WO2021109847A1 - 磁共振成像的匀场控制方法、装置和系统 - Google Patents

磁共振成像的匀场控制方法、装置和系统 Download PDF

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Publication number
WO2021109847A1
WO2021109847A1 PCT/CN2020/128976 CN2020128976W WO2021109847A1 WO 2021109847 A1 WO2021109847 A1 WO 2021109847A1 CN 2020128976 W CN2020128976 W CN 2020128976W WO 2021109847 A1 WO2021109847 A1 WO 2021109847A1
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coil
magnetic field
spherical harmonic
current value
coil array
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PCT/CN2020/128976
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English (en)
French (fr)
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赵华炜
史永凌
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湖南迈太科医疗科技有限公司
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
    • G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor

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  • This application relates to the field of magnetic resonance technology, in particular to a shimming control method, device and system for magnetic resonance imaging.
  • MRI magnetic resonance imaging
  • the MRI sequence may require the spectral line width of the entire imaging area to be as low as about 40hz. This is equivalent to ⁇ B ⁇ 1ppm field change for 1.0TMRI, ⁇ B ⁇ 1/3ppm field change for 3.0TMRI, and ⁇ B ⁇ 1/7ppm field change for 7.0TMRI. Due to structural tolerances, this uniformity is almost impossible to achieve during the manufacture of superconducting magnets. The non-uniformity of the original magnetic field generated by the superconducting magnet itself is generally several hundred ppm (chemical shift).
  • this part can be shimmed with ferromagnetic materials through passive shimming technology.
  • the perturbation magnetic field caused by the change of the magnetic susceptibility of the patient's body will inevitably cause the patient's body to produce a non-uniform field and cause image distortion.
  • Such non-uniform field changes are not only related to the patient, but also to different parts and organs of the body It is also closely related, so the change of the inhomogeneous field is dynamic.
  • First-order shimming is usually done with gradient coils.
  • MRI provides 6 second-order shim coils, which are called X2, Y2, Z2, X-Y, Y-Z, Z-X in engineering.
  • X2, Y2, Z2, X-Y, Y-Z, Z-X 6 second-order shim coils, which are called X2, Y2, Z2, X-Y, Y-Z, Z-X in engineering.
  • X2, Y2, Z2, X-Y, Y-Z, Z-X 6 second-order shim coils
  • the number of spherical harmonic function coils that can be added is limited.
  • the shimming of high-order spherical harmonics is becoming more and more important, and traditional dynamic shimming technology is difficult to meet such high-order shimming requirements.
  • a shimming control method for magnetic resonance imaging comprising:
  • the target current value of each basic coil in the coil array corresponding to the imaging area is determined; wherein the coil array is used in a magnetic resonance device For shimming the magnetic resonance; the nuclear function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array
  • a shimming control device for magnetic resonance imaging including:
  • the measurement module is used to obtain the actual magnetic field distribution of the magnetic resonance imaging area
  • the decomposition module is used to determine the spherical harmonic function expression of the actual magnetic field distribution
  • the target current determination module is used to determine the target current value of each basic coil in the coil array corresponding to the imaging area according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array; wherein, the coil array Set in a magnetic resonance device for shimming magnetic resonance; the nuclear function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array;
  • the control module is configured to perform current control on each basic coil corresponding to the imaging area based on the target current value to achieve shimming.
  • a computer device comprising a memory, a processor, and a computer program stored on the memory and capable of running on the processor, wherein the processor implements the steps of any one of the above methods when the processor executes the computer program .
  • a magnetic resonance imaging system comprising: a magnetic resonance device, a coil array, a coil current controller corresponding to each basic coil in the coil array, and the above-mentioned computer equipment;
  • the coil array is installed on the magnetic pole surface of the magnetic resonance device
  • each coil current controller is connected to the computer device, and the output end is connected to the corresponding basic coil in the coil array;
  • the magnetic resonance device is connected to the computer device.
  • the spherical harmonic function of the actual magnetic field distribution corresponding to the nuclear function of the coil array is used to determine the core function of each basic coil corresponding to the imaging area in the coil array.
  • the target current value, and the core function of the coil array is determined according to the magnetic field vector distribution of the basic coils in the coil array.
  • the imaging area in the coil array corresponds to
  • the basic coil is applied to the target current value determined according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array to achieve shimming, so that the high-order shimming requirement can be met without superimposing the number of coils in space.
  • Figure 1 is a schematic diagram of the components of a magnetic resonance system in an embodiment
  • Figure 2 is a schematic cross-sectional view of a coil array in an embodiment
  • Fig. 3 is a schematic vertical cross-sectional view of the coil array shown in Fig. 2;
  • Fig. 4 is a top view of the coil array shown in Fig. 2;
  • Figure 5 is a schematic cross-sectional view of a coil array in another embodiment
  • Fig. 6 is a schematic vertical cross-sectional view of the coil array shown in Fig. 5;
  • FIG. 7 is a top view of the coil array shown in FIG. 5;
  • FIG. 8 is a schematic flowchart of a shimming control method for magnetic resonance imaging in an embodiment
  • Figure 9 is a schematic diagram of a Z-X coil in an embodiment
  • Figure 10 is a schematic diagram of an X-Y coil in an embodiment
  • Figure 11 is a schematic diagram of the structure of a basic coil in an embodiment
  • Fig. 12 is a vector field diagram generated in space by the basic coil shown in Fig. 11;
  • FIG. 13 shows the current distribution of the array coil 24X17 in an embodiment
  • Fig. 14 is the distribution of the spherical field generated by the current distribution of the array coil of Fig. 13;
  • Fig. 15 is the difference between the field generated by the current distribution of the array coil in Fig. 13 and the field generated by the spherical harmonic function term;
  • FIG. 16 shows the current distribution of the array coil 24X21 in an embodiment
  • Fig. 17 is the distribution of the spherical field generated by the current distribution of the array coil of Fig. 16;
  • Fig. 18 is the difference between the field generated by the current distribution of the array coil of Fig. 16 and the field generated by the spherical harmonic function term;
  • FIG. 19 shows the current distribution of the array coil 24X21 in another embodiment
  • Fig. 20 is the distribution of the spherical field generated by the current distribution of the array coil of Fig. 19;
  • 21 is the difference between the field generated by the current distribution of the array coil of the array coil of FIG. 19 and the field generated by the spherical harmonic function term;
  • 22 is a structural block diagram of a shimming control device for magnetic co-frame imaging in an embodiment
  • Figure 23 is a diagram of the internal structure of a computer device in an embodiment.
  • the shimming control method for magnetic resonance imaging can be applied to the magnetic resonance imaging system as shown in FIG. 1.
  • the system includes a magnetic resonance device 101, a coil array 102, and each basic coil in the coil array 102.
  • the coil array 102 is installed on the magnetic pole surface of the magnetic resonance device 101, the input end of each coil current controller 103 is connected to the computer device 104, the output end is connected to the corresponding basic coil in the coil array 102, and the computer device 104 is also connected to the magnetic resonance device.
