WO1996000400A1 - Susceptibility compensated coils - Google Patents

Susceptibility compensated coils Download PDF

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Publication number
WO1996000400A1
WO1996000400A1 PCT/AU1995/000356 AU9500356W WO9600400A1 WO 1996000400 A1 WO1996000400 A1 WO 1996000400A1 AU 9500356 W AU9500356 W AU 9500356W WO 9600400 A1 WO9600400 A1 WO 9600400A1
Authority
WO
WIPO (PCT)
Prior art keywords
coil
magnetic field
conductor element
diamagnetic
size
Prior art date
Application number
PCT/AU1995/000356
Other languages
French (fr)
Inventor
David Michael Doddrell
Fernando Osmin Zelaya
Stuart Crozier
Original Assignee
The University Of Queensland
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The University Of Queensland filed Critical The University Of Queensland
Priority to AU27070/95A priority Critical patent/AU2707095A/en
Publication of WO1996000400A1 publication Critical patent/WO1996000400A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
    • G01R33/34076—Birdcage coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56527—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to chemical shift effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
    • G01R33/56536—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to magnetic susceptibility variations

Definitions

  • THIS INVENTION relates to susceptibility compensated coils.
  • the invention is directed to improved radio frequency (RF) and gradient coils for use in a nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) apparatus for minimising perturbations of the static magnetic field (B 0 ) in such apparatus.
  • RF radio frequency
  • NMR nuclear magnetic resonance
  • MRI magnetic resonance imaging
  • the material used to form the coils is a multi-layered assembly selected such that the net assembly is "susceptibility compensated" and minimises net spatially dependent perturbation of B 0 .
  • the invention is also directed to a shield designed to minimise magnetic field distortion at the sample due to passive components used in the surrounding coil( s) .
  • nuclear spins within a sample are subjected to a strong static magnetic field (B 0 ) the homogeneity of which is critical to the experimental success of the apparatus.
  • An RF transmitter excites the nuclear spins in the presence of the static field at the Larmor precessional frequency, and RF energy is emitted by the spins as they relax back to the state prior to RF excitation. This emitted energy may be received by the coil that was used to transmit the original excitation or by a separate coil.
  • a multiplicity of coils can be used to operate on any number of nuclear species present in the sample.
  • the RF coils surround the sample radially and external to the RF coils are :;he gradient coils.
  • Gradient coils provide a mechanism for controlled dephasing and/or spatial encoding for use in imaging, localised spectroscopy, high resolution gradient enhanced spectroscopy and related techniques.
  • the RF and gradient coils can introduce large non-uniformities in the static field which make the correction process much more difficult and in some cases limit the degree of correction possible. These non- uniformities arise from the magnetic properties of the constituent parts of the RF and gradient coils. It is an object of the present invention to overcome or ameliorate the abovedescribed disadvantages by providing coil conducting elements which remove, compensate for, or otherwise reduce unwanted effects of the coils on the uniformity of the static field.
  • the present invention provides a multi-layer conductor element suitable for use in a coil of the type used in NMR spectroscopy or imaging, the conductor element comprising a selected combination of diamagnetic and/or paramagnetic materials of such type, size and/or shape so as to minimise spatial perturbation of a static magnetic field caused by introducing the coil into the .magnetic field.
  • B the flux density
  • H the magnetic intensity
  • ⁇ the permeability of the local medium
  • ⁇ the susceptibility of the local medium
  • ⁇ a scalar potential
  • the spatial perturbation of the static magnetic field can be minimised.
  • the equations are solved by finite element analysis computational methods.
  • the present invention provides a multi-layer shield suitable for use in NMR spectroscopy or imaging, the shield being adapted to be placed between passive components used in an RF coil and the subject of the NMR spectroscopy or imaging, the shield comprising a selected combination of diamagnetic and/or paramagnetic materials of such type, size and/or shape so as to minimise perturbations of the magnetic field near the sample caused by the coil passive components.
  • the shield is suitably in the form of a guard ring which is placed internally of the coil, and surrounding the sample.
