System and method for portable magnetic resonance imaging using a rotating array of magnets

Patent metadata

Field	Value
Publication number	US-9910115-B2
Application number	US-201314099194-A
Country	US
Kind code	B2
Filing date	Dec 6, 2013
Priority date	Oct 22, 2012
Publication date	Mar 6, 2018
Grant date	Mar 6, 2018

Abstract

A portable magnetic resonance imaging (“MRI”) system that uses static magnetic field inhomogeneities in the main magnet for encoding the spatial location of nuclear spins is provided. Also provided is a spatial-encoding scheme for a low-field, low-power consumption, light-weight, and easily transportable MRI system. In general, the portable MRI system spatially encodes images using spatial inhomogeneities in the polarizing magnetic field rather than using gradient fields. Thus, an inhomogeneous static field is used to polarize, readout, and encode an image of the object. To provide spatial encoding, the magnet is rotated around the object to generate a number of differently encoded measurements. An image is then reconstructed by solving for the object most consistent with the data.

First claim

What is claimed is:

1. A portable magnetic resonance imaging (“MRI”) system, comprising:
a magnet assembly extending along a longitudinal axis to define a region configured to receive an object to be imaged and generate a magnetic field that includes known spatial inhomogeneities in a plane transverse to the longitudinal axis of the magnet assembly;
a rotator coupled to the magnet assembly and configured to rotate the magnet assembly about its longitudinal axis through a plurality of different rotation angles;
a radio frequency (RF) coil for generating RF energy and receiving magnetic resonance signals from an object positioned in the magnet assembly; and
a controller configured to:
direct the rotator to rotate the magnet assembly through the plurality of different rotation angles;
direct the RF coil to generate RF energy and receive responsive magnetic resonance signals at each rotation angle to acquire imaging data by reading out magnetic resonance signals while the magnet assembly is at each of the plurality of different rotation angles;
correlate the known spatial inhomogeneities in the magnetic field generated by the magnet assembly with modulations in a phase of the magnetic resonance signal to determine spatial encoding information imaging data; and
reconstruct an image of the object using the imaging data and the spatial encoding information.

2. The portable MRI system as recited in claim 1 in which the magnet assembly includes a plurality of magnets that includes permanent magnets.

3. The portable MRI system as recited in claim 1 in which the magnet assembly includes a plurality of magnets that include light-weight superconducting magnets.

4. The portable MRI system as recited in claim 1 in which the magnet assembly includes a plurality of magnets and a support is configured to hold the magnets in an annular Halbach array arrangement.

5. The portable MRI system as recited in claim 4 in which:
the magnet assembly further comprises a plurality of end-ring magnets; and
the support is configured to hold the plurality of end-ring magnets in an annular arrangement that is coaxial with the longitudinal axis.

6. The portable MRI system as recited in claim 5 in which the support is configured such that the plurality of end-ring magnets is located at least one of at a proximal end of the plurality of magnets and at a distal end of the plurality of magnets.

7. The portable MRI system as recited in claim 1 in which the RF coil comprises an RF coil array that includes a plurality of RF coil elements configured to generate an RF field whose phase varies linearly along the longitudinal axis of the magnet assembly.

8. The portable MRI system as recited in claim 1 in which the magnet assembly is configured such that the plurality of magnets generate a magnetic field that varies along the longitudinal axis of the magnet assembly.

9. A portable magnetic resonance imaging (“MRI”) system, comprising:
a magnet assembly comprising:
a plurality of magnets, each extending from a proximal end to a distal end along a longitudinal axis of the magnet assembly;
a support configured to hold the plurality of magnets in an annular arrangement so as to define a region configured to receive an object to be imaged and such that the magnets generate a magnetic field that varies with spatial locations in a plane transverse to the longitudinal axis of the magnet assembly;
rotator coupled to the magnet assembly and configured to rotate the magnet assembly about its longitudinal axis through a plurality of different rotation angles;
a radio frequency (RF) coil for generating RF energy and receiving magnetic resonance signals from an object positioned in the magnet assembly;
a controller configured to direct the rotator to rotate the magnet assembly through the plurality of different rotation angles and to direct the RF coil to generate RF energy and receive responsive magnetic resonance signals at each rotation angle;
in which the magnet assembly further comprises:
another plurality of magnets, each extending from a proximal end to a distal end along a longitudinal axis of the magnet assembly; and
another support that is configured to hold the another plurality of magnets in an annular arrangement that is coaxial with the annular arrangement of the plurality of magnets such that the another plurality of magnets generate a linear magnetic field that augments the magnetic field generated by the plurality of magnets.

10. The portable MRI system as recited in claim 9 in which the another support is configured to rotate independently of the support.

11. The portable MRI system as recited in claim 10 , further comprising another rotator coupled to the another support and configured to rotate the another plurality of magnets about the longitudinal axis of the magnet axis through a plurality of different rotation angles.

12. The portable MRI system as recited in claim 9 in which the another plurality of magnets includes permanent magnets.

13. The portable MRI system as recited in claim 12 in which the plurality of magnets includes permanent magnets.

14. The portable MRI system as recited in claim 1 in which each of the plurality of magnets has a polygonal cross-section.

15. A method for magnetic resonance imaging using an annular array of magnets, the steps of the method comprising:
a) arranging an object within an annular array of magnets;
b) generating a radio frequency (RF) field to the object to excite spins therein;
c) receiving magnetic resonance signals responsive to the generated RF field from the object;
d) rotating the annular array of magnets around the object to a different rotation angle to generate modulations in a phase of the magnetic resonance signals received from the object;
e) repeating steps b)-d) a plurality of times to receive magnetic resonance signals from the object at a plurality of different rotation angles; and
f) reconstructing an image of the object from the received magnetic resonance signals using the modulations in the phase of the magnetic resonance signals to determine spatial encoding of the magnetic resonance signals.

16. The method as recited in claim 15 in which step d) includes rotating the annular array of magnets through discrete steps of different rotation angles.

17. The method as recited in claim 15 in which step d) includes continuously rotating the annular array of magnets through the plurality of different rotation angles.

18. The method as recited in claim 15 , in which the annular array of magnets comprises an annular array of permanent magnets.

19. The portable MRI system as recited in claim 1 in which the magnet assembly is configured to produce both linear and higher-order components to create the magnetic field that includes known spatial inhomogeneities.

20. The portable MRI system as recited in claim 1 in which the controller is configured to control the rotator and the RF coil to control intravoxel dephasing when acquiring the imaging data.

21. The portable MRI system as recited in claim 1 in which the controller is configured to control an array of RF coils and using information about spatially varying coil sensitivities when reconstructing the image of the object.

22. The portable MRI system as recited in claim 1 in which the controller is configured to control a bandwidth of RF excitation pulses produced by the RF coil to create a series of constrained spatial regions and use the series of constrained spatial regi

Assignees

• Wald Lawrence L
• Zimmerman Clarissa
• Stockman Jason
• Massachusetts Gen Hospital

Inventors

• Wald Lawrence L
• Zimmerman Clarissa
• Stockman Jason

Classifications

• G01R33/3815

  with superconducting coils, e.g. power supply therefor · CPC title

• G01R33/4824

  using a non-Cartesian trajectory · CPC title

• G01R33/383 Primary

  using permanent magnets · CPC title