Abstract: It is an object of the present invention to facilitate adjustment of magnetic fields. There is provided a magnetic circuit with opposing permanent magnets, comprising: a pair of permanent magnets opposing each other across a gap, the pair of permanent magnets being magnetized in thickness direction; a yoke magnetically coupled to the permanent magnets, and provided outside of the permanent magnets and the gap; a pair of pole pieces each arranged on a gap side of an opposing surface of each of the permanent magnets and having a peripheral projection in opposing direction; and an adjustment permanent magnet piece having magnetic flux amount of at most 2×10?7 Wb provided so as to magnetically communicate with a magnetic field formed in the gap.

Abstract: A matrix coil for generating a variable magnetic field is provided, including a plurality of loops arranged in a series so as to have a substantially common axis and segmented into at least one arc-shaped segment, a variable current source for each of the arc-shaped segments, and a controller. The controller is configured to selectively vary an amount of current provided to each of the arc-shaped segments by the variable current sources so as to achieve a variable base field, one or more variable gradient fields, and one or more variable second order shim fields.

Abstract: For the purpose of acquiring magnetic resonance signals unaffected by any high magnetic field disturbance, magnetic resonance signals are sequentially acquired for a plurality of views; magnetic field disturbance is monitored; the magnetic resonance signal acquisition is repeated for a view at which magnetic field disturbance has occurred; and an image is produced based on magnetic resonance signals after the repetition has been applied.

Abstract: A planar MRI system is disclosed. The system has an open magnet configuration that produces a magnetic field having a remote region of substantial magnetic field homogeneity. Spatial encoding gradient coils and a rf coil provide MRI data for image reconstruction. The open magnet configuration has a ferromagnetic core with a substantially planar core surface layer and a longitudinal axis, and a unipolar current wire pair on a side of the ferromagnetic core adjacent the planar core surface layer. The wire pair is separated along the longitudinal axis and extends in a direction substantially perpendicular to the axis and substantially parallel to the planar core surface layer. The current wire pair provides a magnetic field having a maximum between the current wire pair along a direction perpendicular to the planar core surface layer and in the remote region of substantial magnetic field homogeneity.

Abstract: Briefly in accordance with one aspect, the present technique provides a method for heating a permanent magnet in a magnetic resonance imaging system. The method for heating a permanent magnet includes directly heating a surface of the permanent magnet using a surface heater. The present technique also provides a system for heating a permanent magnet in a magnetic resonance imaging system. The system includes a surface heater configured to directly heat a surface of the permanent magnet.

Abstract: For the purpose of efficiently homogenizing a magnetic field, when homogenizing a strength distribution of a magnetic field generated in a space between a pair of facing pole surfaces, a continuous magnetization distribution for homogenizing the strength distribution of the magnetic field is determined with respect to planes on which magnetic elements are to be disposed for homogenizing the strength distribution of the magnetic field; and magnetic elements are disposed based on the magnetization distribution. The magnetic distribution is determined as a polynomial of an orthogonal function. The polynomial is determined by an optimization method. The optimization method is a method of least squares.

Abstract: The temperature of permanent magnet blocks embedded in several positions in permanent magnets and base yokes will be adjusted by device of a heater to improve the static field uniformity.

Abstract: A new type of coil magnet in which the plane of each turn of the conducting coil is rotated with respect to the central axis. This results in the induced magnetic field being oriented off the central axis. A set of two such disk assemblies are preferably nested, with the current flowing in opposite directions within the two assemblies. This results in the components of the two induced magnetic fields lying along the center axis canceling each other out, leaving only a purely transverse magnetic field. In addition, variations in the angular offset of the nested coils can be used to create a magnetic field having almost any orientation. Three or more such nested disk assemblies can be employed to strengthen and adjust the transverse magnetic field.

Abstract: A superconductive magnet device comprises a pair of oppositely disposed superconductive bodies in which annular superconductive coils are accommodated, and fine chip-shaped ferromagnetic shims disposed on a surface of the pair of superconductive magnet bodies so as to improve uniformity of magnetic field in a uniform magnetic field in a uniform magnetic field space generated in the proximity of the center between the superconductive magnet bodies, wherein ring-shaped ferromagnetic shims are disposed concentrically with the center of annular superconductive coils on the surface of the superconductive magnet bodies.

