WO2000016117A1 - Temperature control for permanent magnet system - Google Patents

Temperature control for permanent magnet system Download PDF

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Publication number
WO2000016117A1
WO2000016117A1 PCT/GB1999/002779 GB9902779W WO0016117A1 WO 2000016117 A1 WO2000016117 A1 WO 2000016117A1 GB 9902779 W GB9902779 W GB 9902779W WO 0016117 A1 WO0016117 A1 WO 0016117A1
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WO
WIPO (PCT)
Prior art keywords
permanent magnetic
temperature
permanent
magnetic material
magnetic field
Prior art date
Application number
PCT/GB1999/002779
Other languages
French (fr)
Inventor
Magnet Technology Limited Oxford
Original Assignee
Kruip, Marcel, Jan, Marie
Parker, Nicholas, David
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 Kruip, Marcel, Jan, Marie, Parker, Nicholas, David filed Critical Kruip, Marcel, Jan, Marie
Publication of WO2000016117A1 publication Critical patent/WO2000016117A1/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
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets
    • 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
    • G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly

Definitions

  • the present invention relates to magnetic field control systems and in particular to systems suitable for use with Magnetic Resonance Imaging systems (MRI).
  • MRI Magnetic Resonance Imaging systems
  • a magnetic field with a high degree of stability and homogeneity is essential for the successful applications of a number of analytical techniques and in particular for MRI.
  • Assemblies comprising large amounts of permanent magnetic material can be used for generating such fields. Deviations from the specified field, which can be caused by manufacturing errors or by the presence of large amounts of ferromagnetic material in the vicinity of the apparatus, must be corrected. This correction of the field can be done by correction coils, by permanent magnetic material, by small amounts of ferromagnetic material or by a combination of any of these techniques.
  • An aim of the present invention is to provide a temperature control system for permanent magnetic assemblies and use this system to control the strength and shape of the magnetic field of each assembly.
  • a magnetic field control system for a magnet comprising a yoke having at least one permanent magnetic assembly mounted thereon, wherein the permanent magnetic assembly is provided with a temperature sensor which is connected to an electronic control circuit which controls the flow of current to a thermoelectric heat pumping device connected to the permanent magnetic assembly thereby controlling the temperature of said permanent magnetic assembly.
  • the permanent magnetic assemblies are provided in opposite relationship with a space therebetween and are each temperature controlled.
  • the temperature of each of the permanent magnet assemblies is independently controlled by an electronic control circuit so that the magnitude and shape of the magnetic field can be changed for each permanent magnetic assembly.
  • FIG. 1 which shows a cross-sectional view of a C-shaped magnet embodying the magnetic field control system in accordance with the present invention
  • Figure 2 shows a permanent magnetic assembly which is disc-shaped which is sub-divided into an inner and outer ring.
  • a C-shaped magnet assembly comprising a yoke 1, two opposite facing magnetic pole pieces 2 each comprising an equal amount of permanent magnetic material 3 such as NdFeB material, and each constituting a permanent magnetic assembly.
  • the assemblies are spaced from the yoke 1 by spacers 4.
  • the temperature of the permanent magnetic material 3 is measured by temperature sensors 5 such as the thermistors or thermal resistive devices.
  • the signal from the temperature sensors 5 is used as an input to a respective control circuit 6 which controls the temperature of each of the permanent magnetic material assemblies by controlling the current to thermoelectric heat pumping devices 7.
  • NdFeB material If NdFeB material is used, then a rise in temperature of 1°C of the two opposing permanent magnetic assemblies will result in a change of the magnetic field in the centre of the apparatus by 0.1%. A difference in temperature between the two permanent magnetic assemblies of 2°C will create a gradient in the magnetic field in the order of 0.1% per m for a magnet with a typical dimensions of 1 m.
  • FIG 2 shows an example where each of the permanent magnetic assemblies is discshaped.
  • the disc is sub-divided into an outer ring 8 of permanent magnetic material and an inner ring 9 of permanent magnetic material. If the permanent magnetic material has a negative temperature coefficient the outer ring 8 is at a higher temperature than the inner ring 9, a positive second order field shape will result.
  • the present invention provides a means of field correction without the requirement of correction coils and/or a shimming element such as permanent magnets or ferromagnetic shims. Furthermore, the present invention provides a means for continuous field control without the need of power supplies of high specification.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

In order to control the magnetic field in a permanet magnet arrangement for magnetic resonance imaging comprising opposing permanent magnet assemblies, a temperature sensor (5) is provided in each of the permanent magnetic material which is connected to a respective electronic circuit (6) which provides current to a thermoelectric heat pumping device (7) connected to the permanent magnetic material. In this way the temperature of the permanent magnetic material is controlled and therefore the field of the magnet is controlled. Each of the permanent magnetic assemblies may be of disc shaped and each disc may have an inner ring (9) and outer ring (8). If the permanent magnetic material has a negative temperature coefficient then a higher temperature on the outer ring rather than the inner ring will result in a positive second order field shape. The present invention avoids the use of correction coils and/or shimming elements and also avoids the need for the use of high specification power supplies to control the magnetic field.

