CN110501663A - A kind of ultralow field biplane nuclear magnetic resonance often leads main magnet and its construction method - Google Patents
A kind of ultralow field biplane nuclear magnetic resonance often leads main magnet and its construction method Download PDFInfo
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- CN110501663A CN110501663A CN201910904021.9A CN201910904021A CN110501663A CN 110501663 A CN110501663 A CN 110501663A CN 201910904021 A CN201910904021 A CN 201910904021A CN 110501663 A CN110501663 A CN 110501663A
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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
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
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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
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3858—Manufacture and installation of gradient coils, means for providing mechanical support to parts of the gradient-coil assembly
Abstract
The invention discloses a kind of ultralow field biplane nuclear magnetic resonance often to lead main magnet and its construction method, one group of octagon coil is symmetrical arranged by axis direction, one group of octagon coil includes the big octagon coil of outer ring and the small octagon coil of inner ring, and small octagon coil is arranged in the width range of big octagon coil, so that the small octagon coil and big octagon coil in one group of octagon coil are in the same plane.The present invention can obtain bigger magnetic pole pitch under more inexpensive, and make magnetic fluctuation bigger less than the field homogeneity region of 100ppm.
Description
Technical field
The present invention relates to magnetic resonance magnet design fields, and in particular to a kind of coil and design for generating six rank uniform magnetic fields
Method.
Background technique
Usually there are three types of technical solutions for magnetic resonance main magnet, the first is permanent-magnet, and second is superconducting magnet, third
Kind is resistive magnet.Permanent-magnet and superconducting magnet technology are complicated, and volume and weight is all very huge, and resistive magnet is strong in magnetic field
Spending not high occasion can do lighter, have use in many scientific experiments.The magnetic resonance equipment master of existing a large amount of commercializations
Will be based on middle High-Field, magnetic field strength is higher, and the signal-to-noise ratio of image is higher, this be why the original that High-Field is all pursued by current producer
Cause.But the magnetic field strength the high also stronger in the presence of interfering with magnetizing field the superposition of main field therewith, causes image fuzzy, is
This influence is eliminated, needs to introduce the powerful shim coil of multiple groups, so that magnetic resonance magnet technology is complicated.On the other hand existing
There is the narrow space of magnetic resonance equipment, people, which is typically only capable to lie in, enters magnet on a mobile bed, narrow space will cause
Patient constrains, and causes uncomfortable.Furthermore metal parts can generate very big influence to the radio frequency of magnetic resonance and gradient component, lead
Cause can not be imaged, and have to avoid during magnetic resonance imaging.
With the development of electronic technology, make it possible the signal that can not be obtained under low field of early stage now, in recent years
Become the new hot spot of Instrument Development by the ultra-low field magnetic resonance technology that Harvard University dominates.In order to design human body magnetic resonance imaging
Meet magnetic fluctuation in the region 0.4m and be no more than the main magnet that 100ppm is required, team, Harvard University uses full-size 2.2m high
Four Circumferential coils structure of biplane.Biplane construction can maximize expansion magnetic pole pitch, but under identical height limitation,
Making toroidal coil structure can not maximally utilize the homogeneous area between pole plate.
Application No. is a kind of 201410071472.6 octagon tricyclic field coils, and it is real to also use octagon configuration
The existing six rank uniformitys, but it is not four loop constructions, and there is one group of coil in the position of center homogeneous area, cannot function as human body
The magnetic resonance magnet of sitting formula.The method that embodiment refers to is also to establish equation solution under the conditions of fixed structure.
Application No. is the round wires that a kind of 201410573456.7 big homogeneity range three-dimensional magnetic coil and its manufacturing method use
Configuration is enclosed, and is more than in addition four sets of coils are also equipped with one group of shim coil as compensation, structure is extremely complex, and is not suitable for
The magnetic resonance magnet of human body sitting formula.
Summary of the invention
The present invention is to propose that a kind of ultralow field biplane nuclear-magnetism is total to solve above-mentioned the shortcomings of the prior art place
Vibration often leads main magnet and its construction method, to obtain bigger magnet spaces under more inexpensive, and magnetic field is met
The region of uniformity requirement is bigger than Circumferential coils structure.
