CN116256680B - Passive shimming structure and method of Halbach magnet for magnetic resonance - Google Patents
Passive shimming structure and method of Halbach magnet for magnetic resonance Download PDFInfo
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- CN116256680B CN116256680B CN202310546471.1A CN202310546471A CN116256680B CN 116256680 B CN116256680 B CN 116256680B CN 202310546471 A CN202310546471 A CN 202310546471A CN 116256680 B CN116256680 B CN 116256680B
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- 238000000034 method Methods 0.000 title claims abstract description 26
- 230000005415 magnetization Effects 0.000 claims abstract description 11
- 238000005259 measurement Methods 0.000 claims description 22
- 238000000926 separation method Methods 0.000 claims description 7
- 238000005457 optimization Methods 0.000 claims description 3
- 230000035699 permeability Effects 0.000 claims description 3
- 238000004458 analytical method Methods 0.000 abstract description 8
- 238000012545 processing Methods 0.000 abstract description 3
- 238000005481 NMR spectroscopy Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 4
- 230000005389 magnetism Effects 0.000 description 4
- 238000011160 research Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 2
- 238000012565 NMR experiment Methods 0.000 description 1
- 238000007792 addition Methods 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000002595 magnetic resonance imaging Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000000655 nuclear magnetic resonance spectrum Methods 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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- 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
- G01R33/387—Compensation of inhomogeneities
- G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/02—Permanent magnets [PM]
- H01F7/0273—Magnetic circuits with PM for magnetic field generation
- H01F7/0278—Magnetic circuits with PM for magnetic field generation for generating uniform fields, focusing, deflecting electrically charged particles
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
- Y02A90/30—Assessment of water resources
Abstract
The invention discloses a passive shimming structure of a Halbach magnet for magnetic resonance, which comprises shimming magnetic sheets, a shimming inner shell and a nonmagnetic shimming plate, wherein the shimming inner shell is arranged in the Halbach magnet, the nonmagnetic shimming plate is arranged in the shimming inner shell, and the shimming magnetic sheets are arranged on the nonmagnetic shimming plate. The passive shimming structure has the advantages of simple processing, low cost, convenient disassembly and assembly and the like, and can realize rapid passive shimming of the Halbach magnet. The invention also discloses a passive shimming method of the Halbach magnet for magnetic resonance, which is based on the target magnetic field, does not need to carry out harmonic analysis on the magnetic field, and can avoid the problem that the magnetization component is difficult to determine in the passive shimming method based on the harmonic analysis, thereby improving the passive shimming efficiency.
Description
Technical Field
The invention relates to the technical field of magnetic resonance, in particular to a passive shimming structure of a Halbach magnet for magnetic resonance, and also relates to a passive shimming method of the Halbach magnet for magnetic resonance.
Background
Nuclear magnetic resonance is widely applied to a plurality of fields such as physics, chemistry, life sciences and the like. Depending on the operating principle and the field of application, magnetic resonance instrument systems can be classified into nuclear magnetic resonance spectroscopy (NMR) and Magnetic Resonance Imaging (MRI), where magnets are one of the most important components of the magnetic resonance instrument system. Compared with the common superconducting magnet with large volume and high maintenance cost, the permanent magnet has the advantages of small volume and low use cost, so that the permanent magnet has great development potential in the research and application fields of a low-cost portable nuclear magnetic resonance system.
The Halbach magnet is one of permanent magnets frequently used in a magnetic resonance system, has the advantages of light weight, high field strength and small stray field outside the magnet, and has wide application prospect in the field of portable nuclear magnetic resonance instrument research. However, the initial magnetic field uniformity of the as-manufactured Halbach magnets is often poor, typically less than 10 -4 The magnitude is difficult to directly meet the practical application requirements of the magnetic resonance instrument. Thus, good initial magnetic field uniformity is the basis for application of Halbach magnets to magnetic resonance instruments, and improving initial magnetic field uniformity is a constantly sought-after goal in Halbach magnet design. On the basis, the magnetic field uniformity of the Halbach magnet can be improved to the extent of carrying out NMR experiments through a proper shimming flow. To a certain extent, shimming methods and techniques to improve the homogeneity of the magnetic field are critical in determining whether Halbach magnets can be applied to magnetic resonance apparatus.
