CN110927642B - Shimming control method, device and system for magnetic resonance imaging - Google Patents
Shimming control method, device and system for magnetic resonance imaging Download PDFInfo
- Publication number
- CN110927642B CN110927642B CN201911235512.5A CN201911235512A CN110927642B CN 110927642 B CN110927642 B CN 110927642B CN 201911235512 A CN201911235512 A CN 201911235512A CN 110927642 B CN110927642 B CN 110927642B
- Authority
- CN
- China
- Prior art keywords
- coil
- magnetic field
- spherical harmonic
- field distribution
- determining
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
- G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
Abstract
The application relates to a shimming control method, a shimming control device and a shimming control system for magnetic resonance imaging. The method comprises the following steps: acquiring an actual magnetic field distribution of a magnetic resonance imaging region; determining a spherical harmonic representation of the actual magnetic field distribution; determining a target current value of each basic coil corresponding to an imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; the coil array is arranged in the magnetic resonance equipment and used for shimming magnetic resonance; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array; and carrying out current control on each basic coil corresponding to the imaging region based on the target current value to realize shimming. The method applies a target current value determined according to the spherical harmonic expression of actual magnetic field distribution and the kernel function of the coil array to a basic coil corresponding to an imaging region in the coil array to realize shimming, so that the requirement of high-order shimming can be met without overlapping coil number in space.
Description
Technical Field
The present application relates to the field of magnetic resonance technology, and in particular, to a shimming control method, apparatus, and system for magnetic resonance imaging.
Background
One of the biggest engineering challenges in modern Magnetic Resonance Imaging (MRI) is to provide a super strong, highly uniform magnetic field in the imaging zone. To avoid signal loss or loss due to spin phase changes during signal acquisition, an MRI sequence may require a spectral line width of the entire imaging region as low as about 40 hz. This corresponds to a Δ B ≈ 1ppm field variation for 1.0TMRI, a Δ B ≈ 1/3ppm field variation for 3.0TMRI, and a Δ B ≈ 1/7ppm field variation for 7.0 TMRI. Due to structural tolerances, such uniformity is almost impossible to achieve at the time of superconducting magnet manufacture. The original magnetic field generated by the superconducting magnet itself has a non-uniformity degree of several hundred ppm (chemical shift), and usually, the original magnetic field can be shimmed by adopting a ferromagnetic material through a passive shimming technology. The image distortion is caused by the fact that the disturbing magnetic field caused by the change of the magnetic susceptibility of the patient body inevitably causes the patient body to generate non-uniform fields, and the change of the non-uniform fields is not only related to the individual patient but also related to different parts and organ tissues of the human body, so the change of the non-uniform fields is dynamic.
First order shimming is typically done with gradient coils. Typical MRI provides 6 second order shim coils, which are known in the engineering as X2, Y2, Z2, X-Y, Y-Z, Z-X. However, in practice, the number of spherical harmonic coils that can be incorporated is limited due to space limitations. However, in high-field, especially ultra-high-field MRI imaging, the shimming of higher-order spherical harmonic terms becomes more and more important, and the conventional dynamic shimming technology cannot meet the requirements of the higher-order shimming.
Disclosure of Invention
In view of the above, it is necessary to provide a shimming control method, apparatus and system for magnetic resonance imaging that can meet the requirements for shimming of higher orders.
A method of shimming for magnetic resonance imaging, the method comprising:
acquiring an actual magnetic field distribution of a magnetic resonance imaging region;
determining a spherical harmonic representation of the actual magnetic field distribution;
determining a target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; wherein the coil array is arranged in a magnetic resonance device for shimming magnetic resonance; the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array
And carrying out current control on each basic coil corresponding to the imaging region based on the target current value to realize shimming.
A shimming control apparatus for magnetic resonance imaging, comprising:
a measurement module for acquiring an actual magnetic field distribution of the magnetic resonance imaging region;
a decomposition module for determining a spherical harmonic representation of the actual magnetic field distribution;
the target current determining module is used for determining a target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; wherein the coil array is arranged in a magnetic resonance device for shimming magnetic resonance; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array;
and the control module is used for carrying out current control on each basic coil corresponding to the imaging region based on the target current value so as to realize shimming.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of any of the above methods when executing the computer program.
A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any of the preceding claims.
A magnetic resonance imaging system comprising: the magnetic resonance equipment, the coil array, the coil current controller corresponding to each basic coil in the coil array and the computer equipment are adopted;
the coil array is arranged on the magnetic pole surface of the magnetic resonance equipment;
the input end of each coil current controller is connected with the computer equipment, and the output end of each coil current controller is connected with the corresponding basic coil in the coil array;
the magnetic resonance device is connected with the computer device.
According to the shimming control method for magnetic resonance imaging, for the actual magnetic field distribution which is actually tested, the spherical harmonic expression of the actual magnetic field distribution corresponding to the actual magnetic field distribution and the kernel function of the coil array are utilized, the target current value of each basic coil corresponding to the imaging region in the coil array is determined, the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array, and when the shimming of a high-order spherical harmonic item in the ultrahigh-field MRI imaging is carried out, the target current value determined according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array is applied to the basic coil corresponding to the imaging region in the coil array to realize shimming, so that the high-order shimming requirement can be met without superposing the number of coils on the space.
