Abstract: A NMR measurement apparatus comprising a cryostat (10) in which a superconducting magnet coil system (9) is disposed in a first tank (8) having cryogenic liquid and surrounded by additional cooling devices such as radiation shields (5, 6), superinsulating foil (7) and, if appropriate, a second tank (3) having cryogenic liquid, is characterized by a pulse tube cooler (11) cryotechnically connected to at least one of the additional cooling devices in a good heat conducting fashion with this cooling device being mechanically attached in the cryostat (10) in such a fashion that vibrational and cryotechnical decoupling is achieved between the cooling device and the first tank (8) having the cryogenic liquid and, in particular, between the cooling device and the superconducting magnet coil system (9).

Abstract: The invention concerns a superconducting magnet configuration for a high resolution NMR spectrometer which is highly stable over time and having a cryostat (21) with a vertical room temperature bore (23). A transverse access (32) through the cryostat (21) to the room temperature bore (23) is provided for at an easily accessible height directly above the upper end of the superconducting magnet coil (25) to substantially simplify the introduction of a sample. In a system having two helium tanks (26, 27), it is advantageous to have the access (32) arranged between these helium tanks.

Abstract: An electromagnet for use in an MRI apparatus includes an annular vessel inside of which annular windings, energizable to produce a magnetic field, are contained together with cold iron components. The iron components are mechanically anchored with respect to the windings. A pair of iron rings is positioned so that one ring is provided at each end of the magnet in close proximity to the annular windings. The rings are formed so as to define a flared opening at each end of a cylindrical space within the magnet which, in use of the magnet for MRI purposes, is occupied by a patient.

Abstract: Two MR magnetic field probes arranged in a centrally symmetrical fashion in relation to the magnetic field center, are attached in the examination area of the magnet. The output signals of the two MR magnetic field probes are supplied to a multiplying RF mixer, and a sum frequency signal is obtained from the output signal of the RF mixer, and the actual value of the basic field is determined from the frequency of this output signal.

Abstract: A magnet contains a magnetic yoke and two pole shoes, between which a magnetic field of great homogeneity is formed. The pole shoes are provided with special pole plates. At least one pole plate (11d) is separated from a base part (11b) facing the yoke by a narrow correction air gap (15), and can be aligned by means of mechanical setting devices. According to the invention, each pole shoe (11) has a bead-like edge piece (11c) for field correction at its edge area (17b), which surrounds an inner pole shoe area (17a). In this region, the pole plate (11d), which can be aligned laterally separated from the edge piece (21).

Abstract: A closed magnetic resonance imaging (MRI) magnet has a single superconductive coil assembly including a coil housing containing a cryogenic fluid dewar containing a pair of longitudinally-outermost impregnated superconductive main coils and at-least-one cryostable additional superconductive coil such as a pair of additional main coils, a pair of bucking coils, and/or a pair of shielding coils. An open MRI magnet has two spaced-apart superconductive coil assemblies and an imaging volume having a center. Each coil assembly has a cryostable superconductive main coil and an impregnated bucking coil with the impregnated bucking coil being the closest superconductive coil to the center of the imaging volume.

Abstract: In a magnet arrangement for a diagnostic magnetic resonance apparatus, first and second units operate in combination to generate a magnetic field, the second unit being arranged at a distance from the first, the units determining a region having a substantially homogeneous magnetic field, which is arranged between the two magnetic field-generating units. An access to the region is oriented obliquely to the spacing of the two magnetic field-generating units. The magnetic field-generating units respectively have first and second outer transversal dimensions with the second outer transversal dimension being smaller than the first outer transversal dimension. The first magnetic field-generating unit has an opening that is fashioned as an additional access to the region.

Abstract: A magnet arrangement for a diagnostic magnetic resonance apparatus has an electromagnet arrangement for the production of a homogeneous magnetic field oriented along an axis in an imaging volume. The electromagnet arrangement has first and second windings arranged opposite one another at a distance from one another, transverse to the axis. In relation to the axis, an axial access and a transverse access to the imaging volume are present between the first and second windings.

