Shimming method and device of magnetic resonance imaging equipment

Abstract

The invention discloses a shimming method and device for MRI equipment, and relates to the technical field of MRI. According to the method, the magnetic force distribution used for representing the magnetic force borne by the shimming strip at different positions in the process of inserting the shimming strip into the shimming hole can be obtained, the constraint condition is constructed based on the magnetic force distribution of each shimming strip, and then the objective function is solved based on the constraint condition. A magnetic field of an imaging space of the MRI device is shimmed with a solution based on the objective function, i.e., the first shimming sheet distribution. According to the method, the constraint condition can be constructed based on the magnetic force distribution of each shimming strip, so that the magnetic force borne by the shimming strips can be ensured to be within a controllable range when the shimming strips are inserted into the shimming holes in the shimming process, the shimming strips can be prevented from falling off due to overlarge stress, the shimming efficiency of the MRI equipment is improved, and the shimming efficiency of the MRI equipment is improved. And the safety of the shimming process is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of magnetic resonance imaging, and in particular to a method and device for shimming a magnetic resonance imaging device. Background Art

[0002] Magnetic resonance imaging (MRI) equipment includes a magnet that can generate a magnetic field. Due to manufacturing process, transportation or material reasons, the magnet cannot generate a high uniformity magnetic field that meets the requirements in the imaging space of the MRI equipment, thereby affecting the imaging quality of the MRI equipment. Summary of the invention

[0003] The present application provides a method and device for shimming an MRI device, and the technical solution is as follows:

[0004] In one aspect, a shimming method for an MRI device is provided, wherein the MRI device comprises: a plurality of shimming holes, each shimming hole being used to install a shimming bar; the method comprises:

[0005] Acquire the magnetic force distribution of each shim bar among the plurality of shim bars, wherein the magnetic force distribution of each shim bar is used to characterize the magnetic force exerted on the shim bar at different positions during the process of inserting the shim bar into the shim hole;

[0006] Constructing constraint conditions based at least on the magnetic force distribution of each of the shim strips, and constructing an objective function based on the sum of the thicknesses of all shims in the plurality of shim strips;

[0007] Solving the objective function based on the constraint condition to obtain a first shim distribution, where the first shim distribution is used to indicate the thickness of a shim required to be set for each shim slot of each shim strip;

[0008] Based on the first shim distribution, the magnetic field in the MRI imaging space is shimmed.

[0009] Optionally, the magnetic force distribution of each shim strip is represented in the form of a magnetic force matrix. The constraint condition is constructed based at least on the magnetic force distribution of each shim strip, including:

[0010] Setting each element in the magnetic force matrix of each shim strip to be less than or equal to the maximum magnetic force to obtain a plurality of first constraint conditions;

[0011] Each of the elements is the magnetic force exerted on the shim strip at one of the positions during the process of inserting the shim strip into the shim hole.

[0012] Optionally, the constraint condition is established based at least on the magnetic force distribution of each of the shim strips, further comprising:

[0013] Acquire a second constraint condition based on a uniformity expression of the magnetic field, wherein the uniformity expression is used to characterize the uniformity of the magnetic field when the shim strips are inserted;

[0014] The thickness of the shims in each of the shim slots is set to be less than or equal to the maximum thickness, thereby obtaining a third constraint condition.

[0015] Optionally, the magnetic resonance imaging device further includes: a magnet, each of the shim strips is provided with a plurality of shim slots, and the shim slots are used to place the shim pieces; before obtaining the second constraint condition based on the uniformity expression of the magnetic field, the method further includes:

[0016] Acquire a sensitivity coefficient matrix of the MRI device, wherein the sensitivity coefficient matrix is ​​used to characterize the strength of the axial magnetic field generated by the shims of unit thickness in each of the shim slots at each sampling point on the surface of the sphere in the imaging space;

[0017] Acquire a magnetic induction intensity distribution matrix of the imaging space, wherein the magnetic induction intensity distribution matrix is ​​used to indicate the magnetic induction intensity generated by the magnet at each of the sampling points;

[0018] Based on the sensitivity coefficient matrix and the magnetic induction intensity distribution matrix, an expression for uniformity of the magnetic field is obtained.

[0019] Optionally, the axial magnetic field is characterized by axial magnetic induction intensity; the element a in the i-th row and j-th column of the sensitivity coefficient matrix ij satisfy:

[0020]

[0021] Among them, M z is the magnetization vector of the shim in the axial direction of the magnet of the magnetic resonance imaging device, μ0 is the vacuum magnetic permeability, s is the area of ​​the shim, (x i ,y i , z i ) is the coordinate of the i-th sampling point, (x j ,y j , z j ) is the center coordinate of the shim plate in the jth shim slot.

[0022] Optionally, the magnetic force distribution F of the nth shim strip among the plurality of shim strips is n satisfy:

[0023] F n =M z ×s×(ΔB z ·x n );

[0024] Among them, M z is the magnetization vector of the shim in the axial direction of the magnet of the magnetic resonance imaging device, s is the area of ​​the shim, ΔB z is the magnetic field gradient matrix of the target area where the shim hole corresponding to the nth shim strip is located, and the target area is the area where the shim hole and its extension line are located, x n is a second shim distribution of the nth shim strip, where the second shim distribution is used to indicate the thickness of the shims in each shim slot in the nth shim strip.

[0025] On the other hand, a shimming device for a magnetic resonance imaging device is provided, wherein the MRI comprises: a gradient coil, wherein a plurality of shimming holes are arranged on the gradient coil, and each shimming hole is used to install a shimming bar; the device comprises:

[0026] an acquisition module, used for acquiring the magnetic force distribution of each shim bar among the plurality of shim bars, wherein the magnetic force distribution of each shim bar is used for characterizing the magnetic force received by the shim bar at different positions during the process of inserting the shim bar into the shim hole;

[0027] A construction module, configured to construct a constraint condition based at least on the magnetic force distribution of each of the shim strips, and to construct an objective function based on the sum of the thicknesses of all shims in the plurality of shim strips;

[0028] A solution module, used for solving the objective function based on the constraint condition to obtain a first shim distribution, wherein the first shim distribution is used for indicating the thickness of the shims required to be set for each shim slot of each shim strip;

[0029] A shimming module is used to shim the magnetic field in the imaging space of the MRI based on the first shim piece distribution.

[0030] Optionally, the magnetic force distribution of each of the shim strips is represented in the form of a magnetic force matrix. The construction module is used for:

[0031] Setting each element in the magnetic force matrix of each shim strip to be less than or equal to the maximum magnetic force to obtain a plurality of first constraint conditions;

[0032] Each of the elements is the magnetic force exerted on the shim strip at one of the positions during the process of inserting the shim strip into the shim hole.

[0033] On the other hand, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the method described in the above aspects is implemented.

[0034] On the other hand, a computer program product is provided, wherein the computer program product comprises a computer program or computer instructions, and when the computer program or the computer instructions are executed by a processor, the method as described in the above aspects is implemented.

[0035] The beneficial effects brought about by the technical solution provided by this application include at least:

[0036] The present application provides a shimming method and device for an MRI device. The method can obtain a magnetic force distribution for characterizing the magnetic force received by the shim strip at different positions during the process of inserting the shim strip into the shim hole, and at least construct a constraint condition based on the magnetic force distribution of each shim strip, and then solve the objective function based on the constraint condition, so as to shim the magnetic field of the imaging space of the MRI device based on the solution of the objective function (i.e., the first shim piece distribution). Since the method can shim the imaging space of the MRI device, the uniformity of the magnetic field in the imaging space can be improved, thereby ensuring that the imaging quality of the MRI device is high. In addition, since the method can construct a constraint condition based on at least the magnetic force distribution of each shim strip, that is, the magnetic force received by the shim strip can be considered when determining the first shim piece distribution, it can be ensured that when the shim strip is inserted into the shim hole during the shimming process, the magnetic force received by the shim strip is within a controllable range, thereby preventing the shim strip from falling off due to excessive force, improving the efficiency of shimming the MRI device, and ensuring the safety of the shimming process.

[0037] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a partial structural schematic diagram of an MRI device provided in an embodiment of the present application;

[0039] Figure 2 is a schematic diagram of the structure of a shim strip provided in an embodiment of the present application;

[0040] Figure 3 is a flow chart of a shimming method for an MRI device provided in an embodiment of the present application;

[0041] Figure 4 is a flow chart of another shimming method for MRI equipment provided in an embodiment of the present application;

[0042] Figure 5 It is a schematic diagram of isomagnetic lines on the surface of a 45 cm sphere before the magnetic field in the imaging space of the MRI device is shimmed;

[0043] Figure 6It is a schematic diagram of isomagnetic lines on the surface of a 45 cm sphere after the magnetic field in the imaging space of the MRI device is uniformed by the method provided in the embodiment of the present application;

[0044] Figure 7 This is a schematic diagram of a change trend of the magnetic force exerted on the first to sixth shim bars of the 12 shim bars provided in an embodiment of the present application during the process of being inserted into the shim holes;

[0045] Figure 8 This is a schematic diagram of a change trend of the magnetic force exerted on the 7th to 12th shim bars among the 12 shim bars provided in an embodiment of the present application during the process of being inserted into the shim holes;

[0046] Fig. 9 It is a structural schematic diagram of a shimming device of an MRI device provided in an embodiment of the present application;

[0047] Fig.10 It is a structural schematic diagram of another shimming device of an MRI device provided in an embodiment of the present application;

[0048] Fig.11 It is a structural diagram of a computing device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0050] The present application embodiment provides an MRI device, see Figure 1 The MRI device includes a gradient coil 01 and a magnet ( Figure 1 (not shown in the figure), the gradient coil 01 may be in a circular ring shape. Optionally, the magnet may be a superconducting magnet.

[0051] A plurality of shimming holes A may be provided on the end surface of one end of the gradient coil 01. Figure 1 As shown, the multiple shim holes A are evenly arranged along the circumference of the gradient coil 01. Each shim hole A can extend along the axial direction of the gradient coil 01 (i.e., the axial direction of the magnet) and is used to install a shim bar (also referred to as a shim tray). The shim bar can be used to shim the magnetic field of the imaging space of the MRI device. The imaging space can be approximated as a sphere. Among them, the length of each shim hole A can be equal to the length of the shim bar. The length direction is parallel to the axial direction of the magnet 01.

[0052] Figure 2is a schematic diagram of the structure of a shim strip provided in an embodiment of the present application. Figure 2 The shim bar 02 is in a strip shape, and a plurality of shim slots B are arranged on the shim bar 02. The plurality of shim slots B are arranged along the length direction of the shim bar 02, and each shim slot B is used to place a shim sheet.

[0053] It should be understood that the shim strip 02 is made of non-magnetic material. The shim sheet is made of magnetic material, such as iron, that is, the shim sheet is an iron sheet.

[0054] The present application embodiment provides a shimming method for an MRI device, which is applied to a computing device. The MRI device includes a plurality of shimming holes, each of which is used to install a shimming bar. The MRI device can be Figure 1 The MRI device shown. That is, the multiple shimming holes can be set on the gradient coil of the MRI device. Optionally, the computing device can be a laptop, a tablet computer or a desktop computer. Figure 3 , the method comprising:

[0055] Step 101: Obtain the magnetic force distribution of each shim bar among a plurality of shim bars.

[0056] The magnetic force distribution of each shim bar is used to characterize the magnetic force exerted on the shim bar at different positions during the process of inserting the shim bar into the shim hole. In other words, each element in the magnetic force distribution is the magnetic force exerted on the shim bar at one position during the process of inserting the shim bar into the shim hole.

[0057] Step 102: constructing constraint conditions based at least on the magnetic force distribution of each shim strip, and constructing an objective function based on the sum of thicknesses of all shims in the plurality of shim strips.

[0058] In an embodiment of the present application, a computing device may construct constraints based on the magnetic force distribution of each shim strip, the uniformity of the magnetic field in the imaging space of the MRI device when the shim strip is inserted, and the thickness of the shim piece in each shim slot, and construct an objective function based on the sum of the thickness of the shim pieces in all shim slots included in the multiple shim strips.

[0059] Step 103: Solve the objective function based on the constraint conditions to obtain a first shim distribution.

[0060] The first shim distribution is used to indicate the thickness of the shims required to be set for each shim slot of each shim strip.

[0061] Step 104: Shimming the magnetic field in the imaging space of the MRI device based on the first shim slice distribution.

[0062] After the computing device obtains the first shim distribution, for each shim slot, the computing device can load the shim for the shim slot based on the thickness of the shim required to be set in the shim slot indicated in the first shim distribution. Afterwards, the computing device can obtain the magnetic field distribution on the surface of the sphere in the imaging space through the measuring device, and judge based on the magnetic field distribution whether the uniformity of the magnetic field in the imaging space meets the uniformity requirement, that is, the uniformity is less than the uniformity threshold. If the computing device determines that the uniformity of the magnetic field meets the uniformity requirement, the operation can be terminated. If the computing device determines that the uniformity of the magnetic field still does not meet the uniformity requirement, step 103 can be continued until the uniformity of the magnetic field meets the uniformity requirement.

[0063] In summary, the embodiment of the present application provides a shimming method for an MRI device, which can obtain a magnetic force distribution for characterizing the magnetic force received by the shim strip at different positions during the process of inserting the shim strip into the shim hole, and construct a constraint condition based on the magnetic force distribution of each shim strip, and then solve the objective function based on the constraint condition, so as to shim the magnetic field of the imaging space of the MRI device based on the solution of the objective function (i.e., the first shim piece distribution). Since the method can shim the magnetic field of the imaging space of the MRI device, the uniformity of the magnetic field of the imaging space can be improved, thereby ensuring that the imaging quality of the MRI device is high. In addition, since the method can construct a constraint condition based on the magnetic force distribution of each shim strip, that is, the magnetic force received by the shim strip can be considered when determining the first shim piece distribution, it can be ensured that when the shim strip is inserted into the shim hole during the shimming process, the magnetic force received by the shim strip is within a controllable range, thereby preventing the shim strip from falling off due to excessive force, improving the efficiency of shimming the MRI device, and ensuring the safety of the shimming process.

[0064] Figure 4 is a flow chart of another shimming method of an MRI device provided in an embodiment of the present application, wherein the MRI device comprises: a plurality of shimming holes, each shimming hole being used to install a shimming bar. Figure 4 , the method may include:

[0065] Step 201: Obtain a sensitivity coefficient matrix of an MRI device.

[0066] The sensitivity coefficient matrix is ​​used to characterize the strength of the axial magnetic field generated by the shims of unit thickness in each shim slot at each sampling point on the surface of the sphere in the imaging space. The axial magnetic field refers to the component of the magnetic field generated by the shims at the sampling point in the axial direction of the magnet.

[0067] The number of rows I of the sensitivity coefficient matrix A is the total number of all sampling points on the spherical surface of the imaging space, and the number of columns J is the total number of all shim slots included in the multiple shim strips. And the element a in the i-th row and j-th column of the sensitivity coefficient matrix A isij The magnitude of the axial magnetic field generated by the shim sheet of unit thickness in the jth shim slot at the ith sampling point among the I sampling points can be characterized. For example, assuming that the total number of the plurality of shim strips is 12, each shim strip is provided with 24 shim slots, and the total number of all sampling points is 576, then I is 576, J is 288, that is, the sensitivity coefficient matrix is ​​a matrix of 576 rows and 288 columns. The 576 sampling points are evenly distributed on the surface of the sphere.

[0068] Since the strength of the magnetic field is usually characterized by magnetic induction intensity, the axial magnetic field in the embodiment of the present application can be characterized by axial magnetic induction intensity. The axial magnetic induction intensity is the component of the magnetic induction intensity generated by the shims of unit thickness in each shim slot at each sampling point on the surface of the sphere in the imaging space in the axial direction of the magnet. Accordingly, the sensitivity coefficient matrix may include: the shims of unit thickness in each shim slot and the axial magnetic induction intensity at each sampling point.

[0069] Optionally, for each shim in the plurality of shims, the computing device may determine the axial magnetic flux density generated by the shim at the sampling point based on the distance from the shim to each sampling point and the magnetization vector of the shim in the axial direction of the magnet. The axial magnetic flux density is negatively correlated with the distance and positively correlated with the magnetization vector. The magnetization vector may be pre-stored by the computing device.

[0070] For example, the axial magnetic induction intensity a of the shim sheet of unit thickness in the jth shim slot at the i-th sampling point among I sampling points is ij Can satisfy:

[0071]

[0072] In formula (1), M z is the magnetization vector, μ0 is the vacuum magnetic permeability, and s is the area of ​​the shim. (x i ,y i , z i ) is the coordinate of the i-th sampling point, (x j ,y j , z j ) is the center coordinate of the shim plate in the jth shim slot.

[0073] Step 202: Obtain a magnetic induction intensity distribution matrix of an imaging space of an MRI device.

[0074] The magnetic induction intensity distribution matrix is ​​used to characterize the magnetic induction intensity generated at each sampling point on the spherical surface of the imaging space. In other words, the magnetic induction intensity distribution matrix can reflect the magnetic field distribution on the surface of the imaging space.

[0075] In an embodiment of the present application, the measuring device can measure the magnetic induction intensity at all sampling points on the spherical surface of the imaging space, and send the measured magnetic induction intensity to the computing device. The computing device can then obtain the magnetic induction intensity distribution matrix of the imaging space based on the magnetic induction intensity at all sampling points. The measuring device can be a magnetic resonance magnetometer.

[0076] Step 203: Based on the sensitivity coefficient matrix and the magnetic induction intensity distribution matrix, obtain the uniformity expression of the magnetic field in the imaging space.

[0077] The uniformity expression can be used to characterize the uniformity of the magnetic field in the imaging space when the shim strip is inserted. Shim sheets are placed inside the shim strip.

[0078] In the embodiment of the present application, the computing device can determine the uniformity expression of the magnetic field in the imaging space when the shim strips are inserted based on the sensitivity coefficient matrix, the magnetic induction intensity distribution matrix and the first shim distribution to be solved.

[0079] Optionally, the uniformity expression may satisfy the following formula (2):

[0080]

[0081] In formula (2), A is a sensitivity coefficient matrix, X is a first shim distribution to be solved, and the first shim distribution is used to indicate the thickness of shims in each shim slot in all shim strips. B is a magnetic flux density distribution measured in step 202, and B0 is a target magnetic field.

[0082] It can be understood that the first shim distribution can be represented in the form of a first shim distribution matrix.

[0083] Step 204: Obtain the magnetic force distribution of each shim bar among the plurality of shim bars.

[0084] In an embodiment of the present application, for each of the multiple shim holes, the computing device can obtain the magnetic field distribution of the target area where the shim hole and its extension line are located through simulation software, and determine the gradient change of the magnetic field in the target area based on the magnetic field distribution. The gradient change can be characterized by a magnetic field gradient matrix. The extension direction of the extension line is the axial direction of the magnet.

[0085] Afterwards, for each shim strip, the computing device can determine the magnetic force distribution of the shim strip based on the second shim piece distribution of the shim strip and the magnetic field gradient matrix of the target area of ​​the shim hole corresponding to the shim strip. The magnetic force distribution of the shim strip is used to characterize the magnitude of the magnetic force to which the shim strip is subjected during the process of inserting the shim strip into the shim hole. The second shim piece distribution is used to indicate the thickness of the shim pieces in each shim slot of the shim strip. The shim hole corresponding to the shim strip refers to the shim hole into which the shim strip needs to be inserted. Optionally, the second shim piece distribution can be represented in the form of a second shim piece distribution matrix, and the magnetic force distribution can be represented in the form of a magnetic force matrix.

[0086] Assuming that the total number of multiple shim strips is N, the magnetic force distribution F of the nth shim strip among the N shim strips is n Can satisfy:

[0087] F n =M z ×s×(ΔB z ·x n ) Formula (3)

[0088] In formula (3), ΔB z is the magnetic field gradient matrix of the target area of ​​the shim hole corresponding to the nth shim strip, x n is the second shim distribution of the nth shim strip.

[0089] Step 205: construct constraint conditions based on the magnetic force distribution of each shim bar, the uniformity of the magnetic field in the imaging space when the shim bars are inserted, and the thickness of the shims in each shim slot, and construct an objective function based on the sum of the thicknesses of all shims in the multiple shim bars.

[0090] In an embodiment of the present application, the computing device may set each element in the magnetic force matrix of each shim strip to be less than or equal to the maximum magnetic force to obtain a plurality of first constraints. Furthermore, the computing device may obtain a second constraint based on an expression of the uniformity of the magnetic field in the imaging space. In addition, the computing device may also set the thickness of the shim strip to be less than or equal to the maximum thickness to obtain a third constraint. The maximum magnetic force distribution and the maximum thickness may both be pre-stored by the computing device.

[0091] That is, the computing device can obtain the following constraints:

[0092] AX-(1+ε)B0≤-B Formula (4)

[0093] -AX+(1-ε)B0≤B Formula (5)

[0094] 0≤t≤t max Formula (6)

[0095]

[0096] In formula (4) and formula (5), ε is the uniformity threshold, and in formula (6), t is the thickness of the shim sheet, t max is the maximum thickness. In formula (7), F max is the maximum magnetic force.

[0097] Furthermore, the computing device may construct an objective function based on the sum of the thicknesses of the shims in the shim slots included in all shim strips. The objective function is a function that aims to minimize the sum of the thicknesses of the shims in all shim strips. For example, the expression of the objective function may satisfy:

[0098] ||X||1Formula (8)

[0099] Formula (8) represents the 1-norm of the first shim distribution. When the first shim distribution is represented in the form of a first shim distribution matrix, the 1-norm refers to the sum of the absolute values ​​of all elements of the first shim distribution matrix, that is, the sum of the thicknesses.

[0100] Step 206: Solve the objective function based on the constraint conditions to obtain a first shim distribution.

[0101] In the embodiment of the present application, the computing device can construct a minimization optimization model according to the objective function and the constraint conditions, and optimize the minimization optimization model using an optimization algorithm to minimize the objective function and obtain an optimal solution to the objective function. The optimal solution is the first shim distribution.

[0102] Optionally, the optimization algorithm may be a linear programming algorithm.

[0103] Step 207: Shimming the magnetic field in the imaging space of the MRI device based on the first shim slice distribution.

[0104] After the computing device obtains the first shim distribution, for each shim slot, the computing device may load the shim for the shim slot based on the thickness of the shim required to be set in the shim slot indicated in the first shim distribution. Afterwards, the computing device may obtain the magnetic field distribution on the surface of the sphere in the imaging space through the measuring device, and determine whether the uniformity of the magnetic field in the imaging space meets the uniformity requirement based on the magnetic field distribution. If the computing device determines that the uniformity of the magnetic field meets the uniformity requirement, the operation may be terminated. If the computing device determines that the uniformity of the magnetic field still does not meet the uniformity requirement, step 202 may be continued until the uniformity of the magnetic field meets the uniformity requirement.

[0105] In an embodiment of the present application, for each shim slot, a computing device may calculate the number of shim plates required to be set in the shim slot by rounding off based on the thickness of the shim plates required to be set in the shim slot indicated in the first shim plate distribution and the thickness of each shim plate, and install the shim plates according to the number of shim plates to load the shim slot with the shim plates.

[0106] Assuming that the diameter of the imaging space is 45 centimeters (cm), before the magnetic field is uniformed, the magnetic induction intensity of multiple (e.g., 576) sampling points on the surface of a 45 cm sphere is measured using a magnetic resonance magnetometer to obtain Figure 5 After the magnetic field of the imaging space is shimmed by the shimming method provided in the embodiment of the present application, the following can be obtained: Figure 6 Schematic diagram of isomagnetic lines shown.

[0107] Figure 5 and Figure 6 The isomagnetic line diagram shown can reflect the magnetic field distribution on the surface of the sphere, and the horizontal axis of the isomagnetic line diagram is the azimuth (φ) of the spherical coordinate system where the sphere is located, and the vertical axis is the elevation (θ) of the spherical coordinate system. The units of the azimuth and elevation are both radians (rad). In the isomagnetic line diagram, points with the same field strength are connected together. That is, points with the same magnetic induction intensity are connected together, and the unit of magnetic induction intensity is Tesla (T).

[0108] In order to show the uniformity of the magnetic field, Figure 5 and Figure 6 In the schematic diagram of isomagnetic lines shown, the unit of magnetic induction intensity is converted from Tesla to parts per million (ppm). The ppm is the unit of uniformity. The uniformity is the difference between the maximum value and the minimum value.

[0109] from Figure 5 It can be seen that the maximum and minimum values ​​of the sphere surface before shimming are quite different, greater than 200ppm. This shows that the uniformity of the magnetic field in the imaging space is low before shimming. Figure 6 It can be seen that the maximum and minimum values ​​of the imaging space after shimming are slightly different, less than 10 ppm. It can be seen that after shimming using the method provided in the embodiment of the present application, the uniformity of the magnetic field in the imaging space is effectively improved.

[0110] Assumption F max is 200 Newtons (N), that is, when the shim bar is inserted into the shim hole, the maximum magnetic force it receives is set to 200 N. Assuming that the total number of shim bars is 12, refer to Figure 7 and Figure 8 , Figure 7The figure shows the changing trend of the magnetic force on the 1st to 6th shim bars among the 12 shim bars during the process of inserting into the shim hole. Figure 8 The figure shows the variation trend of the magnetic force to which the 7th to 12th shim bars among the 12 shim bars are subjected during the process of being inserted into the shim holes. Figure 7 and Figure 8 In the figure, the horizontal axis is the longitudinal distance Z from the center of the shim strip to the center of the magnet, in meters (m), and the vertical axis is the magnetic force exerted on the shim strip, in N.

[0111] from Figure 7 and Figure 8 It can be seen that the magnetic force exerted on each shim bar during the process of being inserted into the shim hole does not exceed 200 N. In this way, a high safety can be ensured when the shim bars are inserted.

[0112] MRI equipment includes a magnet that can generate a magnetic field. Due to manufacturing process, transportation or material reasons, the magnet cannot generate a high uniformity magnetic field that meets the requirements in the imaging space of the MRI equipment, thereby affecting the imaging quality of the MRI equipment.

[0113] In the related art, the magnetic field uniformity of the imaging space can be improved by a passive shimming method. The passive shimming method is: firstly place the shim sheet in the shim slot of the shim bar, then insert the shim bar into the shim hole of the MRI device, and improve the magnetic field uniformity of the imaging space by continuously optimizing and iterating the distribution of the shim sheet in the shim bar. In the process of optimizing the distribution of the shim sheet, the thickness of the shim sheet is usually used as the objective function, and the maximum thickness of the shim sheet in the shim slot is used as the constraint condition to calculate the distribution of the shim iron sheet.

[0114] However, after shimming is arranged according to the distribution result of shimming obtained by the above passive shimming method, when the shimming bar provided with shimming is inserted into the fixing slot, the shimming bar may fall off due to the strong magnetic force, resulting in low safety and efficiency of shimming.

[0115] In high field strength environments, for operational safety, the magnets need to be de-energized before the shimming bars are inserted into the shimming holes. However, this will increase the consumption of liquid helium and still cannot solve the problem of low shimming efficiency.

[0116] Based on this, the embodiment of the present application provides a shimming method, which can obtain the magnetic force distribution used to characterize the magnetic force received by the shim strip at different positions during the process of inserting the shim strip into the shim hole, and construct constraints based on the magnetic force distribution of each shim strip, and then solve the objective function based on the constraint condition, so as to shim the magnetic field of the imaging space of the MRI device based on the solution of the objective function (i.e., the first shim piece distribution). Since the method can construct constraints based on the magnetic force distribution of each shim strip, that is, the magnetic force received by the shim strip can be considered when determining the first shim piece distribution, it can be ensured that when the shim strip is inserted into the shim hole during the shimming process, the magnetic force received by the shim strip is within a controllable range, thereby preventing the shim strip from falling off due to excessive force, and effectively reducing the number of times the magnet is lowered, thereby saving working hours and liquid helium, and improving the efficiency of shimming the MRI device.

[0117] It is understandable that the order of the steps of the shimming method of the MRI device provided in the embodiment of the present application can be appropriately adjusted, and the steps can be increased or decreased accordingly according to the situation. Any technician familiar with the technical field can easily think of a change within the technical scope disclosed in the present application, and all of them should be included in the protection scope of the present application, so they will not be repeated.

[0118] In summary, the embodiment of the present application provides a shimming method for an MRI device, which can obtain a magnetic force distribution for characterizing the magnetic force received by the shim strip at different positions during the process of inserting the shim strip into the shim hole, and construct a constraint condition based on the magnetic force distribution of each shim strip, and then solve the objective function based on the constraint condition, so as to shim the magnetic field in the imaging space of the MRI device based on the solution of the objective function (i.e., the first shim piece distribution), thereby improving the uniformity of the magnetic field and ensuring the imaging quality. In addition, since the method can construct a constraint condition based on the magnetic force distribution of each shim strip, that is, the magnetic force received by the shim strip can be considered when determining the first shim piece distribution, it can be ensured that when the shim strip is inserted into the shim hole during the shimming process, the magnetic force received by the shim strip is within a controllable range, thereby preventing the shim strip from falling off due to excessive force, improving the efficiency of shimming the MRI device, and ensuring the safety of the shimming process.

[0119] The present application provides a shimming device for an MRI device, which can be applied to a computing device. The MRI device includes: a plurality of shimming holes, each of which is used to install a shimming bar. Fig. 9 , the device 300 comprises:

[0120] The acquisition module 301 is used to acquire the magnetic force distribution of each shim bar among the multiple shim bars. The magnetic force distribution of each shim bar is used to characterize the magnetic force exerted on the shim bar at different positions during the process of inserting the shim bar into the shim hole.

[0121] The construction module 302 is used to construct constraint conditions based on at least the magnetic force distribution of each shim strip, and to construct an objective function based on the sum of thicknesses of all shims in the plurality of shim strips.

[0122] The solving module 303 is used to solve the objective function based on the constraint conditions to obtain a first shim distribution, where the first shim distribution is used to indicate the thickness of the shims required to be set for each shim slot of each shim strip.

[0123] The shimming module 304 is used to shim the magnetic field in the MRI imaging space based on the first shim slice distribution.

[0124] Optionally, the magnetic force distribution of each shim strip is represented in the form of a magnetic force matrix. The construction module 302 can be used for:

[0125] Setting each element in the magnetic force matrix of each shim strip to be less than or equal to the maximum magnetic force to obtain a plurality of first constraint conditions;

[0126] Each element is the magnetic force exerted on the shim strip at a position during the process of being inserted into the shim hole.

[0127] Optionally, the building block 302 may also be used to:

[0128] A second constraint condition is obtained based on a uniformity expression of the magnetic field, where the uniformity expression is used to characterize the uniformity of the magnetic field when the shim strips are inserted;

[0129] The thickness of the shims in each shim slot is set to be less than or equal to the maximum thickness, thereby obtaining the third constraint condition.

[0130] Optionally, the magnetic resonance imaging device further comprises: a magnet, each shim bar is provided with a plurality of shim slots, and the shim slots are used to place shim sheets. Fig.10 , the device may also include:

[0131] The second acquisition module 305 is used to obtain a sensitivity coefficient matrix of the MRI device before obtaining the second constraint condition based on the uniformity expression of the magnetic field. The sensitivity coefficient matrix is ​​used to characterize the strength of the axial magnetic field generated by the shim sheets of unit thickness in each shim slot at each sampling point on the spherical surface in the imaging space.

[0132] It is understandable that, for the sake of distinction, the acquisition module 301 for acquiring the magnetic force distribution of each of the multiple shim strips is referred to as the first acquisition module 301 , and the acquisition module for acquiring the sensitivity coefficient matrix is ​​referred to as the second acquisition module 305 .

[0133] The third acquisition module 306 is used to acquire the magnetic induction intensity distribution matrix of the imaging space. The magnetic induction intensity distribution matrix is ​​used to indicate the magnetic induction intensity generated by the magnet at each sampling point.

[0134] The fourth acquisition module 307 is used to acquire a uniformity expression of the magnetic field based on the sensitivity coefficient matrix and the magnetic induction intensity distribution matrix.

[0135] Optionally, the axial magnetic field is characterized by the axial magnetic induction intensity. The element a in the i-th row and j-th column of the sensitivity coefficient matrix ij satisfy:

[0136]

[0137] Among them, M z is the magnetization vector of the shim in the axial direction of the magnet, μ0 is the vacuum permeability, s is the area of ​​the shim, (x i ,y i , z i ) is the coordinate of the i-th sampling point, (x j ,y j , z j ) is the center coordinate of the shim plate in the jth shim slot.

[0138] Optionally, the magnetic force distribution F of the nth shim strip among the plurality of shim strips n satisfy:

[0139] F n =M z ×s×(ΔB z ·x n );

[0140] Among them, M z is the magnetization vector of the shim in the axial direction of the magnet, s is the area of ​​the shim, ΔB z is the magnetic field gradient matrix of the target area where the shim hole corresponding to the nth shim strip is located. The target area is the area where the shim hole and its extension line are located. n is the second shim distribution of the nth shim strip, and the second shim distribution is used to indicate the thickness of the shims in each shim slot in the nth shim strip.

[0141] In summary, the embodiment of the present application provides a shimming device for an MRI device, which can obtain a magnetic force distribution for characterizing the magnetic force received by the shim strip at different positions during the process of inserting the shim strip into the shim hole, and construct a constraint condition based on the magnetic force distribution of each shim strip, and then solve the objective function based on the constraint condition, so as to shim the magnetic field of the imaging space of the MRI device based on the solution of the objective function (i.e., the first shim piece distribution). Since the device can shim the magnetic field of the imaging space of the MRI device, the uniformity of the magnetic field can be improved, thereby ensuring that the imaging quality of the MRI device is high. In addition, since the device can construct a constraint condition based on the magnetic force distribution of each shim strip, that is, the magnetic force received by the shim strip can be considered when determining the first shim piece distribution, it can be ensured that when the shim strip is inserted into the shim hole during the shimming process, the magnetic force received by the shim strip is within a controllable range, thereby preventing the shim strip from falling off due to excessive force, improving the efficiency of shimming the MRI device, and ensuring the safety of the shimming process.

[0142] Fig.11 Schematic diagram of a computing device provided in an embodiment of the present application. Fig.11 As shown, the controller 400 includes: a processor 401 and a memory 403. The processor 401 and the memory 403 are connected, such as through a bus 402. Optionally, the controller 400 may also include a transceiver 404. It should be noted that in actual applications, the transceiver 404 is not limited to one, and the structure of the controller 400 does not constitute a limitation on the embodiments of the present application.

[0143] Processor 401 may be a CPU (Central Processing Unit), a general purpose processor, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. It may implement or execute various exemplary logic blocks, modules and circuits described in conjunction with the disclosure of this application. Processor 401 may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0144] The bus 402 may include a path to transmit information between the above components. The bus 402 may be a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus. The bus 402 may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig.11 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0145] The memory 403 is used to store a computer program corresponding to the shimming method of the MRI device in the above embodiment of the present application, and the computer program is controlled and executed by the processor 401. The processor 401 is used to execute the computer program stored in the memory 403 to implement the content shown in the above method embodiment.

[0146] The present application also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the shimming method of the MRI device provided in the above method embodiment is implemented. For example, Figure 3 or Figure 4 The method shown.

[0147] The present application also provides a computer program product, which includes a computer program or computer instructions. When the computer program or computer instructions are executed by a processor, the shimming method of the MRI device provided in the above method embodiment is implemented. For example, Figure 3 or Figure 4 The method shown.