Drawings
Figure 1 is a schematic diagram of the components of a magnetic resonance system in one embodiment;
FIG. 2 is a schematic cross-sectional view of a coil array in one embodiment;
FIG. 3 is a schematic vertical cross-sectional view of the coil array shown in FIG. 2;
FIG. 4 is a top view of the coil array shown in FIG. 2;
FIG. 5 is a schematic cross-sectional view of a coil array in another embodiment;
FIG. 6 is a schematic vertical cross-sectional view of the coil array shown in FIG. 5;
FIG. 7 is a top view of the coil array shown in FIG. 5;
figure 8 is a flow chart illustrating a shimming control method for magnetic resonance imaging in one embodiment;
FIG. 9 is a schematic diagram of a Z-X coil in one embodiment;
FIG. 10 is a schematic diagram of an X-Y coil in one embodiment;
FIG. 11 is a schematic diagram of the basic coil structure in one embodiment;
FIG. 12 is a view of the vector field generated in space by the base coil of FIG. 11;
FIG. 13 is a current distribution of array coils 24X17 in one embodiment;
FIG. 14 is a distribution of the spherical field produced by the current distribution of the coils of the array of FIG. 13;
FIG. 15 is a graph of the difference between the field produced by the current distribution of the coils of the array of FIG. 13 and the field produced by the spherical harmonic term;
FIG. 16 is a current distribution of array coils 24X21 in one embodiment;
FIG. 17 is a distribution of the spherical field produced by the current distribution of the coils of the array of FIG. 16;
FIG. 18 is a graph of the difference between the field produced by the current distribution of the coils of the array of FIG. 16 and the field produced by the spherical harmonic term;
FIG. 19 is a current distribution of the array coils 24X21 in another embodiment;
FIG. 20 is a plot of the spherical field generated by the current distribution of the coils of the array of FIG. 19;
FIG. 21 is a difference between a field produced by a current distribution of an array coil of the array coil of FIG. 19 and a field produced by a spherical harmonic term;
FIG. 22 is a block diagram of a shimming control apparatus for magnetic co-frame imaging according to an embodiment;
FIG. 23 is a diagram illustrating an internal structure of a computer device according to an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The shimming control method for magnetic resonance imaging provided by the present application can be applied to a magnetic resonance imaging system as shown in fig. 1, and the system includes a magnetic resonance device 101, a coil array 102, a coil current controller 103 corresponding to each basic coil in the coil array 102, and a computer device 104. Wherein, the coil array 102 is installed on the magnetic pole surface of the magnetic resonance device 101, the input end of each coil current controller 103 is connected with the computer device 104, the output end is connected with the corresponding basic coil in the coil array 102, and the computer device 104 is also connected with the magnetic resonance device 101. Wherein, each basic coil is provided with an independent coil current controller 103 for supplying power, and the coil current controller 103 provides a direct constant current stable current source for the corresponding basic coil in the coil array 102. The computer device implements shimming control of magnetic resonance imaging, determines current values required to be applied to the coil array, controls the coil current controller 103 to apply the current values to the corresponding basic coils of the coil array 102 so as to realize dynamic shimming, and finally the computer device 104 images according to data of magnetic resonance.
The coil array of the present application is a coil array composed of S basic coils C, as shown in fig. 2-4, and arranged in an array distributed in a distributable space, so as to dynamically adjust the non-uniform field generated by all spherical harmonic terms to be eliminated. Based on the shimming control method for magnetic resonance imaging of the present application, the basic coil distribution of the coil array can be arbitrarily distributed as required, and the coil array of one embodiment is shown in fig. 5 to 7.
As shown in fig. 8, the computer device executes a shimming control method for magnetic resonance imaging, comprising the following steps:
s802: an actual magnetic field distribution of a magnetic resonance imaging region is acquired.
The imaging region refers to a magnetic resonance region of interest set by a medical staff according to an examination part of a subject. For example, if the examination site of the subject is a heart, the medical staff sets a magnetic resonance region corresponding to the heart as an imaging region. The actual magnetic field distribution refers to the magnetic field distribution of the imaging region resulting from the measured magnetic resonance. Specifically, the main magnetic field distribution of the imaging region can be measured using a surveying instrument.
And S804, determining the spherical harmonic expression of the actual magnetic field distribution.
And for the main magnetic field distribution of the measured imaging region, carrying out Legendre polynomial expansion on the main magnetic field distribution under a spherical coordinate system to obtain a spherical harmonic expression of the actual magnetic field distribution, wherein the expanded polynomial is as follows:
wherein B is the magnetic field in the spherical coordinate system (r, theta, phi), P(n,m)(cos) is Legendre polynomial, a(n，m)And b(n,m)Are spherical harmonic term coefficients. The traditional dynamic shimming is realized by aiming at each spherical harmonic function item Bn,mA special basic coil is designed. Here, the
Bn,m(r,θ,φ)＝rn[a(n,m)cos(mφ)+b(n,m)sin(mφ)]P(n,m)(cosθ) (2)
Has B0,0A coil whose purpose is to adjust the center frequency. First order shimming is typically done with gradient coils. Typical MRI provides 6 second order base coils, which are known in the engineering as X2, Y2, Z2, X-Y, Y-Z, Z-X. A typical Z-X is shown in fig. 9 and a typical X-Y coil is shown in fig. 10.
