CN103713268B - A kind of magnetic resonance system and method for shimming with auxiliary shim coil - Google Patents
A kind of magnetic resonance system and method for shimming with auxiliary shim coil Download PDFInfo
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Abstract
The invention discloses a kind of magnetic resonance system and method for shimming with auxiliary shim coil. Described magnetic resonance system comprises magnet, and described magnet inwall is provided with radio-frequency coil and gradient coil, and wherein, the front/rear end of described magnet is respectively arranged with auxiliary shim coil. Magnetic resonance system and the method for shimming with auxiliary shim coil provided by the invention, to assist shim coil and radio frequency gradient circle to separate independent setting, and described auxiliary shim coil is located at the front/rear end of described magnet, thereby make the shape of auxiliary shim coil and electrical current to need to arrange flexibly according to shimming, be not subject to the restriction of space and gradient coil, reach very high equal effect effective use amount that reduces magnetic material in shimming process.
Description
Technical field
The present invention relates to a kind of magnetic resonance system and method for shimming, relate in particular to one and there is auxiliary shimming lineMagnetic resonance system and the method for shimming of circle.
Background technology
The imaging region of MRI system (magnetic resonance imaging system) needs equally distributed main field, but actualMagnetic field can not be uniformly distributed completely, for this reason, need to carry out shimming operation to magnetic resonance system. Use and surveyMeasuring appratus is measured the main magnetic field distribution in certain area, and the main field measuring is carried out under spherical coordinate systemLegendre polynomial expansion, expansion multinomial is:
Wherein, the main field that Bz is magnet, R0 is the reference sphere half while carrying out Legendre polynomial expansionFootpath,For Legnedre polynomial, Anm，BnmFor launching multinomial coefficient, be called again hamonic function coefficient,Can represent with A (n, m) and B (n, m) respectively. N, m can be described as the exponent number of hamonic function. By polynomial propertyThe known A of matter (0,0) is main field mean value, and other are the non-homogeneous item of main field. In order to make magnetic fieldMore even, need to will reduce except A (0,0) coefficient entry in addition by some approach, these approach are just referred to asBody even field.
Generally, exponent number is greater than at 20 o'clock, hamonic function coefficient Anm，BnmTo the inhomogeneity shadow of main fieldRing very littlely, even can ignore, for 3 rank of hamonic function coefficient, to 20 rank items, its rank item value conventionally alsoSmaller, adopt high saturated magnetic induction material to carry out shimming by the approach of passive shimming, have wellShimming effect.
But be second order and single order item for hamonic function coefficient low order item, after magnet completes, general feelingsUnder condition, low order item value can be larger, particularly A (2,0) reach sometimes hundreds of ppm (ppm: 1,000,000/,Magnetic field intensity departs from unit), in addition, before patient starts scanning, due to patient self cause a small amount ofInhomogeneities also can increase part A (2,0) and A (1,0). For single order item and second order term, it is passive to adoptShimming, need to adopt a large amount of high saturation magnetization materials, and the effect of shimming neither be very desirable, simultaneouslyWhen magnetic material is too much, magnetic resonance system is in the time of imaging, and the eddy current that magnetic material produces can be lowered into image quality.
Therefore, conventionally adopt the initiatively mode of shimming for the method for shimming of second order term and single order item, adoptHot-wire coil carries out shimming, and such as to single order item, gradient coil itself just can play shimming effect, forSecond order term, needs by magnetic field inwall, special shim coil being set,
But because the space of magnet cylinder inwall is very limited, in order not take too many patient's free space, pastToward shim coil can be done very thin and can not be around too many line, electrical current can not be too large like this, otherwiseHeat can be too high, or simply without shim coil, so just limited the uniformization effect of coil to second order term.
Summary of the invention
Technical problem to be solved by this invention is to provide a kind of magnetic resonance system with auxiliary shim coilAnd method for shimming, the shape of auxiliary shim coil and electrical current can need to arrange flexibly according to shimming, noBe subject to the restriction of space and gradient coil, reach very high shimming effect and effectively reduce magnetic material in shimming processThe use amount of material.
The present invention solves the problems of the technologies described above the technical scheme adopting to be to provide one and to have auxiliary shimmingThe magnetic resonance system of coil, comprises magnet, and described magnet inwall is provided with radio-frequency coil and gradient coil,Wherein, the front/rear end of described magnet is respectively arranged with auxiliary shim coil.
Further, described auxiliary shim coil forms round the vertical direction coiling of magnet main shaft.
