Adjustable permanent magnet assembly for NMR and MRI
System and methods for designing and using single-sided magnet assemblies for magnetic resonance imaging (MRI) are disclosed. The single-sided magnet assemblies can include an array of permanent magnets disposed at selected positions. At least one of the permanent magnets can be configured to rotate about an axis of rotation in the range of at least +/−10 degrees and can include a magnetization having a vector component perpendicular to the axis of rotation. The single-sided magnet assemblies can further include a magnet frame that is configured to hold the permanent magnets in place while allowing the at least one of the permanent magnets to rotate about the axis of rotation.
1. A magnetic resonance imaging (MRI) method comprising:
providing an array of permanent magnets to one side of an imaging object;
selecting a target region;
rotating a plurality of elongated permanent magnets about substantially parallel axes of rotation extending longitudinally through the elongated permanent magnets to one or more orientations to move a desired magnetic field sensitive volume from a first target region to the selected target region, wherein the selected target region comprises a magnetic field having +/−1% homogeneity; and
performing an MRI measurement of the imaging object at the selected target region.
2. The method of claim 1 , further comprising using substantially all resonance frequencies within the selected target region to selectively perform MRI within the target region.
3. The method of claim 1 , wherein the one or more permanent magnet include magnetizations that are substantially perpendicular to the one or more axes of the rotation.
4. The method of claim 1 , wherein at least one of the permanent magnets include a cylindrical permanent magnet (PM) rod.
5. The method of claim 1 , wherein the one or more orientations are predetermined after selecting the target region.
6. The method of claim 1 , wherein the one or more orientations are predetermined before selecting the target region.
7. The method of claim 6 , wherein the one or more predetermined orientations are stored in a memory.
8. The method of claim 1 , wherein the plurality of elongated permanent magnets include magnetizations that are substantially perpendicular to the axes of rotation extending longitudinally through the elongated permanent magnets.
9. A magnetic resonance imaging (MRI) device comprising:
an array of permanent magnets that are configured to rotate about one or more axes of rotation, wherein the array of permanent magnets include a plurality of elongated permanent magnets configured to rotate about substantially parallel axes of rotation extending longitudinally through the elongated permanent magnets;
a processor configured to:
select a target region;
command one or more permanent magnets to one or more orientations to move a desired magnetic field sensitive volume from a first target region to the selected target region, wherein the selected target region comprises a magnetic field having +/−1 homogeneity; and
perform an MRI measurement at the selected target region.
10. The MRI device of claim 9 , wherein the array of permanent magnets includes four cylindrical permanent magnet (PM) rods.
11. The MRI device of claim 10 , wherein the four cylindrical permanent magnet (PM) rods include magnetizations that are substantially perpendicular to the axes of rotation thereof.
12. The MRI device of claim 11 further comprising one or more servo motors that are configured to rotate one or more PM rods to the predetermined orientations at the command of the processor.
13. The MRI device of claim 9 , further comprising a radio frequency (RF) coil disposed between the array of permanent magnets and the target region.
14. The MRI device of claim 13 , wherein the RF coil is a flat coil comprising one more or more windings of conductors.
15. The MRI device of claim 9 , further comprising a gradient coil disposed between the array of permanent magnets and the target region.
16. The MRI device of claim 15 , wherein the gradient coil comprises one or more conductive traces in a printed circuit board (PCB).
17. The MRI device of claim 9 , wherein the device is portable.
18. The method of claim 9 , wherein the plurality of elongated permanent magnets include magnetizations that are substantially perpendicular to the axes of rotation extending longitudinally through the elongated permanent magnets.