And (3) expanding the magnetic field distribution obtained by measurement by using the formula under a spherical coordinate system to obtain the spherical harmonic expression of the actual magnetic field distribution, wherein the spherical harmonic expression of the actual magnetic field distribution represents the actually measured magnetic field distribution condition.
S806, determining target current values of all basic coils corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; the coil array is arranged in the magnetic resonance equipment and used for shimming magnetic resonance; the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array.
Specifically, consider a base coil C having a thickness h, width w, and length l, as shown in fig. 11. The coil conducting wire is wound into the shape of figure 11, and can be single-layer or multi-layer according to the requirement to form a basic coil C with the total number of turns of eta turns. The vector field generated in space according to the biot-savart law is shown in fig. 12.
Here, r0Is the position of the point circle C at p points, R 'is the coordinate of the point field at q points, R ═ R' -R0. Fig. 12 shows the magnetic field vector distribution around a single basic coil C. Considering only B in MRI imagingzA component magnetic field. The current I of a certain coil C in the coil array S is unchanged. So that it can be obtained from the formula (3)
Here, the first and second liquid crystal display panels are,
is a kernel function that indicates the relationship of the spatial field source and the field point. For coil array S, the field at r
Has the following mathematical relationship
Where, i is 1 … s,
the field is the sum of the fields generated by all coils at point r'. The target field of a certain spherical harmonic function item to be adjusted can be reached
The objective function of the dynamic shimming is
Similarly, if a plurality of target fields of certain spherical harmonic terms are to be adjusted, equation (8) can be achieved
Finding the minimum Φ by optimizing equation (8) or (9)min→ 0. Equation (9) can also be converted into the following relationship to directly solve the obtained current
Combining equation (6) to obtain
Usually there are s unknown currents I for an array of s coilsiI is 1 … s. Selecting t target magnetic field points in space
j is 1 … t. Thus, the formula (11) can be changed to
Here, the first and second liquid crystal display panels are,
wherein A is a t × s matrix, I is an s-dimensional unknown current vector,
is the target magnetic field vector in dimension t. In general, the numerical solution of equation (12) is a difficult task because the problem is represented by the Fredholm first-class integral equation. It belongs to the category of the so-called morbid problem. To make the system relax naturally, formula (12) is selected as hyperAnd (5) determining an equation set, namely t is more than or equal to s. To solve this problem, a regularization method is considered which transforms the ill-conditioned problem (11) into an adaptive problem:
here, A*Is a conjugate matrix, A*A is an s × s square matrix and Λ is an s × s identity matrix. α is a very small number, and when α → 0, I approaches the true solution. The selection of the linear operator α Λ, which generally helps to suppress the sharp oscillations in the function I, uses a standard LU decomposition method to solve equation (14) quickly to obtain the target current values for each elementary coil.
In order to improve the response speed of the dynamic shimming, the dynamic shimming current of each normalized spherical harmonic field can be pre-corresponded and calculated in advance in a specific imaging delta region of the MRI, and the dynamic adjustment of the field can be completed immediately once the field of the target imaging delta region is obtained.
Specifically, determining a target current value of each basic coil corresponding to the imaging region in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array includes:
determining a proportionality coefficient according to a spherical harmonic expression of the standardized magnetic field distribution of the imaging region and a spherical harmonic expression of the actual magnetic field distribution, which are acquired in advance;
adjusting the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the proportional coefficient, and determining the target current value of each basic coil corresponding to the actual magnetic field distribution; and determining the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the kernel function of the coil array.
Wherein the proportionality coefficient is a ratio of a spherical harmonic representation of the normalized magnetic field distribution to a spherical harmonic representation of the actual magnetic field distribution. The normalized magnetic field distribution is a magnetic product distribution generated by normalizing a current value, and the spherical harmonic expression of the normalized magnetic field distribution is the spherical harmonic expression of the magnetic product distribution generated by normalizing the current. The normalized current values and the spherical harmonic representation of the normalized magnetic field distribution are stored in a database by pre-calculation.
Specifically, the spherical harmonic expression of the normalized magnetic field distribution may be obtained by performing legendre polynomial expansion on the theoretical magnetic field distribution generated in advance according to a standard current required for non-uniformity of an original magnetic field generated by the superconducting magnet itself in a spherical coordinate system.
Specifically, the scale factor β of the imaging region δn,mIs composed of
Wherein, Bn,mFor spherical harmonic representation of the actual magnetic field distribution,
is a spherical harmonic representation of the normalized magnetic field distribution.
The standardized current value is a standard current required by the non-uniformity of the original magnetic field generated by the superconducting magnet, and is calculated in advance by the system. In practical application, the normalized current value is adjusted by using the ratio between the actual magnetic field distribution and the normalized condition, and the target current value of each basic coil corresponding to the actual magnetic field distribution is obtained.
And because the spherical harmonic expression of the standardized current value and the standardized magnetic field distribution is obtained by pre-calculation, the calculation time is saved and the response speed of the magnetic resonance shimming is improved in the actual application.
