CN103713268A - Magnetic resonance system having auxiliary shim coils and shimming method thereof - Google Patents
Magnetic resonance system having auxiliary shim coils and shimming method thereof Download PDFInfo
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- CN103713268A CN103713268A CN201210378580.9A CN201210378580A CN103713268A CN 103713268 A CN103713268 A CN 103713268A CN 201210378580 A CN201210378580 A CN 201210378580A CN 103713268 A CN103713268 A CN 103713268A
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Abstract
The invention discloses a magnetic resonance system having auxiliary shim coils and a shimming method thereof. The magnetic resonance system comprises a magnet; a radio frequency coil and a gradient coil are arranged at the inner wall of the magnet; and auxiliary shim coils are respectively arranged at the front end surface and the rear end surface of the magnet. According to the invention, because the auxiliary shim coils, the radio frequency coil and the gradient coil are respectively and independently arranged and the auxiliary shim coils are arranged at the front end surface and the rear end surface of the magnet, the shapes of the auxiliary shim coils and the power-on current can be arranged flexibly according to the shimming demand; limitation of the space and the gradient coil can be eliminated; and the excellent shimming effect can be realized and the using amount of magnetic materials during the shimming process can be effectively reduced.
Description
Technical field
The present invention relates to a kind of magnetic resonance system and method for shimming, relate in particular to a kind of magnetic resonance system and method for shimming with auxiliary shim coil.
Background technology
The imaging region of MRI system (magnetic resonance imaging system) needs equally distributed main field, but actual magnetic field can not be uniformly distributed completely, for this reason, need to carry out shimming operation to magnetic resonance system.Use surveying instrument to measure the main magnetic field distribution in certain area, the main field measuring is carried out under spherical coordinate system to Legendre polynomial expansion, expansion polynomial expression is:
Wherein, the main field that Bz is magnet, R0 is the reference sphere radius surface while carrying out Legendre polynomial expansion,
for Legendre polynomial, A
nm, B
nmfor launching multinomial coefficient, be called again hamonic function coefficient, can with A (n, m) and B (n, m), represent respectively.N, m can be described as the exponent number of hamonic function.By the known A of polynomial character (0,0), be main field mean value, other are the non-homogeneous item of main field.In order to make magnetic field more even, need to will reduce except A (0,0) coefficient entry in addition by some approach, these approach are just referred to as body even field.
Generally, exponent number is greater than at 20 o'clock, hamonic function coefficient A
nm, B
nmvery little on the inhomogeneity impact of main field, even can ignore, for 3 rank of hamonic function coefficient, to 20 rank items, its rank item value is conventionally also smaller, and the approach by passive shimming adopts high saturated magnetic induction material to carry out shimming, has good shimming effect.
But be second order and single order item for hamonic function coefficient low order item, after magnet completes, generally 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, a small amount of unevenness causing due to patient self also can increase part A (2,0) and A (1,0).For single order item and second order term, adopt passive shimming, need to adopt a large amount of high saturation magnetization materials, and the effect of shimming neither be very desirable, when magnetic material is too much simultaneously, magnetic resonance system is when imaging, and the eddy current that magnetic material produces can be lowered into image quality.
Therefore, for the method for shimming of second order term and single order item, conventionally adopt the mode of active shimming, adopt hot-wire coil to carry out shimming, such as to single order item, gradient coil itself just can play shimming effect, for second order term, need by special shim coil being set at magnetic field inwall
But because the space of magnet cylinder inwall is very limited, in order not take too many patient's free space, tend to shim coil to do very thin and can not be around too many line, electrical current can not be too large like this, otherwise heating 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 matters to be solved by this invention is to provide a kind of magnetic resonance system and method for shimming with auxiliary shim coil, the shape of auxiliary shim coil and electrical current can need to arrange flexibly according to shimming, be not subject to the restriction of space and gradient coil, reach very high shimming effect effective use amount that reduces magnetic material in shimming process.
The present invention solves the problems of the technologies described above the technical scheme adopting to be to provide a kind of magnetic resonance system with auxiliary shim coil, comprise magnet, 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.