  • the device 101 is connected.
  • each basic coil has an independent coil current controller 103 for power supply, and the coil current controller 103 provides a direct constant current stable current source for the corresponding basic coil in the coil array 102.
  • the computer equipment implements the shimming control of magnetic resonance imaging, determines the current value that needs to be applied to the coil array, and controls the coil current controller 103 to apply the current value to the basic coil corresponding to the coil array 102 to achieve dynamic shimming.
  • the computer The device 104 performs imaging based on magnetic resonance data.
  • the coil array of the present application consists of S basic coils C forming a coil array, as shown in Figure 2-4, arranged in an array and distributed in a distributable space, for all the non-uniformities caused by the spherical harmonic function items that need to be eliminated
  • the field is dynamically adjusted.
  • the basic coil distribution of the coil array can be arbitrarily distributed as required.
  • the coil array of an embodiment is shown in Figs. 5-7.
  • the computer equipment executes a shimming control method for magnetic resonance imaging, which includes the following steps:
  • the imaging area refers to the area of interest set by the medical staff according to the examination site of the subject.
  • the medical staff will use the magnetic resonance area corresponding to the heart as the imaging area.
  • the actual magnetic field distribution refers to the magnetic field distribution of the imaging area generated by the measured magnetic resonance.
  • a measuring instrument can be used to measure the main magnetic field distribution of the imaging area.
  • b (n, m) are the coefficients of the spherical harmonic function.
  • Traditional dynamic shimming is to design a special basic coil for each spherical harmonic function term B n,m.
  • B 0,0 coil There is a B 0,0 coil whose purpose is to adjust the center frequency.
  • First-order shimming is usually done with gradient coils.
  • MRI provides 6 second-order basic coils, which are called X2, Y2, Z2, XY, YZ, ZX in engineering.
  • a typical ZX is shown in Figure 9 and a typical XY coil is shown in Figure 10.
  • the spherical harmonic function expression of the actual magnetic field distribution is obtained.
  • the spherical harmonic function expression of the actual magnetic field distribution represents the actual measured magnetic field distribution happening.
  • S806 Determine the target current value of each basic coil corresponding to the imaging area in the coil array according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array; wherein the coil array is set in the magnetic resonance device for magnetic resonance Perform shimming; the core function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array.
  • FIG. 11 a basic coil C, as shown in FIG. 11, whose thickness is h, width is w, and length is l.
  • the coil wire is wound into the shape of Figure 11, which can be single-layered or multi-layered as required to form a basic coil C with a total number of ⁇ turns.
  • the vector field generated in space is shown in Figure 12.
  • r 0 is the position of the coil C at the p point
  • r′ is the coordinates of the q point field
  • R r′-r 0 .
  • Figure 12 shows the magnetic field vector distribution around a single basic coil C. In MRI imaging, only the B z component magnetic field is considered. For a coil C in the coil array S, its current I does not change. So from formula (3) we can get
  • the field is the sum of the fields generated by all coils at point r'.
  • the target field of a certain spherical harmonic function term to be adjusted can be achieved
  • Equation (9) can also be converted into the following relationship and directly solved to obtain the current
  • equation (12) is a difficult task because the problem is represented by Fredholm's first type integral equation. It belongs to the category of so-called pathological problems. In order to relax the system naturally, the equation (12) is selected as the overdetermined equations, that is, t ⁇ s. In order to solve this problem, a regularization method is considered, which transforms the ill-conditioned problem (11) into a well-posed problem:
  • a * is the A conjugate matrix
  • a * A is the s ⁇ s square matrix
  • ⁇ is the s ⁇ s identity matrix.
  • ⁇ is a very small number.
  • the dynamic shimming current of each normalized spherical harmonic function field can be corresponding and calculated in advance in the specific imaging ⁇ area of MRI. Once the field of the target imaging ⁇ area is obtained, the field can be completed immediately Dynamic adjustment.
  • determining the target current value of each basic coil in the coil array corresponding to the imaging area includes:
  • the normalized current value of each basic coil corresponding to the imaging area in the pre-calculated coil array is adjusted according to the proportional coefficient, and the target current value of each basic coil corresponding to the actual magnetic field distribution is determined; wherein, in the pre-calculated coil array
  • the normalized current value of each basic coil corresponding to the imaging area is determined according to the kernel function of the coil array.
  • the proportional coefficient is the ratio of the spherical harmonic function expression of the standardized magnetic field distribution to the spherical harmonic function expression of the actual magnetic field distribution.
  • the standardized magnetic field distribution is the magnetic production distribution produced by the standardized current value
  • the spherical harmonic function expression of the standardized magnetic field distribution is the spherical harmonic function expression of the magnetic production distribution produced by the standardized current. Both the standardized current value and the spherical harmonic function expression of the standardized magnetic field distribution are stored in the database through pre-calculation.
  • the expression of the spherical harmonic function of the standardized magnetic field distribution can be based on the theoretical magnetic field distribution generated by the standard current required for the non-uniformity of the original magnetic field generated by the superconducting magnet itself, and perform Legendre in the spherical coordinate system. Expand the polynomial to obtain the spherical harmonic function expression of the standardized magnetic field distribution.
  • the scale factor ⁇ n,m of the imaging area ⁇ is Among them, B n,m is the spherical harmonic function expression of the actual magnetic field distribution, It is the spherical harmonic function expression of the standardized magnetic field distribution.
  • the standardized current value is the standard current required for the non-uniformity of the original magnetic field generated by the superconducting magnet itself, which is calculated in advance by the system.
  • the normalized current value is adjusted by using the proportional coefficient between the actual magnetic field distribution and the normalized situation, and the target current value of each basic coil corresponding to the actual magnetic field distribution is obtained.
  • the shimming control method for magnetic resonance imaging further includes: predetermining the value of the collimated current And the spherical harmonic function expression of standardized magnetic field distribution
  • the standardized magnetic field distribution is the magnetic field distribution generated by the standardized current value
  • pre-determining the standardized current value and the spherical harmonic function expression of the standardized magnetic field distribution includes: pre-determining the spherical harmonic function expression of the standardized magnetic field distribution, and pre-determining the standardized current value based on the kernel function of the coil array, including: Biot-Savart law determines the distribution of the magnetic field vector generated by the basic coil in space; determines the kernel function of the coil array according to the magnetic field vector distribution of each basic coil in the coil array; determines the corresponding imaging area of the coil array according to the kernel function Magnetic field distribution; determine the objective function of each spherical harmonic function term shimming according to the magnetic field distribution; determine the quasi-current value and the spherical harmonic function expression of the standardized magnetic field distribution according to the objective function of each spherical harmonic function term shimming.
  • the normalized current value of each basic coil corresponding to the imaging area in the coil array is estimated using the same method as the previous current calculation method for the actual magnetic field distribution, and will not be repeated here.