Description

TEMPERATURE CONTROL FOR PERMANENT MAGNET SYSTEM
The present invention relates to magnetic field control systems and in particular to systems suitable for use with Magnetic Resonance Imaging systems (MRI).
A magnetic field with a high degree of stability and homogeneity is essential for the successful applications of a number of analytical techniques and in particular for MRI.
Assemblies comprising large amounts of permanent magnetic material can be used for generating such fields. Deviations from the specified field, which can be caused by manufacturing errors or by the presence of large amounts of ferromagnetic material in the vicinity of the apparatus, must be corrected. This correction of the field can be done by correction coils, by permanent magnetic material, by small amounts of ferromagnetic material or by a combination of any of these techniques.
Most permanent magnetic materials with sufficient energy density to be useful for applications such as MRI are generally very sensitive to temperature variations. By sub-dividing the field generating assemblies into appropriate areas, each with their own temperature control, a fine control of the field is possible.
An aim of the present invention is to provide a temperature control system for permanent magnetic assemblies and use this system to control the strength and shape of the magnetic field of each assembly.
According to the present invention there is a magnetic field control system for a magnet comprising a yoke having at least one permanent magnetic assembly mounted thereon, wherein the permanent magnetic assembly is provided with a temperature sensor which is connected to an electronic control circuit which controls the flow of current to a thermoelectric heat pumping device connected to the permanent magnetic assembly thereby controlling the temperature of said permanent magnetic assembly.
According to an aspect of the present invention, the permanent magnetic assemblies are provided in opposite relationship with a space therebetween and are each temperature controlled.
According to a further aspect of the invention, the temperature of each of the permanent magnet assemblies is independently controlled by an electronic control circuit so that the magnitude and shape of the magnetic field can be changed for each permanent magnetic assembly.
An embodiment of the present invention will now be described with reference to the accompanying drawings, wherein:
Figure 1 which shows a cross-sectional view of a C-shaped magnet embodying the magnetic field control system in accordance with the present invention, and,
Figure 2 shows a permanent magnetic assembly which is disc-shaped which is sub-divided into an inner and outer ring.
Referring to Figure 1 there is shown a C-shaped magnet assembly comprising a yoke 1, two opposite facing magnetic pole pieces 2 each comprising an equal amount of permanent magnetic material 3 such as NdFeB material, and each constituting a permanent magnetic assembly. The assemblies are spaced from the yoke 1 by spacers 4. The temperature of the permanent magnetic material 3 is measured by temperature sensors 5 such as the thermistors or thermal resistive devices. The signal from the temperature sensors 5 is used as an input to a respective control circuit 6 which controls the temperature of each of the permanent magnetic material assemblies by controlling the current to thermoelectric heat pumping devices 7. If NdFeB material is used, then a rise in temperature of 1°C of the two opposing permanent magnetic assemblies will result in a change of the magnetic field in the centre of the apparatus by 0.1%. A difference in temperature between the two permanent magnetic assemblies of 2°C will create a gradient in the magnetic field in the order of 0.1% per m for a magnet with a typical dimensions of 1 m.
Referring to Figure 2, if the magnetic material is further sub-divided, it makes it possible to correct for more complicated field corrections. Figure 2 shows an example where each of the permanent magnetic assemblies is discshaped. The disc is sub-divided into an outer ring 8 of permanent magnetic material and an inner ring 9 of permanent magnetic material. If the permanent magnetic material has a negative temperature coefficient the outer ring 8 is at a higher temperature than the inner ring 9, a positive second order field shape will result.
By using the control system as described above, the present invention provides a means of field correction without the requirement of correction coils and/or a shimming element such as permanent magnets or ferromagnetic shims. Furthermore, the present invention provides a means for continuous field control without the need of power supplies of high specification.

