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CN101615214B - Method for conducting performance analysis on magnetic resonance imaging RF coil - Google Patents

Method for conducting performance analysis on magnetic resonance imaging RF coil Download PDF

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CN101615214B
CN101615214B CN 200910089558 CN200910089558A CN101615214B CN 101615214 B CN101615214 B CN 101615214B CN 200910089558 CN200910089558 CN 200910089558 CN 200910089558 A CN200910089558 A CN 200910089558A CN 101615214 B CN101615214 B CN 101615214B
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coil
field
rf
simulation
magnetic
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CN101615214A (en )
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李烨
蒋晓华
郭彦
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清华大学
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Abstract

A simulation method for conducting performance analysis on a magnetic resonance imaging RF coil belongs to the technical field of magnetic resonance imaging, and is characterized by comprising the steps of first establishing an RF coil space simulation model, calculating skin depth of a conductor, conducting mesh generation on the simulation model according to the skin depth, setting simulation boundary conditions, then using electromagnetic field finite element numerical calculation software to calculate various electromagnetic parameters, according to the electromagnetic parameters, calculating the inductance of the RF coil, the self resistance of the coil, load eddy-current loss equivalent resistance and the uniformity and signal-to-noise ratio of the magnetic field; and finally, according to the calculation result, selecting appropriate cross section dimension of the conductor and coil size. The method improves the self resistance of the conductor, the load eddy-current loss and the calculation accuracy of space electromagnetic field distribution.

Description

一种对磁共振成像RF线圈进行性能分析的方法 A method for magnetic resonance imaging RF coil performance analysis

技术领域 FIELD

[0001] 本发明属于电磁场有限元分析领域,尤其涉及磁共振成像(MRI)射频接收线圈的设计。 [0001] The present invention belongs to the field of electromagnetic finite element analysis, in particular, it relates to the design of magnetic resonance imaging (MRI) of the radio frequency receiving coil.

背景技术 Background technique

[0002] 磁共振成像(MRI)是一种利用核磁共振现象进行成像的技术。 [0002] Magnetic resonance imaging (MRI) is an imaging technology using NMR phenomenon. 作为共振信号的接收天线,射频接收线圈的性能对MRI系统成像的质量有着直接的影响。 Resonance signals as a receiving antenna, the performance of the RF receiving coil has a direct impact on the quality of the MRI imaging system. MRI图像的信噪比(SNR, Signal to Noise Ratio)、分辨率和成像速度在很大程度上取决于射频接收线圈的SNR;而图像的均勻性则依赖于射频接收线圈和发射线圈的均勻性。 MRI image noise ratio (SNR, Signal to Noise Ratio), resolution and imaging speed depends largely on the SNR of the radio frequency receiving coil; and the uniformity of the image depends on the uniformity of the RF receiving coil and a transmitting coil . 其电磁设计指标有: Electromagnetic design specifications are:

[0003] (1)射频线圈通入单位有效值射频电流时产生的磁场的均勻度HD,Homogeneous Degree : [0003] The uniformity of the magnetic field generated when the effective value of the RF current (1) into the RF coil unit HD, Homogeneous Degree:

[0004] [0004]

Figure CN101615214BD00041

[0005] 其中:BmaX、Bmin分别是通入单位有效值射频电流时,线圈在所关心区域内产生的磁感应强度的最大值和最小值。 [0005] wherein: when Bmax, Bmin units are fed RMS RF current, magnetic induction coil in the area of ​​interest minimum and maximum values.

[0006] (2)线圈的信噪比: [0006] (2) The signal to noise ratio of the coil:

[0007] [0007]

Figure CN101615214BD00042

[0008] 其中,B是射频线圈通入单位有效值射频电流时在该点产生的磁感应强度的有效值;Reff是线圈的噪声电阻。 [0008] wherein, B is the effective value of the magnetic induction coil RF unit into a radio frequency current generated when the effective value at that point; Reff is the noise resistance of the coil.