Abstract: In a method for reducing noise during operation of a magnetic resonance apparatus, a gradient coil which exhibits a vibratory node during operation of the apparatus is attached to a holder exclusively in a region of the vibratory node. In a magnetic resonance apparatus, a gradient coil having at least one vibratory node along a longitudinal length thereof during operation of the magnetic resonance apparatus is attached to the holder exclusively in a region of the vibratory node.

Abstract: A magnetic resonance imaging apparatus includes a main magnet having a frame (19) with two magnetic elements (1) arranged thereon. The magnetic elements (1) have substantially parallel faces (3) that face each other so as to define a gap (5) between the magnetic elements. The magnetic elements (1) have magnetic poles of opposite polarities for generating a static magnetic field in the gap (5). A patient support (45) is provided for supporting a patient (47) so that a part of the patient that is to be examined is located in the gap (5). In order to improve the accessibility of the patient (47) without increasing the width of the gap (5), a supporting member (37) is arranged so as to support the frame (19) in such a position that the normals (41) to the planes of the substantially parallel faces (3) of the magnetic elements (1) extend in a direction that encloses an angle between 30.degree. and 60.degree. with the vertical direction.

Abstract: A planar magnetic resonance imaging (MRI) magnet having a superconductive coil assembly including a toroidal-shaped coil housing which surrounds a bore, has a longitudinal axis, and contains at least three concentric, annular-shaped superconductive coils coaxially aligned with the axis. The coils produce a magnetic resonance imaging volume having a center located outside the bore. Preferably, the bore is generally completely filled with magnetic material, and the magnetic resonance imaging volume is located completely outside the bore which provides for improved patient and physician access during MRI-guided biopsy as well as during MRI imaging.

Abstract: A magnetic resonance imaging apparatus includes a main magnet having a frame (19) with two magnetic elements (1) arranged thereon. The magnetic elements (1) have substantially parallel faces (3) that face each other so as to define a gap (5) between the magnetic elements. The magnetic elements (1) have magnetic poles of opposite polarities for generating a static magnetic field in the gap (5). A patient support (45) is provided for supporting a patient (47) so that a part of the patient that is to be examined is located in the gap (5). In order to improve the accessibility of the patient (47) without increasing the width of the gap (5), a supporting member (37) is arranged so as to support the frame (19) in such a position that the normals (41) to the planes of the substantially parallel faces (3) of the magnetic elements (1) extend in a direction that encloses an angle between 30.degree. and 60.degree. with the vertical direction.

Abstract: In a diagnostic nuclear magnetic resonance apparatus having a main magnetic field and gradient coils for generating gradient fields, the gradient coils including conductors that run essentially perpendicularly to the direction of the main magnetic field, compensating coils for reducing the main magnetic field present in the environment of the conductors are allocated to these conductors. By reducing the effect of the main magnetic field in regions near these conductors, oscillations of these conductors arising due to switching of the gradient current are reduced, thereby reducing bothersome noises which arise during the production of an image.

Abstract: An apparatus for generating a corrective magnetic field in a nuclear magnetic resonance (NMR) spectrometer. The apparatus has saddle-type, spirally wound coils whose number is in excess of the number of controlled magnetic field components. Each coil is made to produce plural magnetic field components. The coils of a simple shape are combined to correct axial magnetic field components and rotation direction magnetic field components. Electrical currents supplied to the coils are controlled so as to minimize the total amount of heat generated by all the coils. The center of each coil lies on the z-axis. The coils are stacked on top of each other along the z-axis and arranged symmetrically with respect to the z-axis. One power supply is connected to each one coil. Since the number of the coils is greater than the number of controlled magnetic field components, other arbitrary conditions are added, as well as the controlled magnetic field-components, in determining the currents.

Abstract: A permanent magnet assembly having a central elliptical bore, suitable for reception of a patient in an MRI system, is formed of a plurality of elliptically shaped sections disposed along an axis of the bore. Each section is subdivided into a plurality of segments in which each segment is constructed of bricks of magnetic material. Each brick has the shape of a right parallel piped. In any one of the segments, all of the bricks are arranged parallel to a common plane which is parallel to the bore axis. The bricks are magnetized with magnetization vector oriented in a common direction perpendicular to the plane. Full bricks are employed throughout all of the segments with the exception of a plurality of bricks along a surface of the bore wherein truncation of one or more of the bricks may be required to attain a desired homogeneity to a dipole magnetic field within the field.

