Abstract: In a magnetic resonance imaging apparatus, a main magnet assembly (12) produces a uniform magnetic field through an imaging region (14). An imaging region is defined within a subject by selecting gradient magnetic fields spatially encode the main magnetic field. A whole body birdcage radio frequency coil (26) excites magnetic resonance in dipoles of the subject. The resonance signals are received by the whole body coil (26) and by a second, local birdcage radio frequency coil (16). The first radio frequency coil (26) produces and is sensitive to a uniform radio frequency field in the imaging region (14) while the second radio frequency coil (28) is sensitive to a field that varies sinusoidally in space. From one radio frequency excitation, the two birdcage coils (26, 16) receive different sets of data with which to fill k-space, accelerating data collection.

Abstract: In a magnetic resonance imaging apparatus, a main magnet assembly (12) produces a uniform magnetic field through an imaging region (14). An imaging region is defined within a subject by selecting gradient magnetic fields spatially encode the main magnetic field. A whole body birdcage radio frequency coil (26) excites magnetic resonance in dipoles of the subject. The resonance signals are received by the whole body coil (26) and by a second, local birdcage radio frequency coil (16). The first radio frequency coil (26) produces and is sensitive to a uniform radio frequency field in the imaging region (14) while the second radio frequency coil (28) is sensitive to a field that varies sinusoidally in space. From one radio frequency excitation, the two birdcage coils (26, 16) receive different sets of data with which to fill k-space, accelerating data collection.

Abstract: A gradient coil assembly (22) generates magnetic field gradients across the main magnetic field of a magnetic resonance imaging apparatus and includes a base gradient coil set which generates magnetic field gradients which are substantially linear over a first useful imaging volume, and a correction gradient coil set which generates magnetic field gradients having substantially no first order moment. The correction gradient coil set produces third and higher order moments which combine with higher order terms of the base gradient coil set to produce magnetic field gradients which are substantially linear over a second useful imaging volume different from the first useful imaging volume. In a preferred embodiment, the second volume is continuously variable by adjusting the amounts of current applied to the base and correction coils.

Abstract: A gradient coil assembly (22) generates magnetic field gradients across the main magnetic field of a magnetic resonance imaging apparatus and includes a base gradient coil set which generates magnetic field gradients which are substantially linear over a first useful imaging volume, and a correction gradient coil set which generates magnetic field gradients having substantially no first order moment. The correction gradient coil set produces third and higher order moments which combine with higher order terms of the base gradient coil set to produce magnetic field gradients which are substantially linear over a second useful imaging volume different from the first useful imaging volume. In a preferred embodiment, the second volume is continuously variable by adjusting the amounts of current applied to the base and correction coils.

Abstract: A gradient coil assembly generates magnetic field gradients across the main magnetic field of a magnetic resonance imaging apparatus and includes a primary gradient coil (22p) switchable between a first configuration which generates magnetic field gradients which are substantially linear over a first useful imaging volume, and a second configuration which generates magnetic field gradients which are substantially linear over a second useful imaging volume. A first shield coil set (22s1) is complimentary to the primary gradient coil in one of the first and second configurations, and a second shield coil set (22s2), when either used alone or in combination with the first shield coil, is complimentary to the other of the first and second configurations.

Abstract: Methods of designing an active shield for substantially zeroing an electro-magnetic field on one side of a predetermined boundary in open magnetic resonance imaging systems and in open electric systems are provided. The methods include defining a finite length geometry for a primary structure which, in the case of zeroing a magnetic field, carries a first current distribution on its surface. A finite length geometry is also defined for a secondary structure which, in the case of zeroing a magnetic field, carries a second current distribution on its surface. In the case of zeroing an electric field, the current distributions are replaced with charge distributions. A total magnetic or electric field resulting from a combination of the first and second current or charge distributions respectively is constrained such that normal components (in the magnetic field case) or tangential components (in the electric field case) thereof substantially vanish at the surface of one of the primary and secondary structures.