The present invention adopts the following technical scheme that in order to solve the technical problem
The characteristics of a kind of ultralow field biplane nuclear magnetic resonance of the present invention often leads main magnet is: being symmetrical arranged one in the axial direction
Group octagon coil, one group of octagon coil includes the big octagon coil of outer ring and the small octagon of inner ring
Coil, and the small octagon coil is arranged in the width range of the big octagon coil, so that described one
Small octagon coil and big octagon coil in group octagon coil is in the same plane；
The center for enabling the big octagon coil is away from the ratio with apothemIn the small octagon coil
The heart is away from the ratio with apothemAnd the ratio of the apothem between big octagon coil and small octagon coil is
Enable the big octagon coil identical with the current direction of small octagon coil, and big octagon coil and
Ampere-turn between small octagon coil accumulates ratio
The characteristics of ultralow field biplane nuclear magnetic resonance of the present invention often leads the construction method of main magnet is by following step
It is rapid to carry out:
Step 1, the model equation group that four loop construction of octagon is established using formula (1):
In formula (1), β1For big octagon coil center away from the ratio with apothem, β2For in small octagon coil
The heart is away from the ratio with apothem, and the ratio of apothem of the q between big octagon coil and small octagon coil, i is big
Octagon coil and small octagon coil ampere-turn product ratio, A are structure control parameter；
Step 2, definition cyclic variable are n, and initialize n=1；
The structure control parameter A that step 3, setting n-th recyclen, and formula (1) is solved, obtain corresponding construction control
Parameter A processednStructural parameters (β under control1,β2,q,i)n；
Step 4, the apothem or distance of shaft centers that one big octagon coil is determined according to structure design requirement, and according to
Corresponding structural parameters (β1,β2,q,i)nThe distance of shaft centers and apothem of its excess-three octagon coil is calculated, to sentence
Determine structural parameters (β1,β2,q,i)nWhether structure design requirement is met；If meeting, with the corresponding construction controling parameter AnControl
Structural parameters (β under system1,β2,q,i)nThe nuclear magnetic resonance for obtaining meeting structure design requirement often leads main magnet structure, otherwise, will
After n+1 is assigned to n, return step 3.
The characteristics of construction method of the present invention, is, as A < 0, often leads master using formula (1) obtained nuclear magnetic resonance
In magnet structure, the distance of shaft centers of big octagon coil is greater than the distance of shaft centers of small octagon coil；As A=0, utilize formula (1)
Obtained nuclear magnetic resonance is often led in main magnet structure, and the apothem of four octagon coils is all the same；As A > 0, utilize
Formula (1) obtained nuclear magnetic resonance is often led in main magnet structure, and the distance of shaft centers of big octagon coil is less than small octagon coil
Distance of shaft centers.
Compared with prior art, the beneficial effects of the present invention are:
1, the present invention proposes the general solution model equation of four loop construction of octagon using octagon as basic configuration
Group and design method can design the coil distributed architecture close to structural requirement in the value of adjustment structure parameter A, to mention
High design efficiency and flexibility.
2, a kind of biplane nuclear magnetic resonance proposed by the present invention often leads main magnet compared with annular four loop constructions of traditional round,
Under same space height limitation, broader magnetic pole plate spacing and bigger field homogeneity region can be obtained, at the same time
Cost is lower.
Detailed description of the invention
Fig. 1 is the overall construction drawing of octagon main magnet of the present invention；
Fig. 2 is the octagon loop construction installation diagram that the present invention constitutes single magnetic pole；
Fig. 3 a is embodiment calculation model structural schematic diagram side view；
Fig. 3 b is embodiment calculation model structural schematic diagram front view and the sample track figure for counting magnetic field homogeneity；
Fig. 4 a is 0.5m spheric region of the present invention boundary magnetic field strength figure；
Fig. 4 b is 0.5m spheric region of the present invention boundary uniformity of magnetic field distribution map；
Fig. 5 a is 0.4m spheric region of the present invention boundary magnetic field strength figure；
Fig. 5 b is 0.4m spheric region of the present invention boundary uniformity of magnetic field distribution map.
Specific embodiment
In the present embodiment, it is in ultralow field that a kind of ultralow field biplane nuclear magnetic resonance, which often leads main magnet,3He polarization magnetic resonance
In the research of lung imaging technique, in order to study the lung of human body under vertical state and the design scheme that proposes.In view of needs
Human body is sitting among the effective coverage of magnetic resonance, is needed broader magnetic pole pitch than traditional sprawl and is guaranteed imagewise uniform degree
Area size, therefore, as shown in Figure 1, the main magnet includes the octagon coil that four axis are overlapped, and in the axial direction
Be symmetrical arranged one group of octagon coil, one group of octagon coil include outer ring big octagon coil and inner ring it is small just
Octagon coil, as shown in Fig. 2, and small octagon coil be arranged in the range of big octagon coil width is covered.