Abstract: The invention improves thermal efficiency and control follow-up properties by providing an AC sheet heater and a DC sheet heater on the respective side surfaces of an upper base yoke and a lower base yoke, and a temperature sensor near the center of the upper surface of the upper base yoke, whereby the permanent magnets of the magnet assembly are first heated by use of both the AC and DC sheet heaters, and then, with the temperature monitored by the temperature sensor, the temperature is adjusted by use of only the DC sheet heater.

Abstract: This invention is concerned with actively shielded magnetic resonance (MR) devices and more particularly with protecting such systems in the event of a quench by preventing changes in the stray field outside the magnetic devices. The invention includes dividing the system's coils into groups each comprised of inner and outer coils and arranged so that the net dipole moment, and the contribution to stray field from each group is always close to zero. Each group is connected in parallel to a protective unit, for example a resistor, so that the excess current can flow through the protective unit in the event of a quench; thus avoiding the burnout of the system's coils.

Abstract: A method for operating a superconductive magnet having a superconductor. The magnet is ramped to generally the design current. After that, the magnet is brought to an annealing temperature which is above the operating temperature and below the critical temperature. After that, the magnet is shimmed at a shimming temperature which is at least as cold as the annealing temperature. After that, the magnet is used, at the operating temperature, for a predetermined purpose, such as MRI imaging for medical diagnosis. Preferably, the superconductor has less than twenty-five superconductive filaments.

Abstract: A magnetostatic field generating magnet includes small-diameter coils for generating a low-order magnetic component, a large-diameter coil for generating a high-order magnetic component, a first coil assembly for generating in a predetermined area a main magnetic field obtained by both the low- and high-order magnetic components, and a second coil assembly for generating a shield magnetic field for actively shielding a magnetic field leaking from the main magnetic field.

Abstract: A superconducting magnet apparatus which includes a cryostat vessel for containing therein a coolant for realizing superconductivity, a magnetic flux generating unit disposed within the cryostat vessel and including a superconducting multilayer composite member constituting a sustaining medium for a persistent current which generates a magnetic flux along a center axis of a predetermined magnetic field space, and members holding the magnetic field generating unit within the cryostat vessel.

Abstract: A magnetic resonance imager has a magnetically permeable core and two pole pieces, each pole piece having a face. The pole pieces are arranged on the core such that the pole piece faces are in opposed relationship forming a first gap therebetween. At least one of the pole pieces is comprised of an outer element 23 connected to the core and an inner element 24 connected between the outer element and the first gap. The outer element 23 forms a cup inside which the inner element 24 is disposed. A plurality of screws 11, 12 and 13 are disposed through the outer element 23 and engage the inner element 24 such that a second gap is formed between the inner and outer element. The homogeneity of the magnetic field in the first gap is affected by adjusting the position of the inner element relative to the outer element via screws 11, 12 and 13.

Abstract: A method for passively shimming an open magnet having a magnetic field with an inhomogeneity including an amount of positive 2, 0 Legendre polynomial harmonics. The magnetic field is mapped and the amount of positive 2, 0 Legendre polynomial harmonics of the mapped magnetic field is determined. An adjusted magnetic field is defined equal to the mapped magnetic field minus a nonzero portion of the determined amount of positive 2, 0 Legendre polynomial harmonics. A computer shim code is run which calculates adding shims to reduce the inhomogeneity of the adjusted magnetic field. Shims are added to the open magnet as calculated from the running of the computer shim code.

Abstract: A permanent magnet structure includes a generally shaped frame made of a magnetic material and a pair of opposite polarity magnet members mounted on the opposed surfaces of the legs of the U. The connecting element of the U which connects the legs, is disposed at a sufficient distance from the magnets so that the resulting magnetic field passes substantially entirely between the magnets and through the arms and so that no substantial eddy currents are induced in the connecting element during imaging. Between the connecting element and the magnets, there is disposed a non-conductive, non-magnetic separating member which contacts the two arms and tends to keep them apart. The separating member is so positioned relative to the connecting member and the magnets that effects of the force between the two magnets and the force produced by the magnetic field passing through the arms and connecting element are counterbalanced. This results in a structure which is mechanically stable.