[0009] 噪声电阻包括线圈自身电阻以及负载中涡流损耗折合到线圈上的等效电阻。 [0009] Noise resistance of the coil itself comprises a load resistor, and an eddy current loss equivalent to the equivalent resistance of the coil. 计算线圈自身的高频电阻时,常用的方法是近似认为电流集中在趋肤深度内,且电流密度均勻分布。 Calculating the high frequency resistance of the coil itself, commonly used method is to approximate that current concentration in the skin depth, and a uniform current density. 由于实际上电流密度在趋肤深度内也是随与边缘的距离变化的,这种方法计算的线圈自身电阻偏小。 In fact since the current density is within the skin depth and with distance from the edge of change calculated in this way small resistance coil itself. 计算负载涡流损耗时,常用的方法是不考虑导体内电流的分布,并且忽略负载涡流对空间电场的影响的近似条件下,通过计算导体内电流在负载中产生的电场强度,进而求出负载涡流损耗。 When calculating load eddy current loss, commonly used method is not considered conductor current distribution, and the approximation ignores the influence of load of the eddy current field in the space by calculating the electric field strength generated by current in a conductor in the load, and thus the eddy current load is obtained loss. 实际上负载涡流对其附近区域电磁场的削弱作用是不可忽略的,因此这种方法计算的负载涡流损耗偏大。 Indeed load vortex its vicinity electromagnetic field weakening effect is not negligible, so this method of calculating the load is too large eddy current loss.

[0010] 本发明中通过采用电磁场有限元数值计算的方法,避免上述近似所带来的误差, 极大得提高了计算的准确性。 [0010] The method of the present invention, by using Finite Element numerical calculation, to avoid errors caused by the approximate, have greatly improved the accuracy of calculation.

发明内容 SUMMARY

[0011] 本发明的目的在于提供一种对磁共振成像RF线圈进行性能分析的方法,其步骤如下: [0011] The object of the present invention to provide an RF coil of a magnetic resonance imaging method for performance analysis, comprises the following steps:

[0012] 步骤(1),把如下设定参数输入计算机: [0012] Step (1), to set the parameter entered into a computer:

[0013] RF线圈的几何尺寸,线圈导体的横截面的几何尺寸,导体材料的电导率、磁导率, 通入线圈中的射频电流的幅值和频率,对于有负载的情况,还需要输入负载的空间尺寸;[0014] 步骤O),根据实际RF线圈和负载,建立空间仿真模型; [0013] RF coil geometry, the geometry of the cross section of the coil conductors, the conductor material conductivity, magnetic permeability, RF current in coil into amplitude and frequency, for a load, also need to enter the spatial dimensions of the load; [0014] step O), and the RF coil according to the actual load, establishing spatial simulation model;

[0015] 步骤(3),根据所述射频电流的频率计算导体的趋肤深度,并据此对所述空间仿真模型进行网格剖分: [0015] Step (3), calculated according to the frequency of the RF conductor current skin depth, and accordingly the simulation model space meshes are:

[0016] 步骤(3. 1),按如下公式计算所述导体的趋肤深度ds : [0016] Step (3.1), is calculated as follows skin depth of the conductor ds:

[0017] [0017]

Figure CN101615214BD00051

[0018] 其中,f是所述射频电流的频率,μ是所述导体材料的磁导率,P是所述导体材料的电阻率; [0018] where, f is the frequency of the RF current, μ is the permeability of the conductor material, P is the resistivity of the conductor material;

[0019] 步骤(3. 2),在二维模型中,用尺寸为1/2到1/5趋肤深度的三角形网格单元剖分趋肤深度内的导体区域。 [0019] Step (3.2), in a two-dimensional model, with a size of 1/2 to 1/5 of the skin depth of the triangular mesh decomposing conductor area within the skin depth. 在三维模型中,在趋肤深度内的导体区域被分为了平行于导体边界的3〜10层; In the three-dimensional model, in the conductor area within the skin depth of the conductor it is divided parallel to the boundary layer of 3~10;

[0020] 步骤(4),设置以下仿真条件: [0020] Step (4), provided the following simulation conditions:

