Magnetic resonance imaging system including active shield gradient coils for magnetically canceling leakage gradient field

摘要

In a magnetic resonance imaging apparatus, there are provided: an MR (magnetic resonance) imaging unit having an imaging hole at a substantially central portion thereof, into which an object under medical examination is inserted; a superconducting coil unit stored within an outer vessel which is positioned around the imaging hole, and including a superconducting coil assembly for uniformly producing a static magnetic field to be applied to the object, and at least one heat shield tube or thermally shielding the superconducting coil assembly stored therein; a gradient field coil assembly provided between the outer vessel and imaging hole; for producing a gradient magnetic field so as to be superimposed with the static magnetic field. Further, it employs a active shield gradient coil assembly for producing a gradient shield field, and disposed within the outer vessel in such a manner that the active shield gradient coil assembly is thermally coupled to the heat shield tube and also magnetically coupled with a leakage field leaked from the gradient magnetic field of the gradient field coil assembly, whereby the leakage field is magnetically canceled by the gradient shield field and substantially no eddy current is produced in the heat shield tube.