Abstract: A magnet field generating apparatus for MRI, comprising:a plurality of permanent magnet assemblies disposed continuously around the angular inner circumference of a hexagonal tubular yoke to provide a uniform magnetic field at the center portion of the hollow space inside said permanent magnet assemblies; the permanent magnet assemblies forming a main magnetic field by a pair of oppositely disposed permanent magnet assemblies which are trapezoidal or square in cross-section; other pairs of permanent magnet assemblies having a triangular or square cross-section; each of the pairs of oppositely disposed permanent magnet assemblies has a side surface in contact with a part of the inner peripheral surface of the yoke and forms a plurality of permanent magnet blocks which are magnetized perpendicularly to the side surface in contact with the yoke so that the permanent magnet assemblies are magnetized perpendicularly to the side surface thereof in contact with the yoke; magnetic pole pieces disposed on each surface

Abstract: A method is described which corrects magnetic field inhomogeneities in a magnetic resonance (MR) imaging system that takes into account the effects of a subject on the magnetic fields. A magnetic resonance sequence is applied to the subject to extract MR response signals from the subject indicating the magnetic field inhomogeneity over space. The changes of magnetic field inhomogeneity with a change in radial variable .rho. (or r, in a cylindrical coordinate system) are calculated. A derivative with respect to a radial variable is calculated of a generalized 3D infinite series polynomial, such as a Legendre polynomial expressed in spherical coordinates. These inhomogeneity changes are then fit to 3D polynomial derivative to result in coefficients [dI.sub.c ]. Similarly coefficients of a derivative shim coil calibration matrix [dM] are determined for each shim coil modeling the effect of each shim coil is on the magnetic field within the imaging volume.

Abstract: In a method and apparatus for shimming a magnet system of a nuclear magnetic resonance tomography system, an apparatus-specific matrix is determined, which indicates the effect on the magnetic field for each shim channel. A phase difference matrix is subsequently formed by means of calculation of the phase differences between three-dimensional spatially resolved nuclear magnetic resonance raw data sets obtained with different echo times. This phase of difference matrix gives the field deviation for each pixel. In this phase difference matrix, the phase differences between consecutive pixels are calculated in several spatial directions, thereby determining a phase error data set. Finally, on the basis of the predefined matrix and of this phase error data set, currents for the individual shim channels are determined.

Abstract: The disclosure relates to an open magnetic structure for producing an intense, stable magnetic field, which is amplitude and direction-controlled in a region adjacent to said structure, having at least one magnetic source (4) for producing said magnetic field, characterized in that it also comprises at least one pole piece (5, 6) associated with the magnetic source and having a shape designed so as to control the magnetic field produced.Application to petroleum or oil research in drilled wells and to surface magnetic imaging.

Abstract: An inspection apparatus using magnetic resonance includes magnetic field generators for generating a static magnetic field, a gradient magnetic field and a radio frequency magnetic field, respectively, a signal detector for detecting magnetic resonance signals from an inspected object, a computer for executing arithmetic operations for detection signals from the signal detector and an output device of the result of the arithmetic operations by the computer. The gradient magnetic field generator includes first and second gradient coils, the first gradient coil is a coil fixed to a magnet for generating a static magnetic field, the second gradient coil is a movable coil, and the magnetic field generated by the second gradient coil at a conducting portion of the magnet is offset by the magnetic field generated by the first gradient coil. According to this construction, an eddy current that occurs with the time change of the gradient magnetic field can be reduced.

Abstract: A closed magnetic resonance imaging (MRI) magnet has a single superconductive coil assembly including a toroidal-shaped coil housing containing a pair of superconductive main coils and at least one additional superconductive main coil. A pair of generally-non-permanently-magnetized ferromagnetic rings is spaced radially inward and apart from the superconductive main coils. The ferromagnetic rings allow the design of a shorter MRI magnet because the ferromagnetic rings overcome the gross magnetic field distortions in the imaging volume of the magnet (created by removing some of the additional longitudinally-outermost superconductive main coils, otherwise used in the magnet, to make the magnet shorter) to produce a magnetic field of high uniformity within the imaging volume.