  • the standardized current value of each basic coil corresponding to the imaging area in the pre-calculated coil array is adjusted according to the proportional coefficient, and the target current value of each basic coil corresponding to the actual magnetic field distribution is determined, including:
  • the proportional coefficient and the normalized current value of each basic coil corresponding to the imaging area in the coil array determine the current value of each spherical harmonic function item of the basic coil; accumulate the current value of each spherical harmonic function item of the basic coil to obtain the target of the basic coil Current pool.
  • the basic coil distribution of the array coil can be arbitrarily distributed as required.
  • the whole dynamic shimming procedure is the same, as long as the kernel function is calculated by formula (5) according to the spatial distribution of the basic coil.
  • S808 Perform current control on each basic coil corresponding to the imaging area based on the target current value to achieve shimming.
  • the target current value is sent to the coil controller corresponding to each basic coil in the imaging area, and the coil controller applies the corresponding target current value to the basic coil to shimm the imaging area.
  • the spherical harmonic function of the actual magnetic field distribution corresponding to the nuclear function of the coil array is used to determine the core function of each basic coil corresponding to the imaging area in the coil array.
  • the target current value, and the core function of the coil array is determined according to the magnetic field vector distribution of the basic coils in the coil array.
  • the imaging area in the coil array corresponds to
  • the basic coil is applied to the target current value determined according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array to achieve shimming, so that the high-order shimming requirement can be met without superimposing the number of coils in space.
  • the proportional coefficient is determined by the corresponding spherical harmonic function expression of the actual magnetic field distribution and the spherical harmonic function expression of the standardized magnetic field distribution, so that the normalized current value of each basic coil is adjusted according to the proportional coefficient, and each corresponding to the actual magnetic field distribution is obtained.
  • the target current value of the basic coil since the standardized current value and the spherical harmonic function expression of the standardized magnetic field distribution are calculated in advance, in actual application, the calculation time is saved, and the response speed of the magnetic resonance shimming is improved.
  • the zonal (band-shaped) term of the spherical harmonic function is usually easier to align.
  • the tesseral (field-shaped) term is very difficult to adjust, and the adjustment of the expensive tesseral term is extremely challenging.
  • two array coils are used to demonstrate the power of the dynamic shimming method.
  • the performance of the array coil dynamic shimming is very good, the uniformity after shimming is less than 1ppm, and the adjustment rate is about 90%, and the array The peak current in the coil is less than 5 amperes.
  • the coil array is 24X21, that is, 24 coils are uniformly distributed on the circumference and 21 coils are uniformly distributed on the axial direction.
  • the uniformity of the field after shimming of the array coil is less than 1ppm, and the adjustment rate is more than 90%.
  • the peak currents in the array coils are all less than 5 amperes.
  • Figure 14 shows the distribution of the spherical field produced by the current distribution of the array coil, and Figure 15 shows the difference between the field produced by the current distribution of the array coil and the field produced by the spherical harmonic function term.
  • the peak-to-peak value of the field generated by the original spherical harmonic function term is 5 ppm
  • the peak-to-peak value after shimming with the array coil is 0.35 ppm, and its adjustment rate reaches 93%.
  • Figure 16 shows the current distribution of the array coil.
  • Figure 17 shows the distribution of the spherical field produced by the current distribution of the array coil, and
  • Figure 18 shows the difference between the field produced by the current distribution of the array coil and the field produced by the spherical harmonic function term.
  • the peak-to-peak value of the field generated by the original spherical harmonic function term is 5 ppm
  • the peak-to-peak value after shimming with the array coil is 0.22 ppm, and its adjustment rate reaches 96%.
  • Figure 19 shows the current distribution of the array coil.
  • Figure 20 shows the distribution of the spherical field produced by the current distribution of the array coil, and
  • Figure 21 shows the difference between the field produced by the current distribution of the array coil and the field produced by the spherical harmonic function term.
  • the peak-to-peak value of the field generated by the original spherical harmonic function term is 5 ppm
  • the peak-to-peak value after shimming with the array coil is 0.24 ppm, and its adjustment rate reaches 95%.
  • the present application also provides a shimming control device for magnetic resonance imaging, including:
  • the measurement module 2201 is used to obtain the actual magnetic field distribution of the magnetic resonance imaging area.
  • the decomposition module 2202 is used to determine the spherical harmonic function expression of the actual magnetic field distribution.
  • the target current determination module 2203 is configured to determine the target current value of each basic coil in the coil array corresponding to the imaging area according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array; wherein, the coil The array is arranged in the magnetic resonance equipment for shimming the magnetic resonance; the nuclear function of the coil array is determined according to the magnetic field vector distribution of each basic coil in the coil array.
  • the control module 2204 is configured to perform current control on each basic coil corresponding to the imaging area based on the target current value to achieve shimming.
  • the target current determination module includes:
  • the ratio determination module is configured to determine the ratio coefficient according to the pre-acquired spherical harmonic function expression of the standardized magnetic field distribution of the imaging area and the spherical harmonic function expression of the actual magnetic field distribution.
  • the current calculation module is configured to adjust the standardized current value of each basic coil corresponding to the imaging area in the pre-calculated coil array according to the proportional coefficient, and determine the target current value of each basic coil corresponding to the actual magnetic field distribution; wherein, The normalized current value of each basic coil corresponding to the imaging area in the pre-calculated coil array is determined according to the kernel function of the coil array.
  • the device also includes a preprocessing module for first determining the spherical harmonic function expression of the standardized magnetic field distribution, and pre-determining the standardized current value based on the core function of the coil array, and the standardized magnetic field distribution is the magnetic field distribution generated by the standardized current value .
  • the preprocessing module is used to determine the magnetic field vector distribution generated by the basic coil in space based on Biot-Savart law, and determine the magnetic field vector distribution of each basic coil in the coil array.
  • the kernel function of the coil array the corresponding magnetic field distribution of each imaging area in the coil array is determined according to the kernel function
  • the shimming objective function of each spherical harmonic function term is determined according to the magnetic field distribution
  • the shimming objective function of each spherical harmonic function term is determined according to the spherical harmonic function term.
  • the objective function of shimming is to determine the standardized current value and the spherical harmonic function expression of standardized magnetic field distribution.
  • the current calculation module is configured to determine the spherical harmonics of the basic coils according to the proportional coefficients of the spherical harmonic function terms and the normalized current values of the basic coils corresponding to the imaging area in the coil array.
  • the current value of the function item is accumulated by the current value of each spherical harmonic function item of the basic coil to obtain the target current pool of the basic coil.
  • control module is configured to send the target current value to the coil controller corresponding to each basic coil in the imaging area, and the coil controller applies the corresponding target current to the basic coil Value to shimm the imaging area.
  • the above-mentioned shimming control device for magnetic resonance imaging uses the spherical harmonic function of the actual magnetic field distribution corresponding to the actual magnetic field distribution to express the kernel function of the coil array to determine the basic coil corresponding to the imaging area in the coil array.
  • the target current value, and the core function of the coil array is determined according to the magnetic field vector distribution of the basic coils in the coil array.
  • the imaging area in the coil array corresponds to
  • the basic coil is applied to the target current value determined according to the spherical harmonic function expression of the actual magnetic field distribution and the core function of the coil array to achieve shimming, so that the high-order shimming requirements can be met without superimposing the number of coils in space.