Further, the number of turn of described auxiliary shim coil is 1～500.
Further, described auxiliary shim coil is 10mm-20mm along the width of magnet major axes orientation.
Further, described magnet periphery is also provided with shell.
Further, described auxiliary shim coil is arranged in shell and the gap of magnet on major axes orientation.
Further, on described auxiliary shim coil, be provided with cooling device.
Further, described cooling device is water pipe or cool air hose.
Further, described water pipe or cool air hose are arranged in auxiliary shim coil surface, or auxiliary shimmingThe side of coil.
Further, described auxiliary shim coil is two identical coils, be symmetrically distributed in magnet beforeRear end face.
Further, described two auxiliary shim coils connect same power supply or connect two different electricitySource, size of current when energising in two auxiliary shim coils is identical with direction.
Further, described two auxiliary shim coils connect different passages or the connection of same power supplyTwo different electrical power, size of current when energising in two auxiliary shim coils is identical, opposite direction.
Further, described two auxiliary shim coils connect the different passages of same power supply or connect twoIndividual different power supply, the size of current difference of two auxiliary shim coils when energising.
In order to address the above problem, the present invention also provides a kind of method for shimming of magnetic resonance system, in employingState the magnetic resonance system with auxiliary shim coil, comprise the steps: a1) by the main field of described magnetBe distributed under spherical coordinate system and launch, and calculate second order hamonic function coefficient value; B1) make described two to assist evenField coil passes into the electric current that size is identical with direction, and the size of described electric current is described second order hamonic function coefficient valueOpposite number and the described auxiliary shim coil ratio of second order hamonic function coefficient value that 1 ampere-hour produces of switching on;C1) after two auxiliary shim coils are according to described current electrifying, the main field of described magnet is sat at ballUnder mark system, again launch, and recalculate second order hamonic function coefficient value; D1) described in judgement, recalculateWhether second order hamonic function coefficient value is within the scope of referential data; E1) if so, auxiliary shim coil shimming finishesAuxiliary shimming finishes, otherwise repeat a1)-d1) step until the second order hamonic function coefficient value recalculating fallWithin the scope of referential data.
Further, described referential data scope is 0-30ppm
Further, described referential data is 0ppm.
In order to address the above problem, the present invention also provides the method for shimming of another kind of magnetic resonance system, adoptsThe above-mentioned magnetic resonance system with auxiliary shim coil comprises the steps: a2) by the main field of described magnetBe distributed under spherical coordinate system and launch, and calculate single order hamonic function coefficient value; B2) make described two to assist evenField coil passes into opposite direction, the electric current that size is identical, and the size of described electric current is that described single order hamonic function isNumerical value and the described auxiliary shim coil ratio of single order hamonic function coefficient value that 1 ampere-hour produces of switching on; C2)After two auxiliary shim coils are according to described current electrifying, by the main field of described magnet at spherical coordinate systemUnder again launch, and recalculate single order hamonic function coefficient value; D2) described in judgement, recalculate single orderWhether hamonic function coefficient value is within the scope of referential data; E2) if so, auxiliary shim coil shimming finishes,Otherwise repeat a2)-d2) step is until the single order hamonic function coefficient value recalculating drops on referential data scopeIn.
Further, described referential data scope is 0-30ppm
Further, described referential data can be 0ppm.
In order to address the above problem, the present invention also provides the method for shimming of another kind of magnetic resonance system, adoptsThe above-mentioned magnetic resonance system with auxiliary shim coil comprises the steps: a3) by the main field of described magnetBe distributed under spherical coordinate system and launch, and calculate single order hamonic function coefficient value and second order hamonic function coefficient; B3)Make a described auxiliary shim coil pass into electric current, the size of described electric current is described single order hamonic function coefficient valueWith the described auxiliary shim coil ratio of single order hamonic function coefficient value that 1 ampere-hour produces of switching on; Make described anotherAn auxiliary shim coil passes into electric current, the size of described electric current be described second order hamonic function coefficient value with described inThe auxiliary shim coil ratio of second order hamonic function coefficient value that 1 ampere-hour produces of switching on; C3) auxiliary at twoShim coil according to described current electrifying after, by the main field of described magnet under spherical coordinate system again exhibitionOpen, and recalculate single order hamonic function coefficient value and second order hamonic function coefficient; D3) described in judgement, again countCalculate single order hamonic function coefficient value and second order hamonic function coefficient value respectively whether within the scope of referential data; E3)If so, auxiliary shim coil shimming finishes, otherwise repeats a3)-d3) step until recalculate oneRank hamonic function coefficient value and second order hamonic function coefficient value drop on respectively within the scope of referential data.
