Patent ID: 6157278
Filing Date: 2000-12-05
Classification: G01R,H01F

Abstract:
Open magnetic apparatus for use in an MRI or IMRI device to produce a predetermined volume of substantially uniform magnetic field directed parallel to an axis of symmetry of said volume, the apparatus comprising:a first electromagnet assembly disposed at a first position along said axis, said first electromagnet assembly includes at least a first electromagnet coil, said at least first coil is radially symmetric with respect to said axis;a second electromagnet assembly disposed at a second position spaced apart from said first position of said electromagnet assembly along said axis, said second electromagnet assembly includes at least a second electromagnet coil, said at least second coil is radially symmetric with respect to said axis, said at least first coil and said at least second coil are equidistant from the center of said volume, said first electromagnet assembly and said second electromagnetic assembly are adapted for generating a first magnetic field within said volume;a first permanent magnet assembly positioned at a third position disposed between said first position and said second position along said axis, said first permanent magnet assembly has an inner surface facing said volume and an outer surface facing said first electromagnet assembly, said first permanent magnet assembly includes,a first permanent magnet having an outer diameter, said first permanent magnet is radially symmetric with respect to said axis and has a first magnetization direction parallel to said axis,at least a second annular permanent magnet coaxial with said first permanent magnet, said at least second permanent magnet has an inner diameter larger than said outer diameter of said first permanent magnet, said second permanent magnet is radially symmetric with respect to said axis and has a second magnetization direction parallel to said axis, anda first low magnetic permeability frame for supporting said first permanent magnet and said at least second permanent magnet; anda second permanent magnet assembly opposed to said first permanent magnet assembly, said second permanent magnet assembly is positioned at a fourth position spaced apart from said third position along said axis, said second permanent magnet assembly has an inner surface facing said volume and an outer surface facing said second electromagnet assembly, said second permanent magnet assembly includes,a third permanent magnet having an outer diameters, said third permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said first magnetization direction,at least a fourth permanent magnet coaxial with said third permanent magnet, said at least fourth permanent magnet has an inner diameter larger than said outer diameter of said third permanent magnet, said fourth permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said second magnetization direction, anda second low magnetic permeability frame for supporting said third permanent magnet and said at least fourth permanent magnet,wherein the inner surface of said first permanent magnet assembly and the inner surface of said second permanent magnet assembly define an open region therebetween, said volume is disposed within said open region, said third position of said first permanent magnetic assembly and said fourth position of second permanent magnetic assembly are equidistant along said axis from the center of said volume and wherein said first permanent magnetic assembly and said second permanent magnetic assembly are adapted to generate a second magnetic field superimposed on said first magnetic field to provide said substantially uniform magnetic field within said volume.