  • the corresponding spherical harmonic function expression of the actual magnetic field distribution and the spherical harmonic function expression of the standardized magnetic field distribution are used to determine the proportionality coefficient, so as to adjust the standardized current value of each basic coil according to the proportionality coefficient. Obtain the target current value of each basic coil corresponding to the actual magnetic field distribution.
  • the standardized current value and the spherical harmonic function expression of the standardized magnetic field distribution are calculated in advance, in actual application, the calculation time is saved, and the response speed of the magnetic resonance shimming is improved.
  • each module in the above-mentioned magnetic resonance imaging shimming control device can be implemented in whole or in part by software, hardware and a combination thereof.
  • the above-mentioned modules may be embedded in the form of hardware or independent of the processor in the computer equipment, or may be stored in the memory of the computer equipment in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.
  • a computer device is provided.
  • the computer device may be a terminal, and its internal structure diagram may be as shown in FIG. 23.
  • the computer equipment includes a processor, a memory, a network interface, a display screen and an input device connected through a system bus.
  • the processor of the computer device is used to provide calculation and control capabilities.
  • the memory of the computer device includes a non-volatile storage medium and an internal memory.
  • the non-volatile storage medium stores an operating system and a computer program.
  • the internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium.
  • the network interface of the computer device is used to communicate with an external terminal through a network connection.
  • the computer program is executed by the processor to realize a shimming control method for magnetic resonance imaging.
  • the display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen
  • the input device of the computer equipment can be a touch layer covered on the display screen, or it can be a button, trackball or touchpad set on the computer equipment shell , It can also be an external keyboard, touchpad, or mouse.
  • FIG. 23 is only a block diagram of part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied.
  • the specific computer device may Including more or fewer parts than shown in the figure, or combining some parts, or having a different arrangement of parts.
  • a computer device including a memory and a processor, and a computer program is stored in the memory, and the processor implements the magnetic resonance imaging shimming control method of the foregoing embodiments when the computer program is executed.
  • a computer-readable storage medium is provided, and a computer program is stored thereon.
  • the computer program is executed by a processor, the magnetic resonance imaging shimming control method of the above-mentioned embodiments is implemented.
  • Non-volatile memory may include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory.
  • Volatile memory may include random access memory (RAM) or external cache memory.
  • RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous chain Channel (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