Further, described referential data scope is 0-30ppm.
Further, described referential data can be 0ppm.
The present invention contrasts prior art following beneficial effect: 1, provided by the invention have an auxiliary shimmingThe magnetic resonance system of coil, will assist shim coil and radio-frequency coil and gradient coil to separate independent setting,And described auxiliary shim coil is located at the front/rear end of described magnet, thereby make the shape of auxiliary shim coilCan need to arrange flexibly according to shimming with electrical current, not be subject to the restriction of space and gradient coil; 2, phaseFor existing shim coil, the shim coil in the present invention not only has better shimming effect to second order term,But also can, by adjusting sense of current and big or small mode, reach the shimming object to single order item, veryTo being can reach equal very high effect simultaneously for single order item and second order term, and effectively reduce shimming mistakeThe use amount of magnetic material in journey.
Brief description of the drawings
Fig. 1 is the magnetic resonance system structural representation that the present invention has auxiliary shim coil;
Fig. 2 is auxiliary shim coil side structure schematic diagram of the present invention;
Fig. 3 is auxiliary shim coil Facad structure schematic diagram of the present invention;
Fig. 4 is the auxiliary shim coil Facad structure schematic diagram with water pipe cooling device of the present invention;
Fig. 5 is that the Distribution of Magnetic Field of the logical formed objects of two auxiliary shim coils of the present invention and directional current is shownIntention;
Fig. 6 is the Distribution of Magnetic Field of the logical formed objects of two auxiliary shim coils of the present invention, opposite direction electric currentSchematic diagram;
Fig. 7 is the Distribution of Magnetic Field schematic diagram of the logical different electric currents of two auxiliary shim coils of the present invention.
In figure:
Auxiliary equal field coil 3 power supplys of 1 magnet 2
4 wire 5 internal diameter 6 external diameters
7 water pipe 71 water inlet pipe 72 outlet pipes
Detailed description of the invention
Below in conjunction with drawings and Examples, the invention will be further described.
Fig. 1 is the magnetic resonance system structural representation that the present invention has auxiliary shim coil.
Refer to Fig. 1, the magnetic resonance system with auxiliary shim coil provided by the invention comprises shell (figureDo not show) and magnet 1, described shell is arranged on the periphery of magnet 1, magnet 1 inwall be provided with radio-frequency coil andGradient coil (not shown), wherein, auxiliary shim coil 2 is for to divide and to offer with radio-frequency coil and gradient coilThe absolute coil of putting, and auxiliary shim coil 2 is arranged at respectively the front/rear end of magnet 1.
The above-mentioned magnetic resonance system with auxiliary shim coil, current most magnet 1 mainly passes throughSuperconducting coil coiling forms, for the uniformity in magnetic field, in the time that exponent number is greater than 2, by passive evenMode have shimming effect clearly, for 1 rank item, its rank item value be far longer than 3 rank items withOn rank item value, the shimming mode that therefore typically uses gradient coil is carried out even lower these rank item values, and rightIn second order term, particularly A (2,0) this, it generally can reach 300ppm, by passive shimmingMode, cannot realize shimming effect, therefore needs to come with special shim coil the value of even lower A (2,0).Shim coil of the prior art is placed on magnet cylinder inwall, because the space of magnet cylinder inwall extremely hasLimit, in order not take too many patient's free space, tend to shim coil to do very thin and can not be around too muchLine, electrical current can not be too large like this, otherwise heating can be too high, or simply without shim coil, thisSample has just limited coil to the particularly uniformization effect of A (2,0) of single order item.
Therefore, in the present invention by two symmetrical distributing installations of auxiliary shim coil in magnet 1 front and back endFace, coil, round the vertical direction coiling of magnet main shaft, is parallel to the coiling of magnet end face, for activeReduce most of A (2,0), also can reduce most of A (1,0) simultaneously, thereby reach equal very high effectThe use amount of magnetic material in fruit effectively minimizing shimming process.
