U.S. Philips Corporation

Johannes A Overweg

Gerardus Nerius Peeren

Cornelis L Ham

Wilhelmus R Mens

Paul Bernard Bunk

An extremely efficient magnet system having a comparatively large angle of aperture can be obtained for magnetic resonance imaging by a reduction of fields of all orders in a common approach affecting active and passive as well as positive and negative oriented coil elements. Passive soft-magnetic ring segments are arranged in two pairs and located within a plurality of larger diameter active magnetic coils. The active coils include a central coil and outer coils wherein the outer coils are smaller than the central coil. The coils are in a helium Dewar vessel and arranged such that the system has an aperture of about 90.degree.. The central active coil may have a larger radius than the smaller outer coils.

Magnet system for magnetic resonance imaging

A magnet system for generating a uniform magnetic field in an examination zone (5) in an accommodation space of magnetic resonance apparatus is formed by a first, approximately cylindrical electromagnetic coil system (1) which encloses the examination zone and which is symmetrically arranged relative to a symmetry axis (9) and relative to a asymmetry plane (11) extending perpendicularly to the symmetry axis, and a second, approximately cylindrical electromagnetic coil system (7) which is arranged so as to be symmetrical relative to the symmetry axis and relative to the symmetry plane and which is arranged so as to be concentric with the first coil system, the magnetic dipole moments of the first and the second coil system being oppositely directed and substantially equal. The first coil system (1) includes a central coil (13) which is symmetrically arranged relative to the symmetry plane (11) and two pairs of further coils (15, 17) which are symmetrically arranged relative to the symmetry plane, the second coil system (7) including a central coil (21) symmetrically arranged relative to the symmetry plane and a pair of further coils (23) symmetrically arranged relative to the symmetry plane. As a result, despite the use of only eight coils the magnet system generates a highly uniform central magnetic field and only a very small stray field.

Actively shielded magnet for magnetic resonance apparatus

In a magnetic resonance apparatus comprising a superconducting magnet system (1) for generating a steady magnetic field there is also included a superconducting shielding coil system (22) in order to compensate for magnetic field variations induced in the magnet by external magnetic flux variations. The shielding coil system (22) comprises coil sections (24) of different diameters.

Magnetic resonance apparatus comprising a superconducting shielding

A high order multipole gradient field generating system in a magnetic resonant imaging apparatus comprises spaced quadrants of windings, the windings of each quadrant generating adjacent fields in each quadrant in opposing relation. The multipole system is located adjacent to a lower order conventional gradient field coil system to shield the region of interest from field aberrations, the multipole system generating a relatively strong local magnetic field adjacent to the coils of the gradient field coil system and a negligible change in field in the region of interest. The multipole system causes a frequency shift of the aberrations in the region of interest which are outside the detection frequency range such that the conventional gradient field system signal is substantially unaffected by the multipole system in the region of interest.

Magnetic resonance imaging apparatus with artefact reduction

In a magnetic resonance apparatus a system of concentric cylinders of superconductive material maintain an effective steady magnetic field in a measured space within the inner cylinder which field is very homogeneous and is, moreover, very constant in time without requiring a large electric power. In a particular embodiment a magnetic field cylinder produces a strong magnetic field, a stabilization cylinder within the magnetic field cylinder ensures a good homogeneity and stabilization of the effective magnetic field, while a screening cylinder provided outside the magnetic field cylinder reduces the external stray field of the system.

Superconductive magnet system comprising superconductive cylinders

In a magnetic resonance apparatus a gradient coil system and an r.f. coil are combined so as to form a magnetically, electrically and structurally integrated coil system with current conductors in substantially the same cylinder. Thus, a substantial saving is realized as regards the activation energy required for generating gradient fields as well as for generating r.f. fields and notably r.f. stray-fields are also reduced.

Magnetic resonance apparatus comprising integrated gradient r.f. coils

In a gradient coil system for a magnetic resonance apparatus arc conductors of notably X coils and Y coils are stacked axially or radially so as to form rigid stacks. The arc conductors are interconnected by means of electrical conductors and the stacks are also interconnected, so that a rigid, self-supporting coil system is obtained. Because the coil system is composed of rigid elements, is comparatively open and does not require a coil former, the production of noise in a magnetic resonance apparatus comprising such a coil system is substantially reduced and field disturbances due to coil deformations are also reduced.

Magnetic resonance apparatus comprising a low-noise gradient coil

In a magnetic resonance apparatus a gradient coil system in which 'return' arc conductors, which contribute substantially less to the gradient field formation because they are situated further outwards radially and/or axially from the center of the system, are positioned to compensate for stray fields of 'effective' are conductors, which are more centrally situated and which contribute more substantially to the gradient field formation. Due to both radial and axial displacement of the return arc conductors relative to the effective arc conductors, the measuring space of the apparatus can be conically shaped, so that a higher patient accessibility is achieved or a smaller diameter can be imparted to a central portion.

Magnetic resonance apparatus comprising an improved gradient coil system

A magnetic resonance imaging apparatus utilizes a gradient coil system with different arc angles for different arc conductors of the essentially saddle-shaped coil elements of the magnet. As result, the arc conductors can be oriented nearer to the radial symmetry plane so that not only the spatial field homogeneity in an active zone is maintained or improved, but also the efficiency of the gradient magnet system is substantially increased and the power stored in the coil is reduced, thus enabling faster switching.

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Eindhoven, Netherlands

Johannes A Overweg