The performance of the magnetic resonance instrument is greatly dependent on the magnetic field uniformity, especially in the field of NMR research, the higher the magnetic field uniformity is, the higher the signal-to-noise ratio and the resolution of the NMR spectrum peak signals obtained by the instrument are, so that the NMR instrument obtains higher performance indexes. Therefore, in order to expand the application range of the Halbach magnet in the nuclear magnetic resonance field, shimming is necessary for the Halbach magnet. Generally shimming can be divided into active shimming and passive shimming. The active shimming is to generate a specific space magnetic field through a plurality of groups of energized coils to compensate uneven components in a basic magnetic field, so that the shimming purpose is achieved. However, for Halbach magnets with poor basic magnetic fields, the problem of large coil heating values occurs with direct active shimming, and the shimming effect is also very limited. And passive shimming can be used for magnets with poor magnetic field uniformity and lays a foundation for active shimming. Passive shimming is therefore an indispensable key step in Halbach magnet design.
The passive shimming method used by the Halbach magnet at present is mainly based on harmonic analysis of a magnetic field, a plurality of magnetic blocks are formed into a special array, and a specific harmonic magnetic field is generated through superposition to counteract uneven harmonic components in a basic magnetic field, so that the shimming purpose is realized. However, this method is generally complex and time-consuming to calculate, and has a problem that the magnetization component is difficult to determine, which results in an influence on the efficiency of passive shimming.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a passive shimming structure of a Halbach magnet for magnetic resonance and a passive shimming method of the Halbach magnet for magnetic resonance. The passive shimming structure has the advantages of simple processing, low cost, convenient disassembly and assembly and the like, and can realize rapid passive shimming of the Halbach magnet. Compared with the conventional passive shimming method based on harmonic analysis of the Halbach magnet, the passive shimming method is based on the target magnetic field, does not need to carry out harmonic analysis on the magnetic field, and can avoid the problem that magnetization components are difficult to determine in the passive shimming method based on harmonic analysis, so that the passive shimming efficiency is improved.
In order to solve the technical problems, the invention adopts the following technical scheme:
the passive shimming structure of the Halbach magnet for magnetic resonance comprises shimming magnetic sheets, a shimming inner shell and a nonmagnetic shimming plate, wherein the shimming inner shell is arranged in the Halbach magnet, the nonmagnetic shimming plate is arranged in the shimming inner shell, and the shimming magnetic sheets are arranged on the nonmagnetic shimming plate.
As described above, the shimming inner shell is cylindrical, the end of the shimming inner shell is provided with a connecting flange, and the connecting flange is fixed on the end face of the Halbach magnet.
The nonmagnetic shim plates are two and are symmetrically arranged parallel to the central axis of the shim inner shell as described above.
The nonmagnetic shimming plate is provided with the fixing part extending out of the shimming inner shell, and the fixing part is fixed on the connecting flange.
As described above, concentric circles with different diameters and rays with different direction angles taking the center as the starting point are carved on the centers of the nonmagnetic shimming plates, and the intersection point of the rays and the concentric circles is the patch position.