Abstract: A primary field magnet assembly, of the type used in magnetic resonance imaging systems, which has been designed with the capability to suppress eddy currents during magnetic resonance imaging through the use of eddy current suppressing material. In addition, this invention includes the use of high conductivity material to decouple the imaging system radio frequency antennas from their environment, which generally includes the primary field magnet assembly, and can be used to preserve the signal-to-noise performance of the scanner. Such highly conductive material is effective when employed in combination with the primary field magnet assembly described herein.

Abstract: Nuclear magnetic resonance signals are multiply excited and a plurality of data sets corresponding to the nuclear magnetic resonance signals are obtained and are used for calculating the coefficients of a spherical harmonic function that describes the magnetic field distribution in the examination space. Each data set acquired in this way has a weighting that correlates with the plausibility (reliability) of the data set allocated to it. Taking the respective weighting into consideration, coefficients of the spherical harmonic functions are acquired from the data sets acquired and are used to calculate respective currents that are supplied to the corresponding shim coils.

Abstract: A compact, open geometry U-shaped magnet formed by parallel iron slabs and a flux return is activated by a coil which surrounds the flux return. The inner surfaces of the iron slabs and an outer surface of the coil are substantially contiguous. The field homogeneity within the compact, open geometry U-shaped magnet is improved by controlling the reluctance of a secondary flux flow circuit extending away from the pair of parallel iron slabs. The geometry of the compact, open geometry U-shaped magnet also provides for utilization of an automatic active shimming system.

Abstract: A magnetic resonance imaging apparatus includes a magnet assembly (10) for generating a temporally constant primary magnetic field through a central bore (14). The central bore is surrounded by a gradient coil assembly (30) including a dielectric former (32) and gradient coils (34, 36, 38) for generating magnetic field gradient pulses across the examination region. A radio frequency coil assembly (50) including a birdcage coil (52) is mounted inside of the gradient coil assembly and surrounding the examination region. A radio frequency shield (60) includes a dielectric sheet (62) having a plurality of first metal foil strips (72) defined on each surface. The metal strips are defined by etching or cutting gaps (70) in a continuous sheet of copper foil, leaving bridges (74) across the gaps adjacent opposite ends of the foil strips.

Abstract: A primary field magnet assembly, of the type used in magnetic resonance imaging systems, which has been designed with the capability to suppress eddy currents during magnetic resonance imaging through the use of eddy current suppressing material. In addition, this invention includes the use of high conductivity material to decouple the imaging system radio frequency antennas from their environment, which generally includes the primary field magnet assembly, and can be used to preserve the signal-to-noise performance of the scanner. Such highly conductive material is effective when employed in combination with the primary field magnet assembly described herein.

Abstract: A gradient system for a nuclear spin resonance (NMR) tomograph with a main magnet system producing a homogeneous magnetic field directed along a z-axis inside a measuring volume, wherein the main magnet system provides access to the measuring volume along the z-axis and transversely to the z-axis, and wherein the gradient system comprises two first partial gradient systems which are located at opposite sides of a central plane perpendicular to the z-axis, across the measuring volume. At least one of the two partial gradient systems is movable between at least two positions along the z-axis. In this way, with a small constructional size and with a simple manufacturing procedure, a gradient system is obtained with high performance capability with respect to generated gradient strength for given ampere turns, high linearity of the generated gradient fields, minimum inductance and minimum electrical resistance of the conductor segments.

Abstract: An open magnetic resonance imaging (MRI) magnet having first and second spaced-apart superconductive coil assemblies each including a toroidal-shaped coil housing containing a superconductive main coil. A generally annular-shaped permanent magnet array is associated with each coil assembly, being generally coaxially aligned with the associated coil assembly and being spaced radially inward and radially apart from the associated coil assembly's superconductive main coil. The permanent magnet arrays overcome the gross magnetic field distortions in the imaging volume of the superconductive main coils (created by the open space between the magnet's superconductive coil assemblies) to produce a magnetic field of high uniformity within the imaging volume.