  • the guard ring magnetically shields the internal sample from the effects of passive components and interconnections in an RF probe. Furthermore, by suitable selection of the materials, size and shape of the multi-layer guard rings as described above, magnetic field distortion is minimised. Two or more such shields may be used in a single probe.
  • FIG. 1 is a sectional view of a multi-layer wire used to form a coil according to one embodiment of the invention
  • Fig. 2 illustrates the perturbed field when using a conventional wire
  • Fig. 3 illustrates the perturbed field when using the wire of Fig. 1;
  • Fig. 4 is a perspective view of a guard ring according to a further embodiment of the invention.
  • Fig. 1 illustrates, in cross section, a wire conductor suitable for forming an RF coil (for use as either a transmitter and/or receiver coil) or a gradient coil, in NMR spectroscopy or imaging apparatus.
  • the present invention is not limited to wire coils, but is also applicable to coils of other constructions, such as interconnected wires or deposited and etched conductors.
  • the wire 1 is a multi-layer wire, and comprises an inner conductor 2 of diameter D 1 surrounded by an outer tubular conductor 3 of outer diameter D 2 .
  • the wire 1 is used to form a coil which is placed in a static magnetic field B Q .
  • the wire illustrated in Fig. 1 is of circular cross- section, it will be understood that the invention is not restricted to any particular shape, orientation, material or layer arrangement.
  • the geometry of the conductor element may or may not be symmetrical in any coordinate system.
  • the materials, size, shape or configuration of the layers are chosen so that spatial perturbation of the static magnetic field B 0 is cancelled or otherwise minimised.
  • the selected materials may comprise diamagnetic and paramagnetic materials, or a combination of both.
  • the resultant susceptibility of the coil is suitably compensated to minimise field perturbation.
  • B 0 (III)
  • v 2 ⁇ 0 (IV) subject ttoo tthhee bboouunnddaarryy conditions that the normal component of B and the tangential components of H are continuous across any boundary and where B is the flux density, H the magnetic intensity, ⁇ the permeability of the local medium, ⁇ the susceptibility of the local medium and ⁇ a scalar potential.
  • Conductors constructed in accordance with this method can be used in both RF and gradient coils, in discrete wire coils or distributed sheet patterns.
  • Fig. 2 illustrates the resultant perturbed field (i.e. net field-static) when a wire having the cross section shown in Fig. 1 is placed in a static field of 4.7 Tesla in the Y-direction.
  • Fig. 3 shows the nulling of the spatial dependence of the field when D 2 is reduced to 12.5mm.
  • the present invention provides compensation for the perturbations and distortions of the magnetic field B 0 resulting from the passive components used in coils, such as ceramic capacitors and their interconnections, etc.
  • such compensation is in the form of a partial magnetostatic shield or guard ring 4 which is placed internally of the passive components 5 so as to shield the effects of these components and connections.
  • the shield or guard ring 4 is a multi-layer conductor designed to prevent local distortion of B 0 from perturbing the field near the sample (not shown) located within the ring 4.
  • Each side of the shield is considered differently to reflect the different magnetostatic conditions on either side of the shield 4.
  • the thickness, size and configuration of the layers of the shield, and the materials of the individual layers, are selected, using the appropriate magnetostatic equations given above to reduce the distortionary effects which would otherwise result from placing the passive components in the static magnetic field.
  • a multiplicity of shields can be used in each probe, with appropriate consideration given to reducing the eddy current induction of such rings when gradient pulsing is used in a probe.

Abstract

A multi-layer conductor element (1) is used to form a coil for use as a RF or gradient coil in NMR apparatus. The conductor element (1) comprises layers of diamagnetic and/or paramagnetic materials (2, 3), the material type, size and/or shape being selected to minimise spatial perturbation of the static magnetic field caused by the presence of the coil therein. For any given situation, the appropriate magnetostatic equations are formulated, and the selection of material type, size and/or shape is governed by the solution of the equations. By appropriate combination of the positive susceptibility of paramagnetic material and the negative susceptibility of diamagnetic material, the resultant susceptibility of the coil is compensated to minimise field perturbation. A multi-layer shield (4) comprising paramagnetic and/or diamagnetic materials is placed within a coil to minimise local distortion of the magnetic field caused by the presence of passive elements (5) in the coil.