Abstract: An open-type magnet device for MRI includes a pair of upper and lower magnet assemblies, and shims are provided on opposite sides of their cooling containers and/or in holes passing through central portions of the cooling containers so as to facilitate providing a highly homogeneous static magnetic field.

Abstract: A magnetic resonance apparatus has a basic field magnet for providing a uniform magnetic basic field, a gradient coil system for coding within the basic field as well as a passive shim system for homogenizing the magnetic basic field. This passive shim system is composed of shim iron plates that are placed in the magnetic basic field. A device is provided with which the temperature of these shim iron plates is controlled.

Abstract: A magnet device includes two sets of static magnetic field generation sources spaced from each other in the vertical direction such that the uniform magnetic field region (patient space) is between then. Each set has concentric current carrying coils to generate a uniform magnetic field in a first direction (the vertical direction).

Abstract: A superconductive magnet device comprises a pair of oppositely disposed superconductive bodies in which annular superconductive coils are accommodated, and fine chip-shaped ferromagnetic shims disposed on a surface of the pair of superconductive magnet bodies so as to improve uniformity of magnetic field in a uniform magnetic field space generated in the proximity of the center between the superconductive magnet bodies, wherein ring-shaped ferromagnetic shims are disposed concentrically with the center of annular superconductive coils on the surface of the superconductive magnet bodies.

Abstract: A product line of MRI systems includes a first MRI system including a first yoke and a plurality of magnet blocks forming a first central assembly disposed on the first yoke. The product line also includes a second MRI system including a second yoke, a plurality of magnet blocks forming a second central assembly disposed on the second yoke and shaped the same as the first central assembly, and a first set of magnet blocks mounted to the second yoke at a periphery of the second central assembly.

Abstract: An open C magnet system for magnetic resonance imaging comprises circular NdFeB poles, a single piece yoke having beveled inside and outside faces between the vertical post section and the horizontal arms of the yoke, a necked-in mid-section of the vertical post, flat Nebdymium (NdFeB) corner plates in face to face relationship with the inside beveled faces between the vertical post and the horizontal arms.

Abstract: The object of the present invention is to minimize the residual magnetic induction in a circular pole piece included in a magnetic circuit for magnetic resonance imaging. A circular pole piece is divided into two portions, that is, a center portion and a marginal portion. A soft magnetic material that exhibits a high permeability (for example, 10000 or more) with a relatively small external magnetic field (for example, ranging from 20 A/m to 60 A/m) applied thereto is adopted as a soft magnetic material to be made into a center-portion laminate block. A soft magnetic material that exhibits a high permeability (for example, 6000 or more) with a relatively large external magnetic field (for example, ranging from 50 A/m to 150 A/m) applied thereto is adopted as a soft magnetic material to be made into a marginal-portion laminate block 103b.

Abstract: In a method for aligning a magnetic field-modifying structure (74) in a magnet bore (12) of a magnetic resonance imaging scanner (8), a reference magnetic field map of the magnet bore (12) is measured without the magnetic field-modifying structure (74) inserted. The magnetic field-modifying structure (74) is inserted into the magnet bore (12). A second magnetic field map of the magnetic bore (12) is measured with the magnetic field-modifying structure (74) inserted. At least one odd harmonic component of the first and second magnetic field maps is extracted. The magnetic field-modifying structure (74) is aligned in the magnet bore (12) based on a comparison of the odd harmonic component of the first and second magnetic field maps.

Abstract: For the purpose of providing a static magnetic field generating apparatus employing permanent magnets that allows easy adjustment of a static magnetic field, eight grooves are provided in a columnar yoke and the other opposing columnar yoke, and the shape or material of insert members is changed to modify magnetic resistance of the columnar yoke and the other opposing columnar yoke when the insert members are fitted; thus, magnetic flux formed in a space between permanent magnets can be easily modified, and hence, a static magnetic field can be easily adjusted.

Abstract: A magnetic resonance imaging apparatus includes a unit (shim coil) that corrects uniformity of a magnetic field, a temperature detecting unit that detects a temperature of a magnet or its surroundings, and a control unit that controls the shim coil based on the detected temperature. The control unit calculates an error component for changing the uniformity of the magnetic field at the detected temperature of the magnet or its surroundings, based on a temperature characteristic of uniformity of the magnetic field calculated in advance. Further, the control unit calculates a shim current that generates a correction magnetic field for canceling the error component, and drives the shim coil based on this shim current.