Specifically, the shimming control method for magnetic resonance imaging further comprises the following steps: predetermining normalized current value
And spherical harmonic representation of normalized magnetic field distribution
Normalized magnetic field distribution is the magnetic field distribution produced by normalized current values
Wherein predetermining the normalized current value and the spherical harmonic representation of the normalized magnetic field distribution comprises: predetermining a spherical harmonic representation of a normalized magnetic field distribution, and predetermining a normalized current value based on a kernel function of the coil array, comprising: determining the vector distribution of the magnetic field generated by the basic coil in space based on the Biao-Saval law; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array; determining corresponding magnetic field distribution of each imaging area in the coil array according to the kernel function; determining a target function of shimming of each spherical harmonic item according to the magnetic field distribution; and determining the normalized current value and the spherical harmonic expression of the normalized magnetic field distribution according to the objective function of shimming of each spherical harmonic item.
Specifically, the pre-calculation of the standardized current value of each basic coil corresponding to the imaging region in the coil array is the same as the current calculation method for the actual magnetic field distribution, and is not described herein again.
Specifically, the method for adjusting the standard current value of each basic coil corresponding to the imaging region in the pre-calculated coil array according to the proportionality coefficient and determining the target current value of each basic coil corresponding to the actual magnetic field distribution includes: determining the current value of each spherical harmonic item of the basic coil according to the proportionality coefficient of each spherical harmonic item and the standardized current value of each basic coil corresponding to the imaging area in the coil array; and accumulating the current values of all spherical harmonic terms of the basic coil to obtain a target current pool of the basic coil.
From the algorithm itself, the basic coil distribution of the array coils can be arbitrarily distributed as desired. The entire dynamic shimming procedure is the same as long as the kernel function is calculated from the spatial distribution of the basic coils with equation (5).
And S808, current control is carried out on each basic coil corresponding to the imaging region based on the target current value to realize shimming.
Specifically, a target current value is sent to a coil controller corresponding to each basic coil of the imaging region, and the coil controller applies the corresponding target current value to the basic coil to shim the imaging region.
According to the shimming control method for magnetic resonance imaging, for the actual magnetic field distribution which is actually tested, the spherical harmonic expression of the actual magnetic field distribution corresponding to the actual magnetic field distribution and the kernel function of the coil array are utilized, the target current value of each basic coil corresponding to the imaging region in the coil array is determined, the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array, and when the shimming of a high-order spherical harmonic item in the ultrahigh-field MRI imaging is carried out, the target current value determined according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array is applied to the basic coil corresponding to the imaging region in the coil array to realize shimming, so that the high-order shimming requirement can be met without superposing the number of coils on the space.
Further, a proportionality coefficient is determined by using the spherical harmonic expression of the corresponding actual magnetic field distribution and the spherical harmonic expression of the standardized magnetic field distribution, so that the standardized current value of each basic coil is adjusted according to the proportionality coefficient, and the target current value of each basic coil corresponding to the actual magnetic field distribution is obtained. And because the spherical harmonic expression of the standardized current value and the standardized magnetic field distribution is obtained by pre-calculation, the calculation time is saved and the response speed of the magnetic resonance shimming is improved in the actual application.
The shimming control method for magnetic resonance imaging of the present application will now be described with reference to practical examples.
When shimming an MRI imaging region, the zonal term of the spherical harmonic function is generally easier to be uniform, the tesseral term is difficult to adjust, and the adjustment of the expensive tesseral term is more challenging. The powerful capability of the dynamic shimming method is demonstrated here by two array coils.
Firstly, the coil array is selected to be 24X17, namely 24 coils are uniformly distributed on the circumference, and 17 coils are uniformly distributed on the axial direction. From table one it can be seen that some of the spherical harmonic terms that are very difficult under the conventional approach are listed, and that the peak-to-peak value of the field produced for each spherical harmonic term is 5ppm before shimming. The shimmed uniformity of the array coil is less than 1ppm, the adjustment rate is about 90%, and the peak current in the array coil is less than 5 amperes up to the spherical harmonic function term (n is 5, m is 5). As the spherical harmonic term changes increase, the array coil begins to fail substantially in the spherical harmonic terms (n 6, m 6). Table two shows the shimming when the spherical harmonic terms (n is 8, m is 1 … 6) are used. The dynamic shimming of the array coil is very good in performance up to the spherical harmonic terms (n is 8, and m is 5), the shimming uniformity is less than 1ppm, the adjusting rate is about 90%, and the peak current in the array coil is less than 5 amperes. The array coil essentially begins to fail in the spherical harmonic terms (n 8, m 6). It can be seen that the array coil is very effective not only for the zonal field, but also for the tesseral field at m ≦ 5.
Watch 1
Watch two
The following example is a coil array of 24X21, i.e. 24 coils evenly distributed in the circumference and 21 coils evenly distributed in the axial direction. The peak-to-peak value of the field generated for each spherical harmonic term was also 5ppm before shimming. From table three, it can be seen that except for the spherical harmonic terms (n is 6, m is 6), only 60% is adjusted, the spherical harmonic terms (n is 7, m is 7) is 80% adjusted, the uniformity of the fields of the rest spherical harmonic terms after shimming of the array coil is less than 1ppm, and the adjustment rate exceeds 90%. And the peak currents in the coils of the array are less than 5 amps. As the spherical harmonic term changes increase, the array coil begins to fail substantially in the spherical harmonic terms (n 8, m 8). Table four shows the shimming when the spherical harmonic terms (n is 11, m is 1 … 6) are used. The dynamic shimming of the array coil is very good in performance up to the spherical harmonic terms (n is 11, and m is 5), the shimming uniformity is less than 1ppm, and the adjusting rate is about 90%. The array coil essentially begins to fail in the spherical harmonic terms (n 11, m 6). It can be seen that the array coil is very effective for both high order zonal and tesseral fields.