Description

"SUSCEPTIBILITY COMPENSATED COILS"
THIS INVENTION relates to susceptibility compensated coils. In particular, the invention is directed to improved radio frequency (RF) and gradient coils for use in a nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) apparatus for minimising perturbations of the static magnetic field (B0) in such apparatus. The material used to form the coils is a multi-layered assembly selected such that the net assembly is "susceptibility compensated" and minimises net spatially dependent perturbation of B0.
The invention is also directed to a shield designed to minimise magnetic field distortion at the sample due to passive components used in the surrounding coil( s) .
BACKGROUND ART In an NMR spectroscopy or imaging device, nuclear spins within a sample are subjected to a strong static magnetic field (B0) the homogeneity of which is critical to the experimental success of the apparatus. An RF transmitter excites the nuclear spins in the presence of the static field at the Larmor precessional frequency, and RF energy is emitted by the spins as they relax back to the state prior to RF excitation. This emitted energy may be received by the coil that was used to transmit the original excitation or by a separate coil.
A multiplicity of coils can be used to operate on any number of nuclear species present in the sample. The RF coils surround the sample radially and external to the RF coils are :;he gradient coils. Gradient coils provide a mechanism for controlled dephasing and/or spatial encoding for use in imaging, localised spectroscopy, high resolution gradient enhanced spectroscopy and related techniques.
Placing the coils (both RF and gradient) in the static magnetic field perturbs the field uniformity (as indeed does the sample). The effects of such perturbations include reduced signal-to-noise ratios, reduced spectral resolution and reduced spatial resolution (in imaging experiments), etc. Those perturbations caused by the sample are usually corrected by the process of "shimming" in which an array of electromagnets, designed to produce various orders of spherical harmonics of the field, are used interactively to correct any distortion of the NMR signal due to inhomogeneities in the static field. This correction process involves the interactive adjustment of many parameters such as shim currents (up to 30 or 40 such parameters are common) and is error prone.
The RF and gradient coils can introduce large non-uniformities in the static field which make the correction process much more difficult and in some cases limit the degree of correction possible. These non- uniformities arise from the magnetic properties of the constituent parts of the RF and gradient coils. It is an object of the present invention to overcome or ameliorate the abovedescribed disadvantages by providing coil conducting elements which remove, compensate for, or otherwise reduce unwanted effects of the coils on the uniformity of the static field. SUMMARY OF THE INVENTION
In one broad form, the present invention provides a multi-layer conductor element suitable for use in a coil of the type used in NMR spectroscopy or imaging, the conductor element comprising a selected combination of diamagnetic and/or paramagnetic materials of such type, size and/or shape so as to minimise spatial perturbation of a static magnetic field caused by introducing the coil into the .magnetic field.
The selection of the layer materials, size and/or shape is governed by the solution of appropriate magnetostatic equations. In one form of the invention, these equations comprise B =μH ( I ) μ =1 + X (ID v.B =0 (III) v2Φ = 0 (IV) where B is the flux density, H is the magnetic intensity, μ is the permeability of the local medium, χ is the susceptibility of the local medium and Φ is a scalar potential. The boundary conditions dictate that the normal component of B and the tangential components of H are continuous across any boundary.
By using a combination of paramagnetic and diamagnetic materials to form the coil conductors, chosen according to the solution of magnetostatic equations for any particular situation, the spatial perturbation of the static magnetic field can be minimised. Typically, the equations are solved by finite element analysis computational methods.
