CN109856575A - A kind of method, apparatus, equipment and the storage medium of the passive shimming of determining magnetic resonance - Google Patents
A kind of method, apparatus, equipment and the storage medium of the passive shimming of determining magnetic resonance Download PDFInfo
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Abstract
The invention discloses a kind of methods of determining passive shimming of magnetic resonance, including the intracorporal magnetic field data of chamber before the not set shimming piece of acquisition as initial field data, and obtain target field data；The minimum value of loss function is determined by the initial field data, the loss function is the function of the difference between the adjustment field after determining target field and the setting shimming piece；The loss function meets the constraint condition based on frequency analysis constraint condition and based on target field analysis；Adjustment field data when by loss function minimum determines the thickness of the shimming piece and the spatial arrangement of the shimming piece.The restrictive condition and the restrictive condition based on target field that the present invention incorporates harmonic component, are mixed with two methods of harmonic component and target field, keep their superiority and inferiority complementary, obtain and the more similar adjustment field of target field.The present invention also provides device, equipment and the computer storage medium of a kind of passive shimming of determination magnetic resonance with above-mentioned beneficial effect.
Description
Technical field
The present invention relates to electromagnetic scanning field, more particularly to a kind of determining passive shimming of magnetic resonance method, apparatus, set
Standby and storage medium.
Background technique
Mr imaging technique with the characteristics such as its superior soft tissue separating capacity and harm to the human body be small gradually at
For the indispensable a part of hospital imaging department.And medical superconducting magnetic resonance (1.5 or 3T) is in signal-to-noise ratio, resolution ratio and imaging
More traditional Permanent magnetic MR has apparent advantage in speed.One of design difficulty of superconducting magnetic resonance is to require very high
Magnetic field homogeneity, peak-to-peak value will be lower than 10ppm (hundred a ten thousandths).But due to some uncertain factors or error,
The uniformity of initial fields is in 400-600ppm or so, so need further to optimize this initial fields, i.e. shimming process.
Currently invention addresses realize shimming process, existing passive method for shimming or be base by passive method for shimming
In frequency analysis, its shortcoming is that can not still be eliminated for high-order harmonic wave component, and the harmonic wave sometimes eliminated and different
Surely obtain a good overall uniformity；It is based on target field analysis, its shortcoming is that control that cannot be selective
Certain harmonic components are made, so as to cause certain unnecessary the number of iterations, the problem of declining the uniformity of magnetic field entirety, because
How this, reduce the uniformity (uniformity is lower, and magnetic field is more uniform) in magnetic field, and being that those skilled in the art are urgently to be resolved asks
Topic.
Summary of the invention
The object of the present invention is to provide method, apparatus, equipment and the storage medium of a kind of determining passive shimming of magnetic resonance, with
Solve the problems, such as that the uniformity of magnetic field totality in the prior art is higher.
To solve the technical problem, the present invention provides a kind of method of passive shimming of determining magnetic resonance, comprising:
The intracorporal magnetic field data of chamber before obtaining not set shimming piece obtains target field data as initial field data；
The minimum value of loss function is determined by the initial field data, the loss function is to determine target field and setting
The function of the difference between adjustment field after the shimming piece；The loss function meet based on frequency analysis constraint condition and
Constraint condition based on target field analysis；
Adjustment field data when by loss function minimum determines the thickness of the shimming piece and the space of the shimming piece
Arrangement.
Optionally, described that damage is determined by the initial field data in the method for the determining passive shimming of magnetic resonance
Functional minimum value is lost, determines following loss function specifically by the initial field data
Minimum value；
Wherein J is the azimuth position of the shimming piece, and I is the axial position of the shimming piece, εfFor coefficient of relaxation, εh
For the admissible harmonic wave uniformity, x (i, j) is adjustment field data, tmaxThe maximum shimming that can be filled for each spatial position is thick
Degree, BzFor axial magnetic field strength, anm, bnmFor the axial magnetic field strength BzGroups of samples under spherical coordinates at related Le
Allow the coefficient component of German side's journey, subscript s indicates that this data is the data of the initial fields, and subscript r indicates that this data is the tune
The data of whole field.
Optionally, in the method for the determining passive shimming of magnetic resonance, the loss function further includes weight coefficient, institute
The coefficient matrix that weight coefficient is the adjustment field is stated, for determining imaging region size, initial magnetic field field strength distribution and magnet
Influence size of the inner diameter size to the adjustment field.