Watch III
Watch four
Fig. 13 to 15 show the shimming cases specific to the array coil 24X17 for the even term (n-8, m-4) of the spherical harmonics. Fig. 13 shows the current distribution of the array coil, and since the spherical harmonic terms (n-8 and m-4) are symmetrical, it can be seen that the current distribution of the array coil is also symmetrical for the single spherical harmonic term. Fig. 14 shows the distribution in the spherical field generated by the current distribution of the array coils, and fig. 15 shows the difference between the field generated by the current distribution of the array coils and the field generated by the spherical harmonic term. As described above, the peak-to-peak value of the field generated by the original spherical harmonic term is 5ppm, the peak-to-peak value after shimming by the array coil is 0.35ppm, and the adjustment rate reaches 93%.
Fig. 16-18 show the shimming case for the array coil 24X21 specific to the odd term spherical harmonics (n-11, m-1). Fig. 16 shows the current distribution of the array coil. Fig. 17 shows the distribution in the spherical field generated by the current distribution of the array coils, and fig. 18 shows the difference between the field generated by the current distribution of the array coils and the field generated by the spherical harmonic term. The peak-to-peak value of the field generated by the original spherical harmonic function is 5ppm, the peak-to-peak value after shimming by the array coil is 0.22ppm, and the adjustment rate reaches 96%.
Fig. 19-21 illustrate shimming cases specific to the array coil 24X21 for higher order spherical harmonic odd terms (n-11, m-3). Fig. 19 shows the current distribution of the array coil. Fig. 20 shows the distribution in the spherical field generated by the current distribution of the array coils, and fig. 21 shows the difference between the field generated by the current distribution of the array coils and the field generated by the spherical harmonic term. As mentioned above, the peak-to-peak value of the field generated by the original spherical harmonic function is 5ppm, the peak-to-peak value after shimming by the array coil is 0.24ppm, and the adjustment rate reaches 95%.
As shown in fig. 22, the present application further provides a shimming control apparatus for magnetic resonance imaging, including:
a measurement module 2201 for acquiring an actual magnetic field distribution of the magnetic resonance imaging region.
A decomposition module 2202 for determining a spherical harmonic representation of the actual magnetic field distribution.
A target current determining module 2203, configured to determine a target current value of each basic coil corresponding to the imaging region in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and a kernel function of the coil array; wherein the coil array is arranged in a magnetic resonance device for shimming magnetic resonance; and the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array.
A control module 2204, configured to perform current control on each basic coil corresponding to the imaging region based on the target current value to implement shimming.
In another embodiment, a target current determination module includes:
and the proportion determining module is used for determining a proportion coefficient according to the spherical harmonic expression of the standardized magnetic field distribution of the imaging region and the spherical harmonic expression of the actual magnetic field distribution which are acquired in advance.
The current calculation module is used for adjusting the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the proportional coefficient and determining the target current value of each basic coil corresponding to the actual magnetic field distribution; and determining the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the kernel function of the coil array.
The device also comprises a preprocessing module used for determining spherical harmonic function expression of the standardized magnetic field distribution and predetermining standardized current values based on the kernel function of the coil array, wherein the standardized magnetic field distribution is the magnetic field distribution generated by the standardized current values.
In another embodiment, the preprocessing module is configured to determine a magnetic field vector distribution generated by the basic coils in space based on biot-savart law, determine a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array, determine a corresponding magnetic field distribution of each imaging region in the coil array according to the kernel function, determine an objective function for shimming each spherical harmonic term according to the magnetic field distribution, and determine a normalized current value and a spherical harmonic expression of the normalized magnetic field distribution according to the objective function for shimming each spherical harmonic term.
In another embodiment, the current calculating module is configured to determine a current value of each spherical harmonic term of the basic coil according to the scaling factor of each spherical harmonic term and a normalized current value of each basic coil corresponding to the imaging region in the coil array, and accumulate the current values of each spherical harmonic term of the basic coil to obtain a target current pool of the basic coil.
In another embodiment, the control module is configured to send the target current values to a coil controller corresponding to each basic coil of the imaging region, and the coil controller applies the corresponding target current values to the basic coils to shim the imaging region.
The shimming control device for magnetic resonance imaging determines the target current value of each basic coil corresponding to the imaging region in the coil array by utilizing the spherical harmonic expression of the actual magnetic field distribution corresponding to the actual magnetic field distribution and the kernel function of the coil array for the actual tested magnetic field distribution, wherein the kernel function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array, and when shimming a high-order spherical harmonic item in ultrahigh-field MRI imaging, the basic coil corresponding to the imaging region in the coil array is applied with the target current value determined according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array to realize shimming, so that the high-order shimming requirement can be met without superposing the number of coil turns on space.
