Patent ID: 6479999
Filing Date: 2002-11-12
Classification: G01R

Abstract:
A magnetic resonance imaging apparatus comprising:a main magnet system for generating a main magnetic field through an examination region; a radio frequency coil disposed adjacent the examination region for transmitting radio frequency signals into the examination region and selectively exciting dipoles disposed therein; a radio frequency transmitter for driving the radio frequency coil; a receiver which receives magnetic resonance signals from resonating dipoles within the examination region; an image processor which reconstructs an image representation from the received magnetic resonance signals for display on a human readable display; and a gradient coil assembly for generating magnetic field gradients across the main magnetic field, the gradient coil assembly including: a primary gradient coil set disposed about the examination region including an array of conductive coil loops which are switchable between a first configuration in which a current flowing thereon generates magnetic field gradients which are substantially linear over a first useful imaging volume and a second configuration in which a current flowing therein generates magnetic field gradients which are substantially linear over a second useful imaging volume which is smaller than the first; a first shielding coil set disposed about the primary coil set including an array of conductive coil loops arranged such that a current flowing thereon substantially shields a fringe field from the primary coil set when the primary coil set is operating in the first configuration; and a second shielding coil set disposed about the primary coil set including an array of conductive coil loops arranged such that a current flowing thereon substantially shields a fringe field from the primary coil set when the primary coil set is operating in the second configuration.