Optionally, in the method for the determining passive shimming of magnetic resonance, the determination method of the weight coefficient are as follows:
Obtain target field data；
Determine the difference of the target field data Yu the initial field data each point；
Determine the spatial position of difference pole, the difference pole is the point of the maximum absolute value of the difference；
The ratio for determining the contribution of the shimming piece of each point to the difference pole, the contribution ratio as above-mentioned ratio；
It determines the inverse ratio of the contribution ratio, and the inverse ratio is normalized, obtain the weight coefficient.
Optionally, described that damage is determined by the initial field data in the method for the determining passive shimming of magnetic resonance
Lose functional minimum value specifically:
The minimum value of loss function is determined by the initial field data using L2,1 norm.
Optionally, the chamber in the method for the determining passive shimming of magnetic resonance, before the not set shimming piece of acquisition
After intracorporal magnetic field data is as initial field data, further includes:
Deconvolution processing is carried out to the initial field data；
The minimum value that loss function is determined by the initial field data further include:
Initial field data by carrying out deconvolution processing determines the minimum value of loss function.
The present invention also provides a kind of devices of determining passive shimming of magnetic resonance, comprising:
Module is obtained, for obtaining the intracorporal magnetic field data of chamber before not set shimming piece as initial field data, and is obtained
Take target field data；
Computing module, for determining the minimum value of loss function by the initial field data, the loss function is true
The function of the difference between adjustment field to set the goal after field and the setting shimming piece；The loss function, which meets, is based on harmonic wave
Analysis constraint condition and constraint condition based on target field analysis；
Determining module determines thickness and the institute of the shimming piece for passing through adjustment field data when loss function minimum
State the spatial arrangement of shimming piece.
Optionally, in the device of the determining passive shimming of magnetic resonance, institute's data are calculated module and are specifically used for:
The loss function further includes weight coefficient, and the weight coefficient is the coefficient matrix of the adjustment field, for true
Imaging region size, initial magnetic field field strength distribution and magnet inner diameter size are determined to the influence size of the adjustment field.
The present invention also provides a kind of equipment of determining passive shimming of magnetic resonance, comprising:
Memory, for storing computer program；
Processor, when for executing the computer program realize it is above-mentioned it is any as described in determination magnetic resonance it is passively even
The step of method of field.
The present invention also provides a kind of computer readable storage mediums, which is characterized in that the computer-readable storage medium
Computer program is stored in matter, when the computer program is executed by processor realize it is above-mentioned it is any as described in determination magnetic
Resonate passive shimming method the step of.
The method of the passive shimming of determining magnetic resonance provided by the present invention, including in the cavity before the not set shimming piece of acquisition
Magnetic field data as initial field data, and obtain target field data；Determine loss function most by the initial field data
Small value, the loss function are the function of the difference between the adjustment field after determining target field and the setting shimming piece；Institute
State constraint condition of the loss function satisfaction based on frequency analysis constraint condition and based on target field analysis；Pass through loss function minimum
When adjustment field data, determine the thickness of the shimming piece and the spatial arrangement of the shimming piece.The present invention incorporates harmonic wave point
The restrictive condition of amount and the restrictive condition based on target field by sensitivity coefficient matrix majorization, are mixed with harmonic component and target field
Two methods keep their superiority and inferiority complementary, can both eliminate certain harmonic waves, also ensure overall uniformity, and then make magnetic field
The uniformity decline, obtain and the more similar adjustment field of target field.
Detailed description of the invention
For the clearer technical solution for illustrating embodiment of the present invention or the prior art, below will to embodiment or
Attached drawing needed to be used in the description of the prior art is briefly described, it should be apparent that, the accompanying drawings in the following description is only
Some embodiments of the present invention, for those of ordinary skill in the art, without creative efforts, also
Other drawings may be obtained according to these drawings without any creative labor.
Fig. 1 is the design diagram of passive shimming in the prior art；
Fig. 2 is a kind of process signal of specific embodiment of the method for the determining passive shimming of magnetic resonance provided by the invention
Figure；
Fig. 3 is that the process of another specific embodiment of the method for the determining passive shimming of magnetic resonance provided by the invention is shown
It is intended to；
Fig. 4 is that the process of another specific embodiment of the method for the determining passive shimming of magnetic resonance provided by the invention is shown
It is intended to；
Fig. 5 is a kind of structural representation of specific embodiment of the device of the determining passive shimming of magnetic resonance provided by the invention
Figure；
Fig. 6 is a kind of magnetic simulation of specific embodiment of the method for the determining passive shimming of magnetic resonance provided by the invention
Schematic diagram；
Fig. 7 is a kind of magnetic simulation schematic diagram of specific embodiment of the prior art.