Claims

1. A magnetic field control system for a magnet comprising a yoke having at least one permanent magnetic assembly mounted thereon, wherein the permanent magnetic assembly is provided with a temperature sensor which is connected to an electronic control circuit which controls the flow of current to a thermoelectric heat pumping device connected to the permanent magnetic assembly thereby controlling the temperature of said permanent magnetic assembly.
2. A magnetic field control system as claimed in claim 1, wherein the permanent magnetic assemblies are provided in opposite relationship with a space their between and are each temperature controlled.
3. A magnetic field control system as claimed in claim 1 or claim 2, wherein the temperature of each of the permanent magnet assemblies is independently controlled by an electronic control circuit so that the magnitude and shape of the magnetic field can be changed for each permanent magnetic assembly.
4. A magnetic field control system substantially as hereinbefore described with reference to the accompanying drawings.
PCT/GB1999/002779 1998-09-11 1999-08-23 Temperature control for permanent magnet system WO2000016117A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9819724.719980911 1998-09-11
GB9819724A GB2341448B (en) 1998-09-11 1998-09-11 Magnetic field control systems

Publications (1)

Publication Number Publication Date
WO2000016117A1 true WO2000016117A1 (en) 2000-03-23

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PCT/GB1999/002779 WO2000016117A1 (en) 1998-09-11 1999-08-23 Temperature control for permanent magnet system

Country Status (2)

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GB (1) GB2341448B (en)
WO (1) WO2000016117A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105044634A (en) * 2015-08-12 2015-11-11 上海健康医学院 Permanent magnet device for magnetic resonance analysis
US11709214B2 (en) 2019-08-21 2023-07-25 Bruker Switzerland Ag Temperature-control system for MR apparatuses with a permanent magnet arrangement

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2341449B (en) * 1998-09-11 2003-03-26 Oxford Magnet Tech Stabilisation of a magnetic field of a magnetic reasonance imaging apparatus
US6577125B2 (en) * 2000-12-18 2003-06-10 Halliburton Energy Services, Inc. Temperature compensated magnetic field apparatus for NMR measurements
EP1642156B1 (en) 2003-05-02 2020-03-04 Halliburton Energy Services, Inc. Systems and methods for nmr logging
GB2422201B (en) 2003-10-03 2007-06-06 Halliburton Energy Serv Inc System And Methods For T1-Based Logging
CN106227257B (en) * 2016-07-01 2018-08-21 沈阳东软医疗系统有限公司 A kind of temperaturecontrol sensor and protection circuit
NL2027307B1 (en) * 2021-01-13 2022-07-25 Vdl Enabling Tech Group B V A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly.

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JPH05212012A (en) * 1992-02-10 1993-08-24 Hitachi Medical Corp Magnetic resonance imaging system
US5320103A (en) * 1987-10-07 1994-06-14 Advanced Techtronics, Inc. Permanent magnet arrangement
JPH08215168A (en) * 1995-02-17 1996-08-27 Ge Yokogawa Medical Syst Ltd Magnetic field uniformity adjustment method and its device
US5652517A (en) * 1995-03-31 1997-07-29 Ge Yokogawa Medical Systems, Limited Magnet assembly for MRI apparatus
WO1999005531A2 (en) * 1997-07-23 1999-02-04 Odin Technologies Ltd. Permanent magnet assemblies for use in medical applications

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JPH03109042A (en) * 1989-09-22 1991-05-09 Hitachi Medical Corp Static magnetic field generation equipment for nuclear magnetic resonance imaging apparatus
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JP3446973B2 (en) * 1994-06-09 2003-09-16 株式会社日立メディコ Magnetic resonance imaging equipment
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US5320103A (en) * 1987-10-07 1994-06-14 Advanced Techtronics, Inc. Permanent magnet arrangement
JPH05212012A (en) * 1992-02-10 1993-08-24 Hitachi Medical Corp Magnetic resonance imaging system
JPH08215168A (en) * 1995-02-17 1996-08-27 Ge Yokogawa Medical Syst Ltd Magnetic field uniformity adjustment method and its device
US5652517A (en) * 1995-03-31 1997-07-29 Ge Yokogawa Medical Systems, Limited Magnet assembly for MRI apparatus
WO1999005531A2 (en) * 1997-07-23 1999-02-04 Odin Technologies Ltd. Permanent magnet assemblies for use in medical applications

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105044634A (en) * 2015-08-12 2015-11-11 上海健康医学院 Permanent magnet device for magnetic resonance analysis
CN105044634B (en) * 2015-08-12 2018-01-19 上海健康医学院 Magnetic resonance analysis permanent magnet device
US11709214B2 (en) 2019-08-21 2023-07-25 Bruker Switzerland Ag Temperature-control system for MR apparatuses with a permanent magnet arrangement

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Publication number Publication date
GB2341448B (en) 2003-08-20
GB2341448A (en) 2000-03-15
GB9819724D0 (en) 1998-11-04

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