Magnetic field generating apparatus for MRI

Abstract

A magnetic field generating apparatus for a magnetic resonance imaging (MRI) apparatus, including soft ferrite disposed adjacently to a gradient magnetic field coil which is disposed in a gap and serves to form a static magnetic field. The soft ferrite has saturated magnetic flux density (Rs) more than 0.4 T, coersive force (He) less than 50 A/m, and specific resistance ρ more than 10 -5 Ω·cm. The magnetic field generating apparatus thus constructed has a magnetic circuit arrangement that a pair of permanent magnetic bodies which are disposed so as to confront each other and define the gap are magnetically connected through a yoke, and pole pieces are fixedly secured to the surfaces of the respective permanent magnetic bodies facing the gap, thereby generating the magnetic field in the gap.

What is claimed is: .[.1. A magnetic field generating apparatus for MRI, comprising: 
     
        segments have a thickness ratio of 0.25 to 2..].2. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein the Mn-Zn series soft ferrite segments are of a saturated magnetic flux density Bs of more than 0.5 T, a coercive force Hc of less than 10 A/m and 
     
     
        a specific resistance ρ of more than 10 -3  Ω·m. 3. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein a plurality of Mn-Zn series soft ferrite segments, each having a rectangular plate shape, are deposited integrally on the base members by an insulative adhesive agent to be in a desired 
     
     
        formation. 4. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein the base members are made of pure iron. 
     
     
        . A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein a core made of soft iron material is provided on the base members at a central part of the soft ferrite segments and for 
     
     
        mounting thereon a gradient magnetic field coil. 6. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein 
     
     
        the thickness ratio t/T is 1 to 1.5. 7. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein the 
     
     
        annular convex portion is made of a soft iron material. 8. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein the annular convex portion is divided into the plural 
     
     
        circumferential sections by radially extended slits. 9. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein 
     
     
        the annular convex portion is made of soft ferrite. 10. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein 
     
     
        the plurality of magnet bodies are formed by permanent magnets. 11. A magnetic field generating apparatus according to claim .[.1.]. .Iadd.12.Iaddend., wherein the plurality of magnet bodies are formed with an electro-magnet or a combination of permanent magnets and 
     
     
        electro-magnets. .Iadd.12.  A magnetic field generating apparatus for MRI, comprising: a pair of magnet bodies arranged to form an air gap;   yokes for supporting and magnetically connecting said pair of magnet bodies; and   a pair of pole pieces, each pole piece being formed with a base member, an annular projection and a plurality of soft ferrite segments, the base member being made of soft iron material and disposed on a surface of each of said pair of magnet bodies to confront said air gap, said annular projection extending around the circumference of said base member, and said soft ferrite segments being made of Mn-Zn series soft ferrite and deposited to be closely adjacent one another on a surface of the base member and not on said annular projection, each said pole piece forming a substantially circular convex portion around a center of the base member, wherein a thickness t of the base member and a thickness T of the ferrite segments have a thickness ratio t/T of 0.25 to 2..Iaddend.