Further, for the actual magnetic field distribution which is actually tested, the spherical harmonic expression of the actual magnetic field distribution corresponding to the actual magnetic field distribution and the spherical harmonic expression of the standardized magnetic field distribution are used for determining a proportionality coefficient, so that the standardized current value of each basic coil is adjusted according to the proportionality coefficient, and the target current value of each basic coil corresponding to the actual magnetic field distribution is obtained. And because the spherical harmonic expression of the standardized current value and the standardized magnetic field distribution is obtained by pre-calculation, the calculation time is saved and the response speed of the magnetic resonance shimming is improved in the actual application.
Specific limitations of the shimming control apparatus for magnetic resonance imaging can be referred to the above limitations of the shimming control method for magnetic resonance imaging, and are not described herein again. The modules in the shimming control device for magnetic resonance imaging can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 23. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is for implementing a method of shimming for magnetic resonance imaging when executed by a processor. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 23 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, a computer device is provided, which includes a memory and a processor, the memory stores a computer program, and the processor implements the shimming control method of magnetic resonance imaging of the above embodiments when executing the computer program.
In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored, which, when being executed by a processor, implements the shimming control method of magnetic resonance imaging of the above-mentioned embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. Non-volatile memory can include read-only memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus Direct RAM (RDRAM), direct bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (11)
1. A method of shimming for magnetic resonance imaging, the method comprising:
acquiring an actual magnetic field distribution of a magnetic resonance imaging region;
determining a spherical harmonic representation of the actual magnetic field distribution;
determining a target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; wherein the coil array is arranged in a magnetic resonance device for shimming magnetic resonance; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array;
current control is carried out on each basic coil corresponding to the imaging region based on the target current value to realize shimming;
determining a target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array, wherein the determining comprises the following steps:
determining a proportionality coefficient according to a spherical harmonic expression of the standardized magnetic field distribution of the imaging region and a spherical harmonic expression of the actual magnetic field distribution, which are acquired in advance;
determining the current value of each spherical harmonic item of the basic coil according to the proportionality coefficient of each spherical harmonic item and the standardized current value of each basic coil corresponding to the imaging area in the coil array; accumulating the current values of all spherical harmonic terms of the basic coil to obtain a target current value of the basic coil; and determining the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the kernel function of the coil array.
2. The method of claim 1, further comprising: the method includes the steps of predetermining a spherical harmonic representation of a normalized magnetic field distribution, and predetermining a normalized current value based on a kernel function of the coil array, the normalized magnetic field distribution being a magnetic field distribution resulting from the normalized current value.
3. The method of claim 2, wherein predetermining a spherical harmonic representation of a normalized magnetic field distribution and predetermining a normalized current value based on a kernel function of the coil array comprises:
determining the vector distribution of the magnetic field generated by the basic coil in the space based on the Biao-Saval law;
determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array;
determining corresponding magnetic field distribution of each imaging area in the coil array according to the kernel function;
determining a target function of shimming of each spherical harmonic item according to the magnetic field distribution;
and determining the normalized current value and the spherical harmonic expression of the normalized magnetic field distribution according to the objective function of shimming of each spherical harmonic item.
4. The method of claim 1, wherein current control of each basic coil corresponding to the imaging region based on the target current value to achieve shimming comprises:
and sending the target current value to a coil controller corresponding to each basic coil of the imaging region, and applying the corresponding target current value to the basic coil by the coil controller so as to shim the imaging region.
5. A shimming control apparatus for magnetic resonance imaging, comprising:
a measurement module for acquiring an actual magnetic field distribution of the magnetic resonance imaging region;
a decomposition module for determining a spherical harmonic representation of the actual magnetic field distribution;
the target current determining module is used for determining a target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic expression of the actual magnetic field distribution and the kernel function of the coil array; wherein the coil array is arranged in a magnetic resonance device for shimming magnetic resonance; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array;
the control module is used for carrying out current control on each basic coil corresponding to the imaging region based on the target current value so as to realize shimming;
the target current determination module includes:
the proportion determining module is used for determining a proportion coefficient according to a spherical harmonic expression of the standardized magnetic field distribution of the imaging region and a spherical harmonic expression of the actual magnetic field distribution which are acquired in advance;
the current calculation module is used for determining the current value of each spherical harmonic item of the basic coil according to the proportionality coefficient of each spherical harmonic item and the standardized current value of each basic coil corresponding to the imaging area in the coil array; accumulating the current values of all spherical harmonic terms of the basic coil to obtain a target current value of the basic coil; and determining the standard current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the kernel function of the coil array.
6. The apparatus of claim 5, further comprising a preprocessing module configured to predetermine a spherical harmonic representation of a normalized magnetic field distribution, and to predetermine normalized current values based on a kernel function of the coil array, the normalized magnetic field distribution being a magnetic field distribution resulting from the normalized current values.
7. The apparatus according to claim 6, wherein the preprocessing module is configured to determine a magnetic field vector distribution generated in space by the base coil based on the biot-savart law; determining a kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array; determining corresponding magnetic field distribution of each imaging area in the coil array according to the kernel function; determining a target function of shimming of each spherical harmonic item according to the magnetic field distribution; and determining the normalized current value and the spherical harmonic expression of the normalized magnetic field distribution according to the objective function of shimming of each spherical harmonic item.
8. The apparatus of claim 5, wherein the control module is configured to send the target current values to a coil controller corresponding to each basic coil of the imaging region, and the coil controller applies the corresponding target current values to the basic coils to shim the imaging region.
9. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the method of any of claims 1 to 4 are implemented when the computer program is executed by the processor.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 4.