[0021] A :把空气域的外边界设置为平行边界; [0021] A: The outer boundary of the air domain boundary arranged in parallel;

[0022] B :将导体横截面设置为等电位面,并加载所述射频电流,射频电流有效值记为I ; [0022] B: the conductor cross-section is set to an equipotential surface, the RF current and load, referred to as a radio frequency current effective value I;

[0023] 步骤(5),使用电磁场有限元数值计算软件计算出磁感应强度,电场强度,电流密度,功率损耗和磁场储能; [0023] Step (5), is calculated using an electromagnetic field FEM software calculates the magnetic flux density, electric field strength, current density, power loss and magnetic energy storage;

[0024] 步骤(6),根据步骤(5)得到的仿真结果计算射频线圈的性能参数。 [0024] Step (6), the performance parameters of the RF coil is calculated according to the simulation results obtained in step (5).

[0025] 本发明中的计算方法,通过采用电磁场有限元数值计算的方法,从麦克斯韦方程组出发,综合考虑了各个电流元对空间电磁场的影响,同时对导体趋肤深度内的区域进行了更为细致的网格剖分,从而使得导体自身电阻、负载涡流损耗以及空间电磁场分布的计算结果的准确性都有了不同程度的提高。 Calculation method [0025] of the present invention, by using electromagnetic fields finite element numerical calculation, starting from the Maxwell equations, considering the effect of the respective current cells space electromagnetic field, while the regions within the conductor skin depth in more as detailed meshing, so that the resistance of the conductor itself, and the accuracy of eddy current loss load calculation results of the spatial distribution of the electromagnetic field has a different degree.

附图说明 BRIEF DESCRIPTION

[0026] 图1是无负载射频线圈的三维仿真模型图,1. 1全图,1. 2导体横截面放大图: 1.外层空气域;2.内层空气域;3.线圈(导体);4.线圈轴线;5.趋肤深度内的导体区域, 其中ds是趋肤深度。 [0026] FIG. 1 is a three-dimensional simulation model of the RF coil of FIG no load, full FIG. 11, a cross-sectional enlarged view of the conductor 2: 1. The outer air field; inner air domain 2; 3 coils (conductors. );. a coil axis 4; 5 conductor area within the skin depth, where ds is the skin depth.

[0027] 图2是铜带的单位长度电阻与导体横截面宽度的关系图:一■一导体厚度0. 2mm ; [0027] FIG. 2 is a copper strip conductor resistance per unit length and cross-sectional width of the graph: a thickness of the conductor ■ a 0. 2mm;

[0028] 一•一导体厚度0. 1mm。 [0028] a conductor • a thickness 0. 1mm.

[0029] 图3是铜带的单位长度电阻与导体横截面厚度的关系图:一■一导体宽度5mm ; [0029] FIG. 3 is a copper tape conductor resistance per unit length and cross-sectional thickness of the diagram: ■ a conductor width a 5mm;

[0030] 一•一导体宽度10mm。 [0030] a • a conductor width 10mm.

[0031] 图4是有负载射频线圈二维仿真模型图,4. 1全图,4. 2导体横截面放大图:1.外层空气域;2.内层空气域;3.线圈(导体);4.线圈轴线;5.趋肤深度内的导体区域,其中ds是趋肤深度;6.负载;7.空气域外边界。 [0031] FIG. 4 is a two-dimensional simulation model of the RF coil loads FIG 41 FIG full, 42 cross-sectional enlarged view of the conductor:.... An outer air domain; inner air domain 2; 3 coils (conductors );. a coil axis 4; 5 conductor area within the skin depth, which is the skin depth ds; 6 load; 7 outside air boundary.

[0032] 图5是线圈噪声电阻与圆环形线圈半径的关系图:一■一负载涡流损耗等效电阻; [0032] FIG. 5 is a graph of noise resistance coil radius and an annular coil: ■ an eddy current loss equivalent resistance to a load;

[0033] 一•一线圈导体自身电阻。 [0033] • a coil conductor itself a resistance.

