Magnetic resonance imaging (MRI) system and method
A magnetic resonance imaging (MRI) system and method of magnetic resonance imaging. The preferred MRI system is of lower weight and/or uses less power than conventional MRI systems, due to one or more of magnet design, transmit and receive coil design, selection of RF pulse sequence, synchronization methods, and image reconstruction methods. Preferably, the MRI system is portable.
1. A magnet assembly for a magnetic resonance imaging (MRI) instrument, said magnet assembly comprising:
a body having an opening through said body sized and shaped to receive an object, said opening defining a longitudinal axis through a centre of said opening; and
a plurality of permanent magnet segments, each having a magnetization direction, attached to said body to generate a magnetic field profile within said opening, said plurality of permanent magnets being arranged in each of a first ring and a second ring, said first and second rings being spaced apart from each other along said longitudinal axis, said plurality of permanent magnet segments being evenly spaced apart from adjacent permanent magnet segments in each of said respective first and second rings;
wherein said permanent magnet segments define two rotations of said magnetization directions in each of said respective first and second rings; and
wherein said first ring defines a first plane perpendicular to said longitudinal axis, and said second ring defines a second plane perpendicular to said longitudinal axis, and at least some of said permanent magnet segments in said first or second rings are oriented out of alignment with said respective first or second planes.
2. The magnet assembly as claimed in claim 1 , wherein said plurality of permanent magnet segments includes permanent magnet segments arranged in a third ring positioned between said first and said second rings; wherein said first, second, and third rings are spaced apart from each other along said longitudinal axis; and wherein said third ring defines a third plane perpendicular to said longitudinal axis; and wherein all of said magnetization directions of said permanent magnet segments in said third ring are substantially aligned with said third plane.
3. The magnet assembly as claimed in claim 2 , wherein said plurality of permanent magnet segments includes permanent magnet segments arranged in at least one additional pair of rings positioned outwardly of said first and second rings.
4. The magnet assembly as claimed in claim 2 , wherein said first and second rings each have a smaller diameter than the diameter of said third ring.
5. The magnet assembly as claimed in claim 1 , wherein said body includes magnet holders in each of said first and second rings, adapted to hold said permanent magnet segments in place.
6. The magnet assembly as claimed in claim 5 , wherein each of said permanent magnet segments comprises a pair of spaced apart permanent magnets having the same magnetization direction; and wherein one of said pair of spaced apart permanent magnets is spaced outwardly from the other of said pair of spaced apart permanent magnets, relative to said center of said opening, such that said magnetization directions of said pair of permanent magnets are substantially aligned.
7. The magnet assembly as claimed in claim 5 , wherein each of said magnet holders includes a non-magnetic attachment member sized and shaped to permit said pair of permanent magnets to clamp to said non-magnetic attachment member by the force of their magnetic attraction to one another, across said non-magnetic attachment member.
8. The magnet assembly as claimed in claim 1 , wherein said magnetic field profile has a substantially constant magnetic strength along a portion of said opening along said longitudinal axis, and is substantially uniform radially about said longitudinal axis in a plane perpendicular to said longitudinal axis, over said portion of said opening.
9. The magnet assembly as claimed in claim 1 , wherein said magnetic field profile has a substantially constant magnetic strength along a portion of said opening along said longitudinal axis, and is substantially non-uniform radially about said longitudinal axis in a plane perpendicular to said longitudinal axis, over said portion of said opening.
10. The magnet assembly as claimed in claim 9 , wherein said magnetic strength of said magnetic field profile is linear in a direction perpendicular to said longitudinal axis.
11. The magnet assembly as claimed in claim 1 , wherein said first ring and said second ring are circular or elliptical.
12. An MRI instrument comprising:
a magnet assembly according to claim 1 ; and
a radio frequency coil for generating RF energy and receiving magnetic resonance signals from an object positioned in said magnet assembly.
13. The magnet assembly as claimed in claim 1 , wherein said body is formed from plastic.
14. The magnet assembly as claimed in claim 13 , wherein said body is a one piece construction.
15. The magnet assembly as claimed in claim 13 , wherein said body is formed by 3D printing.
16. The magnet assembly as claimed in claim 1 , wherein said permanent magnet segments are block magnets, each of said block magnet defining a face and having a magnetization direction perpendicular to said face; and wherein at least some said block magnets are attached to said body at an angle relative to said longitudinal axis such that their faces are not parallel to said longitudinal axis, and their magnetization directions are not perpendicular to said longitudinal axis.
17. The MRI instrument as claimed in claim 12 , further comprising a processor for processing said magnetic resonance signals received by said radio frequency coil, and an output device for displaying said processed signals in a visual form.