Abstract: The invention relates to a magnetic resonance imaging (MRI) apparatus (1) comprising a gradient coil assembly (3, 4, 5) for generating gradient magnetic fields in an imaging volume, the gradient coil assembly (3, 4, 5) comprising at least three gradient coils (6) for generating three different gradient magnetic fields. In order to compensate self-induced eddy currents in the gradient coils it is proposed according to the invention to provide a conductive element (71, 72, 73) in close proximity to at least one of the gradient coils (6) in order to compensate self-induced eddy currents in the gradient coil assembly (3, 4, 5). It is thus achieved that undesirable high-order behaviour of the gradient coils is suppressed and that conductive elements (71, 72, 73) are provided in the gradient coil assembly (3, 4, 5) such that undesirable high-order behavior of the gradient coils (3, 4, 5) is suppressed and the nature of the short term self-eddy field becomes similar to that of the gradient coils (3, 4, 5).

Abstract: In this system and method for magnetic resonance imaging, an actively shielded primary coil includes a first and second set of turns each having a prescribed number of turns about an axis, and each being symmetrically positioned radially from the axis and equidistant with respect to a mid plane perpendicular to the axis. A secondary shielding coil includes a third and fourth set of turns each having a prescribed number of turns about the axis and being symmetrically positioned radially from the axis and equidistant with respect to the mid plane. The third set of turns is positioned in close proximity to the first set of turns and outward of the first set of turns. Likewise, the fourth set of turns is positioned in close proximity to the second set of turns and outward of the second set of turns. The first and third sets of turns are in a first prescribed turns ratio and the second and fourth sets of turns are in a second prescribed turns ratio.

Abstract: In a shim tray, a gradient coil system and a magnetic resonance apparatus for the acceptance of the shim tray, the shim tray is sub-divided, in the direction of insertion into the gradient coil system or the magnetic apparatus into at least two sub-trays that can be released from one another.

Abstract: In a magnetic resonance imaging apparatus, a transmitting/receiving coil is attached to a patient at a region of interest and disposed within a static magnetic field, a radio-frequency magnetic field, and a gradient magnetic field and an image of the patient is obtained. A tabletop is used to move the patient in the static field in a horizontal direction within a horizontal plane and up and down in a direction that is perpendicular to the horizontal plane, a patient couch controller causing the tabletop to move, based on the position of the region of interest obtained from the image so that the position of the region of interest is caused to coincide in three dimensions with center of the static magnetic filed and/or the gradient magnetic field.

Abstract: The present invention is directed to a method of shimming a magnet assembly of an MR imaging system such that a desired B0 field strength may be created with minimal inhomogeneities therethrough. With this method, sufficient shimming of the magnet assembly may be achieved without requiring mechanical variations to the magnet assembly after the magnet assembly has been assembled. The invention analyzes variations from the desired B0 field and inhomogeneities at a number of target points along the magnet assembly or B0 field. A comparison is then made at each point to determine a shimming or weighting factor such that the desired overall B0 field strength and targeted field homogeneity is achieved. Active and/or passive shim elements may then be incorporated into the magnet assembly at each target point to achieve the desired overall field strength and minimum overall field homogeneity.

Abstract: The present invention relates to techniques for enlarging an opening, which accommodates a subject, in a superconducting magnet apparatus for use in MRI system, so as to prevent the subject from feeling claustrophobic, and for realizing low magnetic field leakage therefrom, and for reducing the weight thereof, and for realizing a large high magnetic field strength uniform magnetic field region. Static magnetic field generating sources of the superconducting magnet apparatus are constituted by two sets of superconducting coils, the respective sets of which are placed in such a manner as to face each other across a uniform magnetic field generating region. Each of the sets of superconducting coils consists of a main coil for feeding electric current in a specific direction, a bucking coil for feeding electric current in a direction opposite to the direction of the electric current flow passing through the main coil, and a coil for correcting magnetic homogeneity.

Abstract: The present invention relates to a method and system for adjusting a magnetic center field of a magnetic field generator in an MRI. One embodiment of the presenting invention relates to a magnetic field generator system having a magnetic center field. This embodiment comprises opposing posts and opposing yokes connected to the opposing posts, where at least one of the posts has a spacer. At least one permanent magnetic block is connected to at least one of the opposing yokes. Further, at least one spacer is formed in at least one of the posts, the yokes and/or the permanent magnetic block.