[0034] 图6本发明设计过程的流程框图。 [0034] The design process flow diagram of FIG. 6 invention. 具体实施方式 detailed description

[0035] 下面结合附图来说明一下本发明的原理和具体的实施方式。 [0035] Next, to explain the principles and specific embodiments of the present invention in conjunction with the accompanying drawings. 实例一(无负载模型): Examples of a (Model no load):

[0036] 线圈是一个半径为62. Imm的圆环线圈,导体的横截面为宽5. 2mm,厚0. 2mm的矩形。 [0036] radius of the coil is a ring coil 62. Imm, a wide cross-section of the conductor 5. 2mm, a thickness of 0. 2mm rectangular. 导体材料为铜带,磁导率为X10_7H/m,经过测量电阻率为1.889Χ10_8Ω · m。 Conductive material is a copper tape, magnetic permeability X10_7H / m, the resistance was measured after 1.889Χ10_8Ω · m. 线圈中通入射频频率f= 14. 85MHz的电流。 Into the RF coil current f = frequency of 14. 85MHz. A.计算线圈的等效电阻和电感;B.考察单位长度线圈电阻随导体横截面尺寸的关系。 A. Calculate the equivalent resistance and inductance of the coil;. B investigated coil resistance per unit length relationship with the conductor cross-sectional dimension.

[0037] (1)根据实际线圈建立仿真模型。 [0037] (1) a simulation model based on the actual coil.

[0038] 通常空气域半径是导体区域半径的3至5倍。 [0038] Generally air region radius is 3 to 5 times the radius of the conductor regions. 本例中,鉴于导体存在于半径62. Imm 的空间区域内,设置空气域是半径为300mm,高600mm的圆柱体。 In the present embodiment, in view of the conductor is present in the spatial region 62. Imm radius, the radius of an air field is 300mm, 600mm high cylinder. 考虑到线圈的对称性,建立如图1所示的1/8空间模型。 Considering the symmetry of the coil, the establishment of the model shown in FIG. 1 1/8 space.

[0039] (2)计算导体趋肤深度,并剖分网格。 [0039] (2) the skin depth of the conductor is calculated, and the subdivision mesh.

[0040] 根据射频频率f,导体电阻率P,磁导率μ,计算趋肤深度: [0040] The radio frequency f, the resistivity of the conductors P, magnetic permeability μ, skin depth is calculated:

[0041] [0041]

Figure CN101615214BD00061

[0042] 当在三维模型中希望像二维模型那样直接将导体划分为尺寸小于趋肤深度的三维网格单元时,将会由于单元太多导致计算量过大。 [0042] When it is desired that a direct two-dimensional model image dividing a size smaller than a conductor skin depth of the three-dimensional model in three-dimensional grid cell, since the cell will result in too large computation. 在三维模型中,采用将趋肤深度内的导体区域分为了平行于导体边界的3〜10层的方法。 In the three-dimensional model using a trend within the skin depth of the conductor region is divided into a method of 3~10 parallel to the conductor layer boundary. 本算例将趋肤深度内的导体区域分为8 层,如图1右侧所示。 This will tend examples conductor area within the skin depth into layer 8, as shown in Figure 1 on the right side. 外层空气域网格尺寸为50mm,内层空气域网格尺寸为5mm,导体区域网格尺寸为0. 2mm。 Air mesh size of the outer field 50mm, inner domain air mesh size is 5mm, the mesh size of conductor regions 0. 2mm.

[0043] (3)仿真求解条件设置如下: [0043] (3) Simulation Calculation Conditions set as follows:

[0044] A.将空气域外边界设置为平行边界。 [0044] A. The air boundary coordinate points arranged in parallel.

[0045] B.将导体横截面设置为等电位面,并加载/ = l/V^A、频率f= 14. 85MHz的电流。 [0045] B. The cross section of the conductor is set to an equipotential surface, and / = l ^ A, current frequency f = / V 14. 85MHz loading.

[0046] (4)根据仿真结果,计算线圈的噪声电阻。 [0046] (4) According to the simulation result, the noise resistance of the coil is calculated.

