FOV).

6. The MRI system as in claim 1, wherein the at least one digital data processing unit is further configured to unfold at least one unmasked intermediate diagnostic data image to generate the mask which is thereafter used to unfold a masked copy of diagnostic image data.

7. The MRI system as in claim 1, wherein the MRI scan is an echo planar imaging (EPI) scan.

8. The MRI system as in claim 1, wherein the at least one digital data processing unit is further configured to use the coil sensitivity maps generated based upon prescan data provided from one prescan of the object to unfold diagnostic image data generated based upon scan data from a plurality of further MRI scans.

9. The MRI system as in claim 1, wherein the at least one digital data processing unit is further configured to, when a plurality of further MRI scans of the object are performed, use the mask generated in a selected one of the further MRI scans in unfolding respective diagnostic image data of others of the further MRI scans.

10. The MRI system as in claim 1, wherein the at least one digital data processing unit is further configured to unfold diagnostic image data based upon a Nyquist map generated from EPI Nyquist prescan images obtained from a second prescan of the object.

11. A magnetic resonance imaging (MRI) method for effecting parallel MR imaging with reduced unfolding artifacts, said MRI method comprising:

placing an object into an MRI gantry including a static magnetic field coil, gradient magnetic field coils, at least one radio frequency (RF) coil configured to transmit RF signals into an imaging volume, and a plurality of RF receiver coils configured to receive nuclear magnetic resonance (NMR) RF signals from said object when located in the imaging volume;

generating an extended coil sensitivity map corresponding to each of the plurality of receiving RF coils based upon prescan local sensitivity data provided from a preparation MRI scan (prescan) of the object, said prescan local sensitivity data being extended beyond a measured data boundary for processing of spatially misregistered MRI signals;

unfolding MRI scan data provided from a diagnostic MRI scan of the object by parallel imaging matrix inversion using said extended coil sensitivity maps; and

outputting MR image data to a display or to storage in a non-transient digital data storage medium or to an outbound data transmission,

wherein, said method effects either or both of;

(a) generating of said extended coil sensitivity maps by replicating measured local sensitivity map data beyond said measured data boundary; and

/or

(b) generating of a mask image for discriminating against spatially misregistered MRI signals located beyond a boundary of the object, by preliminarily unfolding diagnostic image data to define a boundary of said mask image which is thereafter used to mask diagnostic image data prior to unfolding into an output diagnostic MR image using parallel imaging matrix inversion.

12. The MRI method as in claim 11, wherein a direction of coil sensitivity map extension by replication is in a direction of MRI phase encoding of said diagnostic MRI scan.

13. The MRI method as in claim 11, wherein:

(a) the coil sensitivity maps are extended by replication in at least one direction, and

(b) a mask is generated for the object based upon an unfolded intermediate copy of diagnostic image data; and

(c) said diagnostic image data is thereafter unfolded into an output diagnostic image based upon both the extended coil sensitivity maps and the generated mask.

14. The MRI method as in claim 11, wherein the coil sensitivity maps are extended by replicating points selected from within an area defined by a detected edge corresponding to the object.

15. The MRI method as in claim 11, wherein at least one unmasked intermediate diagnostic data image is unfolded to generate the mask which is thereafter used to unfold a masked copy of diagnostic image data.

16. The MRI method as in claim 11, wherein the MRI scan is an echo planar imaging (EPI) scan.

17. The MRI method as in claim 11, wherein the coil sensitivity maps generated based upon prescan data provided from one prescan of the object are used to unfold diagnostic image data generated based upon scan data from a plurality of further MRI scans.

18. The MRI method as in claim 11, wherein, when a plurality of further MRI scans of the object are performed, the mask generated in a selected one of the further MRI scans is used in unfolding respective diagnostic image data of others of the further MRI scans.

19. The MRI method as in claim 11, wherein the diagnostic image data is unfolded based upon a Nyquist map generated from EPI Nyquist prescan images obtained from a second prescan of the object.

20. A non-transitory computer readable storage medium, having executable computer program instructions recorded thereon, which when executed by at least one processor of a magnetic resonance imaging (MRI) system having an MRI gantry including a static magnetic field coil, gradient magnetic field coils, at least one radio frequency (RF) coil configured to transmit RF signals into an imaging volume and a plurality of RF receiver coils configured to receive nuclear magnetic resonance (NMR) RF signals from an object located in the imaging volume, causes the at least one processor to generate a diagnostic image having reduced unfolding artifacts, by performing operations comprising:

generating an extended coil sensitivity map corresponding to each of the plurality of receiving RF coils based upon prescan local sensitivity data provided from a preparation MRI scan (prescan) of the object, said prescan local sensitivity data being extended beyond a measured data boundary for processing of spatially misregistered MRI signals;

unfolding MRI scan data provided from a diagnostic MRI scan of the object by parallel imaging matrix inversion using said extended coil sensitivity maps; and

outputting MR image data to a display or to storage in a non-transient digital data storage medium or to an outbound data transmission,

wherein, said operations effect either or both of;

(a) generating of said extended coil sensitivity maps by replicating measured local sensitivity map data beyond said measured data boundary; and

/or

(b) generating a mask image for discriminating against spatially misregistered MRI signals located beyond a boundary of the object, by preliminarily unfolding diagnostic image data to define a boundary of said mask image which is thereafter used to mask diagnostic image data prior to unfolding into an output diagnostic MR image using parallel imaging matrix inversion.