In another form, the present invention provides a multi-layer shield suitable for use in NMR spectroscopy or imaging, the shield being adapted to be placed between passive components used in an RF coil and the subject of the NMR spectroscopy or imaging, the shield comprising a selected combination of diamagnetic and/or paramagnetic materials of such type, size and/or shape so as to minimise perturbations of the magnetic field near the sample caused by the coil passive components.
The shield is suitably in the form of a guard ring which is placed internally of the coil, and surrounding the sample. The guard ring magnetically shields the internal sample from the effects of passive components and interconnections in an RF probe. Furthermore, by suitable selection of the materials, size and shape of the multi-layer guard rings as described above, magnetic field distortion is minimised. Two or more such shields may be used in a single probe.
In order that the invention may be more fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a sectional view of a multi-layer wire used to form a coil according to one embodiment of the invention;
Fig. 2 illustrates the perturbed field when using a conventional wire;
Fig. 3 illustrates the perturbed field when using the wire of Fig. 1; and
Fig. 4 is a perspective view of a guard ring according to a further embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENT By way of illustration and simple example, Fig. 1 illustrates, in cross section, a wire conductor suitable for forming an RF coil ( for use as either a transmitter and/or receiver coil) or a gradient coil, in NMR spectroscopy or imaging apparatus. However, the present invention is not limited to wire coils, but is also applicable to coils of other constructions, such as interconnected wires or deposited and etched conductors.
As shown in Fig. 1, the wire 1 is a multi-layer wire, and comprises an inner conductor 2 of diameter D1 surrounded by an outer tubular conductor 3 of outer diameter D2. In use, the wire 1 is used to form a coil which is placed in a static magnetic field BQ. Although the wire illustrated in Fig. 1 is of circular cross- section, it will be understood that the invention is not restricted to any particular shape, orientation, material or layer arrangement. The geometry of the conductor element may or may not be symmetrical in any coordinate system.
Rather, the materials, size, shape or configuration of the layers are chosen so that spatial perturbation of the static magnetic field B0 is cancelled or otherwise minimised. The selected materials may comprise diamagnetic and paramagnetic materials, or a combination of both. For example, by appropriate combination of the positive susceptibility of paramagnetic material and the negative susceptibility of diamagnetic materials, the resultant susceptibility of the coil is suitably compensated to minimise field perturbation.
For a given application of an RF coil, spatial perturbations can be minimised by solving the following set of magnetostatic equations:
B = PH (I) μμ == i + χ (II) v. B = 0 (III) v2Φ = 0 (IV) subject ttoo tthhee bboouunnddaarryy conditions that the normal component of B and the tangential components of H are continuous across any boundary and where B is the flux density, H the magnetic intensity, μ the permeability of the local medium, χ the susceptibility of the local medium and Φ a scalar potential.
Known analytical solutions are available for a variety of shapes. Where analytical solutions are not available, numerical calculations based on finite element and finite difference algorithms can be used to select the appropriate thicknesses of selected materials and their required geometry to produce a compensated conductor. The calculations are normally conducted by computer due to the number of iterations required to solve the equation.
Conductors constructed in accordance with this method can be used in both RF and gradient coils, in discrete wire coils or distributed sheet patterns.
Fig. 2 illustrates the resultant perturbed field (i.e. net field-static) when a wire having the cross section shown in Fig. 1 is placed in a static field of 4.7 Tesla in the Y-direction. The wire comprises a copper wire of diameter D1 = 10mm, plated with platinum such that the outer diameter D2 = 15mm.
Fig. 3 shows the nulling of the spatial dependence of the field when D2 is reduced to 12.5mm. Hence, by appropriate selection of materials, size, shape and/or configuration in accordance with the solution of the magnetostatic equations given above, magnetic field perturbations can be substantially eliminated or reduced to negligible amounts.