[0047] 根据下列公式可以求出线圈电感L,线圈自身电阻Rrail以及负载中涡流损耗折合到线圈上的等效电阻Rsample,以及线圈的噪声电阻Reff : [0047] The following equation can be calculated coil inductance L, and the load coil itself Rrail resistance equivalent to the eddy current loss on the coil Rsample equivalent resistance, noise and the coil resistance Reff:

[0048] Rcoil = ^f [0048] Rcoil = ^ f

[0049] Rsample =^l [0049] Rsample = ^ l

[0050] [0050]

Figure CN101615214BD00062

[0051] Reff = URsample [0051] Reff = URsample

[0052] 式中I是线圈中射频电流有效值,本例中/ = J—是导体中功率损耗有效值,Psample是负载中功率损耗有效值,Wm是磁场储能有效值,这三个值都可以由仿真软件直接给出。 [0052] wherein I is the rms current RF coil, in the present embodiment / = J- conductor RMS power loss, the power loss in the load Psample rms, rms storage Wm of the magnetic field, the three values It can be given directly by the simulation software.

[0053] 线圈各个参数的仿真结果如表1所示。 [0053] The simulation results of the individual parameters shown in Table 1 coil.

[0054] 表1无负载线圈性能参数计算结果 [0054] Table 1 no load coil performance parameter calculation

[0055]—P/mff ffm/ μ J RcoilZm ω IL/ μ H [0055] -P / mff ffm / μ J RcoilZm ω IL / μ H

30.51 ^ 0. 07364 61. 02 0. 2946 ^ 0.07364 30.51 61.02 0.2946

[0056] (5)根据计算结果选择合适的导体横截面尺寸 [0056] (5) selecting a suitable cross-sectional dimension of the conductor according to the calculation result

[0057] 通常负载对线圈导体自身电阻的影响非常小,同时导体横截面的尺寸对负载涡流损耗的影响也非常小;因此我们可以不考虑负载的影响,直接采用无负载的射频接收线圈仿真模型,以使线圈自身电阻小为目标来选择导体横截面的尺寸。 [0057] Generally the load effect on the coil conductor itself resistance is very small, affect the size of conductor cross-section of the load eddy current loss is very small; therefore we can not consider the effect of load, the direct use of radio frequency receive coils simulation model no load so that the resistance of the coil itself to select the size of the small cross section of the target conductor.

[0058] 图2是厚度分别是0. Imm和0. 2mm的两种铜带的单位长度电阻与导体横截面宽度的关系。 [0058] FIG. 2 is a relationship between the thicknesses of the conductor resistance per unit length, and two kinds of copper strip 0. Imm of 0. 2mm in cross-sectional width.

[0059] 图3是宽度分别是5mm和IOmm的两种铜带的单位长度电阻与导体横截面厚度的关系。 [0059] FIG. 3 is a width of 5mm and two kinds of relationships are IOmm copper tape conductor resistance per unit length and cross-sectional thickness.

[0060] 由图可以看出:A.导体宽度的尺寸是决定导体电阻的主要因素;B.导体厚度大于0. 05mm后,继续增加导体厚度,电阻减小不明显;C.导体宽度大于2mm时,线圈电阻近似与宽度成反比。 [0060] As can be seen from FIG.:.. A conductor width size is a major factor in determining the resistance of the conductor; B is greater than 0. 05mm thickness of the conductor, the conductor thickness continues to increase, the resistance decreases obvious; C conductor width greater than 2mm. when the coil resistance is approximately inversely proportional to the width.

[0061] 因此,导体尺寸选取原则:选择导体横截面厚度为0. Imm〜0. 2mm的铜带;导体横截面宽度大于2mm,并根据其他需要选择合适的值。 [0061] Accordingly, conductor size selection principle: selecting a conductor cross-sectional thickness of the copper strip 0. Imm~0 2mm; conductor cross-sectional width greater than 2mm, and the other to select the proper value based.

[0062] 实例二(有负载模型): [0062] Examples of the dicarboxylic (a load model):

[0063] 负载的形状是半径为150mm,高150mm的圆柱,负载的电导率恒定为0. 5S/m,负载的相对磁导率恒定为1。 [0063] The shape of the load that the radius of 150mm, 150mm high cylindrical, constant load conductivity was 0. 5S / m, relative magnetic permeability of a constant load. 关心的成像区域(ROI)是负载正中间的半径50mm,高50mm的圆柱域。 Imaging area (ROI) is concerned with the middle load radius 50mm, 50mm high cylinders domain. 线圈和实例一相同。 And examples of a same coil. 线圈中通入频率f= 14. 85MHz的电流。 Into coil current f = frequency of 14. 85MHz. 线圈边缘与负载边缘距离15mm。 Coil edge 15mm from the edge of the load. 求解线圈和负载上的电流密度分布、线圈的噪声电阻、电感、ROI内的磁场均勻度和ROI内信噪比;并考察线圈参数与线圈半径的关系。 Solving the current density on the coil and load distribution, noise resistance of the coil, the inductance, the magnetic field uniformity within the ROI and ROI in the SNR; and examine the relationship between the parameters of the coil and the coil radius.

[0064] (1)根据实际线圈和负载建立仿真模型。 [0064] (1) The simulation model and the actual load coil. 如图4所示。 As shown in Figure 4.

[0065] 考虑问题的对称性,建立轴对称二维仿真模型。 [0065] consider the issue of symmetry, the establishment of a two-dimensional simulation model symmetry axis. 空气域是半径600mm的球体。 Air fields are 600mm radius sphere.

[0066] (2)计算导体趋肤深度,并剖分网格。 [0066] (2) the skin depth of the conductor is calculated, and the subdivision mesh.

[0067] 根据公式求得趋肤深度为17. 95 μ m。 [0067] The skin depth is obtained from the formula 17. 95 μ m. 导体中网格剖分要考虑趋肤效应的影响。 Meshing conductors to consider the impact of skin effect. 对于二维模型,通常设置趋肤深度内的导体区域的网格尺寸是趋肤深度的1/3到1/5。 For two-dimensional model, the grid size is typically provided to the skin depth of the conductor area within the skin depth is 1/3 to 1/5.

[0068] 本例中,将导体中距离边缘小于20um的区域单独划分出来,设置该区域的网格尺寸为5um。 In [0068] this embodiment, the distance from the edge region of the conductor is less than 20um carved out separately, disposed in the region of mesh size 5um. 趋肤深度外导体区域的网格尺寸为50um,内层空气域网格尺寸为5mm,外层空气域网格尺寸为50mm。 An outer conductor region of the skin depth mesh size of 50um, inner domain air mesh size of 5mm, an outer layer of an air field mesh size 50mm.

[0069] (3)仿真条件设置与求解。 [0069] (3) Set simulation conditions and solution.

[0070] 设置线圈轴线以及空气域外边界为平行边界条件。 [0070] a coil axis parallel to the boundary and the air outside the boundary condition. 设置导体横截面等电位并加载射频电流。 Set a cross-sectional side conductor and load the like RF current.

[0071] (4)根据仿真结果求解线圈性能参数。 [0071] (4) solving the coil performance parameter based on the simulation results.

[0072] 按下式计算磁场的均勻度HD : [0072] The uniformity of the magnetic field is calculated as HD:

Figure CN101615214BD00071

[0074] 其中:Bmax、Bmin分别是通入单位有效值射频电流时,线圈在所关心区域内产生的磁感应强度的最大值和最小值。 [0074] wherein: when Bmax, Bmin units are fed RMS RF current, the coil area of ​​interest within the maximum and minimum magnetic induction.