Abstract: An apparatus is disclosed for generating a magnetic field of high field strength, spatial uniformity and minimal drift of magnetic field intensity over a temperature range of about 0° C. to 175° C. This apparatus may be used in a standard modular logging tool for direct downhole NMR measurements of various parameters of fluid samples of geologic formations near the walls of a borehole. In one embodiment, the apparatus is composed of two tubular permanent magnets made of different magnetic materials with different magnetic temperature coefficients to provide temperature compensation. The apparatus preferably also utilizes a pressure barrel that surrounds the magnets and provides a return path for magnetic flux lines, thereby increasing flux density within the measurement volume.

Abstract: The present invention is directed to a method of shimming a magnet assembly of an MR imaging system such that a desired BO field strength may be created with minimal inhomogeneities therethrough. With this method, sufficient shimming of the magnet assembly may be achieved without requiring mechanical variations to the magnet assembly after the magnet assembly has been assembled. The invention analyzes variations from the desired B0 field and inhomogeneities at a number of target points along the magnet assembly or B0 field. A comparison is then made at each point to determine a shimming or weighting factor such that the desired overall B0 field strength and targeted field homogeneity is achieved. Active and/or passive shim elements may then be incorporated into the magnet assembly at each target point to achieve the desired overall field strength and minimum overall field homogeneity.

Abstract: An imaging system 10 is provided comprising an imaging magnet 16 having a magnet bore 18. A plurality of passive shims 26 is positioned within the magnet bore 18. A plurality of resistive shims 46 is also positioned within the magnet bore 18. A plurality of thermometers 28 is coupled thermally to a select number of the plurality of passive shims 26 and read a passive shim temperature 36. A controller 32 is in communication with the plurality of thermometers 28 and the plurality of resistive shims 46. The controller 32 includes logic adapted to adjust control currents 40 sent to each of the plurality of resistive shims 46 in response to the resistive shim temperatures 36 received from each of the thermometers 28 such that the strength of the magnetic field and its homogeneity is maintained.

Abstract: A cable routing system for an MRI coil having multiple loops and multiple signal cables provides a non-resonant conductive ring surrounding the loops and grounded to define a low electrical field region along which the signal cables may be routed for reduced interference.

Abstract: A superconducting magnet apparatus. By forming one or more holes in each of platelike ferromagnetic substances forming a magnetic shield for focusing the magnetic flux generated by superconducting coils, the flow of lines of magnetic flux is adjusted. Thereby, a static magnetic field in a measurement space is corrected. By disposing coupling tubes for supporting two cooling vessels housing superconducting coils on the rear side with respect to a central axis (Z axis) of the measurement space of the vertical direction, access to the subject is facilitated. In addition, the magnetic shield has an opening portion wider than the superconducting magnet on its side face. After the magnetic shield has been assembled, the superconducting magnet can be inserted from the opening portion.

Abstract: A method for shimming a magnetic field of a magnet in a volume of interest, utilizing ferromagnetic pellets for shimming. The pellets are positioned in a nonmagnetic holder having a predetermined number of pellet holes. The method includes measuring the magnetic field of a magnet in a plurality of locations within the volume of interest, determining a nominal passive shimming mass to compensate the measured magnetic field to approximate a desired magnetic field within the volume of interest; and placing a combination of ferromagnetic pellets from a selection of full strength pellets, nearly full strength pellets, and low strength pellets in the pellet holes to approximate the nominal passive shimming mass.

Abstract: A facility for generating a uniform magnetic field, particularly for generating a basic magnetic field of a magnetic resonance examination apparatus, particularly a medical magnetic resonance tomography apparatus, has a shim device with a guide device to or in which a number of ferromagnetic articles, such as balls, are movably attached. At least two of the articles have ferromagnetic properties differing from one another, such as saturation magnetizations that differ in magnitude from one another. A method for improving the homogeneity of a magnetic field makes use of such a facility.

Abstract: A magnetic resonance imaging (MRI) device for imaging a volume is provided with at least one main magnet for generating a magnetic field, and at least one gradient coil for manipulating the magnetic field generated by the at least one main magnet to image the volume. The magnetic fields generated by the at least one gradient coil are substantially unshielded.