In a further embodiment, the present invention provides compensation for the perturbations and distortions of the magnetic field B0 resulting from the passive components used in coils, such as ceramic capacitors and their interconnections, etc. As shown in Fig. 2, such compensation is in the form of a partial magnetostatic shield or guard ring 4 which is placed internally of the passive components 5 so as to shield the effects of these components and connections. The shield or guard ring 4 is a multi-layer conductor designed to prevent local distortion of B0 from perturbing the field near the sample (not shown) located within the ring 4. Each side of the shield is considered differently to reflect the different magnetostatic conditions on either side of the shield 4. The thickness, size and configuration of the layers of the shield, and the materials of the individual layers, are selected, using the appropriate magnetostatic equations given above to reduce the distortionary effects which would otherwise result from placing the passive components in the static magnetic field.
A multiplicity of shields can be used in each probe, with appropriate consideration given to reducing the eddy current induction of such rings when gradient pulsing is used in a probe.
The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS:
1. A conductor element adapted for use in a coil of the type used in a static magnetic field in NMR apparatus, characterised in that the conductor element comprises a plurality of layers of diamagnetic and/or paramagnetic materials, the material type, size and/or shape being selected to minimise spatial perturbation of the static magnetic field due to the presence of the coil therein.
2. A conductor element as claimed in claim 1 wherein the selection of material type, size and/or shape is governed by the solution of magnetostatic equations appropriate for the particular application.
3. A conductor element as claimed in claim 2 wherein the equations include
B = μH (I) μ = 1 + X (ID v.B = 0 (III) v2Φ = 0 (IV) where B is the flux density, H is the magnetic intensity, μ is the permeability of the local medium, χ is the susceptibility of the local medium and Φ is a scalar potential.
4. A conductor element as claimed in claim 1 wherein the conductor element comprises at least one layer of diamagnetic material juxtaposed with at least one layer of paramagnetic material.
5. A shield member for use in NMR apparatus, the shield member being adapted to be placed between passive components used in an RF coil and a subject sample in the NMR apparatus, characterised in that the shield member comprises a plurality of layers of diamagnetic and/or paramagnetic materials, the material type, size and/or shape being selected to minimise spatial perturbation of the magnetic field near the sample caused by the presence of the passive components in the magnetic field.
6. A shield member as claimed in claim 5 wherein the shield member is in the form of a guard ring adapted to be placed within the coil.
7. A shield member as claimed in claim 5 comprising at least one layer of diamagnetic material juxtaposed with at least one layer of paramagnetic material.
8. A method of forming a coil suitable for use in a static magnetic field in NMR apparatus, comprising the steps of providing at least one conductor element having a plurality of layers of diamagnetic and/or paramagnetic materials, and forming the coil from the conductor element(s), the material type, size and/or shape being selected to minimise spatial perturbation of the static magnetic field due to the presence of the coil therein.
9. A method as claimed in claim 8 further comprising the steps of formulating magnetostatic equations for a particular application, the selection of material type, size and/or shape for that particular application being governed by the solution of such equations.
10. A method as claimed in claim 9 wherein the equations include
B = μH (I) μ = 1 + X (II) v.B = 0 (III) v2Φ = 0 (IV) where B is the flux density, H is the magnetic intensity, μ is the permeability of the local medium, χ is the susceptibility of the local medium and Φ is a scalar potential.
PCT/AU1995/000356 1994-06-23 1995-06-20 Susceptibility compensated coils WO1996000400A1 (en)