[0075] 根据下式计算所关心区域内的区域平均信噪比: [0075] Calculate the average SNR based on the region of interest within the region:

7[0076] 7 [0076]

Figure CN101615214BD00081

[0077] 求解结果如表2 : [0077] The results are shown in Table 2 Solution:

[0078] 表2有负载时圆形线圈性能参数计算结果 [0078] The results circular coil performance parameters Table 2 a load

[0079] [0079]

Figure CN101615214BD00082

[0080] (5)根据计算结果选择合适的线圈尺寸 [0080] (5) to select the appropriate stitch size according to the results

[0081] 采用有负载的仿真模型,考察线圈参数与线圈半径的关系,以使信噪比高为目标来选择线圈的尺寸。 [0081] The simulation model with a load, the coil parameters investigated the relationship between the radius of the coil, so that a high signal to noise ratio of the size of the coil is selected as a target.

[0082] 表3圆形线圈各项性能参数和半径的关系 [0082] Table 3 Relationship between the circular coil and the radius of the various performance parameters

[0083] [0083]

Figure CN101615214BD00083

[0084] 图5是线圈自身电阻以及负载中涡流损耗折合到线圈上的等效电阻随圆环线圈半径的变化情况。 [0084] FIG. 5 is the resistance of the coil itself and the load equivalent to the eddy current losses in the ring with the radius of the coil changes in the equivalent resistance of the coil.

[0085] 从计算结果,可以看出:当线圈半径大于40mm时,负载电阻大于线圈自身电阻;线圈半径小于40mm时,负载电阻小于线圈自身电阻;随着线圈半径的增大,ROI内磁场均勻度HD减小,即ROI内磁场的更加均勻;ROI内的信噪比在线圈半径为50mm左右达到最大值。 [0085] From the calculation results, it can be seen: when the coil radius greater than 40mm, the load resistance is greater than the resistance of the coil itself; the coil radius is less than 40mm, the load resistance is less than the resistance of the coil itself; increases as the radius of the coil, a uniform magnetic field within the ROI HD reduced degree, i.e. more uniform magnetic field within the ROI; signal to noise ratio within the ROI about 50mm maximum radius of the coil.

[0086] 假设磁场均勻度都符合要求,仅考虑使信噪比高时,本例中就应该选择半径50mm 的线圈。 [0086] Suppose the magnetic field uniformity are satisfactory, considering only the high SNR, the present embodiment should be selected radius of the coil of 50mm. 实际选择线圈时需要综合考虑各方面的需要(主要是磁场均勻度和信噪比的需求),选取合适的尺寸。 The actual choice needs to consider the various needs (mainly of the magnetic field homogeneity and signal to noise ratio requirements) of the coil, select the appropriate size.

Claims (2)