Specific embodiment
The method for shimming of mainstream has at present: active shimming method and passive shimming method.
Active shimming method be by installing a series of active shimming coils, and the electric current in regulating winding, come reach to
The high-order harmonic wave to disappear in associated Legendre polynomial, to improve magnetic field's regularity.But due to the limit of size and position
System and cost problem, can only at most disappear at present to 3 order harmonics, and the non-uniform magnetic-field of some high-order terms is not eliminated yet.
The process of passive shimming method is, by installing shimming slot on the outside of gradient coil, placed in each shimming slot it is small and
The thin shimming piece with ferromagnetic properties is as shown in Figure 1, offset main field not by polarizing magnetic field that shimming piece generates
The purpose of uniformity.
The passive shimming technique of mainstream is divided into method of the sum based on frequency analysis based on target field analysis.Based on harmonic wave point
The algorithm of analysis improves uniformity by impure harmonic wave between elimination target field and measurement field；And the method based on target field is then
It is the direct magnetic field difference eliminated between target field and measurement field.
For passive shimming, it is contemplated that the complexity in magnetic field selects suitable optimization method that can not only improve magnetic field
Uniformity, reduce shimming iteration number, moreover it is possible to reduce the usage quantity of shimming piece, to reduce cost, improve making for magnet
With value.Existing optimization method is based on linear programming, by solving optimization problem (a target equation, a several limits
Condition processed) obtain the placement position of specific shimming piece, it is not optimize.
In order to enable those skilled in the art to better understand the solution of the present invention, with reference to the accompanying drawings and detailed description
The present invention is described in further detail.Obviously, described embodiment is only some embodiments of the invention, and
The embodiment being not all of.Based on the embodiment in the present invention, those of ordinary skill in the art are not making creativeness
Every other embodiment obtained, shall fall within the protection scope of the present invention under the premise of labour.
Core of the invention is to provide a kind of method of passive shimming of determining magnetic resonance, a kind of stream of specific embodiment
Journey schematic diagram is as shown in Fig. 2, be called specific embodiment one, comprising:
Step S101: the intracorporal magnetic field data of chamber before obtaining not set shimming piece obtains mesh as initial field data
Mark field data.
Above-mentioned target field data is to wish the data in the ideal magnetic field reached.
Further, the intracorporal magnetic field data of chamber before the not set shimming piece of above-mentioned acquisition as initial field data it
Afterwards, further includes:
Deconvolution processing is carried out to above-mentioned initial field data；
The minimum value of loss function is determined above by above-mentioned initial field data further include:
Initial field data by carrying out deconvolution processing determines the minimum value of loss function.
The detailed process that above-mentioned magnetic field is deconvoluted can are as follows:
Axial magnetic field strength BzIt is multinomial that the composition of sampled point F (r, θ, Φ) under spherical coordinates meets orthogonal Legendre
Formula:
WhereinFor m Associated Legendre solution of n rank,For unknown coefficient.
For passive shimming technique, an orbit radius is R, is placed in position with a thickness of the ferromagnetism shimming piece of tIts polarizing magnetic field generated can eliminate specific ball harmonic wave at point F (r, θ, Φ), can be expressed as:
Wherein, MzFor the intensity of magnetization, εmFor Newman coefficient, as m=0, Newman coefficient is 1；When m is greater than 0, Newman system
Number is 2.
Step S102: determining the minimum value of loss function by above-mentioned initial field data, and above-mentioned loss function is to determine mesh
Mark the function for adjusting the difference between field after field and the above-mentioned shimming piece of setting；Above-mentioned loss function, which meets, is based on frequency analysis
Constraint condition and constraint condition based on target field analysis.