Abstract: Inhomogeneities in the magnetic field in the vicinity of a superconducting NMR receiver coil are avoided by placing the probe, at about room temperature, within the magnetic field, cooling rapidly to just above the critical temperature of the superconductor and then controllably cooling the coil to operating temperature at a rate of 3 K./minute or less.

Abstract: Current supply for MRI magnet having an output impedance which has been tailored to have the desired shape by using voltage and current feedback. The impedance is small at frequencies which are large with respect to the magnet L/R and the impedance is large at very low frequencies.

Abstract: A magnet system for a nuclear spin tomograph having at least one field producing magnet coil S.sub.1 with radius r.sub.s1 arranged in a middle plane which produces a homogeneous magnetic field in an investigational volume directed along a z-axis perpendicular to the middle plane, is characterized in that at least one, preferentially at least two, ferromagnetic rings R.sub.i with radius r.sub.Ri are provided in the middle plane concentric to the magnetic coil S.sub.1. A system of this kind can be substantially more compact in construction than conventional systems with equal produced field strength. In addition substantially reduced currents are required through the coil or coils for field production.

Abstract: A closed magnetic resonance imaging (MRI) magnet has a single superconductive coil assembly including a toroidal-shaped coil housing containing a pair of superconductive main coils and at least one additional superconductive main coil. A pair of generally annular-shaped permanent magnet arrays is spaced radially inward and apart from the superconductive main coils. The permanent magnet arrays allow the design of a shorter MRI magnet because the permanent magnet arrays overcome the gross magnetic field distortions in the imaging volume of the magnet (created by removing some of the additional longitudinally-outermost superconductive main coils, otherwise used in the magnet, to make the magnet shorter) to produce a magnetic field of high uniformity within the imaging volume.

Abstract: A closed magnetic resonance imaging (MRI) magnet has a single superconductive coil assembly including a toroidal-shaped coil housing containing a pair of superconductive main coils. A pair of generally annular-shaped bucking coils, carrying electric current in a direction opposite to that of the superconductive main coils, is spaced radially inward and apart from the superconductive main coils. The bucking coils allow the design of a shorter MRI magnet because the bucking coils overcome the gross magnetic field distortions in the imaging volume of the magnet (created by removing some of the additional longitudinally-outermost superconductive main coils, otherwise used in the magnet, to make the magnet shorter) to produce a magnetic field of high uniformity within the imaging volume.

Abstract: A shielded and open magnetic resonance imaging (MRI) magnet having two spaced-apart, generally toroidal-shaped superconductive coil assemblies. Each coil assembly has a coil housing containing a generally annular-shaped superconductive main and a radially-outwardly spaced-apart shielding coil carrying electric currents in opposing directions. Preferably, supplemental shielding is provided with the addition of: a generally annular permanent magnet configuration internal to, or external of, the coil housings; a generally-non-permanently-magnetized external ferromagnetic shield having at least a portion positioned longitudinally between the coil housings, an external resistive coil; or combinations thereof.

Abstract: A magnet assembly has a generally U-shape, the bight of the U including a permanent magnet which generates a magnetic field whose flux passes through a working volume defined between the arms of the U. The dimensions of the assembly are chosen such that: ##EQU1## where: L.sub.g is the length of the gap between the arms,L.sub.m is the length of the magnet,B.sub.r is the remnant field of the magnet, andB.sub.g is the field in the gap.

Abstract: In a magnetic field generating apparatus for use in MRI comprising cylindrical yokes, a pair of permanent magnets of a trapezoidal section opposed in parallel with each other in the cylindrical yokes with a predetermined gap being defined between each of the pole faces of them, permanent magnets of a triangular section in adjacent with both sides of the trapezoidal permanent magnet in which a magnetic field space having a hexagonal cross section in perpendicular to the longitudinal direction defined by pole faces of the trapezoidal permanent magnets and the pole faces of the triangular permanent magnets, whereinthe trapezoidal permanent magnets comprise rare earth system permanent magnet and the direction of magnetization thereof is identical with the direction of the magnetic field in the magnetic field space, the triangular permanent magnets comprise a ferrite system permanent magnet and the direction of magnetization thereof is at a 90.degree.

