Patent ID: 6842002

Claim:
A magnetic resonance imaging permanent magnet system comprising: a generally C-shaped yoke ( 1 ) formed from a single piece of cast steel; said yoke ( 1 ) having a vertical post ( 24 ), said vertical post having two ends, said yoke further comprising diagonal sections ( 20 , 22 ) extending from each end of said vertical post, said diagonal sections having angled inside and outside faces, said inside faces defining an angle of approximately 45 degrees in relation to said vertical post, and said yoke further comprising substantially horizontal arms ( 10 , 12 , 16 ; and 10 , 14 , 18 ) extending from each of said diagonal sections; a pair of poles ( 2 ) supported on said horizontal arms ( 10 ), each of said poles ( 2 ) being made substantially of permanently magnetized NdFeB and having respective pole faces which are opposed to one another and in a spaced relation to define an imaging volume between said pole faces; said vertical post having a portion of reduced width at its medial extent, with said vertical post ( 24 ) being wider at an intersection thereof with said diagonal sections ( 20 , 22 ); the ends of said horizontal arms ( 12 , 14 ) adjacent said imaging volume being beveled inward on the opposite side from the imaging volume; a substantially flat permanently magnetized NdFeB plate ( 3 ) mounted on the surface of the inside face of each of said diagonal sections ( 20 , 22 ) in face to face relationship with said inside face toward said imaging volume, said inside face and said plate ( 3 ) defining an angle of approximately 45 degrees in relation to said horizontal post, said plates ( 3 ) being poled to oppose leakage flux between the nearest pole ( 2 ) and the post, and to maintain the flux both in the imaging volume and in the vertical post; a pair of composite pole plates ( 4 ), one pole plate mounted on each of said pole faces on either side of the imaging volume, each of said pole plates ( 4 ) comprising a tape wound laminated thin sheet of high resistivity silicon steel with an insulating adhesive between each layer of the tape, and wherein said laminated sheet is segmented into a plurality of wedge-shaped elements, with said wedge-shaped elements being formed into a circular disk shape with an insulating adhesive between the respective wedge-shaped elements; and a pole ring ( 5 ) mounted on each of said pole plates ( 4 ).