Further, the minimum value that loss function is determined above by above-mentioned initial field data, specifically by above-mentioned
Initial field data determines following loss function
Minimum value；
Wherein J is the azimuth position of above-mentioned shimming piece, and I is the axial position of above-mentioned shimming piece, εfFor coefficient of relaxation, εh
For the admissible harmonic wave uniformity, x (i, j) is adjustment field data, tmaxThe maximum shimming that can be filled for each spatial position is thick
Degree, BzFor axial magnetic field strength, anm, bnmFor above-mentioned axial magnetic field strength BzGroups of samples under spherical coordinates at related Le
Allow the coefficient component of German side's journey, subscript s indicates that this data is the data of above-mentioned initial fields, and subscript r indicates that this data is above-mentioned tune
The data of whole field.WithIt can also be expressed based on target field are as follows:WithWherein,For sensitivity coefficient matrix, the method that can be calculated by numerical value or measure correction is asked
Out.
Step S103: adjustment field data when by loss function minimum determines the thickness of above-mentioned shimming piece and above-mentioned even
The spatial arrangement of field piece.
The method of the passive shimming of determining magnetic resonance provided by the present invention, including in the cavity before the not set shimming piece of acquisition
Magnetic field data as initial field data, and obtain target field data；Determine loss function most by above-mentioned initial field data
Small value, above-mentioned loss function are the function of the difference between the adjustment field after determining target field and the above-mentioned shimming piece of setting；On
State constraint condition of the loss function satisfaction based on frequency analysis constraint condition and based on target field analysis；Pass through loss function minimum
When adjustment field data, determine the thickness of above-mentioned shimming piece and the spatial arrangement of above-mentioned shimming piece.The present invention incorporates harmonic wave point
The restrictive condition of amount and the restrictive condition based on target field by sensitivity coefficient matrix majorization, are mixed with harmonic component and target field
Two methods keep their superiority and inferiority complementary, can both eliminate certain harmonic waves, also ensure overall uniformity, and then make magnetic field
The uniformity decline, obtain and the more similar adjustment field of target field.
On the basis of specific embodiment one, the determination method of the minimum value of above-mentioned loss function is defined, is obtained
To specific embodiment two, flow diagram is as shown in Figure 3, comprising:
Step S201: the intracorporal magnetic field data of chamber before obtaining not set shimming piece obtains mesh as initial field data
Mark field data.
Step S202: utilizing L2, and 1 norm determines the minimum value of loss function, above-mentioned loss by above-mentioned initial field data
Function is the function of the difference between the adjustment field after determining target field and the above-mentioned shimming piece of setting；Above-mentioned loss function meets
Constraint condition based on frequency analysis constraint condition and based on target field analysis.
Specifically, with above-mentioned formula (3) citing, illustrate how to determine adjustment field data when above-mentioned loss function determines,
Formula (3) based on L2,1 norm can be written as following form:
Sub- optimization problem is solved using inaccurate augmentation Lagrange multiplier method in order to obtain.Firstly, target letter
Several Augmented Lagrangian Functions are as follows:
Wherein Y is Lagrange multiplier, and λ, u are punishment parameters, and b is the magnetic field error for needing to be compensated, x0For linear gauge
Obtained initial solution is drawn, A is sensitivity coefficient matrix, τfFor tolerance.
Above formula is solved using Intercross iteration method, available:
Y1=u1b-u1Ax-u1εf
Y2=u2εf-u2b-u2Ax
Wherein A is sensitivity coefficient matrix, and x is required above-mentioned shimming piece thickness and shimming piece spatial positional information.
Step S203: adjustment field data when by loss function minimum determines the thickness of above-mentioned shimming piece and above-mentioned even
The spatial arrangement of field piece.
Present embodiment and above-mentioned specific embodiment the difference is that, defined in present embodiment
The method for determining above-mentioned loss function minimum value, remaining step is identical as above-mentioned specific embodiment, not reinflated superfluous herein
It states.
Further, determine that the minimum value of loss function is also calculated using population above by above-mentioned initial field data
Method or linear programming technique.
The locally optimal solution not necessarily globally optimal solution that conventional linear programming technique is found, after successive ignition, algorithm
It is easily ensnared into endless loop, so as to cause the obtained excessive consumption of above-mentioned shimming piece or excessive magnetic field bump.
And present embodiment is used using linear programming as initial solution, L2,1 norm is come excellent as the regular terms of Non-Linear Programming
Magnetizing field reduces the consumption of above-mentioned shimming piece, guarantees magnetic field's regularity, emphasizes the correlation between different responses.It solves simultaneously
The problem for sparse dispersibility of having determined, rarefaction representation can convert luv space to the space of a distinctive, and L2, and 1 norm is about
Shu Wenti has good convergence, can obtain only optimal solution
On the basis of specific embodiment two, weight coefficient is further added, obtains specific embodiment three, process
Schematic diagram is as shown in Figure 4, comprising:
Step S301: the intracorporal magnetic field data of chamber before obtaining not set shimming piece obtains mesh as initial field data
Mark field data.