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Application Number Priority Date Filing Date Title
AU27070/95A AU2707095A (en) 1994-06-23 1995-06-20 Susceptibility compensated coils

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AUPM6387A AUPM638794A0 (en) 1994-06-23 1994-06-23 Susceptibility compensated coils
AUPM6387 1994-06-23

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1847845A1 (en) * 2006-04-19 2007-10-24 Eidgenössische Technische Hochschule (ETH) Susceptibility-matched magnetic field probe and method for manufacturing the same
US7426779B2 (en) 2001-11-05 2008-09-23 Jeol Ltd. Method of fabricating wire member
GB2511048A (en) * 2013-02-20 2014-08-27 Siemens Plc Methods and apparatus for compensating for drift in magnetic field strength in superconducting magnets
GB2511049A (en) * 2013-02-20 2014-08-27 Siemens Plc Methods and apparatus for compensating for drift in magnetic field strength
CN109597010A (en) * 2018-12-04 2019-04-09 北京昆迈生物医学研究院有限公司 A kind of high-performance magnetism screening arrangement and method based on Active Compensation

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4675609A (en) * 1985-09-18 1987-06-23 Fonar Corporation Nuclear magnetic resonance apparatus including permanent magnet configuration
US4707663A (en) * 1985-08-15 1987-11-17 Fonar Corporation Nuclear magnetic resonance apparatus using low energy magnetic elements
US4737717A (en) * 1987-03-26 1988-04-12 Siemens Medical Systems Inc. Magnetic field correction using a channel for positioning magnetic material
US4980641A (en) * 1989-08-11 1990-12-25 General Atomics Method and apparatus of reducing magnetic hysteresis in MRI systems
GB2237883A (en) * 1989-11-08 1991-05-15 Bruker Analytische Messtechnik Nuclear magnetic resonance imaging spectrometer
WO1991014948A1 (en) * 1990-03-23 1991-10-03 Fonar Corporation Eddy current control in magnetic resonance imaging
EP0623939A1 (en) * 1993-05-03 1994-11-09 Commissariat A L'energie Atomique Permanent magnet structure for producing a stable and homogenous magnetic induction in a given volume
JPH06350283A (en) * 1993-06-07 1994-12-22 Toshiba Corp Electromagnetic shielding room

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4707663A (en) * 1985-08-15 1987-11-17 Fonar Corporation Nuclear magnetic resonance apparatus using low energy magnetic elements
US4675609A (en) * 1985-09-18 1987-06-23 Fonar Corporation Nuclear magnetic resonance apparatus including permanent magnet configuration
US4737717A (en) * 1987-03-26 1988-04-12 Siemens Medical Systems Inc. Magnetic field correction using a channel for positioning magnetic material
US4980641A (en) * 1989-08-11 1990-12-25 General Atomics Method and apparatus of reducing magnetic hysteresis in MRI systems
GB2237883A (en) * 1989-11-08 1991-05-15 Bruker Analytische Messtechnik Nuclear magnetic resonance imaging spectrometer
WO1991014948A1 (en) * 1990-03-23 1991-10-03 Fonar Corporation Eddy current control in magnetic resonance imaging
EP0623939A1 (en) * 1993-05-03 1994-11-09 Commissariat A L'energie Atomique Permanent magnet structure for producing a stable and homogenous magnetic induction in a given volume
JPH06350283A (en) * 1993-06-07 1994-12-22 Toshiba Corp Electromagnetic shielding room

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Vol. 95, No. 003; & JP,A,06 350 283 (TOSHIBA CORPORATION) 22 December 1994. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7426779B2 (en) 2001-11-05 2008-09-23 Jeol Ltd. Method of fabricating wire member
EP1847845A1 (en) * 2006-04-19 2007-10-24 Eidgenössische Technische Hochschule (ETH) Susceptibility-matched magnetic field probe and method for manufacturing the same
WO2007118715A1 (en) * 2006-04-19 2007-10-25 Eidgenössische Technische Hochschule (ETH) Susceptibility-matched magnetic field probe and method for manufacturing the same
US8093899B2 (en) 2006-04-19 2012-01-10 Eidgenössische Technische Hochschule (ETH) and Universität Zürich Magnetic field probe and method for manufacturing the same
GB2511048A (en) * 2013-02-20 2014-08-27 Siemens Plc Methods and apparatus for compensating for drift in magnetic field strength in superconducting magnets
GB2511049A (en) * 2013-02-20 2014-08-27 Siemens Plc Methods and apparatus for compensating for drift in magnetic field strength
US9213073B2 (en) 2013-02-20 2015-12-15 Siemens Plc Method and apparatus for compensating for drift in magnetic field strength in superconducting magnets
GB2511048B (en) * 2013-02-20 2016-05-25 Siemens Healthcare Ltd Methods and apparatus for compensating for drift in magnetic field strength in superconducting magnets
GB2511049B (en) * 2013-02-20 2016-05-25 Siemens Healthcare Ltd Methods and apparatus for compensating for drift in magnetic field strength in superconducting magnets
CN109597010A (en) * 2018-12-04 2019-04-09 北京昆迈生物医学研究院有限公司 A kind of high-performance magnetism screening arrangement and method based on Active Compensation

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