11. A magnetic resonance imaging system comprising: a magnetic resonance apparatus, a coil array, coil current controllers corresponding to respective basic coils in the coil array, and a computer apparatus as claimed in claim 9;
the coil array is arranged on the magnetic pole surface of the magnetic resonance equipment;
the input end of each coil current controller is connected with the computer equipment, and the output end of each coil current controller is connected with the corresponding basic coil in the coil array;
the magnetic resonance device is connected with the computer device.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201911235512.5A CN110927642B (en) | 2019-12-05 | 2019-12-05 | Shimming control method, device and system for magnetic resonance imaging |
| PCT/CN2020/128976 WO2021109847A1 (en) | 2019-12-05 | 2020-11-16 | Shimming control method, device, and system for magnetic resonance imaging |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201911235512.5A CN110927642B (en) | 2019-12-05 | 2019-12-05 | Shimming control method, device and system for magnetic resonance imaging |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN110927642A CN110927642A (en) | 2020-03-27 |
| CN110927642B true CN110927642B (en) | 2021-09-10 |
Family
ID=69857182
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201911235512.5A Active CN110927642B (en) | 2019-12-05 | 2019-12-05 | Shimming control method, device and system for magnetic resonance imaging |
Country Status (2)
| Country | Link |
|---|---|
| CN (1) | CN110927642B (en) |
| WO (1) | WO2021109847A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110927642B (en) * | 2019-12-05 | 2021-09-10 | 湖南迈太科医疗科技有限公司 | Shimming control method, device and system for magnetic resonance imaging |
| CN113671431B (en) * | 2021-08-20 | 2023-03-21 | 宁波健信超导科技股份有限公司 | Decoupling method and related device for magnetic resonance high-order shimming coil |
| CN114236440B (en) * | 2021-11-16 | 2022-09-13 | 中国科学院深圳先进技术研究院 | Shimming method and device, electronic equipment and storage medium |
Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0230027B1 (en) * | 1986-01-03 | 1995-08-30 | General Electric Company | Magnet shimming using information derived from chemical shift imaging |
| DE19940694C1 (en) * | 1999-08-27 | 2001-07-26 | Bruker Ag Faellanden | Actively shielded superconducting magnet arrangement with Z · 2 · shim |
| CN1934458A (en) * | 2004-03-17 | 2007-03-21 | 皇家飞利浦电子股份有限公司 | Dynamic shimset calibration for B0 offset |
| CN101435857A (en) * | 2008-12-25 | 2009-05-20 | 北京理工大学 | Cylinder surface even field coil of magnetic nuclear resonance spectrometer and design method thereof |
| JP4615971B2 (en) * | 2003-12-10 | 2011-01-19 | マイクロソフト コーポレーション | Driver specific context for kernel mode shimming |
| CN202870284U (en) * | 2012-07-26 | 2013-04-10 | 宁波鑫高益磁材有限公司 | Active shimming system used for magnetic resonance imaging permanent magnet |
| CN106249184A (en) * | 2016-09-26 | 2016-12-21 | 中国科学院电工研究所 | A kind of dynamic auto method for shimming for nuclear magnetic resonance |
| CN108387857A (en) * | 2017-12-25 | 2018-08-10 | 深圳先进技术研究院 | A kind of local shimming system and method for shimming for magnetic resonance imaging |
| CN109725271A (en) * | 2018-12-29 | 2019-05-07 | 南京国科医工科技发展有限公司 | The shooting parameter determination of array coil and exciting method, device |
| CN109765509A (en) * | 2017-11-09 | 2019-05-17 | 西门子(深圳)磁共振有限公司 | The method for shimming of superconducting magnetic resonance imaging equipment |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2230530A1 (en) * | 2009-03-20 | 2010-09-22 | Koninklijke Philips Electronics N.V. | A tesseral shim coil for a magnetic resonance system |
| JP5943355B2 (en) * | 2011-03-25 | 2016-07-05 | 株式会社日立製作所 | Static magnetic field uniformity adjustment method, static magnetic field generator for magnetic resonance imaging, magnetic field adjustment system, program |
| CN107110922B (en) * | 2014-12-09 | 2020-03-24 | 圣纳普医疗(巴巴多斯)公司 | Solenoid structure and system and method of operation |
| JP6643110B2 (en) * | 2016-01-27 | 2020-02-12 | 株式会社日立製作所 | Magnetic field adjustment device and magnetic resonance imaging device |
| CN109856575B (en) * | 2018-12-29 | 2019-11-01 | 潍坊新力超导磁电科技有限公司 | A kind of method, apparatus, equipment and the storage medium of the passive shimming of determining magnetic resonance |
| CN110308411A (en) * | 2019-08-05 | 2019-10-08 | 北京青檬艾柯科技有限公司 | A kind of high-precision, the quick passive method for shimming of Halbach magnet |
| CN110927642B (en) * | 2019-12-05 | 2021-09-10 | 湖南迈太科医疗科技有限公司 | Shimming control method, device and system for magnetic resonance imaging |
-
2019
- 2019-12-05 CN CN201911235512.5A patent/CN110927642B/en active Active
-
2020