Abstract: Two opposite iron core pole pieces of a magnetic resonance medical imager generate a static magnetic field in a patient imaging volume disposed between the pole pieces. Gradient coils are positioned in the face of a pole piece. Thin disc shaped (42, 44) or ring shaped (41) ferromagnetic parts laminated of layers cut favorably from transformer sheet material are attached to the face of the pole piece. Each layer is electrically insulated from adjacent layers and surfaces by enamel or fixing glue. To reduce eddy currents in these layers, narrow, radially oriented slots (43, 45) are cut in these layers before lamination. The slots are oriented in the adjacent layers so as not to coincide resulting in improved conduction of the magnetic flux in the imaging volume during the production of gradient magnetic fields by the gradient coils.

Abstract: A toroidal housing (18), such as a vacuum dewar, contains magnets (10, 12) for generating a temporally constant magnetic field through a central bore (14). Gradient coils (32, 42) are mounted around the bore defining a space therebetween. A radio frequency shield (78) is disposed radially inward from the gradient coils. Inside the radio frequency shield, an inner shimming assembly (60) includes a dielectric cylinder (62) having annular grooves around its periphery. Segmented ferrous material (66) is arranged in annular rings in the grooves. The ferrous material is segmented into small pieces electrically insulated from each other to limit radio frequency and gradient frequency eddy currents. A radio frequency coil (70) is mounted inside of the annular ferrous shims (66). Preferably, additional shim trays (50) which carry shims (54) are mounted in the space between the primary and secondary gradient coils.

Abstract: In an NMR tomograph with superconducting main field coil (10) and large transverse access opening a compensation of inhomogeneities of the static magnetic field without hindering the axial and transverse access to the investigational volume (V) can be effected by the following elements:ferromagnetic homogeneity elements (20) which are arranged on the surface of the room temperature bore on both sides of the transverse access opening;at least one or more (a number p.gtoreq.1) superconducting correction coils (C.sub.1 and C.sub.p) which can be separately supplied with current and which are coaxial to the main field coil (10), whereby each correction coil (C.sub.1 through C.sub.p) comprises at least two partial coils (C.sub.1i, C.sub.1a through C.sub.pi, C.sub.pa), whereby all partial coils of all correction coils (C.sub.1 through C.sub.p) are cylindrical coils coaxial to a common axis (z) having a diameter less than the inner diameter (d.sub.

Abstract: A magnet including spaced-apart first and second pole pieces with generally opposing first and second pole faces. The first pole face has an axis extending generally towards the second pole face and has a surface region which includes at least two frustoconical surfaces. The frustoconical surfaces are generally coaxially aligned about the axis, and radially-adjacent frustoconical surfaces abut each other. In a second embodiment, points on the surface region located an identical radial distance from the axis are also located a common axial distance along the axis, and a graph of axial distance along the axis versus radial distance from the axis for such points is a curve having a continuous slope with at least two sign reversals. Such contoured pole faces allow for a smoother magnetic field to better reduce axisymmetric magnetic field inhomogeneity.

Abstract: A four-post MRI system used in conjunction with a X-wing transmission coil is disclosed in which the post of the system and the upper and lower gradient coil assemblies are covered in a RF reflective material. The covering may be in applied foil such as copper or aluminum, or may be a screen of conductive metal, or may be a spray-on conductive metal.

Abstract: A magnetic field generating apparatus for a magnetic resonance imaging (MRI) apparatus, including soft ferrite disposed adjacently to a gradient magnetic field coil which is disposed in a gap and serves to form a static magnetic field. The soft ferrite has saturated magnetic flux density (Rs) more than 0.4 T, coersive force (He) less than 50 A/m, and specific resistance .rho. more than 10.sup.-5 .OMEGA..multidot.cm. The magnetic field generating apparatus thus constructed has a magnetic circuit arrangement that a pair of permanent magnetic bodies which are disposed so as to confront each other and define the gap are magnetically connected through a yoke, and pole pieces are fixedly secured to the surfaces of the respective permanent magnetic bodies facing the gap, thereby generating the magnetic field in the gap.