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Abstract

一种磁共振成像的匀场控制方法、装置和系统。磁共振成像的匀场控制方法包括：获取磁共振成像区域的实际磁场分布(S802)；确定实际磁场分布的球谐函数表达(S804)；根据实际磁场分布的球谐函数表达以及线圈阵列(102)的核函数，确定线圈阵列(102)中与成像区域对应的各基本线圈的目标电流值；其中，线圈阵列(102)设置于磁共振设备中用于对磁共振进行匀场；线圈阵列(102)的核函数根据线圈阵列(102)中各基本线圈的磁场矢量分布确定(S806)；基于目标电流值对成像区域对应的各基本线圈进行电流控制实现匀场(S808)。磁共振成像的匀场控制方法对线圈阵列(102)中成像区域对应的基本线圈施加根据实际磁场分布的球谐函数表达与线圈阵列(102)的核函数确定的目标电流值实现匀场，从而无需在空间上叠加线圈数量即可满足高阶匀场要求。

Description

磁共振成像的匀场控制方法、装置和系统 技术领域
本申请涉及磁共振技术领域，特别是涉及一种磁共振成像的匀场控制方法、装置和系统。
背景技术
现代磁共振成像(MRI)中最大的工程挑战之一是在成像区提供一个超强的、高度均匀的磁场。为了避免在信号采集过程中由于自旋相位变化而造成信号的损失或丢失，MRI序列可能需要整个成像区的谱线宽度低至40hz左右。这相当于对1.0TMRI的ΔB≈1ppm场变化，3.0TMRI的ΔB≈1/3ppm场变化，7.0TMRI的ΔB≈1/7ppm场变化。由于结构公差，这种均匀性几乎不可能在超导磁体制造时实现。超导磁体本身产生的原磁场的非均匀度一般在几百个ppm(化学位移)，通常这部分可通过被动匀场技术，采用铁磁性材料进行匀场。由于病人身体磁化率变化引起的扰动磁场，将不可避免地导致病人身体产生非均匀场从而造成图像失真，而此类非均匀场的变化不但与病人个体相关，而且与人体的不同部位和器官组织也息息相关，所以非均匀场的变化是动态的。
一阶匀场通常利用梯度线圈来完成。一般MRI提供6个二阶匀场线圈，工程上称它们为X2、Y2、Z2、X-Y、Y-Z、Z-X。然而，在实践中，由于空间的限制、可加入球谐函数线圈的数量是有限的。但在高场，特别是超高场MRI成像中，高阶球谐函数项的匀场变得越来越重要，而传统的动态匀场技术难以满足此种高阶匀场要求。
发明内容
基于此，有必要针对上述技术问题，提供一种能够满足高阶匀场要求的磁共振成像的匀场控制方法、装置和系统。
一种磁共振成像的匀场控制方法，所述方法包括：
获取磁共振成像区域的实际磁场分布；
确定所述实际磁场分布的球谐函数表达；
根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值；其中，所述线圈阵列设置于磁共振设备中用于对磁共振进行匀场；所述线圈阵列的核函数根据所述线圈阵列中各基本线圈的磁场矢量分布确定
基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场。
一种磁共振成像的匀场控制装置，包括：
测量模块，用于获取磁共振成像区域的实际磁场分布；
分解模块，用于确定所述实际磁场分布的球谐函数表达；
目标电流确定模块，用于根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值；其中，所述线圈阵列设置于磁共振设备中用于对磁共振进行匀场；所述线圈阵列的核函数根据所述线圈阵列中各基本线圈的磁场矢量分布确定；
控制模块，用于基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场。
一种计算机设备，包括存储器、处理器及存储在存储器上并可在处理器上运行的计算机程序，其特征在于，所述处理器执行所述计算机程序时实现上述任一项所述方法的步骤。
一种计算机可读存储介质，其上存储有计算机程序，其特征在于，所述计算机程序被处理器执行时实现上述任一项所述的方法的步骤。
一种磁共振成像系统，包括：磁共振设备、线圈阵列、与所述线圈阵列中各基本线圈对应的线圈电流控制器以及上述的计算机设备；
所述线圈阵列安装在所述磁共振设备的磁极表面；
各所述线圈电流控制器的输入端与所述计算机设备连接，输出端与所述线圈阵列中对应的所述基本线圈连接；
所述磁共振设备与所述计算机设备连接。
上述的磁共振成像的匀场控制方法，对于实际测试的实际磁场分布，利用 其对应的实际磁场分布的球谐函数表达与线圈阵列的核函数，确定线圈阵列中成像区域对应的各基本线圈的目标电流值，而线圈阵列的核函数是根据线圈阵列中各基本线圈的磁场矢量分布确定的，在对超高场MRI成像中高阶球谐函数项的匀场时，对线圈阵列中成像区域对应的基本线圈施加根据实际磁场分布的球谐函数表达与线圈阵列的核函数确定的目标电流值实现匀场，从而无需在空间上叠加线圈数量即可满足高阶匀场要求。
附图说明
图1为一个实施例中磁共振系统的组成部分示意图；
图2为一个实施例中线圈阵列的横截面示意图；
图3为图2所示的线圈阵列的竖截面示意图；
图4为图2所示的线圈阵列的俯视图；
图5为另一个实施例中线圈阵列的横截面示意图；
图6为图5所示的线圈阵列的竖截面示意图；
图7为图5所示的线圈阵列的俯视图；
图8为一个实施例中磁共振成像的匀场控制方法的流程示意图；
图9为一个实施例中Z-X线圈的示意图；
图10为一个实施例中X-Y线圈的示意图；
图11为一个实施例中的基本线圈的结构示意图；
图12为图11所示的基本线圈在空间产生的矢量场图；
图13为一个实施例中阵列线圈24X17的电流分布情况；
图14为图13阵列线圈的电流分布产生的在球面场的分布；
图15为图13阵列线圈的电流分布产生的场和球谐函数项产生的场的差别；
图16为一个实施例中阵列线圈24X21的电流分布情况；
图17为图16阵列线圈的电流分布产生的在球面场的分布；
图18为图16阵列线圈的电流分布产生的场和球谐函数项产生的场的差别；
图19为另一个实施例中阵列线圈24X21的电流分布情况；
图20为图19阵列线圈电流分布产生的在球面场的分布；
图21为图19阵列线圈的阵列线圈的电流分布产生的场和球谐函数项产生的场的差别；
图22为一个实施例中磁共帧成像的匀场控制装置的结构框图；
图23为一个实施例中计算机设备的内部结构图。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本申请进行进一步详细说明。应当理解，此处描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
本申请提供的磁共振成像的匀场控制方法，可以应用于如图1所示的磁共振成像系统中，该系统包括磁共振设备101，线圈阵列102，与线圈阵列102中各基本线圈对应的线圈电流控制器103，以及计算机设备104。其中，线圈阵列102安装在磁共振设备101的磁极表面，各线圈电流控制器103的输入端与计算机设备104连接，输出端与线圈阵列102中对应的基本线圈连接，计算机设备104还与磁共振设备101连接。其中，每个基本线圈有独立的线圈电流控制器103为其供电，线圈电流控制器103为线圈阵列102中对应基本线圈提供直恒流稳定电流源。计算机设备实施磁共振成像的匀场控制，确定需要施加在线圈阵列上的电流值，并控制线圈电流控制器103向线圈阵列102对应的基本线圈施加该电流值，以实现动态匀场，最后计算机设备104根据磁共振的数据成像。
本申请的线圈阵列由S个基本线圈C组成一个线圈阵列，如图2-4所示，排列成一个阵列分布在可分布的空间里，对所有需要消除的球谐函数项所产生的非均匀场进行动态调整。而基于本申请的磁共振成像的匀场控制方法，线圈阵列的基本线圈分布可以根据需要任意分布，一个实施例的线圈阵列如图5-7所示。
如8所示，计算机设备执行一种磁共振成像的匀场控制方法，包括以下步骤：
S802：获取磁共振成像区域的实际磁场分布。
其中，成像区域是指医护人员根据受检者的检查部位所设置的磁共振感兴 趣区域。例如，受检者的检查部位为心脏，则医护人员将心脏对应的磁共振区域作为成像区域。实际磁场分布是指测量得到的磁共振所产生的该成像区域的磁场分布。具体地，可使用测量仪器测量成像区域的主磁场分布。