A passive shimming method of Halbach magnets for magnetic resonance, comprising the steps of:
step 1, constructing a magnetic field distribution measurement system;
step 2, determining a target area;
step 3, determining a magnetic field measurement point of the target area;
step 4, measuring each magnetic field measuring point through a magnetic field distribution measuring system so as to obtain the magnetic field distribution condition of the Halbach magnet;
step 5, calculating an axial magnetic field generated by the shimming magnetic sheet in space;
step 6, establishing an optimization model F to obtain the number of shimming magnetic sheets at the patch position;
，
wherein ,ifor a magnetic field measurement point on the target area,jis a patch position on the nonmagnetic shim plate,X j is the patch positionjThe number of the shimming magnetic sheets is set at the position,mfor the total number of magnetic field measurement points,nfor the total number of patch positions,B i0 for measuring points of magnetic fieldsiThe initial magnetic field value of the location,B t for the desired target magnetic field magnitude,ΔB ji to be at the patch positionjAfter a piece of shimming magnetic sheet is placed at the position, the magnetic field measuring pointiThe magnetic field magnitude change value of the position along the main magnetic field direction of the Halbach magnet is the same as the axial magnetic field direction of the shimming magnetic sheet.
A passive shimming method of Halbach magnets for magnetic resonance, further comprising step 7:
and (5) measuring the magnetic field of each magnetic field measuring point along the main magnetic field direction of the Halbach magnet, calculating the magnetic field uniformity, and returning to the step (5) if the magnetic field uniformity is larger than a set threshold value.
The magnetic field uniformity as described above is based on the following formula:
，
wherein ,Bmax and Bmin The measured magnetic field measurement points are the maximum and minimum values, respectively, of the magnetic field along the main magnetic field direction of the Halbach magnet.
Axial magnetic field in step 5 as described aboveCalculated based on the following formula:
，
wherein ,hrepresenting the thickness parameters of the shim plate,dhis the derivative of the thickness parameter,μ 0 indicating the magnetic permeability of the vacuum,Mindicating the magnetization of the shim plate,Lhalf of the thickness of the circular shimming magnetic sheet,athe radius of the circular shimming magnetic sheet,ρandzrepresents the coordinate parameter of any point in a cylindrical coordinate system established by taking the center of the shimming magnetic sheet as the origin,KandErespectively represent a first kind of complete ellipseThe round integral and the second type of full elliptic integral,
，
，
where n represents the sum number ∈ -! Representing a factorial.
Step 3 as described above comprises the steps of:
the target area is spherical, the target area is divided into a plurality of horizontal layers according to a set interval latitude, and separation circles are arranged between adjacent horizontal layers; dividing each separation circle equally by the defined radius of the set longitude interval, and taking the outer end point of each defined radius as a magnetic field measuring point.
Compared with the prior art, the invention has the following beneficial effects:
the method is accurate and effective, provides a new thought for passive shimming of the Halbach magnet, and provides key technical support for NMR research of the Halbach magnet. The passive shimming structure has the advantages of simple processing, low cost, convenient disassembly and assembly and the like, and can realize the rapid passive shimming of the Halbach magnet. On the basis, the passive shimming method provided by the invention is based on the target magnetic field, harmonic analysis is not required to be carried out on the magnetic field, the problem that the magnetization component is difficult to determine in the passive shimming method based on the harmonic analysis can be avoided, and the passive shimming efficiency can be improved.
Drawings
Figure 1 is a schematic structural diagram of a passive shimming structure of a Halbach magnet for magnetic resonance,
1-Halbach magnet; 2-shimming inner shell; 3-nonmagnetic shimming plates; 4-shimming magnetic sheets; b (B) 0 -main magnetic field direction of Halbach.
Fig. 2 is a schematic structural diagram of a nonmagnetic shim plate.
Fig. 3 is a schematic diagram of the installation of the shim inner shell and the nonmagnetic shim plate.
Figure 4 is a flow chart of a passive shimming method for a Halbach magnet for magnetic resonance.
Fig. 5 is a schematic diagram of the division of the target area.
Detailed Description
The present invention will be further described in detail below in conjunction with the following examples, for the purpose of facilitating understanding and practicing the present invention by those of ordinary skill in the art, it being understood that the examples described herein are for the purpose of illustration and explanation only and are not intended to limit the invention.