With respect to the existing active shim coil that is placed on magnet inwall, auxiliary shim coil 2 of the present inventionNumber of turns can be a lot. The number of turn of coil is by the thickness of wire, maximum electrical current and the need of permissionThe maximum shimming effect reaching determines. The maximum shimming effect that need to reach is larger, and coil turn is more.The maximum electrical current allowing is less, and the coil turn needing is also more. Auxiliary shim coil 2 of the present inventionThe conductor turns of coiling count up to entirely optionally and service condition and determining, such as 1～500 circle, logical very littleIn the situation of electric current, just can reach very high A (2,0) uniformization effect, effectively reduce magnetic in shimming processThe use amount of material.
In addition, wire is thinner, and coil turn that can coiling is more, and auxiliary shim coil 2 of the present invention existsWidth on axis can be very narrow, and such as 10mm-20mm, auxiliary like this shim coil 2 just can be installedIn magnet 1 and the gap of shell on major axes orientation, and do not need additional space.
For single order item, prior art is mainly carried out shimming by gradient coil, and shimming in the present inventionCoil, by adjusting direction or the size of electrical current, not only has better shimming effect to second order term, alsoCan reach the shimming object to single order item, or even have well for single order item and second order term simultaneouslyShimming effect. Concrete step mode is as follows: the energising power supply of two auxiliary shim coils 2 can be sameThe same passage of power supply 3, while energising like this, the electric current of two auxiliary shim coils 2 is consistent all the time, canEven second order term (particularly A (2,0) this); Also can be different passages or the difference of same power supplyPower supply, size of current when energising in two auxiliary shim coils 2 is identical, opposite direction can even oneRank item (A (1,0), A (1,1) B (1,1)); Also can be same power supply different passages or connect two notSame power supply, the size of current difference of two auxiliary shim coils when energising, direction is identical or different,Can even single order item also can even second order term, the effect of shimming is more extensive.
Electrical current size can need to arrange according to place shimming, such as auxiliary shim coil 2 is according to as followsSize coiling: inside radius: 500mm; Outer radius: 700mm; The coiling number of turn: 500 circles; Installation positionPut the center 700mm apart from magnet 1, as shown in Figures 2 and 3. When former and later two auxiliary shim coils 2While all leading to the same direction current of 5A, the shimming that the spherical area that is 220mm at magnet center radius produces is mendedThe value of repaying is 100ppm; In the time that former and later two auxiliary shim coils 2 all lead to the reversing the current of 5A, at magnetCenter radius is that the shimming offset that the spherical area of 220mm produces is 400ppm.
Overheated and cause that ambient temperature raises for fear of coil, as a kind of improvement project, auxiliaryIn shim coil 2, can add cooling device. Refer to Fig. 4, cooling device is by a water inlet 71, oneDelivery port 72 and water pipe 7 form, and water pipe 7 can be arranged in the circumferential surface of auxiliary shim coil 2,Or the side of auxiliary shim coil 2. Fig. 4 mean camber line arrow direction is water (flow) direction, straight arrowsDirection is Inlet and outlet water direction. Cooling device also can use other mode cooling devices such as air-cooled grade, as by upperState water pipe and make hollow tube into, directly blow in pipe with fan, describe in detail no longer one by one at this.
For the magnetic resonance system with auxiliary shim coil, the present invention also provides following three kinds of shimming sidesMethod:
Method one:
A1) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated second order hamonic function systemNumerical value;
B1) make described two auxiliary shim coils pass into the size electric current identical with direction, described electric current greatlyThe 1 ampere-hour generation of switching on of the little opposite number for described second order hamonic function coefficient value and described auxiliary shim coilThe ratio of second order hamonic function coefficient value;
C1) after two auxiliary shim coils are according to described current electrifying, by the main field of described magnetUnder spherical coordinate system, again launch, and recalculate second order hamonic function coefficient value;
D1) described in judgement, recalculate second order hamonic function coefficient value whether within the scope of referential data;
E1) in this way, auxiliary shim coil shimming finishes, otherwise repeats a1)-d1) step is until meter againThe second order hamonic function coefficient value calculating drops within the scope of referential data.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is0ppm-30ppm, is preferably 0ppm.
Method two:
A2) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated single order hamonic function systemNumerical value;
B2) make described two auxiliary shim coils pass into opposite direction, the electric current that size is identical, described electric currentSize be described single order hamonic function coefficient value and described auxiliary shim coil switch on 1 ampere-hour produce oneThe ratio of rank hamonic function coefficient value;
C2) after two auxiliary shim coils are according to described current electrifying, by the main field of described magnetUnder spherical coordinate system, again launch, and recalculate single order hamonic function coefficient value;
D2) described in judgement, recalculate single order hamonic function coefficient value whether within the scope of referential data;
E2) in this way, auxiliary shim coil shimming finishes, otherwise repeats a2)-d2) step is until described heavyThe single order hamonic function coefficient value newly calculating drops within the scope of referential data.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is0ppm-30ppm, is preferably 0ppm.