S804，确定实际磁场分布的球谐函数表达。
对于测量得到的成像区域的主磁场分布，将其在球坐标系下进行勒让德多项式展开，得到实际磁场分布的球谐函数表达，展开的多项式为：
Figure PCTCN2020128976-appb-000001
和b (n,m)是球谐函数项系数。传统动态匀场是通过对每个球谐函数项B n,m设计专门的基本线圈。这里
B n,m(r,θ,φ)＝r n[a (n,m)cos(mφ)+b (n,m)sin(mφ)]P (n,m)(cos θ)      (2)
有B 0,0线圈，其目的是调节中心频率。一阶匀场通常利用梯度线圈来完成。一般MRI提供6个二阶基本线圈，工程上称它们为X2、Y2、Z2、X-Y、Y-Z、Z-X。典型的Z-X如图9所示，典型的X-Y线圈如图10所示。
通过将测量得到的磁场分布，利用上式，将其有球坐标系下进行勒让德多项式展开，得到实际磁场分布的球谐函数表达，实际磁场分布的球谐函数表达表示实际测量的磁场分布情况。
S806，根据实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与成像区域对应的各基本线圈的目标电流值；其中，线圈阵列设置于磁共振设备中用于对磁共振进行匀场；线圈阵列的核函数根据线圈阵列中各基本线圈的磁场矢量分布确定。
具体地，考虑一个基本线圈C，如图11所示，其厚度为h、宽度为w、长度为l。线圈导线绕制成图11形状，根据需要可单层，也可多层，形成总匝数为η匝的基本线圈C。根据毕奥-萨伐尔定律给出其在空间产生的矢量场如图12所示。
Figure PCTCN2020128976-appb-000002
这里，r 0是在p点线圈C的位置、r′是q点场的坐标、R＝r′-r 0。图12展示的是单个基本线圈C周围的磁场矢量分布。在MRI成像时只考虑B z分量磁场。而对线圈阵列S中某个线圈C来讲，其电流I是没有变化的。所以从公式(3)可得到
Figure PCTCN2020128976-appb-000003
这里，
Figure PCTCN2020128976-appb-000004
是核函数，它表明了空间场源和场点的关系。对线圈阵列S而言，在r′处的场
Figure PCTCN2020128976-appb-000005
有如下数学关系
Figure PCTCN2020128976-appb-000006
这里，i＝1…s，
Figure PCTCN2020128976-appb-000007
场是所有线圈产生的场在r′点的总和。要调整的某个球谐函数项的目标场可达成
Figure PCTCN2020128976-appb-000008
其动态匀场的目标函数是
Figure PCTCN2020128976-appb-000009
同样如果要调整的是多个某球谐函数项的目标场时，公式(8)可达成
Figure PCTCN2020128976-appb-000010
通过对公式(8)或(9)进行优化找到最小Φ min→0。公式(9)也可转换成下列关系直接求解获得电流
Figure PCTCN2020128976-appb-000011
结合公式(6)可得到
Figure PCTCN2020128976-appb-000012
通常对与s个线圈的阵列有s个未知电流I i，i＝1…s。在空间选择t个目标 磁场点
Figure PCTCN2020128976-appb-000013
这样公式(11)可变成
Figure PCTCN2020128976-appb-000014
这里，
Figure PCTCN2020128976-appb-000015
其中A为t×s矩阵，I为s维未知电流向量，
Figure PCTCN2020128976-appb-000016
为t维目标磁场向量。一般来说，方程(12)的数值求解是一项困难的工作，因为该问题是由Fredholm第一类积分方程来表示的。它属于所谓病态问题的范畴。为了使系统自然松弛，选择(12)式为超定方程组，即t≥s。为了解决这一问题，考虑了一种正则化方法，它将病态问题(11)变换为适定问题:
Figure PCTCN2020128976-appb-000017
这里，A *是A共轭矩阵、A *A是s×s方阵、Λ是s×s单位矩阵。α是一个很小的数，当α→0时，I趋近于真解。线性算子αΛ的选择通常有助于抑制函数I中的剧烈振荡，采用标准的LU分解方法来快速求解方程(14)，从而得到各基本线圈的目标电流值。
为提高动态匀场的响应速度，在MRI特定成像δ区域可预先对应并提前算好每个正规化的球谐函数场的动态匀场电流，一旦获得目标成像δ区的场就可立刻完成场的动态调节。
具体地，根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值，包括：
根据预先获取的所述成像区域的标准化磁场分布的球谐函数表达与所述实际磁场分布的球谐函数表达，确定比例系数；
根据所述比例系数对预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值进行调整，确定与实际磁场分布对应的各基本线圈的目标电流值；其中，预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值根据 所述线圈阵列的核函数确定。
其中，比例系数为标准化磁场分布的球谐函数表达与实际磁场分布的球谐函数表达的比值。标准化磁场分布为标准化电流值所产生的磁产分布，标准化磁场分布的球谐函数表达，即为标准化电流所产生的磁产分布的球谐函数表达。标准化电流值和标准化磁场分布的球谐函数表达都通过预计算存储在数据库中。
具体地，标准化磁场分布的球谐函数表达可预先根据超导磁体本身产生的原磁场的非均度所需的标准电流所产生的理论磁场分布，将其在有球坐标系下进行勒让德多项式展开，得到标准化磁场分布的球谐函数表达。
具体地，成像区域δ的比例系数β n,m为
Figure PCTCN2020128976-appb-000018
其中，B n,m为实际磁场分布的球谐函数表达，
Figure PCTCN2020128976-appb-000019
为标准化磁场分布的球谐函数表达。
其中，标准化电流值为超导磁体本身产生的原磁场的非均度所需的标准电流，由系统预先计算得到。在实际应用中，利用实际磁场分布与标准化情况下的比例系数，对标准化电流值进行调整，得到与实际磁场分布相应的各基本线圈的目标电流值。
而由于标准化电流值和标准化磁场分布的球谐函数表达是预先计算得到的，在实际应用时，省去了计算时间，提高了磁共振匀场的响应速度。
具体地，该磁共振成像的匀场控制方法还包括：预先确定准化电流值
Figure PCTCN2020128976-appb-000020
及标准化磁场分布的球谐函数表达
Figure PCTCN2020128976-appb-000021
标准化磁场分布为标准化电流值所产生磁场分布
其中，预先确定准化电流值及标准化磁场分布的球谐函数表达，包括：预先确定标准化磁场分布的球谐函数表达，及基于所述线圈阵列的核函数预先确定准化电流值，包括：基于毕奥-萨伐尔定律确定基本线圈在空间产生的磁场矢量分布；根据线圈阵列中各基本线圈的磁场矢量分布，确定线圈阵列的核函数；根据核函数确定线圈阵列中各成像区域的对应的磁场分布；根据磁场分布确定各球谐函数项匀场的目标函数；根据各球谐函数项匀场的目标函数，确定准化电流值及标准化磁场分布的球谐函数表达。
具体地，线圈阵列中所述成像区域对应的各基本线圈标准化电流值的预计 算采用与前面对实际磁场分布的电流计算方法相同，此处不再赘述。
具体地，根据比例系数对预计算的线圈阵列中成像区域对应的各基本线圈标准化电流值进行调整，确定与实际磁场分布对应的各基本线圈的目标电流值，包括：根据各球谐函数项的比例系数与线圈阵列中成像区域对应的各基本线圈标准化电流值，确定基本线圈的各球谐函数项的电流值；对基本线圈的各球谐函数项的电流值进行累加，得到基本线圈的目标电流池。
Figure PCTCN2020128976-appb-000022
从算法本身来看，阵列线圈的基本线圈分布可以根据需要任意分布。整个动态匀场步骤是一样的，只要根据基本线圈的空间分布用公式(5)计算核函数就好。