- 2020-11-16 WO PCT/CN2020/128976 patent/WO2021109847A1/en active Application Filing
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0230027B1 (en) * | 1986-01-03 | 1995-08-30 | General Electric Company | Magnet shimming using information derived from chemical shift imaging |
| DE19940694C1 (en) * | 1999-08-27 | 2001-07-26 | Bruker Ag Faellanden | Actively shielded superconducting magnet arrangement with Z · 2 · shim |
| JP4615971B2 (en) * | 2003-12-10 | 2011-01-19 | マイクロソフト コーポレーション | Driver specific context for kernel mode shimming |
| CN1934458A (en) * | 2004-03-17 | 2007-03-21 | 皇家飞利浦电子股份有限公司 | Dynamic shimset calibration for B0 offset |
| CN101435857A (en) * | 2008-12-25 | 2009-05-20 | 北京理工大学 | Cylinder surface even field coil of magnetic nuclear resonance spectrometer and design method thereof |
| CN202870284U (en) * | 2012-07-26 | 2013-04-10 | 宁波鑫高益磁材有限公司 | Active shimming system used for magnetic resonance imaging permanent magnet |
| CN106249184A (en) * | 2016-09-26 | 2016-12-21 | 中国科学院电工研究所 | A kind of dynamic auto method for shimming for nuclear magnetic resonance |
| CN109765509A (en) * | 2017-11-09 | 2019-05-17 | 西门子(深圳)磁共振有限公司 | The method for shimming of superconducting magnetic resonance imaging equipment |
| CN108387857A (en) * | 2017-12-25 | 2018-08-10 | 深圳先进技术研究院 | A kind of local shimming system and method for shimming for magnetic resonance imaging |
| CN109725271A (en) * | 2018-12-29 | 2019-05-07 | 南京国科医工科技发展有限公司 | The shooting parameter determination of array coil and exciting method, device |
Non-Patent Citations (6)
| Title |
|---|
| A novel target-field method for finite-length magnetic resonance shim coils: I. Zonal shims;Lawrence K Forbes;《Applied Physics》;20011231;第3447-3454页 * |
| Magnetic field shimming of a permanent magnet using a combination of pieces of permanent magnets and a single-channel shim coil for skeletal age assessment of children;Y. Terada;《Journal of Magnetic Resonance》;20131231;第125-133页 * |
| 基于球谐系数的轴向超导匀场线圈设计方法;文聪;《电工电能新技术》;20121231;第60-66页 * |
| 开放式低场永磁MRI磁体的匀场方法研究;赵薇;《电工电能新技术》;20070731;第30-34页 * |
| 永磁磁共振成像系统磁体的梯度匀场方法研究;唐晓英;《北京理工大学学报》;20091231;第279-283页 * |
| 超导磁共振成像系统的无源匀场算法研究;孔霞;《中国优秀博士论文全文数据库 工程科技辑》;20161231;第1-70页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN110927642A (en) | 2020-03-27 |
| WO2021109847A1 (en) | 2021-06-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN110927642B (en) | Shimming control method, device and system for magnetic resonance imaging | |
| US5614827A (en) | Method and apparatus for shimming a magnet system of a nuclear magnetic resonance tomography system | |
| US5345178A (en) | Method for setting the current through shim coils and gradient coils in a nuclear magnetic resonance apparatus | |
| US6140900A (en) | Assymetric superconducting magnets for magnetic resonance imaging | |
| JP4926976B2 (en) | Magnetic resonance imaging system and method | |
| JP2001145609A (en) | Magnetic resonance imaging equipment | |
| WO2013105384A1 (en) | Magnetic resonance imaging apparatus and region-imaging method | |
| JP6001784B2 (en) | Magnetic field adjustment support apparatus, magnetic field adjustment support method, MRI apparatus, and magnet apparatus | |
| US6825667B1 (en) | Magnetic resonance imaging apparatus and method for maintaining high uniformity of magnetic field in magnetic resonance imaging apparatus | |
| JP3682627B2 (en) | Magnetic resonance imaging device | |
| CN104297709A (en) | Gradient magnetic field shimming method based on regularization magnetic field distribution image reconstruction | |
| US5592091A (en) | Method for shimming a magnetic field in an examination space of a nuclear magnetic resonance apparatus including use of fuzzy logic | |
| JP7237460B2 (en) | Magnetic resonance imaging apparatus and multi-slice imaging method | |
| US20130285660A1 (en) | Controlling a Magnetic Resonance System | |
| US20180372827A1 (en) | Magnetic resonance imaging apparatus and medical image processing apparatus | |
| CN112444766A (en) | Magnetic resonance system and shimming method thereof | |
| EP0154996B1 (en) | Magnetic resonance imaging apparatus using shim coil correction | |
| US10866294B2 (en) | Magnetic resonance imaging apparatus, multi-slice imaging method, and shimming value calculation apparatus | |
| JP2003512629A (en) | Permanent magnet and shim design | |
| US20150219733A1 (en) | RF Pulse Alignment | |
| JP2007301348A (en) | Magnetic resonance imaging apparatus and static magnetic field correction method | |
| US10955510B2 (en) | Magnetic resonance imaging apparatus | |
| JP3112929B2 (en) | Magnetic resonance equipment | |
| JP7163061B2 (en) | Magnetic resonance imaging apparatus and multi-slice imaging method | |
| CN112823741A (en) | Magnetic resonance scanning method and magnetic resonance system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |