GB2341448A - Temperature dependent magnetic field control system - Google Patents
Temperature dependent magnetic field control system Download PDFInfo
- Publication number
- GB2341448A GB2341448A GB9819724A GB9819724A GB2341448A GB 2341448 A GB2341448 A GB 2341448A GB 9819724 A GB9819724 A GB 9819724A GB 9819724 A GB9819724 A GB 9819724A GB 2341448 A GB2341448 A GB 2341448A
- Authority
- GB
- United Kingdom
- Prior art keywords
- magnetic field
- temperature
- permanent magnetic
- control system
- permanent
- Prior art date
- Legal status (The legal status 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 status listed.)
- Granted
Links
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
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Magnetic Resonance Imaging Apparatus (AREA)
Abstract
The magnetic field of an MRI system which uses permanent magnets is controlled by regulating the temperature of the magnets. Permanent magnet assemblies 3 include temperature sensors 5 such as thermistors or thermal resistive devices, which provide signals to control circuits 6. These then control the current to thermoelectric heat pumping devices 7, which regulate the temperature of the permanent magnet structures, and thus modify the magnetic field produced. The magnets may be subdivided into regions of varying temperature coefficients, allowing more complicated field corrections.
Description
2341448
MAGNETIC FIELD CONTROL 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
2 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 I 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 discshaped 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 I 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 3 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 PC 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 2T 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 finther subdivided, it makes it possible to correct for more complicated field corrections. Figure 2 shows an example where each of the permanent magnetic assemblies is disc-shaped. 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.
4
Claims (4)
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 I 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.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9819724A GB2341448B (en) | 1998-09-11 | 1998-09-11 | Magnetic field control systems |
PCT/GB1999/002779 WO2000016117A1 (en) | 1998-09-11 | 1999-08-23 | Temperature control for permanent magnet system |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9819724A GB2341448B (en) | 1998-09-11 | 1998-09-11 | Magnetic field control systems |
Publications (3)
Publication Number | Publication Date |
---|---|
GB9819724D0 GB9819724D0 (en) | 1998-11-04 |
GB2341448A true GB2341448A (en) | 2000-03-15 |
GB2341448B GB2341448B (en) | 2003-08-20 |
Family
ID=10838631
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9819724A Expired - Fee Related GB2341448B (en) | 1998-09-11 | 1998-09-11 | Magnetic field control systems |
Country Status (2)
Country | Link |
---|---|
GB (1) | GB2341448B (en) |
WO (1) | WO2000016117A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6566880B1 (en) * | 1998-09-11 | 2003-05-20 | Oxford Magnet Technology Limited | Stabilization of a magnetic field of a magnetic resonance imaging apparatus |
US6577125B2 (en) * | 2000-12-18 | 2003-06-10 | Halliburton Energy Services, Inc. | Temperature compensated magnetic field apparatus for NMR measurements |
US7733086B2 (en) | 2003-05-02 | 2010-06-08 | Halliburton Energy Services, Inc. | Systems and methods for deep-looking NMR logging |
US7755354B2 (en) | 2003-10-03 | 2010-07-13 | Halliburton Energy Services, Inc. | System and methods for T1-based logging |
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. |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN105044634B (en) * | 2015-08-12 | 2018-01-19 | 上海健康医学院 | Magnetic resonance analysis permanent magnet device |
CN106227257B (en) * | 2016-07-01 | 2018-08-21 | 沈阳东软医疗***有限公司 | A kind of temperaturecontrol sensor and protection circuit |
DE102019212508A1 (en) | 2019-08-21 | 2021-02-25 | Bruker Switzerland Ag | Temperature control system for MR devices with permanent magnet arrangement |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH03109042A (en) * | 1989-09-22 | 1991-05-09 | Hitachi Medical Corp | Static magnetic field generation equipment for nuclear magnetic resonance imaging apparatus |
JPH04357936A (en) * | 1991-06-04 | 1992-12-10 | Hitachi Medical Corp | Magnetic resonance imaging device |
JPH07327958A (en) * | 1994-06-09 | 1995-12-19 | Hitachi Medical Corp | Magnetic resonance imaging apparatus |
US5652517A (en) * | 1995-03-31 | 1997-07-29 | Ge Yokogawa Medical Systems, Limited | Magnet assembly for MRI apparatus |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2566410B2 (en) * | 1987-05-11 | 1996-12-25 | 株式会社 日立メデイコ | Nuclear magnetic resonance imaging device |
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 |
JPH09299351A (en) * | 1996-05-16 | 1997-11-25 | Hitachi Medical Corp | Static magnetic field generating device for magnetic resonance imaging device |
US5900793A (en) * | 1997-07-23 | 1999-05-04 | Odin Technologies Ltd | Permanent magnet assemblies for use in medical applications |
JP4203615B2 (en) * | 1998-06-19 | 2009-01-07 | 日立金属株式会社 | Magnetic field generator for MRI |
-
1998
- 1998-09-11 GB GB9819724A patent/GB2341448B/en not_active Expired - Fee Related
-
1999
- 1999-08-23 WO PCT/GB1999/002779 patent/WO2000016117A1/en not_active Application Discontinuation
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH03109042A (en) * | 1989-09-22 | 1991-05-09 | Hitachi Medical Corp | Static magnetic field generation equipment for nuclear magnetic resonance imaging apparatus |
JPH04357936A (en) * | 1991-06-04 | 1992-12-10 | Hitachi Medical Corp | Magnetic resonance imaging device |
JPH07327958A (en) * | 1994-06-09 | 1995-12-19 | Hitachi Medical Corp | Magnetic resonance imaging apparatus |
US5652517A (en) * | 1995-03-31 | 1997-07-29 | Ge Yokogawa Medical Systems, Limited | Magnet assembly for MRI apparatus |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6566880B1 (en) * | 1998-09-11 | 2003-05-20 | Oxford Magnet Technology Limited | Stabilization of a magnetic field of a magnetic resonance imaging apparatus |
US6577125B2 (en) * | 2000-12-18 | 2003-06-10 | Halliburton Energy Services, Inc. | Temperature compensated magnetic field apparatus for NMR measurements |
US7733086B2 (en) | 2003-05-02 | 2010-06-08 | Halliburton Energy Services, Inc. | Systems and methods for deep-looking NMR logging |
US7755354B2 (en) | 2003-10-03 | 2010-07-13 | Halliburton Energy Services, Inc. | System and methods for T1-based logging |
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. |
Also Published As
Publication number | Publication date |
---|---|
GB2341448B (en) | 2003-08-20 |
GB9819724D0 (en) | 1998-11-04 |
WO2000016117A1 (en) | 2000-03-23 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20060911 |