S808，基于目标电流值对成像区域对应的各基本线圈进行电流控制实现匀场。
具体地，向成像区域各基本线圈对应的线圈控制器发送目标电流值，由线圈控制器向基本线圈施加对应的目标电流值，以对所述成像区域进行匀场。
上述的磁共振成像的匀场控制方法，对于实际测试的实际磁场分布，利用其对应的实际磁场分布的球谐函数表达与线圈阵列的核函数，确定线圈阵列中成像区域对应的各基本线圈的目标电流值，而线圈阵列的核函数是根据线圈阵列中各基本线圈的磁场矢量分布确定的，在对超高场MRI成像中高阶球谐函数项的匀场时，对线圈阵列中成像区域对应的基本线圈施加根据实际磁场分布的球谐函数表达与线圈阵列的核函数确定的目标电流值实现匀场，从而无需在空间上叠加线圈数量即可满足高阶匀场要求。
进一步地，利用其对应的实际磁场分布的球谐函数表达与标准化磁场分布的球谐函数表达确定比例系数，从而根据比例系数对各基本线圈标准化电流值进行调整，得到与实际磁场分布相应的各基本线圈的目标电流值。而由于标准化电流值和标准化磁场分布的球谐函数表达是预先计算得到的，在实际应用时，省去了计算时间，提高了磁共振匀场的响应速度。
现在结合实际算例，对本申请的磁共振成像的匀场控制方法进行说明。
在对MRI成像区匀场时，通常球谐函数的zonal(带状)项相比较容易匀，tesseral(田形)项调整起来十分困难，而对高价tesseral项的调整更是极具挑战性。在这里通过两个阵列线圈来展示该动态匀场方法的强大能力。
首先选择线圈阵列为24X17，也就是在圆周均布24个、在轴向均布17个线圈。从表一可以看到所列的是一些在传统方法下非常困难的球谐函数项，并且对每个球谐函数项所产生的场的峰-峰值在匀场前都是5ppm。一直到球谐函数项(n＝5，m＝5)，该阵列线圈匀场后的均匀度都小于1ppm，其调整率都在90％左右，而阵列线圈内的峰值电流都小于5安培。随着球谐函数项变化增大，该阵列线圈在球谐函数项(n＝6，m＝6)时基本开始失效。表二给出了当球谐函数项(n＝8，m＝1…6)的匀场情况。同样一直到球谐函数项(n＝8，m＝5)，该阵列线圈动态匀场的表现都非常不错，匀场后的均匀度都小于1ppm，其调整率都在90％左右，而阵列线圈内的峰值电流都小于5安培。该阵列线圈在球谐函数项(n＝8，m＝6)时基本开始失效。可以看出该阵列线圈不但对zonal场是非常有效的，而且对tesseral场也能在m≤5非常有效。
表一
Figure PCTCN2020128976-appb-000023
表二
Figure PCTCN2020128976-appb-000024
下面的例子为线圈阵列为24X21，即在圆周均布24个、在轴向均布21个线圈。同样对每个球谐函数项所产生的场的峰-峰值在匀场前都是5ppm。从表三可以看出除球谐函数项(n＝6，m＝6)只调整了60％，球谐函数项(n＝7，m＝7)调整了80％，其余的球谐函数项的场在该阵列线圈匀场后的均匀度都小于1ppm，其调整率都超过90％。而阵列线圈内的峰值电流都小于5安培。随着球谐函数项变化增大，该阵列线圈在球谐函数项(n＝8，m＝8)时基本开始失效。表四给出了当球谐函数项(n＝11，m＝1…6)的匀场情况。同样一直到球谐函数项(n＝11，m＝5)，该阵列线圈动态匀场的表现都非常不错，匀场后的均匀度都小于1ppm，其调整率都在90％左右。该阵列线圈在球谐函数项(n＝11，m＝6)时基本开始失效。可以看出该阵列线圈对高阶zonal和tesseral场都是非常有效的。
表三
Figure PCTCN2020128976-appb-000025
Figure PCTCN2020128976-appb-000026
表四
Figure PCTCN2020128976-appb-000027
图13至图15展示了阵列线圈24X17对球谐函数偶数项(n＝8，m＝4)具体的匀场情况。图13展现的是阵列线圈的电流分布情况，由于球谐函数项(n＝8，m＝4)是对称的，可以看出对该单一球谐函数项阵列线圈的电流分布也是对称的。图14展现的是由阵列线圈的电流分布产生的在球面场的分布，而图15给出了阵列线圈的电流分布产生的场和球谐函数项产生的场的差别。如前所述，原球谐函数项产生的场的峰-峰值为5ppm，用该阵列线圈匀场后的峰-峰值为0.35ppm，其调整率达到了93％。
图16-18展示了阵列线圈24X21对球谐函数奇数项(n＝11，m＝1)具体的 匀场情况。图16展现的是阵列线圈的电流分布情况。图17展现的是由阵列线圈的电流分布产生的在球面场的分布，而图18给出了阵列线圈的电流分布产生的场和球谐函数项产生的场的差别。在这里原球谐函数项产生的场的峰-峰值为5ppm，用该阵列线圈匀场后的峰-峰值为0.22ppm，其调整率达到了96％。
图19-21展示了阵列线圈24X21对高阶球谐函数奇数项(n＝11，m＝3)具体的匀场情况。图19展现的是阵列线圈的电流分布情况。图20展现的是由阵列线圈的电流分布产生的在球面场的分布，而图21给出了阵列线圈的电流分布产生的场和球谐函数项产生的场的差别。如前所述，原球谐函数项产生的场的峰-峰值为5ppm，用该阵列线圈匀场后的峰-峰值为0.24ppm，其调整率达到了95％。
如图22所示，本申请还提供一种磁共振成像的匀场控制装置，包括：
测量模块2201，用于获取磁共振成像区域的实际磁场分布。
分解模块2202，用于确定所述实际磁场分布的球谐函数表达。
目标电流确定模块2203，用于根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值；其中，所述线圈阵列设置于磁共振设备中用于对磁共振进行匀场；所述线圈阵列的核函数根据所述线圈阵列中各基本线圈的磁场矢量分布确定。
控制模块2204，用于基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场。
在另一个实施例中，目标电流确定模块，包括：
比例确定模块，用于根据预先获取的所述成像区域的标准化磁场分布的球谐函数表达与所述实际磁场分布的球谐函数表达，确定比例系数。
电流计算模块，用于根据所述比例系数对预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值进行调整，确定与实际磁场分布对应的各基本线圈的目标电流值；其中，预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值根据所述线圈阵列的核函数确定。
该装置还包括预处理模块，用于先确定标准化磁场分布的球谐函数表达， 及基于所述线圈阵列的核函数预先确定准化电流值，所述标准化磁场分布为标准化电流值所产生磁场分布。
在另一个实施例中，预处理模块，用于基于毕奥-萨伐尔定律确定所述基本线圈在空间产生的磁场矢量分布，根据所述线圈阵列中各基本线圈的磁场矢量分布，确定所述线圈阵列的核函数，根据所述核函数确定所述线圈阵列中各成像区域的对应的磁场分布，根据所述磁场分布确定各球谐函数项匀场的目标函数，根据各球谐函数项匀场的目标函数，确定准化电流值及标准化磁场分布的球谐函数表达。
在另一个实施例中，电流计算模块，用于根据各球谐函数项的所述比例系数与所述线圈阵列中所述成像区域对应的各基本线圈标准化电流值，确定基本线圈的各球谐函数项的电流值，对所述基本线圈的各球谐函数项的电流值进行累加，得到所述基本线圈的目标电流池。
在另一个实施例中，控制模块，用于向所述成像区域各基本线圈对应的线圈控制器发送所述目标电流值，由所述线圈控制器向所述基本线圈施加对应的所述目标电流值，以对所述成像区域进行匀场。
上述的磁共振成像的匀场控制装置，对于实际测试的实际磁场分布，利用其对应的实际磁场分布的球谐函数表达与线圈阵列的核函数，确定线圈阵列中成像区域对应的各基本线圈的目标电流值，而线圈阵列的核函数是根据线圈阵列中各基本线圈的磁场矢量分布确定的，在对超高场MRI成像中高阶球谐函数项的匀场时，对线圈阵列中成像区域对应的基本线圈施加根据实际磁场分布的球谐函数表达与线圈阵列的核函数确定的目标电流值实现匀场，从而无需在空间上叠加线圈数量即可满足高阶匀场要求。