Step S302: utilizing L2, and 1 norm determines the minimum value of loss function, above-mentioned loss by above-mentioned initial field data
Function is the function of the difference between the adjustment field after determining target field and the above-mentioned shimming piece of setting；Above-mentioned loss function meets
Constraint condition based on frequency analysis constraint condition and based on target field analysis；Above-mentioned loss function further includes weight coefficient, on
The coefficient matrix that weight coefficient is above-mentioned adjustment field is stated, for determining imaging region size, initial magnetic field field strength distribution and magnet
Influence size of the inner diameter size to above-mentioned adjustment field.
Further, the determination method of above-mentioned weight coefficient are as follows:
Obtain target field data；
Determine the difference of above-mentioned target field data Yu above-mentioned initial field data each point；
Determine the spatial position of difference pole, above-mentioned difference pole is the point of the maximum absolute value of above-mentioned difference；
The ratio for determining the contribution of the shimming piece of each point to above-mentioned difference pole, the contribution ratio as above-mentioned ratio；
It determines the inverse ratio of above-mentioned contribution ratio, and above-mentioned inverse ratio is normalized, obtain above-mentioned weight coefficient.
Further, the formula (3) for being added to above-mentioned weight coefficient can be written as follow form:
Wherein wijFor above-mentioned weight coefficient.
Further, above-mentioned contribution ratio can be obtained by above-mentioned formula (2).
Step S303: adjustment field data when by loss function minimum determines the thickness of above-mentioned shimming piece and above-mentioned even
The spatial arrangement of field piece.
Present embodiment and above-mentioned specific embodiment the difference is that, joined in present embodiment
Weight coefficient, remaining step is identical as above-mentioned specific embodiment, not reinflated herein to repeat.
Present embodiment is equivalent to by introducing above-mentioned weight coefficient and has preset imaging region size, initial
Influence of the factors such as field strength distribution and magnet inner diameter size to above-mentioned adjustment field is strong and weak, enormously simplifies calculating process, mentions
High computational efficiency.
The device of the passive shimming of determination magnetic resonance provided below embodiment of the present invention is introduced, described below
Determine that the device of the passive shimming of magnetic resonance can correspond to each other reference with the method for the above-described determining passive shimming of magnetic resonance.
Fig. 5 is the structural block diagram of the device for the passive shimming of determination magnetic resonance that embodiment of the present invention provides, true referring to Fig. 5
The device for determining the passive shimming of magnetic resonance may include:
Module 100 is obtained, for obtaining the intracorporal magnetic field data of chamber before not set shimming piece as initial field data, and
Obtain target field data；
Computing module 200, for determining the minimum value of loss function by above-mentioned initial field data, above-mentioned loss function is
Determine the function for adjusting the difference between field after target field and the above-mentioned shimming piece of setting；Above-mentioned loss function meets based on humorous
Wave analysis constraint condition and constraint condition based on target field analysis；
Determining module 300, for pass through loss function minimum when adjustment field data, determine above-mentioned shimming piece thickness and
The spatial arrangement of above-mentioned shimming piece.
The device of the passive shimming of determining magnetic resonance provided by the present invention, including by obtain module 100 obtain it is not set
The intracorporal magnetic field data of chamber before shimming piece obtains target field data as initial field data；Passed through by computing module 200
Above-mentioned initial field data determines the minimum value of loss function, above-mentioned loss function be determine target field and be arranged above-mentioned shimming piece it
The function of the difference between adjustment field afterwards；Above-mentioned loss function meets based on frequency analysis constraint condition and based on target field point
The constraint condition of analysis；Pass through adjustment field data when loss function minimum by determining module 300, determines the thickness of above-mentioned shimming piece
The spatial arrangement of degree and above-mentioned shimming piece.The present invention incorporates the restrictive condition of harmonic component and by sensitivity coefficient matrix majorization
Restrictive condition based on target field is mixed with two methods of harmonic component and target field, keeps their superiority and inferiority complementary, can both disappear
Except certain harmonic waves, overall uniformity is also ensured, and then decline the uniformity in magnetic field, obtain and the more similar tune of target field
Whole field.