Method three:
A3) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated single order hamonic function systemNumerical value and second order hamonic function coefficient;
B3) make a described auxiliary shim coil pass into electric current, the size of described electric current is the humorous letter of described single orderNumber system numerical value and the described auxiliary shim coil ratio of single order hamonic function coefficient value that 1 ampere-hour produces of switching on;Make described another auxiliary shim coil pass into electric current, the size of described electric current is described second order hamonic function coefficientValue and the described auxiliary shim coil ratio of second order hamonic function coefficient value that 1 ampere-hour produces of switching on;
C3) after two auxiliary shim coils are according to described current electrifying, by the main field of described magnetUnder spherical coordinate system, again launch, and recalculate single order hamonic function coefficient value and second order hamonic function coefficient;
D3) described in judgement, recalculate single order hamonic function coefficient value and second order hamonic function coefficient value is respectivelyNo within the scope of referential data;
E3) in this way, auxiliary shimming finishes) otherwise repeat a3)-d3) step is until recalculateSingle order hamonic function coefficient value and second order hamonic function coefficient value drop on respectively within the scope of referential data.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is0ppm-30ppm, is preferably 0ppm.
After the geometric parameter of auxiliary shim coil 2 and installation site determine, just can calculate auxiliaryEach hamonic function coefficient that shim coil produces. Each hamonic function coefficient just becomes with the size of current of electrical currentRatio. A (2, the 0) index of getting off such as needs are even is 100ppm, and auxiliary shim coil is 1 at electrical currentThe A (2,0) that ampere-hour produces is 50ppm, just can make A (2,0) to logical 2 Ampere currents of auxiliary shim coilEven lower 100ppm.
Single order item and second order term for the impact of the main field uniformity be mainly A (1,0) and A (2,0) this two, therefore we assist the shimming effect of shim coil to A (1,0) and A (2,0) by curve map. WhenWhen the logical formed objects of auxiliary shim coil 2 and directional current, the magnetic field that auxiliary shim coil produces is along magnetAs shown in Figure 5, wherein, abscissa Z is the position in magnet axis in distribution on axis, and unit is rice(m), ordinate Bz is the magnetic field that auxiliary shim coil produces, and unit is tesla (Tesla). ThisThe Distribution of Magnetic Field that item is corresponding is parabolic type, and major effect item is A (2,0), can even lower HarmonicsIn A (2,0). When the logical formed objects of auxiliary shim coil 2, when opposite direction electric current, Distribution of Magnetic Field asShown in Fig. 6, major effect item is A (1,0), in can even lower Harmonics A (1,0). When auxiliaryWhile helping the logical different electric current of shim coil 2, Distribution of Magnetic Field as shown in Figure 7, major effect item be A (1,0) andA (2,0), the A (2,0) in can even lower Harmonics and A (1,0).
Although the present invention discloses as above with preferred embodiment, so it is not in order to limit the present invention, Ren HebenThose skilled in the art, without departing from the spirit and scope of the present invention, when doing a little amendment and perfect,Therefore protection scope of the present invention is worked as with being as the criterion that claims were defined.
Claims (14)
1. a magnetic resonance system with auxiliary shim coil, comprises magnet, and described magnet inwall is provided with radio-frequency coil and gradient coil, it is characterized in that, the front/rear end of described magnet is respectively arranged with auxiliary shim coil;
Described auxiliary shim coil is two identical coils, is symmetrically distributed in the front/rear end of magnet;
Two auxiliary shim coils connect same power supply or connect two different electrical power, and size of current when energising in two auxiliary shim coils is identical with direction;
Or two auxiliary shim coils connect the different passages of same power supply or connect two different power supplys, and size of current when energising in two auxiliary shim coils is identical, opposite direction;
Or described two auxiliary shim coils connect the different passages of same power supply or connect two different power supplys, the size of current difference of two auxiliary shim coils when energising.
2. the magnetic resonance system with auxiliary shim coil as claimed in claim 1, is characterized in that, described auxiliary shim coil forms round the vertical direction coiling of magnet main shaft.
3. the magnetic resonance system with auxiliary shim coil as claimed in claim 1, is characterized in that, the number of turn of described auxiliary shim coil is 1～500.