[0148] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection portion with one or more wirings (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0149] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0150] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0151] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0152] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0153] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A shimming method for a magnetic resonance imaging device, characterized in that: The magnetic resonance imaging device comprises: a plurality of shimming holes, each shimming hole is used to install a shimming strip; the method comprises: Acquire the magnetic force distribution of each shim bar among the plurality of shim bars, wherein the magnetic force distribution of each shim bar is used to characterize the magnetic force exerted on the shim bar at different positions during the process of inserting the shim bar into the shim hole; Constructing constraint conditions based at least on the magnetic force distribution of each of the shim strips, and constructing an objective function based on the sum of the thicknesses of all shims in the plurality of shim strips; Solving the objective function based on the constraint condition to obtain a first shim distribution, where the first shim distribution is used to indicate the thickness of a shim required to be set for each shim slot of each shim strip; The magnetic field in the imaging space of the magnetic resonance imaging device is shimmed based on the first shim piece distribution.

2. The method according to claim 1, characterized in that The magnetic force distribution of each shim strip is represented in the form of a magnetic force matrix; and the constraint condition is constructed based at least on the magnetic force distribution of each shim strip, including: Setting each element in the magnetic force matrix of each shim strip to be less than or equal to the maximum magnetic force to obtain a plurality of first constraint conditions; Each of the elements is the magnetic force exerted on the shim strip at one of the positions during the process of inserting the shim strip into the shim hole.

3. The method according to claim 2, characterized in that The constraint condition is established based at least on the magnetic force distribution of each of the shim strips, and further includes: Acquire a second constraint condition based on a uniformity expression of the magnetic field, wherein the uniformity expression is used to characterize the uniformity of the magnetic field when the shim strips are inserted; The thickness of the shims in each of the shim slots is set to be less than or equal to the maximum thickness, thereby obtaining a third constraint condition.

4. The method according to claim 3, characterized in that The magnetic resonance imaging device further includes: a magnet, each of the shim strips is provided with a plurality of shim slots, and the shim slots are used to place the shim pieces; before obtaining the second constraint condition based on the uniformity expression of the magnetic field, the method further includes: Acquire a sensitivity coefficient matrix of the magnetic resonance imaging device, wherein the sensitivity coefficient matrix is ​​used to characterize the strength of the axial magnetic field generated by the shims of unit thickness in each of the shim slots at each sampling point on the surface of the sphere in the imaging space; Acquire a magnetic induction intensity distribution matrix of the imaging space, wherein the magnetic induction intensity distribution matrix is ​​used to indicate the magnetic induction intensity generated by the magnet at each of the sampling points; Based on the sensitivity coefficient matrix and the magnetic induction intensity distribution matrix, an expression for uniformity of the magnetic field is obtained.

5. The method according to claim 4, characterized in that The axial magnetic field is characterized by the axial magnetic induction intensity; the element a in the i-th row and j-th column of the sensitivity coefficient matrix ij satisfy: Among them, M z is the magnetization vector of the shim in the axial direction of the magnet, μ0 is the vacuum permeability, s is the area of ​​the shim, (x i ,y i , z i ) is the coordinate of the i-th sampling point, (x j ,y j , z j ) is the center coordinate of the shim plate in the jth shim slot.

6. The method according to any one of claims 1 to 4, characterized in that: The magnetic force distribution F of the nth shim strip among the plurality of shim strips n satisfy: F n =M z ×s×(ΔB z ·x n ); Among them, M z is the magnetization vector of the shim in the axial direction of the magnet of the magnetic resonance imaging device, s is the area of ​​the shim, ΔB z is the magnetic field gradient matrix of the target area where the shim hole corresponding to the nth shim strip is located, and the target area is the area where the shim hole and its extension line are located, x n is a second shim distribution of the nth shim strip, where the second shim distribution is used to indicate the thickness of the shims in each shim slot in the nth shim strip.

7. A shimming device for a magnetic resonance imaging device, characterized in that: The magnetic resonance imaging device comprises: a plurality of shimming holes, each shimming hole is used to install a shimming strip; the device comprises: an acquisition module, used for acquiring the magnetic force distribution of each shim bar among the plurality of shim bars, wherein the magnetic force distribution of each shim bar is used for characterizing the magnetic force received by the shim bar at different positions during the process of inserting the shim bar into the shim hole; A construction module, configured to construct constraint conditions based on the magnetic force distribution of each of the shim strips, and to construct an objective function based on the sum of the thicknesses of all shims in the plurality of shim strips; A solution module, used for solving the objective function based on the constraint condition to obtain a first shim distribution, wherein the first shim distribution is used for indicating the thickness of the shims required to be set for each shim slot of each shim strip; A shimming module is used to shim the magnetic field in the imaging space of the magnetic resonance imaging device based on the first shim piece distribution.

8. The device according to claim 7, characterized in that The building blocks are used to: Constraint conditions are constructed based on the magnetic force distribution of each of the shim strips, the uniformity of the magnetic field in the imaging space when the shim strips are inserted, and the thickness of the shim sheets in each of the shim slots.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program or a computer instruction, and when the computer program or the computer instruction is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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