A magnetic resonance apparatus

摘要

The MRI appts. includes magnets disposed in a toroidal housing for defining a temporally constant magnetic field through a central bore of the toroidal housing, a radio frequency coil disposed in the bore, a radio frequency shield disposed around the radio frequency coil, and a gradient magnetic field coil assembly including a primary magnetic field gradient coil and a shield gradient magnetic field coil. The gradient magnetic field coil assembly is disposed radially outward from and around the radio frequency shield. The segmented ferrous material is disposed in annular rings around the bore. The segmented ferrous material rings are disposed between the radio frequency coil and the radio frequency shield, and the shim trays are disposed between the primary and secondary gradient magnetic field coils. The shim trays carry selectively adjustable numbers of ferrous shims.