Abstract: An MRI apparatus having an open structure includes a static magnetic field generating magnet including magnetic field generating sources arranged above and below an imaging space and magnetic field fluctuation reducing plates arranged inside the magnet. Gradient magnetic field coils are fixed to the static magnetic field generating magnet so as to not be in contact with the magnetic field fluctuation reducing plates. When the strength of the magnetic field generated by the static magnetic field generating magnet fluctuates due to vibration of the gradient magnetic field coils or other devices during an imaging operation of the MRI apparatus, an eddy current is generated on the magnetic field fluctuation reducing plates in response to the magnetic field fluctuation components. Magnetic flux which cancels the static magnetic field fluctuation components is generated due to this eddy current, and consequently, a time-sequentially stable static magnetic field can be obtained.

Abstract: For the purpose of efficiently correcting a quadratic term component of a static magnetic field, when an inhomogeneity error of a static magnetic field generated by a pair of magnets supported by yokes so that the magnets face each other across a space is to be corrected, a quadratic term component of the static magnetic field is corrected by a quadratic term component of a magnetic field generated by a pair of circular loop coils, and a zero-th order term component of the magnetic field from the pair of circular loop coils is compensated by a zero-th order term component of a magnetic field generated by coils wound around the yokes.

Abstract: Superconducting birdcage coil with low-pass and high-pass coil configurations are formed by using strips each with an elongated sapphire substrate with a layer of a high temperature superconductor (HTS) material grown in a wavy pattern over its entire length on one of its main surfaces. A low-pass coil is formed with a pair of ring elements made of an electrically conductive metal and a plurality of such strips arranged parallel to one another and interconnecting these ring elements at junctions which are spaced peripherally along each of the rings. At each of the junctions, the ring element and the HTS layer form a capacitance. A high-pass coil is formed by a plurality of such strips each with electrodes of the HTS material also grown at two end positions separated from each other on the other main surface of its sapphire substrates. These strips are arranged parallel to each other and sequentially around a central axis, each lying in a plane which includes the center axis.

Abstract: The invention concerns a means and a method for stabilizing a magnetic field generated by a superconductingly short-circuited main coil located in a cryostat in the measuring volume of a high-resolution magnetic resonance spectrometer, which comprises compensation coils which are dimensioned and positioned such that they, in their entirety, are suited to largely compensate for field drifts of the superconductingly short-circuited main coil in the measuring volume. The drift compensation coils consist of HTS material and are disposed radially outside of the main coil at a higher temperature level.

Abstract: In a method for calculating conductor tracks of a gradient coil in a gradient coils for a magnetic resonance tomography apparatus and a magnetic resonance tomography apparatus employing such a gradient coil system, conductor tracks are calculated for a primary coil with multiple conductor bundles, and for a second coil which shields the primary coil, as well as for at least one booster coil that is interconnected with the conductor bundles of the primary coil, and with the secondary coil, so that a number of different homogeneity volumes can be produced at the center of the gradient coil system.

Abstract: A process for adjusting an homogeneity of a magnetic field produced by a magnet having a pole includes placing a spherically-shaped magnetic shim element within the magnetic field so as to become magnetized and have a localized effect on the magnetic field. The magnetic field is mapped to provide an original field map, and a sphere action is selected that will adjust the homogeneity of the magnetic field. An effect on the magnetic field caused by the selected sphere action is calculated and combined with the original field map, to provide an adjusted field map, which is compared with the original field map. Based on the comparison, it is determined if the adjusted field map indicates a satisfactory adjustment of the homogeneity of the magnetic field, in which case the selected sphere action is performed.

Abstract: In order to nullify the adverse effect of an external magnetic field on a static magnetic field generated in an MRI system, small-size coils are used to generate a compensation magnetic field. Thus, the component of the static magnetic field to be applied to a magnetic sensor is canceled. The magnetic sensor can therefore detect the external magnetic field highly precisely. A correction current proportional to the external magnetic field detected highly precisely is fed to BO correction coils. Eventually, the external magnetic field that adversely affects the static magnetic field is canceled.