The device of the passive shimming of determination magnetic resonance of present embodiment is for realizing the determining passive shimming of magnetic resonance above-mentioned
Method, it is thus determined that the visible determination magnetic resonance hereinbefore of specific embodiment in the device of the passive shimming of magnetic resonance is passive
The embodiment part of the method for shimming, for example, obtaining module 100, computing module 200, determining module 300 is respectively used to reality
Step S101, S102 and S103 in the method for the existing above-mentioned determining passive shimming of magnetic resonance, so, specific embodiment can join
According to the description of corresponding various pieces embodiment, details are not described herein.
Fig. 6 and Fig. 7 are a kind of a kind of output of specific embodiment of of the invention specific embodiment and the prior art
The Comparative result in magnetic field is set in field strength 3T, carries out simplation verification on the magnetic resonance imager of 160mm diameter sphere product (DSV).
The specification of its passive shimming are as follows: 15 × 12,20mm × 30mm × 0.01mm shimming piece.The uniformity of initial fields is on the left side 440ppm
It is right.
Through the invention the magnet uniformity of calculating simulation can reach 9.49ppm (as shown in Figure 6), and and the prior art
The magnet uniformity that method calculates is minimum can only to arrive 12.41ppm (as shown in Figure 7).
The present invention also provides a kind of equipment, in above equipment, each component part, which can be shared out the work and helped one another, executes any of the above-described implementation
The method of the passive shimming of determination magnetic resonance described in mode.Remaining content can refer to the prior art, no longer be opened up herein
Open description.
Invention additionally provides a kind of computer readable storage medium, it is stored on above-mentioned computer readable storage medium
Computer program, above-mentioned computer program realize determination described in any of the above-described invention embodiment when being executed by processor
The method of the passive shimming of magnetic resonance.Remaining content is referred to the prior art, no longer carries out expansion description herein.
Each embodiment is described in a progressive manner in this specification, what each embodiment stressed be with
The difference of other embodiment, same or similar part may refer to each other between each embodiment.For embodiment party
For device disclosed in formula, since it is corresponding with method disclosed in embodiment, so being described relatively simple, related place
Referring to method part illustration.
It should be noted that in the present specification, relational terms such as first and second and the like are used merely to one
A entity or operation with another entity or operate distinguish, without necessarily requiring or implying these entities or operation it
Between there are any actual relationship or orders.Moreover, the terms "include", "comprise" or its any other variant are intended to
Cover non-exclusive inclusion, so that the process, method, article or equipment for including a series of elements not only includes those
Element, but also including other elements that are not explicitly listed, or further include for this process, method, article or setting
Standby intrinsic element.In the absence of more restrictions, the element limited by sentence "including a ...", it is not excluded that
There is also other identical elements in the process, method, article or equipment for including above-mentioned element.
Professional further appreciates that, in conjunction with each exemplary list of embodiment disclosed herein description
Member and algorithm steps, can be realized with electronic hardware, computer software, or a combination of the two, in order to clearly demonstrate hardware
With the interchangeability of software, each exemplary composition and step are generally described according to function in the above description.This
A little functions are implemented in hardware or software actually, the specific application and design constraint depending on technical solution.Specially
Industry technical staff can use different methods to achieve the described function each specific application, but this realization is not
It is considered as beyond the scope of this invention.
The step of method or algorithm for describing in conjunction with embodiment disclosed herein, can directly use hardware, processor
The combination of the software module or the two of execution is implemented.Software module can be placed in random access memory (RAM), memory, read-only
Memory (ROM), electrically programmable ROM, electrically erasable ROM, register, hard disk, moveable magnetic disc, CD-ROM or skill
In any other form of storage medium well known in art field.
The method, apparatus, equipment and storage medium of the determining passive shimming of magnetic resonance provided by the present invention are carried out above
It is discussed in detail.Used herein a specific example illustrates the principle and implementation of the invention, the above embodiment party
The explanation of formula is merely used to help understand method and its core concept of the invention.It should be pointed out that for the general of the art
, without departing from the principle of the present invention, can be with several improvements and modifications are made to the present invention for logical technical staff, this
A little improvement and modification are also fallen within the protection scope of the claims of the present invention.