进一步地，对于实际测试的实际磁场分布，利用其对应的实际磁场分布的球谐函数表达与标准化磁场分布的球谐函数表达确定比例系数，从而根据比例系数对各基本线圈标准化电流值进行调整，得到与实际磁场分布相应的各基本线圈的目标电流值。而由于标准化电流值和标准化磁场分布的球谐函数表达是预先计算得到的，在实际应用时，省去了计算时间，提高了磁共振匀场的响应速度。
关于磁共振成像的匀场控制装置的具体限定可以参见上文中对于磁共振成像的匀场控制方法的限定，在此不再赘述。上述磁共振成像的匀场控制装置中的各个模块可全部或部分通过软件、硬件及其组合来实现。上述各模块可以硬件形式内嵌于或独立于计算机设备中的处理器中，也可以以软件形式存储于计算机设备中的存储器中，以便于处理器调用执行以上各个模块对应的操作。
在一个实施例中，提供了一种计算机设备，该计算机设备可以是终端，其内部结构图可以如图23所示。该计算机设备包括通过系统总线连接的处理器、存储器、网络接口、显示屏和输入装置。其中，该计算机设备的处理器用于提供计算和控制能力。该计算机设备的存储器包括非易失性存储介质、内存储器。该非易失性存储介质存储有操作系统和计算机程序。该内存储器为非易失性存储介质中的操作系统和计算机程序的运行提供环境。该计算机设备的网络接口用于与外部的终端通过网络连接通信。该计算机程序被处理器执行时以实现一种磁共振成像的匀场控制方法。该计算机设备的显示屏可以是液晶显示屏或者电子墨水显示屏，该计算机设备的输入装置可以是显示屏上覆盖的触摸层，也可以是计算机设备外壳上设置的按键、轨迹球或触控板，还可以是外接的键盘、触控板或鼠标等。
本领域技术人员可以理解，图23中示出的结构，仅仅是与本申请方案相关的部分结构的框图，并不构成对本申请方案所应用于其上的计算机设备的限定，具体的计算机设备可以包括比图中所示更多或更少的部件，或者组合某些部件，或者具有不同的部件布置。
在一个实施例中，提供了一种计算机设备，包括存储器和处理器，存储器中存储有计算机程序，该处理器执行计算机程序时实现上述各实施例的磁共振成像的匀场控制方法。
在一个实施例中，提供了一种计算机可读存储介质，其上存储有计算机程序，计算机程序被处理器执行时实现上述各实施例的磁共振成像的匀场控制方法。
本领域普通技术人员可以理解实现上述实施例方法中的全部或部分流程，是可以通过计算机程序来指令相关的硬件来完成，所述的计算机程序可存储于一非易失性计算机可读取存储介质中，该计算机程序在执行时，可包括如上述各方法的实施例的流程。其中，本申请所提供的各实施例中所使用的对存储器、存储、数据库或其它介质的任何引用，均可包括非易失性和/或易失性存储器。非易失性存储器可包括只读存储器(ROM)、可编程ROM(PROM)、电可编程ROM(EPROM)、电可擦除可编程ROM(EEPROM)或闪存。易失性存储器可包括随机存取存储器(RAM)或者外部高速缓冲存储器。作为说明而非局限，RAM以多种形式可得，诸如静态RAM(SRAM)、动态RAM(DRAM)、同步DRAM(SDRAM)、双数据率SDRAM(DDRSDRAM)、增强型SDRAM(ESDRAM)、同步链路(Synchlink)DRAM(SLDRAM)、存储器总线(Rambus)直接RAM(RDRAM)、直接存储器总线动态RAM(DRDRAM)、以及存储器总线动态RAM(RDRAM)等。
以上实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请专利的保护范围应以所附权利要求为准。

Claims (10)

  1. 一种磁共振成像的匀场控制方法，所述方法包括：
    获取磁共振成像区域的实际磁场分布；
    确定所述实际磁场分布的球谐函数表达；
    根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值；其中，所述线圈阵列设置于磁共振设备中用于对磁共振进行匀场；所述线圈阵列的核函数根据所述线圈阵列中各基本线圈的磁场矢量分布确定；
    基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场。
  2. 根据权利要求1所述的方法，其特征在于，根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值，包括：
    根据预先获取的所述成像区域的标准化磁场分布的球谐函数表达与所述实际磁场分布的球谐函数表达，确定比例系数；
    根据所述比例系数对预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值进行调整，确定与实际磁场分布对应的各基本线圈的目标电流值；其中，预计算的线圈阵列中所述成像区域对应的各基本线圈标准化电流值根据所述线圈阵列的核函数确定。
  3. 根据权利要求2所述的方法，其特征在于，所述方法还包括：预先确定标准化磁场分布的球谐函数表达，及基于所述线圈阵列的核函数预先确定准化电流值，所述标准化磁场分布为标准化电流值所产生磁场分布。
  4. 根据权利要求3所述的方法，其特征在于，预先确定标准化磁场分布的球谐函数表达，及基于所述线圈阵列的核函数预先确定准化电流值，包括：
    基于毕奥-萨伐尔定律确定所述基本线圈在空间产生的磁场矢量分布；
    根据所述线圈阵列中各基本线圈的磁场矢量分布，确定所述线圈阵列的核函数；
    根据所述核函数确定所述线圈阵列中各成像区域的对应的磁场分布；
    根据所述磁场分布确定各球谐函数项匀场的目标函数；
    根据各球谐函数项匀场的目标函数，确定准化电流值及标准化磁场分布的球谐函数表达。
  5. 根据权利要求2所述的方法，其特征在于，根据所述比例系数对预计算的所述线圈阵列中所述成像区域对应的各基本线圈标准化电流值进行调整，确定与实际磁场分布对应的各基本线圈的目标电流值，包括：
    根据各球谐函数项的所述比例系数与所述线圈阵列中所述成像区域对应的各基本线圈标准化电流值，确定基本线圈的各球谐函数项的电流值；
    对所述基本线圈的各球谐函数项的电流值进行累加，得到所述基本线圈的目标电流池。
  6. 根据权利要求1所述的方法，其特征在于，基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场，包括：
    向所述成像区域各基本线圈对应的线圈控制器发送所述目标电流值，由所述线圈控制器向所述基本线圈施加对应的所述目标电流值，以对所述成像区域进行匀场。
  7. 一种磁共振成像的匀场控制装置，包括：
    测量模块，用于获取磁共振成像区域的实际磁场分布；
    分解模块，用于确定所述实际磁场分布的球谐函数表达；
    目标电流确定模块，用于根据所述实际磁场分布的球谐函数表达以及线圈阵列的核函数，确定线圈阵列中与所述成像区域对应的各基本线圈的目标电流值；其中，所述线圈阵列设置于磁共振设备中用于对磁共振进行匀场；所述线圈阵列的核函数根据所述线圈阵列中各基本线圈的磁场矢量分布确定；
    控制模块，用于基于所述目标电流值对所述成像区域对应的各基本线圈进行电流控制实现匀场。
  8. 一种计算机设备，包括存储器、处理器及存储在存储器上并可在处理器上运行的计算机程序，其特征在于，所述处理器执行所述计算机程序时实现权利要求1至6中任一项所述方法的步骤。
  9. 一种计算机可读存储介质，其上存储有计算机程序，其特征在于，所述计算机程序被处理器执行时实现权利要求1至6中任一项所述的方法的步骤。
  10. 一种磁共振成像系统，包括：磁共振设备、线圈阵列、与所述线圈阵列中各基本线圈对应的线圈电流控制器以及如权利要求8所示的计算机设备；
    所述线圈阵列安装在所述磁共振设备的磁极表面；
    各所述线圈电流控制器的输入端与所述计算机设备连接，输出端与所述线圈阵列中对应的所述基本线圈连接；
    所述磁共振设备与所述计算机设备连接。
PCT/CN2020/128976 2019-12-05 2020-11-16 磁共振成像的匀场控制方法、装置和系统 WO2021109847A1 (zh)

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