As shown in fig. 1 to 3, a passive shimming structure of a Halbach magnet for magnetic resonance includes: a shimming inner shell 2, two non-magnetic shimming plates 3 and a plurality of shimming magnetic sheets 4. Wherein, shimming inner shell 2 is cylindric, shimming inner shell 2 installs in Halbach magnet, in this embodiment, the tip of shimming inner shell 2 is provided with flange, flange is fixed at the terminal surface of Halbach magnet, two no magnetism shimming boards 3 are installed in shimming inner shell 2, 2 no magnetism shimming boards 3 are on a parallel with the central axis symmetry setting of shimming inner shell 2, in this embodiment, no magnetism shimming boards 3 are provided with the fixed part that extends shimming inner shell 2, the fixed part is fixed on flange, shimming magnetic sheet 4 is installed on no magnetism shimming board 3 according to the demand.
In this embodiment, the nonmagnetic shimming plate is a shimming aluminum plate.
The nonmagnetic shimming plate 3 can be detached, so that the shimming magnetic sheet 4 is more convenient to install. Concentric circles with different diameters and rays with different direction angles taking the center of a circle as a starting point are carved on the nonmagnetic shimming plate 3, the included angle between adjacent rays is 30 degrees, each concentric circle has 12 intersection points with each ray, and the intersection points are reserved patch positions of the shimming magnetic sheet 4.
A passive shimming method of a Halbach magnet for magnetic resonance, which utilizes the passive shimming structure of the Halbach magnet for magnetic resonance, comprises the following steps:
step 1, constructing a magnetic field distribution measurement system, which comprises a triaxial slipway and a high-precision digital Gaussian meter;
and 2, determining a target area. The target area is a spherical area positioned in the magnetic field center of the Halbach magnet, and the diameter of the spherical area is determined according to the requirement;
and 3, dividing the target area and determining the position of the magnetic field measurement point. Dividing a target area into 14 horizontal layers according to the interval latitude of pi/14, wherein separation circles are arranged between adjacent horizontal layers, so that 13 coaxial separation circles are formed; dividing each separation circle into 12 equal parts according to 12 definition radiuses with pi/12 longitude intervals, and taking the outer end point of each definition radius as a magnetic field measuring point, wherein 156 magnetic field measuring points exist;
and 4, measuring the magnetic field distribution. Measuring 156 magnetic field measurement points by using the constructed magnetic field distribution measurement system, so as to obtain the magnetic field distribution condition of the Halbach magnet;
and 5, screening the shimming magnetic sheet 4 and calculating the characteristics of the shimming magnetic sheet. Selecting shim magnetic sheets 4 with proper diameters and thicknesses according to requirements, and calculating an axial magnetic field generated by the shim magnetic sheets 4 in space according to a formula;
in this embodiment, the axial magnetic field of the shim plate 4 is in the same direction as the main magnetic field of the Halbach magnet, so that only the axial magnetic field generated by the shim plate 4 is considered in calculating its characteristics. Specifically, for a radius ofaThickness of is2LThe circular shimming magnetic sheet is arranged at any point of cylindrical coordinates established by taking the center of the shimming magnetic sheet as an originρ, z, φ) The magnitude of the axial magnetic field generatedB z Can be expressed as the following formula:
（1）
wherein ,hrepresenting thickness parameters of the shim for solving the integral,dhis the derivative of the thickness parameter,μ 0 represents the vacuum permeability, is a constant,Mrepresenting the magnetization of the shim, is a constant, related to the remanence of the shim,ρandzrepresenting any point in a cylindrical coordinate system established by taking the center of a shimming magnetic sheet as an originρ, z, φ) Is used for the coordinate parameters of the (c),KandErepresenting the first and second types of full elliptic integral, respectively, can be expressed as:
，
，
where n represents the sum number ∈ -! It should be noted that, for the shim pieces of the same specification, the magnetization M of the shim piece of the specification can be calculated by measuring the magnetic field variation value of the corresponding magnetic field measurement point before and after placing a shim piece at the set patch position on the nonmagnetic shim plate 3, and for the shim pieces of the same specification, the magnetization M is the same, so that only the magnetic field variation value of one magnetic field measurement point along the main magnetic field direction of the Halbach magnet needs to be measuredΔ B ji (and axial magnetic field)B z Is equal), the coordinate parameters of the magnetic field measurement points are known. The magnetization M can then be solved according to the above formula. After the magnetization intensity M is obtained, the axial magnetic field generated by the standard shimming magnetic sheet in space can be obtained.