  1. 1. 一种对磁共振成像RF线圈进行性能分析的方法,其特征在于所述方法是在计算机中使用电磁场有限元数值计算软件,依次按以下步骤实现的: 步骤(1),把如下设定参数输入计算机:RF线圈的几何尺寸,线圈导体的横截面的几何尺寸,导体材料的电导率、磁导率,通入线圈中的射频电流的幅值和频率,对于有负载的情况,还需要输入负载的空间尺寸; 步骤O),根据实际RF线圈和负载,建立空间仿真模型:按照步骤(1)所述RF线圈的几何尺寸,线圈导体的横截面的几何尺寸,负载的空间尺寸,建立空间仿真模型,其中:空气域半径为导体和负载所在区域半径的3至5倍,从而得到一个所述的球形或圆柱形仿真模型;步骤(3),根据步骤(1)所述射频电流的频率计算导体的趋肤深度,并据此对所述空间仿真模型进行网格剖分:步骤(3. 1),按如下公式计算所 1. A method for magnetic resonance imaging RF coil performance analysis, wherein said method is a finite element numerical calculation using an electromagnetic field in the computer software, implemented in the following steps successively: Step (1), the following settings computer input parameters: RF coil geometry, the geometry of the cross section of the coil conductors, the conductivity of the conductor material, permeability, RF current in coil into amplitude and frequency, for a load, required load size input space; step O), the RF coil and the actual load, establishing the spatial model simulation: according to step (1) of the RF coil geometry, the geometry of the cross section of the coil conductor, the size of the load space, the establishment of space simulation model, wherein: a radius of field of air 3 to 5 times the radius of the conductor and the region where the load, to thereby obtain a spherical or cylindrical simulation model according; step (3), according to step (1) of the RF current skin depth frequency calculation conductors, and accordingly the simulation model space meshes are: step (3.1), is calculated according to the following formulas 导体的趋肤深度ds : Conductor skin depth ds:
    Figure CN101615214BC00021
    其中,f是所述射频电流的频率,μ是所述导体材料的磁导率,P是所述导体材料的电阻率;步骤(3. 2),在二维模型中,用尺寸为1/2到1/5趋肤深度的三角形网格单元剖分趋肤深度内的导体区域;步骤G),设置以下仿真条件: A :把空气域的外边界设置为平行边界;B :将导体横截面设置为等电位面,并加载所述射频电流,射频电流有效值记为I ; 步骤(¾,使用电磁场有限元数值计算软件计算出磁感应强度,电场强度,电流密度,功率损耗和磁场储能;步骤(6),根据步骤(5)得到的仿真结果计算射频线圈的性能参数,包括:所述线圈的电感L,所述线圈的自身电阻Rrail以及负载中涡流损耗折合到所述线圈上的等效电阻Rsample,以及所述线圈的噪声电阻Reff, ρ Wherein, f is the frequency of the RF current, [mu] is the permeability of the conductor material, P is the resistivity of the conductor material; step (3.2), in a two-dimensional model, with a size of 1 / 2 1/5 skin depth trend decomposing triangular meshes within the skin depth of the conductor region; step G), setting the following simulation conditions: a: the outer boundary of an air field is parallel to the boundary; B: the cross-conductor cross section is set to an equipotential surface, the RF current and load, referred to as a radio frequency current effective value I; step (¾, using finite element numerical field calculation software calculates the magnetic flux density, electric field strength, current density, power loss and magnetic storage ; step (6), the RF coil is calculated according to the simulation results obtained in step (5) performance parameters, comprising: inductance of the coil L, the coil's own resistance and Rrail load equivalent to the coil eddy current losses in the noise resistance equivalent resistance Reff Rsample, and the coil, ρ
    Figure CN101615214BC00022
    其中I是线圈中射频电流有效值,Pcoil是导体中功率损耗有效值,Psample是负载中功率损耗有效值,Wm是磁场储能有效值;其中,无负载的情况下,Rsample = 0 ;再按下式计算所关心区域ROI (region of interest)内磁场的均勻度HD : Where I is the current RMS RF coil, Pcoil conductor RMS power loss, the power loss in the load Psample rms, rms stored energy Wm of the magnetic field; wherein, under no load, Rsample = 0; then calculated uniformity within the region of interest ROI (region of interest) of the magnetic field HD:
    Figure CN101615214BC00023
    其中:Bmax、Bmin分别是通入单位有效值射频电流时,线圈在所关心区域内产生的磁感应强度的最大值和最小值;根据下式计算所关心区域内设定点的信噪比: Wherein: Bmax, Bmin each unit is fed RMS RF current, maximum and minimum values ​​of the magnetic induction coil in the area of ​​interest; the region of the point of interest is calculated according to the formula SNR:
    Figure CN101615214BC00031
    其中,B是射频线圈通入单位有效值射频电流时在该设定点产生的磁感应强度的有效值;根据下式计算所关心区域内的区域平均信噪比: Wherein, B is the effective value of the magnetic induction coil RF unit into a radio frequency current generated when the effective value of the set point; average SNR region within the region of interest is calculated according to the following formula:
    Figure CN101615214BC00032
  2. 2.根据权利要求1所述的一种对磁共振成像RF线圈进行性能分析的方法,其特征在于,对于步骤(3.2)中,若为三维模型,在趋肤深度内的导体区域被分为了平行于导体边界的3〜10层。 2. A method for magnetic resonance imaging RF coil performance analysis according to one of the preceding claims, wherein, for step (3.2), when the three-dimensional model, in the conductor area within the skin depth is divided into 3~10 boundary parallel to the conductor layer.
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