In the present embodiment, small one and large one two octagon coils are mounted on the fixation plate on the outside of main magnet, two
A coil all in fixed plate the same side, i.e., coaxially pacify in the space that big octagon coil width is covered by small octagon coil
It fills and is fixedly mounted on by four limited posts close to mounting plate the same side, so that small just in one group of octagon coil
Octagon coil and big octagon coil are in the same plane, and form planar poles；Two groups of identical coil mirror images pair
Claim installation, the apothem of two big octagon coil is equal, enables the center of big octagon coil away from the ratio with apothem
ForTwo small octagon apothem is also equal, enables the center of small octagon coil be away from the ratio with apothem
And the ratio of the apothem between big octagon coil and small octagon coil is
Enable big octagon coil identical with the current direction of small octagon coil, and big octagon coil and small just
Ampere-turn between octagon coil accumulates ratio
In the present embodiment, a kind of construction method that ultralow field biplane nuclear magnetic resonance often leads main magnet be as follows into
Row:
Step 1, the model equation group that four loop construction of octagon is established using formula (1):
In formula (1), β1For big octagon coil center away from the ratio with apothem, β2For in small octagon coil
The heart is away from the ratio with apothem, and the ratio of apothem of the q between big octagon coil and small octagon coil, i is big
Octagon coil and small octagon coil ampere-turn product ratio；A is structure control parameter；
Step 2, definition cyclic variable are n, and initialize n=1；
The structure control parameter A that step 3, setting n-th recyclen, and formula (1) is solved, obtain corresponding construction control
Parameter A processednStructural parameters (β under control1,β2,q,i)n；
Step 4, the apothem or distance of shaft centers that one big octagon coil is determined according to structure design requirement, and according to
Corresponding structural parameters (β1,β2,q,i)nThe distance of shaft centers and apothem of remaining three octagon coils is calculated, to sentence
Determine structural parameters (β1,β2,q,i)nWhether structure design requirement is met；If meeting, with corresponding construction controling parameter AnUnder control
Structural parameters (β1,β2,q,i)nThe nuclear magnetic resonance for obtaining meeting structure design requirement often leads main magnet structure, otherwise, by n+1
After being assigned to n, return step 3.
It in specific implementation, as A < 0, is often led in main magnet structure using formula (1) obtained nuclear magnetic resonance, big positive eight
The distance of shaft centers of side shape coil is greater than the distance of shaft centers of small octagon coil；It is normal using formula (1) obtained nuclear magnetic resonance as A=0
It leads in main magnet structure, the apothem of four octagon coils is all the same；It is total using formula (1) obtained nuclear-magnetism as A > 0
Vibration is often led in main magnet structure, and the distance of shaft centers of big octagon coil is less than the distance of shaft centers of small octagon coil.
In conclusion the present invention can obtain bigger magnetic pole pitch under more inexpensive, and magnetic fluctuation is less than
The field homogeneity region of 100ppm is bigger.
The present embodiment:
Plate loop construction is designed under conditions of maximum height is no more than 1.9m, is realized under the conditions of natural heat dissipation
60Gs main field, it is desirable that spheric region diameter of the uniformity of magnetic field not higher than 100ppm is not less than 0.4m.Therefore spherical region is calculated
Domain diameter is selected as 0.5m, and checking computations regional diameter is selected as 0.4m.
The first step, analysis equation characteristic:
The equation group (1) proposed by the present invention controlled by structure parameter A, suitable solution, needs to set freedom in order to obtain
Parameter A.By third equationIt is found that q=1, at this moment four octagon coil sizes are identical when A=0, only
It can be used as barrel-shaped design, be unable to satisfy the design needs；As A < 0, results in and show the distance of shaft centers of big octagon coil
Greater than the distance of shaft centers of small octagon coil；As A > 0, results in and show that the distance of shaft centers of big octagon coil is less than small eight side
The distance of shaft centers of shape coil, and with the increase of A, the distance between inner coil is continuously increased, and the distance between outer coil is no
It is disconnected to reduce.As A=+ ∞, the line model of size coil is in a plane strictly namely small coil is in big coil
Axial symmetry center, and big coil current is far longer than small coil.Therefore in practice, big coil turn is more, and width is larger, A
A biggish number can be taken, that is, can guarantee small coil in the inside of big coil.In order to reserve installation to magnetic resonance gradient coil
Position selects A > 0, so that the distance of shaft centers of big octagon coil is less than the distance of shaft centers of small octagon coil.
Second step, by multiple adjusting parameter A, iterative solution step 3 and step 4 are just met for when A takes 40.287
Small coil is in big coil, and the ratio between electric current ampere-turn product (total current) meets integer relation, and the present embodiment obtainsRatio
Example, the ratio of big coil and small coil apothem areThe center of big coil is away from the ratio with apothemIt is small
The center of coil is away from the ratio with apothem
Third step is no more than 1.9m qualifications according to maximum height, solves to obtain two linear octagons of big ideal
The distance between be 0.79m, the spacing between two ideal linear small octagon coils is 0.86m.According to Biot's Safa, you are fixed
Rule will meet main field not less than 60Gs, then big coil current is 6000A, and small coil is 180A.