And 6, calculating the patch type of the shimming magnetic sheet 4. Based on the magnetic field distribution of the Halbach magnet measured in step 4 and the axial magnetic field generated in space by the shim calculated in step 5B z The patch mode of the shimming magnetic sheet is calculated through a passive shimming algorithm, and magnetic field deviation among magnetic field measurement points in the magnetic field of the Halbach magnet is compensated, so that shimming is realized;
the passive shimming algorithm calculates the paster mode of the shimming magnetic sheet based on the following steps:
in this embodiment, the difference of the magnetic field magnitudes between the magnetic field measurement points after the shimming magnetic sheet is set at the patch position is used as a constraint condition, and an optimization model F is established:
（2）
wherein ,ifor a magnetic field measurement point on the target area,jis free ofOne patch location on the magnetic shim plate,X j is the patch positionjThe number of the shimming magnetic sheets is set at the position,mfor the total number of magnetic field measurement points,nfor the total number of patch positions,B i0 for measuring points of magnetic fieldsiThe initial magnetic field value of the location,B t for the desired target magnetic field magnitude,ΔB ji to be at the patch positionjAfter a piece of shimming magnetic sheet is placed at the position, the magnetic field measuring pointiThe magnetic field magnitude change value of the position along the main magnetic field direction of the Halbach magnet is the same as the axial magnetic field direction of the shimming magnetic sheet. And (3) optimizing the number of the shimming magnetic sheets at the patch positions to obtain the patch mode of the shimming magnetic sheets.
And 7, verifying the magnetic field uniformity. Re-measuring the magnetic field of each magnetic field measuring point along the main magnetic field direction of the Halbach magnet, verifying whether the magnetic field uniformity is smaller than or equal to a set threshold value, if so, completing passive shimming, and if so, returning to the step 5;
in this embodiment, the method for calculating the magnetic field uniformity is as follows, wherein ,Bmax and Bmin The maximum and minimum values, respectively, of the magnetic field along the main magnetic field direction of the Halbach magnet at the measured magnetic field measurement point.
It should be noted that the specific embodiments described in this application are merely illustrative of the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or its scope as defined in the accompanying claims.
Claims (5)
1. The passive shimming method of a Halbach magnet for magnetic resonance, utilize a passive shimming structure of Halbach magnet for magnetic resonance, the above-mentioned passive shimming structure includes shimming magnetic sheet, shimming inner shell and non-magnetic shimming board, the shimming inner shell is installed in Halbach magnet, the non-magnetic shimming board is installed in shimming inner shell, the shimming magnetic sheet is set up on the non-magnetic shimming board, characterized by, comprising the following steps:
step 1, constructing a magnetic field distribution measurement system;
step 2, determining a target area;
step 3, determining a magnetic field measurement point of the target area;
step 4, measuring each magnetic field measuring point through a magnetic field distribution measuring system so as to obtain the magnetic field distribution condition of the Halbach magnet;
step 5, calculating an axial magnetic field generated by the shimming magnetic sheet in space;
step 6, establishing an optimization model F to obtain the number of shimming magnetic sheets at the patch position;
，
wherein ,ifor a magnetic field measurement point on the target area,jis a patch position on the nonmagnetic shim plate,X j is the patch positionjThe number of the shimming magnetic sheets is set at the position,mfor the total number of magnetic field measurement points,nfor the total number of patch positions,B i0 for measuring points of magnetic fieldsiThe initial magnetic field value of the location,B t for the desired target magnetic field magnitude,ΔB ji to be at the patch positionjAfter a piece of shimming magnetic sheet is placed at the position, the magnetic field measuring pointiThe magnetic field magnitude change value of the position along the main magnetic field direction of the Halbach magnet is the same as the axial magnetic field direction of the shimming magnetic sheet.