4. the magnetic resonance system with auxiliary shim coil as claimed in claim 1, is characterized in that, described auxiliary shim coil is 10mm～20mm along the width of magnet major axes orientation.
5. the magnetic resonance system with auxiliary shim coil as claimed in claim 1, is characterized in that, described magnet periphery is also provided with shell.
6. the magnetic resonance system with auxiliary shim coil as claimed in claim 5, is characterized in that, described auxiliary shim coil is arranged in shell and the gap of magnet on major axes orientation.
7. the magnetic resonance system with auxiliary shim coil as claimed in claim 1, is characterized in that, on described auxiliary shim coil, is provided with cooling device.
8. the magnetic resonance system with auxiliary shim coil as claimed in claim 7, is characterized in that, described cooling device is water pipe or cool air hose.
9. the magnetic resonance system with auxiliary shim coil as claimed in claim 8, is characterized in that, described water pipe or cool air hose are arranged in auxiliary shim coil surface, or the side of auxiliary shim coil.
10. a method for shimming for magnetic resonance system, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 1 with auxiliary shim coil, and the method for shimming of described magnetic resonance system comprises the steps:
A1) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated second order hamonic function coefficient value;
B1) make described two auxiliary shim coils pass into the size electric current identical with direction, the size of described electric current is the switch on ratio of second order hamonic function coefficient value of 1 ampere-hour generation of the opposite number of described second order hamonic function coefficient value and described auxiliary shim coil;
C1), after two auxiliary shim coils are according to described current electrifying, the main field of described magnet again launched under spherical coordinate system, and recalculated second order hamonic function coefficient value;
D1) described in judgement, recalculate second order hamonic function coefficient value whether within the scope of referential data;
E1) if so, auxiliary shim coil shimming finishes, otherwise repeats a1)-d1) step is until recalculate second order hamonic function coefficient value and drop within the scope of referential data.
The method for shimming of 11. 1 kinds of magnetic resonance systems, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 1 with auxiliary shim coil, and the method for shimming of described magnetic resonance system comprises the steps:
A2) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated single order hamonic function coefficient value;
B2) make described two auxiliary shim coils pass into opposite direction, the identical electric current of size, the size of described electric current is the switch on ratio of single order hamonic function coefficient value of 1 ampere-hour generation of opposite number and the described auxiliary shim coil of described single order hamonic function coefficient value;
C2), after two auxiliary shim coils are according to described current electrifying, the main field of described magnet again launched under spherical coordinate system, and recalculated single order hamonic function coefficient value;
D2) described in judgement, recalculate single order hamonic function coefficient value whether within the scope of referential data;
E2) if so, auxiliary shim coil shimming finishes, otherwise repeats a2)-d2) step until the single order hamonic function coefficient value recalculating drop within the scope of referential data.
The method for shimming of 12. 1 kinds of magnetic resonance systems, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 1 with auxiliary shim coil, and the method for shimming of described magnetic resonance system comprises the steps:
A3) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculated single order hamonic function coefficient value and second order hamonic function coefficient value;
B3) make a described auxiliary shim coil pass into electric current, the size of described electric current is the switch on ratio of the single order hamonic function coefficient value that 1 ampere-hour produces of the opposite number of described single order hamonic function coefficient value and described auxiliary shim coil; Make auxiliary shim coil described in another pass into electric current, the size of described electric current is the switch on ratio of second order hamonic function coefficient value of 1 ampere-hour generation of opposite number and the described auxiliary shim coil of described second order hamonic function coefficient value;
C3) main field of described magnet is again launched under spherical coordinate system, and recalculated single order hamonic function coefficient value and second order hamonic function coefficient value;
Whether d3) described in judgement, recalculate single order hamonic function coefficient value and second order hamonic function coefficient value distinguishes within the scope of referential data;
E3) if so, auxiliary shim coil shimming finishes, otherwise repeats a3)-d3) step until the single order hamonic function coefficient value recalculating and second order hamonic function coefficient value drop on respectively within the scope of referential data.
The method for shimming of 13. magnetic resonance systems as described in any one in claim 10～12, is characterized in that, described referential data scope is 0～30ppm.
The method for shimming of 14. magnetic resonance systems as claimed in claim 13, is characterized in that, described referential data is 0ppm.
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| CN106659416B (en) * | 2014-07-03 | 2019-09-24 | 株式会社日立制作所 | MR imaging apparatus and high frequency magnetic field shimming parameter decision method |
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