Permanent magnet assembly for magnetic resonance imaging with non-ferromagnetic frame
An assembly for providing a B 0 magnetic field for a magnetic resonance imaging (MRI) system, the assembly comprising: a plurality of rods extending along a common longitudinal direction and positioned to form a bore extending along the common longitudinal direction, the plurality of rods including a first rod, the first rod comprising: ferromagnetic segments, each having a net magnetization in a plane that is substantially perpendicular to the common longitudinal direction; and non-ferromagnetic segments.
1 . An assembly for providing a B 0 magnetic field in a portable magnetic resonance imaging (MRI) system, the assembly comprising:
a non-ferromagnetic frame defining a bore along a common longitudinal axis;
a plurality of ferromagnetic segments housed in the non-ferromagnetic frame, the ferromagnetic segments disposed about the bore in spaced relation along at least a portion of a circumference of the bore and extending along the common longitudinal axis, the ferromagnetic segments (i) having magnetization orientations that vary with their positions about the bore to provide a substantially homogeneous magnetic field within the bore, and (ii) arranged so that the assembly, when part of the portable MRI system, accommodates insertion of a patient's shoulder within a perimeter of the bore;
at least one gap formed in the non-ferromagnetic frame at a location spaced radially outward from the bore and extending along the common longitudinal axis; and
a panel disposed in the at least one gap, wherein the panel comprises at least one of a gradient coil, a transmit RF coil, a receive RF coil, or a shim coil.
2 . The assembly of claim 1 , wherein the magnetization orientations are arranged in a Halbach or Halbach-like pattern.
3 . The assembly of claim 1 , wherein the assembly weighs less than 120 kg.
4 . The assembly of claim 1 , wherein the magnetization orientations vary according to both angular position around the bore and longitudinal position along the bore.
5 . The assembly of claim 1 , wherein the gap has a width sized for a laminate coil panel between 4 mm and 12 mm.
6 . The assembly of claim 1 , wherein the ferromagnetic segments are fixedly mounted to maintain their magnetization orientation pattern during movement of the MRI system between imaging locations.
7 . The assembly of claim 1 , wherein the substantially homogeneous magnetic field has a homogeneity of 100 ppm to 500 ppm over a volume having a diameter between 15 cm and 25 cm.
8 . The assembly of claim 1 , wherein the non-ferromagnetic frame fixedly secures the ferromagnetic segments and includes one or more mounting features for non-rotational attachment to a support structure of the portable MRI system.
9 . A magnetic assembly for providing a B 0 magnetic field in a portable magnetic resonance imaging (MRI) system that is transportable between imaging locations without disassembly of the magnetic assembly, the magnetic assembly comprising:
a plurality of ferromagnetic segments housed in a non-ferromagnetic support frame, the ferromagnetic segments disposed about a bore along a common longitudinal axis, wherein the ferromagnetic segments are arranged to accommodate a patient's anatomy within the bore during imaging by the portable MRI system;
wherein the ferromagnetic segments have magnetization orientations that vary with their positions about the bore to provide a substantially homogeneous magnetic field within an imaging region situated within the bore;
wherein the non-ferromagnetic support frame fixedly secures the ferromagnetic segments and defines at least one axially extending gap spaced radially outward from the bore, the non-ferromagnetic support frame including one or more mounting features for non-rotational attachment to a support structure of the portable MRI system; and
a panel disposed in the at least one axially extending gap, the panel comprising at least one of a gradient coil, a transmit RF coil, a receive RF coil, or a shim coil.
10 . The magnetic assembly of claim 9 , wherein the magnetization orientations are arranged in a Halbach or Halbach like pattern.
11 . The magnetic assembly of claim 9 , wherein the ferromagnetic segments are fixedly mounted to maintain their magnetization orientation pattern during movement of the MRI system between imaging locations.
12 . The magnetic assembly of claim 9 , wherein the magnetization orientations vary according to both angular position around the bore and longitudinal position along the bore.
13 . The magnetic assembly of claim 9 , wherein the magnetic assembly weighs less than 120 kg.