The present invention relates to magnetic resonance devices and more particularly to magnetic resonance device frames comprising laminated steel layers.
Magnetic resonance studies are typically carried out in strong magnetic fields greater than one kilogauss and require a magnetic field homogeneity of the order of a few parts per million. Magnetic resonance devices comprise a magnet capable of achieving the required field strength while attaining the necessary field homogeneity over the large volume. The magnetic resonance apparatus usually includes a support structure or frame for the magnet, which is typically comprised of solid steel. The ferromagnetic frame defines a magnetic flux return path for eliminating strong leakage magnetic fields.
Typically, the flux return path includes flux return members, supports for the poles and pole stems remote from the magnet poles. Since the ferromagnetic frame is constructed of solid steel, the ferromagnetic frames currently in use are bulky and difficult to fabricate, transport and assemble. Additionally, the bulk of the current solid steel frames contribute to the costliness in manufacturing the frames.
It is further desirable for the support structure or ferromagnetic frame of a magnetic resonance device to comprise ferromagnetic material. The dimensions of the yoke cross sections along the flux return paths become substantial to avoid magnetic saturation of the ferromagnetic yokes at high field strengths. Greater yoke cross-sectional area results, of course, in an increase in magnet weight. The substantial cross-section and weight of these magnets including the ferromagnetic frame limits the maneuverability of the magnet. It is therefore advantageous to have an alternate method of assembling the ferromagnetic frames for certain applications.
Thus, it is desirable to have an apparatus and methods which would permit easy fabrication, transport and assembly of a ferromagnetic frame of a magnetic resonance apparatus.
Accordingly, it is an object of the invention to provide a magnetic resonance device that is easily maneuverable and can easily be transported and assembled in pre-existing buildings.
It is another object of the invention to provide a magnetic resonance device having a frame comprising laminated steel layers.
It is another object of the invention to provide a magnetic resonance device having a ferromagnetic frame elements comprised of layers wherein the weight of the individual layer is substantially less than the weight of existing components.
According to the invention a magnetic resonance device includes a magnet defining a ferromagnetic structure formed of laminated steel layers. The ferromagnetic structure or frame supports a magnet for use in magnetic resonance studies. A pair of opposed ferromagnetic pole pieces are disposed facing each other and defining a patient-receiving gap therebetween for receiving a patient. The ferromagnetic structure includes at least one structural element and defines a flux return path. The structural elements are preferably formed of laminated steel layers.
In a preferred embodiment of the invention, flux return path extends through at least one of the structural elements of the frame formed from laminated steel layers. The ferromagnetic structure may further include a pair of opposed pole supports for supporting the pole pieces. The flux return members may extend between the pole supports. In addition, a pole stem may extend from the each of the supports. The pole stems may be formed of laminated steel layers transverse to the pole axis extending between the pole pieces. The pole axis may be horizontally or vertically oriented.
The magnetic resonance imaging device further includes a magnetic flux source. Preferably, the laminated steel layers are low carbon sheets laminated together using a fastening method such as bolts or epoxy. The sheets preferably have a thickness in the range of about 0.014 inch to about 0.500 inch.
In accordance with another aspect of the invention, the ferromagnetic structure comprises a room wherein the structural elements of the support structure comprise the ceiling, floor, and walls One or more of the structural elements of room may be formed of laminated steel layers.
In accordance with another aspect of the invention, a method of constructing a ferromagnetic structure for a magnetic resonance imaging device at a site where the device will be used is provided. The method includes forming the ferromagnetic frame at the site by laminating steel layers together to form one of the structural elements of the frame. Other elements of the frame are then constructed by building upon the completed structural element, layer by layer. The completed ferromagnetic frame is then provided with a pair of pole pieces in an opposed relationship defining a patient-receiving gap.
In one embodiment of the invention, the method may be implemented to construct the magnetic resonance imaging device in a room of a pre-existing building.
In another embodiment of the invention, each of the structural elements may be formed individually and then the ferromagnetic structure may be constructed by bolting each of the elements together.