Abstract: A superconductive magnet device comprises a pair of oppositely disposed superconductive bodies in which annular superconductive coils are accommodated, and fine chip-shaped ferromagnetic shims disposed on a surface of the pair of superconductive magnet bodies so as to improve uniformity of magnetic field in a uniform magnetic field space generated in the proximity of the center between the superconductive magnet bodies, wherein ring-shaped ferromagnetic shims are disposed concentrically with the center of annular superconductive coils on the surface of the superconductive magnet bodies.

Abstract: For the purpose of efficiently correcting a quadratic term component of a static magnetic field, when an inhomogeneity error of a static magnetic field generated by a pair of magnets (102) supported by yokes (202, 204) so that the magnets face each other across a space is to be corrected, a quadratic term component of the static magnetic field is corrected by a quadratic term component of a magnetic field generated by a pair of circular loop coils (104), and a zero-th order term component of the magnetic field from the pair of circular loop coils is compensated by a zero-th order term component of a magnetic field generated by coils (114) wound around the yokes (204).

Abstract: A magnetic field generator comprises a pair of plate yokes connected by a column yoke. The pair of plate yokes has a pair of opposed surfaces each provided with a permanent magnet including a plurality of neodymium magnets. In a method in which the neodymium magnets are demagnetized and adhesive is ground, the magnetic field generator is heated to 200° C.˜350° C. After the neodymium magnets are demagnetized, the adhesive is removed and the neodymium magnets are removed and collected from the magnetic field generator. In a method in which the adhesive is carbonized, the magnetic field generator is heated to 350° C.˜1000° C. After carbonizing the adhesive, the neodymium magnets are removed and collected. Surfaces of the collected neodymium magnets are polished and the neodymium magnets are reused. Further, the collected neodymium magnets are re-aged and reused.

Abstract: For the purpose of efficiently homogenizing a magnetic field, when homogenizing a strength distribution of a magnetic field generated in a space between a pair of facing pole surfaces, a continuous magnetization distribution for homogenizing the strength distribution of the magnetic field is determined (301-307) with respect to planes on which magnetic elements are to be disposed for homogenizing the strength distribution of the magnetic field; and magnetic elements are disposed (309) based on the magnetization distribution. The magnetic distribution is determined as a polynomial of an orthogonal function. The polynomial is determined by an optimization method. The optimization method is a method of least squares.

Abstract: In a method for operating a magnetic resonance apparatus with a gradient coil system and an active shim system, shim currents of the active shim system and/or offset currents of the gradient coil system are adjusted corresponding to at least one subject-specific parameter of an examination subject.

Abstract: Described herein is a method and system for shimming an MRI magnetic field generating assembly, wherein a plurality of shims are secured relative to a surface of the magnetic field generating assembly to at least partially correct inhomogeneities in the magnetic field generated by the magnetic field generating assembly. In one aspect, the shims are arranged along a plurality of concentric geometric shapes each having at least five sides. In an alternative aspect, the shims are arranged in a plurality of rows and columns, where the rows are normal to the columns. In another aspect, at least one of the shims is a flat plate of magnetic material including a top edge, a bottom edge, side edges, and face surfaces.

Abstract: Apparatus and methods for the adjustment of a magnetic field produced by permanent magnet arrangements facing each other across an air gap include a series of ferromagnetic shim blocks individually adjustably positionable within the magnet arrangements to adjust the strength and uniformity of the magnetic field. A backing plate to which the permanent magnets are attached has channels within which adjusting elements are used to move the shim blocks with relation to the permanent magnets, preferably toward or away from the air gap. Shim blocks are arranged in selected geometric arrays and shapes responsive to the geometry of the magnet arrangements and may be formed as toroidal shapes or as individual blocks of varying sizes.

Abstract: Asymmetric tesseral coils and sets for magnetic resonance applications are provided. Also provided are methods for designing such coils, as well as coils generating arbitrary field profiles. In certain embodiments, the coils are rigorously constrained to have finite dimensions.

Abstract: A magnetic recording medium inspection method for detecting a small protrusion that constitutes a defect on a surface of a magnetic recording medium, the method comprising the steps of flying a glide inspection head at a predetermined height over a surface of the moving magnetic recording medium; detecting a contact duration time during which the glide head is in contact with the protrusion on the surface of the magnetic recording medium using a contact detection sensor attached to the glide inspection head; and determining the small protrusion based on the contact duration time.