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 the side of auxiliary shim coil.
Further, described auxiliary shim coil is two identical coils, is symmetrically distributed in the front/rear end of magnet.
Further, described two auxiliary shim coils connect same power supply or connect two different electrical power, and size of current during energising in two auxiliary shim coils is identical with direction.
Further, described two auxiliary shim coils connect the different passages of same power supply or connect two different electrical power, and size of current during 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 two different power supplys, and during energising, the size of current of two auxiliary shim coils is different.
In order to address the above problem, the present invention also provides a kind of method for shimming of magnetic resonance system, adopt the above-mentioned magnetic resonance system with auxiliary shim coil, comprise the steps: a1) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculate 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; C 1) 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 auxiliary shimming and finishes, otherwise repeats a1)-d1) step until the second order hamonic function coefficient value recalculating drop within 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, adopt the above-mentioned magnetic resonance system with auxiliary shim coil to comprise the steps: a2) main magnetic field distribution of described magnet is launched under spherical coordinate system, and calculate 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 described single order hamonic function coefficient value and described auxiliary shim coil; 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.
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, adopt the above-mentioned magnetic resonance system with auxiliary shim coil to comprise the steps: a3) main magnetic field distribution of described magnet is launched under spherical coordinate system, 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 the switch on ratio of the single order hamonic function coefficient value that 1 ampere-hour produces of described single order hamonic function coefficient value and described auxiliary shim coil; Make described another auxiliary shim coil 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 described second order hamonic function coefficient value and described auxiliary shim coil; C3), 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 and second order hamonic function coefficient; 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 within the scope of referential data respectively.
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, the magnetic resonance system with auxiliary shim coil provided by the invention, to 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 coil and electrical current to need to arrange flexibly according to shimming, be not subject to the restriction of space and gradient coil; 2, with respect to existing shim coil, shim coil in the present invention not only has better shimming effect to second order term, but also can be by adjusting sense of current and big or small mode, reach the shimming object to single order item, or even can reach equal very high effect simultaneously for single order item and second order term, and effectively reduce the use amount of magnetic material in shimming process.
Accompanying drawing explanation
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 the Distribution of Magnetic Field schematic diagram of the logical formed objects of two auxiliary shim coils of the present invention and directional current;
Fig. 6 is the Distribution of Magnetic Field schematic diagram of the logical formed objects of two auxiliary shim coils of the present invention, opposite direction electric current;
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 rising pipes
Embodiment
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 (not shown) and magnet 1, described shell is arranged on the periphery of magnet 1, magnet 1 inwall is provided with radio-frequency coil and gradient coil (not shown), wherein, auxiliary shim coil 2 is for to divide with radio-frequency coil and gradient coil the absolute coil being arranged, 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 forms by superconducting coil coiling, for the homogeneity in magnetic field, when exponent number is greater than 2, mode by passive shimming has shimming effect clearly, for 1 rank item, its rank item value has been far longer than rank item values more than 3 rank items, so even these rank item values down of the shimming mode that typically uses gradient coil, and for second order term, particularly A (2, 0) this, it generally can reach 300ppm, by the mode of passive shimming, cannot realize shimming effect, therefore need to carry out even lower A (2 with special shim coil, 0) value.Shim coil of the prior art is placed on magnet cylinder inwall, because the space of magnet cylinder inwall is very limited, in order not take too many patient's free space, tend to shim coil to do very thin and can not be around too many line, electrical current can not be too large like this, otherwise heating can be too high, or simply without shim coil, so just limited coil to the single order item uniformization effect of A (2,0) particularly.
Therefore, in the present invention by two symmetrical distributing installations of auxiliary shim coil at magnet 1 front/rear end, coil is round the vertical direction coiling of magnet main shaft, be parallel to the coiling of magnet end face, for initiatively reducing most of A (2,0), also can reduce most of A (1 simultaneously, 0) item, thus reach very high equal effect effective use amount that reduces magnetic material in shimming process.