2. A passive shimming method for a Halbach magnet for magnetic resonance according to claim 1, further comprising the step 7 of:
and (5) measuring the magnetic field of each magnetic field measuring point along the main magnetic field direction of the Halbach magnet, calculating the magnetic field uniformity, and returning to the step (5) if the magnetic field uniformity is larger than a set threshold value.
3. A passive shimming method of Halbach magnets for magnetic resonance according to claim 2, characterized in that the magnetic field homogeneity is based on the following formula:
，
wherein ,Bmax and Bmin The measured magnetic field measurement points are the maximum and minimum values, respectively, of the magnetic field along the main magnetic field direction of the Halbach magnet.
4. A passive shimming method of Halbach magnets for magnetic resonance according to claim 2, characterized in that the axial magnetic field in step 5Calculated based on the following formula:
，
wherein ,hrepresenting the thickness parameters of the shim plate,dhis the derivative of the thickness parameter,μ 0 indicating the magnetic permeability of the vacuum,Mindicating the magnetization of the shim plate,Lhalf of the thickness of the circular shimming magnetic sheet,athe radius of the circular shimming magnetic sheet,ρandzrepresents the coordinate parameter of any point in a cylindrical coordinate system established by taking the center of the shimming magnetic sheet as the origin,KandErepresenting the first type of full elliptic integral and the second type of full elliptic integral respectively,
，
，
where n represents the sum number ∈ -! Representing a factorial.
5. A passive shimming method of Halbach magnets for magnetic resonance according to claim 2, characterized in that the step 3 comprises the steps of:
the target area is spherical, the target area is divided into a plurality of horizontal layers according to a set interval latitude, and separation circles are arranged between adjacent horizontal layers; dividing each separation circle equally by the defined radius of the set longitude interval, and taking the outer end point of each defined radius as a magnetic field measuring point.
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| US5418462A (en) * | 1994-05-02 | 1995-05-23 | Applied Superconetics, Inc. | Method for determining shim placement on tubular magnet |
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| CN110706877A (en) * | 2019-09-23 | 2020-01-17 | 东南大学 | Low-cost miniature Halbach magnet with adjustable magnetic field uniformity |
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| CN115831570A (en) * | 2021-09-16 | 2023-03-21 | 中国科学院苏州生物医学工程技术研究所 | Shimming method of Halbach-configuration magnet |
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| WO2016136465A1 (en) * | 2015-02-25 | 2016-09-01 | 株式会社日立製作所 | Magnetic resonance imaging device, static magnetic field homogeneity adjustment method, program, and computer |
| US10527565B2 (en) * | 2015-07-29 | 2020-01-07 | Chevron U.S.A. Inc. | NMR sensor for analyzing core or fluid samples from a subsurface formation |
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| US5418462A (en) * | 1994-05-02 | 1995-05-23 | Applied Superconetics, Inc. | Method for determining shim placement on tubular magnet |
| CN201378203Y (en) * | 2009-04-01 | 2010-01-06 | 沈阳东软波谱磁共振技术有限公司 | Shimming pore plate magnetic field debugging system |
| CN110706877A (en) * | 2019-09-23 | 2020-01-17 | 东南大学 | Low-cost miniature Halbach magnet with adjustable magnetic field uniformity |
| WO2022120502A1 (en) * | 2020-12-11 | 2022-06-16 | Nanalysis Corp. | Pole piece |
| CN115831570A (en) * | 2021-09-16 | 2023-03-21 | 中国科学院苏州生物医学工程技术研究所 | Shimming method of Halbach-configuration magnet |
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| Magnetic Field Correction Using Magnetized Shims;RASTISLAV VADOVI;IEEE TRANSACTlONS ON MAGNETICS;第第25卷卷(第第4期期);3133-3139 * |
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