4th step comprehensively considers the current density and heat dissipation area of copper conductor, and current density is selected to be less than 0.7A/mm2,
Take line pound between retain the gap 5mm and carry out increasing heat radiation area, select 3x10mm flat copper silk-covered wire as raw material, main coil selects
300 circles are selected as, 10 rows are divided into, gap 5mm between every row, then the ideal distance between final magnetic pole is that 0.65m (ignores structural member
Material thickness), the practical pole pitch of final products is 0.62m.
5th step, emulation checking computations:
According to Biot's Sa farr's law, magnetic field distribution is checked, error distribution is calculated, as Fig. 3 a gives calculation model
The side view and Fig. 3 b of structure give the front view of calculation model, and wherein dotted line indicates the sampled point rail of statistics magnetic field homogeneity
Mark.Sampled point is sampled from magnet center point along axial one of magnetic pole, and the distance of 0.25m or 0.2m up-sample 41
Point, then along the radius cambered surface of 0.25m or 0.2, from octagon angle point direction until magnet center 40 points of symmetrical surface sample,
Along perpendicular to octagon side length cambered surface to 40 points of horizontal surface sample, last straight line is to magnet center point sampling 40
Point, in this way 161 sampled points of total sampling.
6th step, uniformity Uniformity are calculated:
If the sampled intensity at center is Bs0, other sampled points are calculated as Bsample, then uniformity statistical formula are as follows:
Under the electric current driving of 20A, magnetic field strength such as Fig. 4 a and Fig. 5 a that coil generates.It is calculated according to national standard resistivity
All-in resistance is 2.9 ohm, and general power is about 1.2kW, much smaller than the magnetic power of Harvard design.
Maximum bulb diameter known to Fig. 4 b less than 100ppm is that 0.43m is further checked in the spheric region of 0.4m
Whether meet design requirement, is as a result showed in Fig. 5 b.It is better than 80ppm in the uniformity of the spheric region of 0.4m as the result is shown.
Therefore the design can satisfy predetermined design demand.
Claims (3)
1. a kind of ultralow field biplane nuclear magnetic resonance often leads main magnet, it is characterized in that: being symmetrical arranged one group positive eight in the axial direction
Side shape coil, one group of octagon coil include the big octagon coil of outer ring and the small octagon coil of inner ring,
And the small octagon coil is arranged in the width range of the big octagon coil, so that described one group positive eight
Small octagon coil and big octagon coil in the shape coil of side is in the same plane；
The center for enabling the big octagon coil is away from the ratio with apothemThe center of the small octagon coil away from
Ratio with apothem isAnd the ratio of the apothem between big octagon coil and small octagon coil is
Enable the big octagon coil identical with the current direction of small octagon coil, and big octagon coil and small just
Ampere-turn between octagon coil accumulates ratio
2. ultralow field biplane nuclear magnetic resonance according to claim 1 often leads the construction method of main magnet, it is characterized in that pressing
Following steps carry out:
Step 1, the model equation group that four loop construction of octagon is established using formula (1):
In formula (1), β1For big octagon coil center away from the ratio with apothem, β2For small octagon hub of a spool away from
With the ratio of apothem, the ratio of apothem of the q between big octagon coil and small octagon coil, i is big positive eight
Side shape coil and small octagon coil ampere-turn product ratio, A are structure control parameter；
Step 2, definition cyclic variable are n, and initialize n=1；
The structure control parameter A that step 3, setting n-th recyclen, and formula (1) is solved, obtain corresponding construction controling parameter
AnStructural parameters (β under control1,β2,q,i)n；
Step 4, the apothem or distance of shaft centers that one big octagon coil is determined according to structure design requirement, and according to corresponding
Structural parameters (β1,β2,q,i)nThe distance of shaft centers and apothem of its excess-three octagon coil is calculated, therefore, it is determined that knot
Structure parameter (β1,β2,q,i)nWhether structure design requirement is met；If meeting, with the corresponding construction controling parameter AnUnder control
Structural parameters (β1,β2,q,i)nThe nuclear magnetic resonance for obtaining meeting structure design requirement often leads main magnet structure, otherwise, by n+1
After being assigned to n, return step 3.
3. construction method according to claim 2, characterized in that as A < 0, utilize formula (1) obtained nuclear magnetic resonance
It often leads in main magnet structure, the distance of shaft centers of big octagon coil is greater than the distance of shaft centers of small octagon coil；As A=0, utilize
Formula (1) obtained nuclear magnetic resonance is often led in main magnet structure, and the apothem of four octagon coils is all the same；As A > 0,
It is often led in main magnet structure using formula (1) obtained nuclear magnetic resonance, the distance of shaft centers of big octagon coil is less than small octagon
The distance of shaft centers of coil.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112444761A (en) * | 2020-11-06 | 2021-03-05 | 北京航空航天大学 | Design method of octagonal axial shimming coil |
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