Claims (10)
1. a kind of method of the passive shimming of determining magnetic resonance characterized by comprising
The intracorporal magnetic field data of chamber before obtaining not set shimming piece obtains target field data as initial field data；
The minimum value of loss function is determined by the initial field data, the loss function is to determine described in target field and setting
The function of the difference between adjustment field after shimming piece；The loss function meets based on frequency analysis constraint condition and is based on
The constraint condition of target field analysis；
Adjustment field data when by loss function minimum determines the thickness of the shimming piece and the space row of the shimming piece
Cloth.
2. determining the method for the passive shimming of magnetic resonance as described in claim 1, which is characterized in that described to pass through the initial fields
Data determine the minimum value of loss function, determine following loss function specifically by the initial field data
Minimum value；
Wherein J is the azimuth position of the shimming piece, and I is the axial position of the shimming piece, εfFor coefficient of relaxation, εhFor can
The harmonic wave uniformity of permission, x (i, j) are adjustment field data, tmaxFor the maximum shimming thickness that each spatial position can fill, Bz
For axial magnetic field strength, anm, bnmFor the axial magnetic field strength BzGroups of samples under spherical coordinates at related Legendre
The coefficient component of equation, subscript s indicate that this data is the data of the initial fields, and subscript s indicates that this data is the adjustment field
Data.
3. determining the method for the passive shimming of magnetic resonance as claimed in claim 2, which is characterized in that the loss function further includes
Weight coefficient, the weight coefficient is the coefficient matrix of the adjustment field, for determining imaging region size, initial magnetic field field strength
Distribution and magnet inner diameter size are to the influence size for adjusting field.
4. determining the method for the passive shimming of magnetic resonance as claimed in claim 3, which is characterized in that the determination of the weight coefficient
Method are as follows:
Obtain target field data；
Determine the difference of the target field data Yu the initial field data each point；
Determine the spatial position of difference pole, the difference pole is the point of the maximum absolute value of the difference；
The ratio for determining the contribution of the shimming piece of each point to the difference pole, the contribution ratio as above-mentioned ratio；
It determines the inverse ratio of the contribution ratio, and the inverse ratio is normalized, obtain the weight coefficient.
5. determining the method for the passive shimming of magnetic resonance as described in claim 1, which is characterized in that described to pass through the initial fields
Data determine the minimum value of loss function specifically:
The minimum value of loss function is determined by the initial field data using L2,1 norm.
6. determining the method for the passive shimming of magnetic resonance as described in claim 1, which is characterized in that not set even in the acquisition
After the intracorporal magnetic field data of chamber before piece is as initial field data, further includes:
Deconvolution processing is carried out to the initial field data；
The minimum value that loss function is determined by the initial field data further include:
Initial field data by carrying out deconvolution processing determines the minimum value of loss function.
7. a kind of device of the passive shimming of determining magnetic resonance characterized by comprising
Module is obtained, for obtaining the intracorporal magnetic field data of chamber before not set shimming piece as initial field data, and obtains mesh
Mark field data；
Computing module, for determining the minimum value of loss function by the initial field data, the loss function is to determine mesh
Mark the function for adjusting the difference between field after field and the setting shimming piece；The loss function, which meets, is based on frequency analysis
Constraint condition and constraint condition based on target field analysis；
Determining module determines the thickness of the shimming piece and described even for passing through adjustment field data when loss function minimum
The spatial arrangement of field piece.
8. determining the method for the passive shimming of magnetic resonance as claimed in claim 7, which is characterized in that institute's data are calculated module and specifically used
In:
The loss function further includes weight coefficient, the weight coefficient be it is described adjustment field coefficient matrix, for determine at
As area size, initial magnetic field field strength distribution and magnet inner diameter size are to the influence size of the adjustment field.
9. a kind of equipment of the passive shimming of determining magnetic resonance characterized by comprising
Memory, for storing computer program；
Processor realizes such as determining magnetic resonance quilt described in any one of claim 1 to 5 when for executing the computer program
The step of method of dynamic shimming.
10. a kind of computer readable storage medium, which is characterized in that be stored with computer on the computer readable storage medium
Program is realized when the computer program is executed by processor as determining magnetic resonance described in any one of claim 1 to 5 is passive
The step of method of shimming.
Priority Applications (1)
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| CN115526046A (en) * | 2022-09-27 | 2022-12-27 | 江西嘉百乐商业管理集团有限公司 | Magnetic resonance passive shimming device and generation method, device, system and equipment thereof |
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