Composite shimming and four-group reverse proportional gradient external compensation coil system and method for simultaneous measurement of heart and brain

Abstract

The invention discloses a composite shimming and four-group reverse proportional gradient external compensation coil system and method for simultaneous measurement of heart and brain. The method comprises the following steps: a shimming coil subsystem forms an axial cuboid uniform region in a manner that a multi-coil composite configuration is matched with non-uniform current excitation; each gradient field coil of the gradient coil subsystem is divided into four segments along the axial direction, inner and outer windings are reversely electrified, and a gradient linear region is expanded according to a non-linear proportion of current; the measurement control unit obtains magnetic field information in real time and drives the two subsystems to output a compensation magnetic field. According to the method, standardized types are classified according to site sizes, magnetic field fluctuation and gradient are taken as threshold values, shimming and gradient coil parameters are optimized, and coil constants are determined through simulation verification. According to the invention, large-scale cuboid uniform region and high-linearity gradient compensation required by heart and brain synchronous measurement are realized, low-frequency magnetic field fluctuation and gradient interference are inhibited, and the device is simple in structure and adapts to various building environments.

Description

Technical Field

[0001] This invention belongs to the fields of biomedical engineering, extremely weak magnetic field measurement and active magnetic field shielding technology, and in particular relates to a composite shimming field and four sets of reverse proportional gradient external compensation coil system and method for simultaneous heart and brain measurement. Background Technology

[0002] Magneto-cardiography (MCG), magnetoencephalography (MEG), and wearable biomagnetic measurements based on optically pumped magnetometers (OPMs) are highly sensitive to residual environmental magnetic fields and their spatial gradients. In zero-magnetic-medical measurement scenarios, in addition to requiring the background static magnetic field bias compensation to near zero, it is also necessary to maintain a highly uniform magnetic field environment within the effective measurement range of the human body.

[0003] However, existing active magnetic field compensation technologies have the following shortcomings: Traditional Helmholtz coil configurations can usually only achieve high field uniformity within a limited volume. When the sensor array distribution range expands or needs to cover the human head and chest simultaneously, a single-sized shimming coil cannot guarantee the magnetic field consistency of the entire measurement area. In addition, for magnetically shielded chambers / barrel environments with openings, the openings of the shielding body will introduce leakage magnetic gradient interference along the opening direction, resulting in systematic differences in magnetic field strength at different locations in space, making it difficult to simultaneously compensate the magnetic field residuals of multiple measurement points to zero.

[0004] Therefore, there is an urgent need for a compensation scheme that can provide a highly uniform zero magnetic environment over a larger spatial range while suppressing the leakage magnetic gradient at the opening, in order to meet the higher requirements of magnetic field spatial coverage and uniformity for applications such as novel combined heart and brain measurements. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a composite shimming system and method for simultaneous heart and brain testing, along with four sets of reverse proportional gradient external compensation coils, to resolve the issues present in the prior art.

[0006] To achieve the above objectives, the present invention provides a composite shimming and four sets of reverse proportional gradient external compensation coil systems for simultaneous cardiac and cerebrovascular testing, comprising: The shimming coil subsystem is used to generate a uniform magnetic field in three orthogonal directions, including the X, Y and Z directions. The coil group that generates the uniform magnetic field in the Z direction adopts a multi-coil composite shimming configuration and is equipped with non-uniform current excitation to form a cuboid uniform magnetic field region extending along the Z direction at the center of the test space. The gradient coil subsystem is used to generate three first-order gradient fields: the rate of change of the magnetic field in the X direction along the Z direction, the rate of change of the magnetic field in the Y direction along the Z direction, and the rate of change of the magnetic field in the Z direction along the Z direction. Each gradient field coil is divided into at least four independent windings along the Z direction. The winding pairs located on the outer side along the Z direction have opposite current-carrying directions to the winding pairs located on the inner side, and the current amplitudes are configured according to a preset nonlinear ratio. The gradient linear region is extended within the uniform cuboid region. The measurement and control unit is used to acquire ambient magnetic field information in real time and drive the shimming coil subsystem and gradient coil subsystem to output a compensation magnetic field to counteract the ambient magnetic field and the corresponding gradient disturbance.

[0007] Optionally, the coil group that generates a uniform magnetic field in the Z direction in the shimming coil subsystem adopts a three-coil composite shimming configuration or a four-coil composite shimming configuration. The non-uniform ratio of the driving current of each coil is set to suppress the central bulge of the axial magnetic field intensity or compensate for the end attenuation.

[0008] Optionally, the driving current of at least four independent windings of each gradient field coil in the gradient coil subsystem is configured as a ratio of 1:γ:-γ:-1 with alternating positive and negative values ​​and nonlinear amplitude, where γ is the current amplitude ratio coefficient between the inner winding and the outer winding, and its value ranges from 0.125 to 0.3.

[0009] Optionally, each coil of the shimming coil subsystem and the gradient coil subsystem is installed against the wall, and the coils are arranged in a layered, staggered or recessed manner.

[0010] Optionally, the measurement and control unit includes a magnetic field sensor array, a multi-channel current source, and a feedback control unit; The magnetic field sensor array is used to collect multi-point magnetic field data in the test space in real time. The feedback control unit establishes the magnetic field response matrix of the uniform coil subsystem and the gradient coil subsystem at the target sampling point based on the Biot-Savart law, and solves the compensation current command of each coil group by the least squares method or regularization algorithm. The multi-channel current source drives the shimming coil subsystem and the gradient coil subsystem to output a compensation magnetic field according to the compensation current command.

[0011] Optionally, the shimming coil subsystem and the gradient coil subsystem have multiple standardized configurations preset according to the size of the installation site; For sites with a depth dimension not greater than the first preset value, the Z-direction shimming coil adopts a three-coil structure and the current ratio is configured as 1:α:1, where α is 0.25 to 0.3; For a site where the depth dimension is not less than the second preset value and the ratio of the width dimension to the depth dimension is not greater than the third preset value, the Z-direction shimming coil adopts a three-coil structure and the current ratio is configured as β:1:β, where β is greater than 1; For sites where the ratio of width to depth is not less than the fourth preset value, the Z-direction shimming coil adopts a three-coil structure with a current ratio of 1:0.1:1, and the gradient coil corresponding to the rate of change of the Z-direction magnetic field along the Z-direction adopts a double-coil reverse layout with a current ratio of 1:-1. The current ratio of the gradient coil in the four-winding structure is configured as 1:γ:-γ:-1, where γ is taken from 0.125 to 0.3 depending on the site size.

[0012] The present invention also provides a method for the above-described system, comprising: S1. Obtain the floor height and orthogonal dimensions of the site to be installed, and classify the site into a preset standardized site type based on the dimension data; S2. Perform multi-point magnetic field measurements within the space to be compensated, and extract the fluctuation characteristics of the environmental magnetic field and the gradient characteristics along the Z direction as the compensation target threshold. S3. Based on the coverage of the synchronous measurement of heart and brain, set a target of a uniform cuboid area extending along the Z direction; S4. Based on the Biot-Savart law, establish a magnetic field response model for a rectangular coil array. With the goal of maximizing the uniformity volume ratio within the target uniform region, solve for the optimal coil spacing and current distribution ratio of the uniform coil subsystem according to the standardized site type and compensation target threshold. S5. Based on the optimization results of the shimming coil subsystem, with the optimization objective of minimizing the gradient nonlinear error in the Z direction, the optimal segmentation position, winding turn distribution, and current ratio of the gradient coil subsystem are solved according to the standardized site type. S6. Establish a simulation model based on the optimal coil spacing, current distribution ratio, segment position, winding turns distribution and current ratio, verify the uniformity of the residual magnetic field and gradient linearity in the target uniform region, and determine the coil constant based on the simulation results. The coil constant is used to match the range of the multi-channel current source.

[0013] Optionally, in step S4, a non-integer current ratio variable is used as the optimization parameter, and a numerical iterative algorithm is used to solve for the optimal coil spacing and current distribution ratio of the uniformity coil subsystem, with the maximization of the uniformity volume ratio as the convergence criterion.

[0014] Optionally, the coil constant determined in S6 is used to match the range of the multi-channel current source, the range being determined based on the environmental magnetic field fluctuation characteristics and the gradient characteristics along the Z direction.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: The uniform zone shape conforms to the human body: a rectangular uniform zone of 0.85m × 0.85m × (1.7~2.2m) is achieved. Compared with the traditional cube design, the effective coverage area along the human body axis is significantly increased within the same room size, perfectly meeting the anatomical span requirements of simultaneous measurement of the heart and brain.

[0016] High gradient compensation accuracy: The proposed gradient Helmholtz coil design controls the linear error of the gradient field to within 10%, and the linear region length covers the entire shielded barrel area, effectively solving the problem of short linear region and inability to compensate the entire barrel in traditional Maxwell coils.

[0017] Simplified structure and close fit to the wall: To adapt to confined rooms and avoid interference with the three-dimensional uniform field coil and magnetic shielding facilities, the coil adopts a physical structure design of layered installation close to the wall: the outer coil is laid close to the four walls and the top / bottom of the room to ensure that the coils do not overlap or block each other, and the obstacles such as doors and windows are taken into account, which improves the convenience of wiring, heat dissipation and maintenance during construction. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart illustrating an embodiment of the present invention; Figure 2 This is a schematic diagram of the coil layout structure in a small room according to Embodiment 1 of the present invention; (a) is B x (a) is a schematic diagram of the coil layout; (b) is B y Coil layout diagram; (c) is B z Coil layout diagram; (d) is d B x / d z Coil layout diagram; (e) is d B y / d z Coil layout diagram; (f) is d B z / d z Coil layout diagram; Figure 3 This is a schematic diagram of the coil layout structure in a square room according to Embodiment 2 of the present invention; (a) is B x (a) is a schematic diagram of the coil layout; (b) is B y Coil layout diagram; (c) isB z Coil layout diagram; (d) is d B x / d z Coil layout diagram; (e) is d B y / d z Coil layout diagram; (f) is d B z / d z Coil layout diagram; Figure 4 This is a schematic diagram of the coil layout structure in a long, deep room according to Embodiment 3 of the present invention; (a) is B x (a) is a schematic diagram of the coil layout; (b) is B y Coil layout diagram; (c) is B z Coil layout diagram; (d) is d B x / d z Coil layout diagram; (e) is d B y / d z Coil layout diagram; (f) is d B z / d z Coil layout diagram; Figure 5 A schematic diagram of the coil layout structure for a wide room according to Embodiment 4 of the present invention; (a) is B x (a) is a schematic diagram of the coil layout; (b) is B y Coil layout diagram; (c) is B z Coil layout diagram; (d) is d B x / d z Coil layout diagram; (e) is d B y / d z Coil layout diagram; (f) is d B z / d z Coil layout diagram; Figure 6 The shimming coil of Embodiment 2 of the present invention B x , B y as well as B z Simulation results of the uniform region; (a) is Bx Simulation results of the uniform region; (b) is B y Simulation results of the uniform region; (c) is B z Simulation results of the uniform region; Figure 7 The gradient field coil d in Embodiment 2 of the present invention B x / d z d B y / d z and d B z / d z Simulation results of linearity deviation; (a) is d B x / d z Simulation results of linearity deviation; (b) is d B y / d z Simulation results of linearity deviation; (c) is d B z / d z Simulation results of linearity deviation. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a composite shimming and four sets of reverse proportional gradient external compensation coil systems for simultaneous cardiac and cerebrovascular testing, including: A six-dimensional active compensation rectangular coil array is deployed outside or inside the passive magnetic shielding facility, the coil array comprising at least components for generating... X , Y , Z A shim coil subsystem with three orthogonal uniform magnetic fields and used to generate d B x / d z d B y / d z d Bz / d z A gradient coil subsystem with three first-order gradient fields, wherein the coil array is mounted close to the wall and physical interference between coils is avoided through a layered / staggered structure; Determine the coil configuration of the shimming coil subsystem and the gradient coil subsystem: Z The shimming coil group, based on the traditional two-coil Helmholtz system, incorporates at least one auxiliary coil in the middle to form a three-coil or four-coil composite shimming configuration. The central bulge or end attenuation is suppressed by adjusting the driving current ratio of each coil. The gradient coil subsystem is designed for gradient fields (d) varying along the Z-axis. B x / d z d B y / d z d B z / d z The coil is divided into at least four segments or four groups of independent windings along the Z-axis, wherein the first and fourth groups form an outer coil pair and the second and third groups form an inner coil pair. The outer coil pair and the inner coil pair are energized in opposite directions and their amplitudes are configured proportionally to expand the gradient linear region. Both the shimming coil subsystem and the gradient coil subsystem adopt a large-scale rectangular coil structure. By optimizing the geometric spacing of the coils and the ratio of the driving current between multiple turns of the coil, an extended rectangular uniform magnetic field region is formed in the center of the test space. The uniform region is a cuboid extending along the Z-axis, and its length is... L The coil array is 1.7m to 2.2m long, with a cross-section of at least 0.85m × 0.85m, to cover the range of simultaneous cardiac and cerebral measurements. The coil array adopts a simplified wall-mounted configuration, and eliminates physical interference between coils through layered, staggered, and recessed design, while also taking into account the avoidance of on-site obstacles such as doors and windows to facilitate construction. It is equipped with a magnetic field sensor array, a low-noise multi-channel current source, and a feedback control unit, which calculates the compensation current based on the measured magnetic field and drives the coils in real time to counteract the environmental magnetic field and its gradient disturbances.

[0022] The coil group that generates a uniform magnetic field in the shimming coil subsystem adopts a three-coil or four-coil composite structure, while breaking through the limitation of the traditional Helmholtz coil with equal current (1:1) and adopting a non-uniform current excitation strategy. For small rooms with limited length (approximately 5 meters in depth), the Z-axis shimming coil adopts a three-coil structure, with a current ratio set to 1: α :1, of which α The value is between 0.25 and 0.3. By reducing the current density of the intermediate coil, the central bulge of the axial magnetic field strength is suppressed, thereby flattening the magnetic field distribution in a limited space and extending the length of the uniform region. For long, deep rooms with ample length (approximately 7 meters in depth), the Z-axis shimming coil employs a three-coil structure, with the current ratio set as follows: β :1: β ,in β If the value is greater than 1 (e.g., 1.4), the field strength attenuation caused by the long distance is compensated by increasing the current in the end coil, so that the magnetic field uniformity in the uniform region is less than 5%.

[0023] The gradient coil subsystem proposes a gradient Helmholtz coil configuration, with the specific coil current ratio as follows: By configuring alternating positive and negative current ratios with non-linear amplitudes (e.g., 1: γ :- γ :-1), where γ This is the proportional coefficient for the intermediate coil current, with a value ranging from 0.125 to 0.3; The current configuration generates zero crossover at the center point, while the intermediate auxiliary coil cancels out the higher-order nonlinear gradient terms, thereby significantly extending the linear region of the gradient field along the Z-axis, making the gradient linearity error less than 10% in the entire cuboid target area.

[0024] A design method for a composite shimming and four sets of reverse proportional gradient external compensation coil systems for simultaneous cardiac and cerebrovascular testing includes the following steps: S1. Site Classification and Modeling: Obtain data on the floor height, east-west length, north-south length, and floor area of ​​the site to be installed, and classify the site into small rooms, square rooms, long and deep rooms, or wide rooms. S2. Environmental magnetic field feature extraction: Multi-point magnetic field measurement is performed in the space to be compensated. Bandpass filtering is performed on the 1-100Hz frequency band signal to extract the peak value of magnetic field fluctuation and the gradient value along the Z-axis, which are used as the compensation target threshold. S3. Setting the cuboid target domain: Based on the geometric dimensions of the heart and brain magnetic shielding barrel (length 1.7m to 2.2m), set the uniform area target in the form of a cuboid (0.85m×0.85m×L, where L is the barrel length), instead of the traditional cube target; S4. Matrix coil configuration optimization: Based on the Biot-Savart law, establish the magnetic field response matrix of the rectangular coil array, introduce non-integer current ratio variables, and take maximizing the uniformity volume ratio within the cuboid region as the objective function to solve for the optimal coil spacing and current distribution ratio. S5. Gradient linearity extension design: To address leakage magnetic interference in the opening direction, a multi-segment gradient coil is designed. By adjusting the current direction and amplitude of multiple paired coils, the gradient nonlinearity error in the long axis direction is minimized. S6. Simulation Verification and Parameter Verification: Use finite element simulation to verify the uniformity (<5%) and gradient linearity (<10%) of the residual magnetic field in the target area, and calculate the coil constant to match the power supply range.

[0025] (I) Theoretical Basis and Design Methods; The core design of this invention lies in utilizing the Biot-Savart law and Taylor series expansion method in electromagnetic field theory to design the superposition of magnetic fields generated by multiple rectangular Helmholtz coils, synthesizing a specific spatial distribution. Reverse optimization of coil parameters is then performed for non-spherical or cubic target regions.

[0026] (1) Magnetic field calculation model; According to the Biot-Savart theorem, the magnetic induction intensity produced by a current-carrying conductor at a point in space in a vacuum is... B for: (1) in, μ0 The permeability of free space, I For current, dl The integral unit representing the current element vector on the coil. r and r' Let || be the position vector of the field point and the source point. r–r' || represents the distance between the field point and the source point.

[0027] For a classic Helmholtz coil pair, when the coil radius is R and the spacing is also R, the axial magnetic induction intensity BH is: (2) Where N is the number of turns of the coil.

[0028] Further simplification yields: (3) (2) Magnetic field homogeneity and gradient linearity error index; To quantitatively evaluate the magnetic field uniformity and linear response within the target region, the following indicators are defined: Magnetic field uniformity error It can be expressed by the following formula: (4) in, B i For the first in the target area i The magnetic flux density at each sampling point B 0 The magnetic flux density is the magnetic flux density at the center reference point of the target region.

[0029] The gradient linearity error δ can be expressed by the following formula: (5) in, z i For the first i The z-coordinate of each point relative to the center of the target area k and b The slope and intercept are used for linear fitting of the magnetic field data of the target area.

[0030] (II) Environmental magnetic field characteristics and design parameters; The design input is based on field measurement data from 10 hospital departments: Frequency band: 1-100Hz (focus on power frequency and low frequency disturbances).

[0031] Fluctuation amplitude: East-West ( Z 93.18 nT, north-south direction ( X 105.85 nT, Earth-space direction ( Y 131.61 nT (East-West, North-South, and Earth-Ground static magnetism are 4000 nT, 35000 nT, and 35000 nT, respectively).

[0032] Gradient magnitude: Z-axis gradient approximately 62-92 nT / m.

[0033] Design specifications: Within the defined cuboid target area, uniformity error <5% and gradient linearity error <10%.

[0034] (III) Specific example configuration; Example 1: Small room configuration; Designed for small rooms, with a floor area of ​​14 m² 2 A room coil measuring 5m in length and 2.5m in height is used to compensate for magnetocardiography or magnetoencephalography. The target area is 0.85m × 0.85m × 1.7m (cubic prism).

[0035] Its coil layout is as follows Figure 2 As shown, the coil configuration parameters are: B x The shim coil is located at YOZ flat, X The coordinates are ±1.4 m, close to the wall, such as... Figure 2 As shown in (a) above. The current ratio of the two coils is 1:1, and the coil constant is 324.20 nT / A (per turn). The estimated controllable magnetic field is 2.62 mA to 326.51 mA, and 850 pT to 105.85 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 100-110 A.

[0036] B y The shim coil is located at XOZ flat,Y The coordinates are ±1.25 m, close to the wall, such as... Figure 2 As shown in (b) above. The current ratio of the two coils is 1:1, and the coil constant is 369 nT / A (per turn). The estimated controllable magnetic field is 2.3 mA to 356.67 mA, and 850 pT to 131.61 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 90-100 A.

[0037] B z The shimming coils consist of three sets of rectangular coils, located at... XOY flat, Z The coordinates are -2.5 m, 0 m, 2.5 m, as shown. Figure 2 As shown in (c). The three-coil current ratio is 1:0.25:1, and the coil constant is 218.74 nT / A (per turn). An estimated controllable magnetic field of 2.51 mA to 425.98 mA and 550 pT to 93.18 nT is required. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 35-40 A.

[0038] d B x / d z Gradient coils are located YOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -2.5 to -1.25 m, -1.25 to 0 m, 0 to 1.25 m, and 1.25 to 2.5 m. Figure 2 As shown in (d) in the diagram. The current ratio is 1:0.25:-0.25:-1, and the coil gradient constant is 165.35 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 10 pT / A / m to 91.72 nT / A / m, from 0.06 mA to 640.18 mA.

[0039] d B y / d z Gradient coils are located XOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -2.5 to -1.25 m, -1.25 to 0 m, 0 to 1.25 m, and 1.25 to 2.5 m. Figure 2 As shown in (e). The current ratio is 1:0.3:-0.3:-1, and the coil gradient constant is 219.64 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 20 pT / A / m to 88.21 nT / A / m, from 0.09 mA to 401.60 mA.

[0040] d B z / d z The gradient coils employ a four-coil layout, located at... XOY flat, ZThe coordinates are -2.5 m, -1.25 m, 1.25 m, 2.5 m, as shown. Figure 2 As shown in (f). The current ratio is 1:1:-1:-1, and the coil gradient constant is 474.23 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 30 pT / A / m to 62.37 nT / A / m, from 0.06 mA to 131.51 mA.

[0041] Example 2: Square room configuration; Designed for square rooms, with a floor area of ​​17 square meters. 2 A room coil measuring 5 m in length and 2.5 m in height is used to compensate for magnetocardiography or magnetoencephalography. The target area is 0.85 m × 0.85 m × 2.0 m (cubic prism).

[0042] Its coil layout is as follows Figure 3 As shown, the coil configuration parameters are: B x The shim coil is located at YOZ flat, X The coordinates are ±1.75 m, close to the wall, such as... Figure 3 As shown in (a) above. The current ratio of the two coils is 1:1, and the coil constant is 244.83 nT / A (per turn). The estimated controllable magnetic field is 3.47 mA to 432.36 mA, and 850 pT to 105.85 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 140-150 A.

[0043] B y The shim coil is located at XOZ flat, Y The coordinates are ±1.25 m, close to the wall, such as... Figure 3 As shown in (b) of the diagram. The current ratio of the two coils is 1:1, and the coil constant is 364.75 nT / A (per turn). The estimated controllable magnetic field ranges from 2.33 mA to 360.82 mA, and from 850 pT to 131.61 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 90-100 A.

[0044] B z The shimming coils consist of three sets of rectangular coils, located at... XOY flat, Z The coordinates are -2.5 m, 0 m, 2.5 m, as shown. Figure 3As shown in (c). The three-coil current ratio is 1:0.3:1, and the coil constant is 242.29 nT / A (per turn). An estimated controllable magnetic field of 2.27 mA to 384.57 mA and 550 pT to 93.18 nT is required. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 15-20 A.

[0045] d B x / d z Gradient coils are located YOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -2.5 to -1.25 m, -1.25 to 0 m, 0 to 1.25 m, and 1.25 to 2.5 m. Figure 3 As shown in (d) in the diagram. The current ratio is 1:0.3:-0.3:-1, and the coil gradient constant is 127.94 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 10 pT / A / m to 91.72 nT / A / m, from 0.0447 mA to 827.38 mA.

[0046] d B y / d z Gradient coils are located XOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -2.5 to -1.25 m, -1.25 to 0 m, 0 to 1.25 m, and 1.25 to 2.5 m. Figure 3 As shown in (e). The current ratio is 1:0.3:-0.3:-1, and the coil gradient constant is 223.71 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 20 pT / A / m to 88.21 nT / A / m, from 0.089 mA to 394.29 mA.

[0047] d B z / d z The gradient coils employ a four-coil layout, located at... XOY flat, Z The coordinates are -2.5 m, -1.25 m, 1.25 m, 2.5 m, as shown. Figure 3 As shown in (f). The current ratio is 1:1:-1:-1, and the coil gradient constant is 441.845 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 30 pT / A / m to 62.37 nT / A / m, from 0.068 mA to 141.15 mA.

[0048] Example 3: Long-depth room configuration; For rooms with a long and deep interior, the design occupies an area of ​​24.5 m². 2A room coil measuring 7 m in length and 2.5 m in height is used to compensate for magnetocardiography or magnetoencephalography. The target area is 0.85 m × 0.85 m × 2.2 m (cubic prism).

[0049] Its coil layout is as follows Figure 4 As shown, the coil configuration parameters are: B x The shim coil is located at YOZ flat, X The coordinates are ±1.75 m, close to the wall, such as... Figure 4 As shown in (a) above. The current ratio of the two coils is 1:1, and the coil constant is 235.72 nT / A (per turn). The estimated controllable magnetic field is 3.61 mA to 449.07 mA, and 850 pT to 105.85 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 140-150 A.

[0050] B y The shim coil is located at XOZ flat, Y The coordinates are ±1.25 m, close to the wall, such as... Figure 4 As shown in (b) of the diagram. The current ratio of the two coils is 1:1, and the coil constant is 344.09 nT / A (per turn). The estimated controllable magnetic field ranges from 2.47 mA to 393.94 mA, and from 850 pT to 131.61 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 100-110 A.

[0051] B z The shimming coils consist of three sets of rectangular coils, located at... XOY flat, Z The coordinates are -1.4 m, 0 m, 1.4 m, as shown. Figure 4 As shown in (c). The three-coil current ratio is 1.4:1:1.4, and the coil constant is 609.94 nT / A (per turn). A controllable magnetic field of 0.90 mA to 152.77 mA is estimated to be 550 pT to 93.18 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 6-7 A.

[0052] d B x / d z Gradient coils are located YOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -3.5 to -1.75 m, -1.75 to 0 m, 0 to 1.75 m, and 1.75 to 3.5 m. Figure 4As shown in (d) in the diagram. The current ratio is 1:0.25:-0.25:-1, and the coil gradient constant is 87.099 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 10 pT / A / m to 91.72 nT / A / m, from 0.115 mA to 1215.33 mA.

[0053] d B y / d z Gradient coils are located XOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -3.5 to -1.75 m, -1.75 to 0 m, 0 to 1.75 m, and 1.75 to 3.5 m. Figure 4 As shown in (e). The current ratio is 1:0.125:-0.125:-1, and the coil gradient constant is 88.85 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 20 pT / A / m to 88.21 nT / A / m, from 0.09 mA to 992.76 mA.

[0054] d B z / d z The gradient coils employ a four-coil layout, located at... XOY flat, Z The coordinates are -3.5 m, -1.5 m, 1.5 m, 3.5 m, as shown. Figure 4 As shown in (f). The current ratio is 1:1:-1:-1, and the coil gradient constant is 314.57 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 30 pT / A / m to 62.37 nT / A / m, from 0.095 mA to 198.26 mA.

[0055] Example 4: Wide room configuration; Designed for wide rooms, with a floor area of ​​175 m² 2 A room coil measuring 7 m in length and 2.5 m in height is used to compensate for magnetocardiography or magnetoencephalography. The target area is 0.85 m × 0.85 m × 2.2 m (cubic prism).

[0056] Its coil layout is as follows Figure 5 As shown, the coil configuration parameters are: B x The shim coil is located at YOZ flat, X The coordinates are ±12.5 m, close to the wall, such as... Figure 5As shown in (a) above. The current ratio of the two coils is 1:1, and the coil constant is 3.28 nT / A (per turn). The estimated controllable magnetic field is 2.59 mA to 322.73 mA, 850 pT to 105.85 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 100-110 A.

[0057] B y The shim coil is located at XOZ flat, Y The coordinates are ±1.25 m, close to the wall, such as... Figure 5 As shown in (b) of the diagram. The current ratio of the two coils is 1:1, and the coil constant is 211.31 nT / A (per turn). The estimated controllable magnetic field is 4.02 mA to 622.83 mA, and 850 pT to 131.61 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 160-170 A.

[0058] B z The shimming coils consist of three sets of rectangular coils, located at... XOY flat, Z The coordinates are -3.5 m, 0 m, 3.5 m, as shown. Figure 5 As shown in (c). The three coil current ratio is 1:0.1:1, and the coil constant is 106.95 nT / A (per turn). The estimated controllable magnetic field ranges from 5.14 mA to 871.23 mA, and from 550 pT to 93.18 nT. Complete elimination of the Earth's magnetic field requires an additional DC bias of approximately 35-40 A.

[0059] d B x / d z Gradient coils are located YOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -3.5 to -2.1 m, -2.1 to -0.7 m, 0.7 to 2.1 m, and 2.1 to 3.5 m, respectively. Figure 5 As shown in (d) in the diagram. The current ratio is 1:0.25:-0.25:-1, and the coil gradient constant is 0.11 nT / A / m (per turn). The estimated controllable magnetic field gradient for 1000 turns is 0.09 mA to 962.31 mA, and 10 pT / A / m to 91.72 nT / A / m.

[0060] d B y / d z Gradient coils are located XOZ The plane is divided into four segments along the Z-axis, with Z-coordinates of -3.5 to -2.1 m, -2.1 to -0.7 m, 0.7 to 2.1 m, and 2.1 to 3.5 m, respectively. Figure 5As shown in (e). The current ratio is 1:0.25:-0.25:-1, and the coil gradient constant is 84.65 nT / A / m (per turn). The controllable magnetic field gradient is estimated to be 20 pT / A / m to 88.21 nT / A / m, from 0.24 mA to 1042.02 mA.

[0061] d B z / d z The gradient coils employ a dual-coil layout, located at... XOY flat, Z The coordinates are ±3.5 m, such as Figure 5 As shown in (f). The current ratio is 1:1, and the coil gradient constant is 470.98 nT / A / m (per turn). The estimated controllable magnetic field gradient is 30 pT / A / m to 62.37 nT / A / m, from 0.074 mA to 132.42 mA.

[0062] Based on the COMSOL simulation results verifying the uniformity and linearity deviations, the four designed three-field, three-gradient coil groups can meet the measurement range of cardiac and cerebral magnetic resonance imaging (MRI) in both the uniform and gradient linear regions. Their simple structure allows for efficient use of space while further enhancing the internal test signal quality through control, thus reducing external interference. The simulation results of Example 2 are shown below. Figure 6 , Figure 7 As shown. Considering practical situations, the number of coil turns can be increased several times over depending on the specific noise fluctuation level, in order to reduce the current or improve controllability.

[0063] This invention addresses the limitation of existing Helmholtz coils, which generate spherical or cubic uniform regions that cannot meet the elongated spaces required for simultaneous measurement of the human heart and brain. It proposes an innovative configuration based on a rectangular coil array. By constructing four standardized coil layout schemes for different site sizes (small, square, long-depth, and wide), and utilizing specific non-uniform current excitation (such as 1:0.25:1 and 1.4:1:1.4), the uniform magnetic field region is significantly extended axially, forming a cuboid magnetic field region of 0.85m × 0.85m × (1.7~2.2m). Simultaneously, a multi-segment gradient Helmholtz coil design is proposed, achieving high linearity gradient compensation along the opening direction. This invention effectively suppresses low-frequency magnetic field fluctuations and gradient interference in complex hospital environments, providing a high-precision zero-magnetic environment for simultaneous detection of heart and brain magnetocardiography based on atomic magnetometers.

[0064] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A composite shimming field and four sets of reverse proportional gradient external compensation coil systems for simultaneous cardiac and cerebrovascular testing, characterized in that, include: The shimming coil subsystem is used to generate a uniform magnetic field in three orthogonal directions, including the X, Y and Z directions. The coil group that generates the uniform magnetic field in the Z direction adopts a multi-coil composite shimming configuration and is equipped with non-uniform current excitation to form a cuboid uniform magnetic field region extending along the Z direction at the center of the test space. The gradient coil subsystem is used to generate three first-order gradient fields: the rate of change of the magnetic field in the X direction along the Z direction, the rate of change of the magnetic field in the Y direction along the Z direction, and the rate of change of the magnetic field in the Z direction along the Z direction. Each gradient field coil is divided into at least four independent windings along the Z direction. The winding pairs located on the outer side along the Z direction have opposite current-carrying directions to the winding pairs located on the inner side, and the current amplitudes are configured according to a preset nonlinear ratio. The gradient linear region is extended within the uniform cuboid region. The measurement and control unit is used to acquire ambient magnetic field information in real time and drive the shimming coil subsystem and gradient coil subsystem to output a compensation magnetic field to counteract the ambient magnetic field and the corresponding gradient disturbance.

2. The composite shimming and four sets of reverse proportional gradient external compensation coil system for simultaneous heart and brain testing according to claim 1, characterized in that, The coil group that generates a uniform magnetic field in the Z direction in the shimming coil subsystem adopts a three-coil composite shimming configuration or a four-coil composite shimming configuration. The non-uniform ratio of the driving current of each coil is set to suppress the central bulge of the axial magnetic field intensity or compensate for the end attenuation.

3. The composite shimming and four sets of reverse proportional gradient external compensation coil system for simultaneous heart and brain testing according to claim 1, characterized in that, In the gradient coil subsystem, the driving current of at least four independent windings of each gradient field coil is configured as a ratio of 1:γ:-γ:-1 with alternating positive and negative values ​​and nonlinear amplitude, where γ is the current amplitude ratio coefficient between the inner winding and the outer winding, and its value ranges from 0.125 to 0.

3.

4. The composite shimming and four sets of reverse proportional gradient external compensation coil system for simultaneous heart and brain testing according to claim 1, characterized in that, Each coil of the shimming coil subsystem and the gradient coil subsystem is installed against the wall, and the coils are arranged in a layered, staggered or recessed manner.

5. The composite shimming and four sets of reverse proportional gradient external compensation coil system for simultaneous heart and brain testing according to claim 1, characterized in that, The measurement and control unit includes a magnetic field sensor array, a multi-channel current source, and a feedback control unit; The magnetic field sensor array is used to collect multi-point magnetic field data in the test space in real time. The feedback control unit establishes the magnetic field response matrix of the uniform coil subsystem and the gradient coil subsystem at the target sampling point based on the Biot-Savart law, and solves the compensation current command of each coil group by the least squares method or regularization algorithm. The multi-channel current source drives the shimming coil subsystem and the gradient coil subsystem to output a compensation magnetic field according to the compensation current command.

6. The composite shimming and four sets of reverse proportional gradient external compensation coil system for simultaneous heart and brain testing according to claim 1, characterized in that, The shimming coil subsystem and the gradient coil subsystem have multiple standardized configurations preset according to the size of the installation site; For sites with a depth dimension not greater than the first preset value, the Z-direction shimming coil adopts a three-coil structure and the current ratio is configured as 1:α:1, where α is 0.25 to 0.3; For a site where the depth dimension is not less than the second preset value and the ratio of the width dimension to the depth dimension is not greater than the third preset value, the Z-direction shimming coil adopts a three-coil structure and the current ratio is configured as β:1:β, where β is greater than 1; For sites where the ratio of width to depth is not less than the fourth preset value, the Z-direction shimming coil adopts a three-coil structure with a current ratio of 1:0.1:1, and the gradient coil corresponding to the rate of change of the Z-direction magnetic field along the Z-direction adopts a double-coil reverse layout with a current ratio of 1:-1. The current ratio of the gradient coil in the four-winding structure is configured as 1:γ:-γ:-1, where γ is taken from 0.125 to 0.3 depending on the site size.

7. A method for use in the system according to any one of claims 1 to 6, characterized in that, include: S1. Obtain the floor height and orthogonal dimensions of the site to be installed, and classify the site into a preset standardized site type based on the dimension data; S2. Perform multi-point magnetic field measurements within the space to be compensated, and extract the fluctuation characteristics of the environmental magnetic field and the gradient characteristics along the Z direction as the compensation target threshold. S3. Based on the coverage of the synchronous measurement of heart and brain, set a target of a uniform cuboid area extending along the Z direction; S4. Based on the Biot-Savart law, establish a magnetic field response model for a rectangular coil array. With the goal of maximizing the uniformity volume ratio within the target uniform region, solve for the optimal coil spacing and current distribution ratio of the uniform coil subsystem according to the standardized site type and compensation target threshold. S5. Based on the optimization results of the shimming coil subsystem, with the optimization objective of minimizing the gradient nonlinear error in the Z direction, the optimal segmentation position, winding turn distribution, and current ratio of the gradient coil subsystem are solved according to the standardized site type. S6. Establish a simulation model based on the optimal coil spacing, current distribution ratio, segment position, winding turns distribution and current ratio, verify the uniformity of the residual magnetic field and gradient linearity in the target uniform region, and determine the coil constant based on the simulation results. The coil constant is used to match the range of the multi-channel current source.

8. The method according to claim 7, characterized in that, In S4, a non-integer current ratio variable is used as the optimization parameter, and a numerical iterative algorithm is used to solve for the optimal coil spacing and current distribution ratio of the uniformity coil subsystem, with the maximization of the uniformity volume ratio as the convergence criterion.

9. The method according to claim 7, characterized in that, The coil constant determined in S6 is used to match the range of the multi-channel current source, and the range is determined based on the environmental magnetic field fluctuation characteristics and the gradient characteristics along the Z direction.

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