Eddy current control in NMR imaging systems

A primary field magnet assembly for use in medical NMR imaging systems, comprising:

• a) a ferromagnetic structure which provides a return path for magnetic flux,
• b) means for generating said magnetic flux, said means magnetically coupled to said ferromagnetic structure to establish magnetic flux flowing through said ferromagnetic structure,
• c) two opposed ferromagnetic poles spaced apart from one another and forming a gap therebetween for receiving a portion of human anatomy therein, said ferromagnetic poles being magnetically coupled to said ferromagnetic structure to develop a magnetic field between said poles,
• d) a layer of high permeability magnetic material, said material providing means to reduce eddy currents in said ferromagnetic poles, and said material placed proximate to a surface of each said pole which faces said gap, and
• e) means for preventing radio frequency absorption by said high permeability magnetic material, said means overlying said high permeability magnetic material for each of said ferromagnetic poles.