With respect to the existing active shim coil that is placed on magnet inwall, the number of turns of auxiliary shim coil 2 of the present invention can be a lot.The number of turn of coil by the thickness of wire, the maximum electrical current of permission and the maximum shimming effect that need to reach determine.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.The conductor turns of the coiling of auxiliary shim coil 2 of the present invention counts up to entirely optionally and service condition and determining, such as 1～500 circle, the in the situation that of logical very little electric current, just can reach very high A (2,0) uniformization effect, effectively reduces the use amount of magnetic material in shimming process.
In addition, wire is thinner, and coil turn that can coiling is more, the width of auxiliary shim coil 2 of the present invention on axis can be very narrow, such as 10mm-20mm, auxiliary like this shim coil 2 just can be arranged in magnet 1 and the gap of shell on major axes orientation, and does not need additional space.
For single order item, prior art is mainly carried out shimming by gradient coil, and shim coil in the present invention, by adjusting direction or the size of electrical current, not only second order term is had to better shimming effect, can also reach the shimming object to single order item, or even have good shimming effect simultaneously for single order item and second order term.Concrete step mode is as follows: the energising power supply of two auxiliary shim coils 2 can be the same passage of same power supply 3, and while switching on like this, the electric current of two auxiliary shim coils 2 is consistent all the time, can even second order term (particularly A (2,0) this); Also can be the different passages of same power supply or different power supplys, size of current during energising in two auxiliary shim coils 2 be identical, and opposite direction can even single order item (A (1,0), A (1,1) B (1,1)); Also can be the different passages of same power supply or connect two different power supplys, during energising, the size of current of two auxiliary shim coils be different, and 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 following size coiling: inside radius: 500mm; External radius: 700mm; The coiling number of turn: 500 circles; Installation site is apart from the center 700mm of magnet 1, as shown in Figures 2 and 3.When former and later two auxiliary shim coils 2 all lead to the same direction current of 5A, the shimming offset that the spherical area that is 220mm at magnet center radius produces is 100ppm; When former and later two auxiliary shim coils 2 all lead to the inverse current of 5A, the shimming offset that the spherical area that is 220mm at magnet center radius produces is 400ppm.
Overheated and cause that ambient temperature raises, and as a kind of improvement project, can add cooling device in auxiliary shim coil 2 for fear of coil.Refer to Fig. 4, cooling device is comprised of a water inlet 71, water delivering orifice 72 and water pipe 7, 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, and straight arrows direction is Inlet and outlet water direction.Cooling device also can be used other mode cooling devices such as air-cooled grade, as made above-mentioned water pipe into hollow tube, directly with fan, in pipe, blows, and at this, describes in detail no longer one by one.
For the magnetic resonance system with auxiliary shim coil, the present invention also provides following three kinds of method for shimming:
Method one:
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) in this way, auxiliary shim coil shimming finishes, otherwise repeats a1)-d1) step until the second order hamonic function coefficient value recalculating drop within the scope of referential data.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is 0ppm-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 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 described single order hamonic function coefficient value and described auxiliary shim coil;
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) in this way, auxiliary shim coil shimming finishes, otherwise repeats a2)-d2) step until described in the single order hamonic function coefficient value that recalculates drop within the scope of referential data.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is 0ppm-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 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 the switch on ratio of the single order hamonic function coefficient value that 1 ampere-hour produces of described single order hamonic function coefficient value and described auxiliary shim coil; Make described another auxiliary shim coil 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 described second order hamonic function coefficient value and described auxiliary shim coil;
C3), 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 and second order hamonic function coefficient;
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) in this way, auxiliary shimming finishes) otherwise repeat a3)-d3) step until the single order hamonic function coefficient value recalculating and second order hamonic function coefficient value drop within the scope of referential data respectively.
Described referential data scope is definite according to clinical demand, and preferably, described referential data is 0ppm-30ppm, is preferably 0ppm.
After the geometric parameter of auxiliary shim coil 2 and installation site determine, just can calculate each hamonic function coefficient that auxiliary shim coil produces.Each hamonic function coefficient is directly proportional to the size of current of electrical current.The A getting off such as needs are even (2,0) index is 100ppm, and auxiliary shim coil is that the A (2,0) that 1 ampere-hour produces is 50ppm at electrical current, just can make the even lower 100ppm of A (2,0) to logical 2 Ampere currents of auxiliary shim coil.
Single order item and second order term are mainly these two of A (1,0) and A (2,0) for the impact of main field uniformity coefficient, thus we by the auxiliary shim coil of curve map the shimming effect to A (1,0) and A (2,0).When the logical formed objects of auxiliary shim coil 2 and directional current, the magnetic field that auxiliary shim coil produces along the distribution in magnet axis as shown in Figure 5, wherein, horizontal ordinate Z is the position in magnet axis, unit is rice (m), ordinate Bz is the magnetic field that auxiliary shim coil produces, and unit is tesla (Tesla).This corresponding Distribution of Magnetic Field is parabolic type, and major effect item is A (2,0), in can even lower Harmonics A (2,0).When the logical formed objects of auxiliary shim coil 2, during opposite direction electric current, as shown in Figure 6, major effect item is A (1,0) to Distribution of Magnetic Field, in can even lower Harmonics A (1,0).When the logical different electric current of auxiliary shim coil 2, as shown in Figure 7, major effect item is A (1,0) and A (2,0) to Distribution of Magnetic Field, A (2,0) and A (1,0) item in can even lower Harmonics.
Although the present invention discloses as above with preferred embodiment; so it is not in order to limit the present invention, any those skilled in the art, without departing from the spirit and scope of the present invention; when doing a little modification and perfect, so protection scope of the present invention is worked as with being as the criterion that claims were defined.
Claims (18)
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.
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 shimming line 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 shimming line 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 6, 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 7, 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. the magnetic resonance system with auxiliary shim coil as described in claim 1～9 any one, is characterized in that, described auxiliary shim coil is two identical coils, is symmetrically distributed in the front/rear end of magnet.
11. magnetic resonance systems with auxiliary shim coil as claimed in claim 10, it is characterized in that, described two auxiliary shim coils connect same power supply or connect two different electrical power, and size of current during energising in two auxiliary shim coils is identical with direction.
12. magnetic resonance systems with auxiliary shim coil as claimed in claim 10, it is characterized in that, described two auxiliary shim coils connect the different passages of same power supply or connect two different electrical power, and size of current during energising in two auxiliary shim coils is identical, opposite direction.
13. magnetic resonance systems with auxiliary shim coil as claimed in claim 10, it is characterized in that, described two auxiliary shim coils connect the different passages of same power supply or connect two different power supplys, and during energising, the size of current of two auxiliary shim coils is different.
The method for shimming of 14. 1 kinds of magnetic resonance systems, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 11 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 until the second order hamonic function coefficient value recalculating drop within the scope of referential data.
The method for shimming of 15. 1 kinds of magnetic resonance systems, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 12 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 described single order hamonic function coefficient value and described auxiliary shim coil;
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 16. 1 kinds of magnetic resonance systems, is characterized in that, described magnetic resonance system adopts the magnetic resonance system described in claim 13 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;
B 3) 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 described single order hamonic function coefficient value and described auxiliary shim coil; Make described another auxiliary shim coil 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 described second order hamonic function coefficient value and described auxiliary shim coil;
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;
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 within the scope of referential data respectively.
The method for shimming of 17. magnetic resonance systems as described in any one in claim 14-16, is characterized in that, described referential data scope is 0-30ppm.
The method for shimming of 18. magnetic resonance systems as claimed in claim 17, is characterized in that, described referential data is 0ppm.
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| CN106659416A (en) * | 2014-07-03 | 2017-05-10 | 株式会社日立制作所 | Magnetic resonance imaging device and high frequency magnetic field shim parameter determination method |
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| CN112444766B (en) * | 2020-11-05 | 2023-09-26 | 上海联影医疗科技股份有限公司 | Magnetic resonance system and shimming method thereof |
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