CN101548193A - Mri用鸟笼式发射天线 - Google Patents

Mri用鸟笼式发射天线 Download PDF

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CN101548193A
CN101548193A CNA2008800010129A CN200880001012A CN101548193A CN 101548193 A CN101548193 A CN 101548193A CN A2008800010129 A CNA2008800010129 A CN A2008800010129A CN 200880001012 A CN200880001012 A CN 200880001012A CN 101548193 A CN101548193 A CN 101548193A
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CN101548193B (zh
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勒兹万·拉泽尔
沃尔夫冈·伦茨
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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
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
    • 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
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
    • G01R33/34046—Volume type coils, e.g. bird-cage coils; Quadrature bird-cage coils; Circularly polarised coils
    • G01R33/34076—Birdcage coils
    • 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
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification
    • G01R33/3657—Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil
    • 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
    • G01R33/42—Screening
    • G01R33/422—Screening of the radio frequency field
    • 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
    • G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
    • G01R33/36—Electrical details, e.g. matching or coupling of the coil to the receiver
    • G01R33/3642—Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification

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Abstract

一种磁共振用发射天线，其具有复数个自第一末端(1′)延伸至第二末端(1″)的天线杆(1)。所述天线杆(1)围绕一中心轴分布。所述天线杆在第一末端(1′)由第一端接元件(3)端接，所述第二末端(1″)由第二端接元件(6)端接。所述第一端接元件(3)设计为具有复数个端环段(4)的端环，所述端环段通过端环电容(5)彼此耦合。所述第二端接元件(6)采取不同于所述第一端接元件(3)的设计。所述发射天线具有可使所述发射天线失谐的失谐电路(7)。所述失谐电路(7)布置在所述第二端接元件(6)一侧。

Description

MRI用鸟笼式发射天线
技术领域
本发明涉及一种根据权利要求1前序部分所述的磁共振用发射天线。
背景技术
磁共振成像(尤其是头部的磁共振成像)越来越多地采用分离式的发射天线和接收天线。这类天线通常又称为线圈。在使用分离式的发射天线和接收天线的情况下，要求发射天线采用可失谐设计。
在现有技术中，发射天线通常设计为鸟笼式谐振器。在此情况下，发射天线通常具有两个用作端接元件的端环，其中，这两个端环采取相同设计。端环特定而言由复数个端环段构成，这些端环段通过端环电容器彼此耦合。个别情况下也用所谓的TEM谐振器来代替鸟笼式谐振器。
现有技术中的已知发射天线在待检对象对称以及静态磁场相对较弱(约1.5特斯拉以下)的情况下工作良好。但是当待检对象不对称，静态磁场较强(例如3特斯拉及以上)时，射频发射场的质量会有所下降。
发明内容
本发明的目的是提供一种磁共振用发射天线，这种发射天线即使在待检对象不对称、静态磁场较强的情况下也能提供高质量的射频发射场。
这个目的通过一种具有权利要求1的特征的磁共振用发射天线而达成。有利改进方案由各从属权利要求给出。
本发明涉及一种磁共振用发射天线，其中，
—所述发射天线具有复数个自第一末端延伸至第二末端的天线杆，
—所述天线杆围绕一中心轴分布，
—所述天线杆在第一末端由第一端接元件(terminating element)端接(terminate)，在第二末端由第二端接元件端接，
一所述第一端接元件设计为具有复数个端环段的端环，所述端环段通过端环电容彼此耦合，
—所述发射天线具有一个能使所述发射天线失谐的失谐电路，
其中，所述第二端接元件(6)采取不同于所述第一端接元件(3)的设计，所述失谐电路(7)布置在所述第二端接元件(6)一侧。
根据一种优选设计方案，天线杆至少基本平行于中心轴延伸。
根据本发明，第一端接元件——也像现有技术那样——设计为具有复数个端环段的端环，这些端环段通过端环电容彼此耦合。第二端接元件则采取不同于第一端接元件的设计。失谐电路布置在第二端接元件一侧。
所述发射天线通常具有一个在径向外侧包围天线杆的射频屏蔽件。
为能优化射频发射场的质量，从径向看，天线杆与射频屏蔽件之间可以存在一个天线杆间距，这个天线杆间距在第一端接元件到第二端接元件之间可以发生变化。这种变化特定而言可以是线性变化。
作为替代或补充方案，从径向看，第一端接元件与射频屏蔽件之间可以存在一个第一端接元件间距，第二端接元件与射频屏蔽件之间可以存在一个第二端接元件间距，这两个端接元件间距可以彼此不等。
第二端接元件和射频屏蔽件可为同一元件。
作为替代方案，第二端接元件可设计为另一端环。在此情况下，第二端接元件的电感优选应小于第一端接元件的电感。实现较小电感的方法例如是，第二端接元件的截面大于第一端接元件的截面(特定而言是在径向厚度相同的情况下具有较大的轴向宽度)。作为替代或补充方案，第二端接元件可设计为连续式短路环。
所述发射天线原则上可设计为全身天线。其优选设计为头部线圈。
所述发射天线原则上可调整为任意大小的谐振频率。所述发射天线优选调整为至少与3特斯拉静态磁场中的氢的拉莫尔频率一样大的谐振频率。
失谐电路可布置在天线杆与第二端接元件之间。作为替代方案，失谐电路可布置在第二端接元件中。
失谐电路优选具有复数个PIN二极管，其中，这些PIN二极管在调谐情况下处于接通状态。
所述发射天线通常具有复数个用于向发射天线输送信号和/或用于从发射天线输出信号的传输线。这些传输线优选布置在第二端接元件一侧。
附图说明
下面借助附图和实施例对其他优点和技术细节进行说明，其中：
图1为磁共振用发射天线的侧视图；
图2为图1所示的发射天线的截面图；
图3为图1所示的发射天线的第一方案的展开图；
图4为图1所示的发射天线的第二方案的展开图；
图5为另一发射天线的局部侧视图；以及
图6为图5所示的发射天线的局部展开图。
具体实施方式
如图1和图2所示，磁共振用发射天线具有复数个天线杆1。每个天线杆1均自相应天线杆1的第一末端1′延伸至第二末端1″。
根据一种优选设计方案，天线杆1(至少基本)平行于中心轴2延伸。天线杆1的数量最小为四。通常为十六或三十二。但也可以采用其他数量，例如六、八、十二、二十四或四十个天线杆1。
一般情况下，天线杆1都精确地平行于中心轴2延伸。但也可以采用替代性设计方案，即天线杆1所定义的方向只是基本平行于中心轴2。在第二种情况下，各天线杆1所呈现的方向具有第一子分量和第二子分量。这两个子分量互为补充，从而构成天线杆1的方向。
第一子分量(精确地)平行于中心轴2。第二子分量与中心轴2正交。只要第一子分量大于第二子分量，天线杆1的方向就基本平行于中心轴2。举例而言，通过下述方式可使天线杆1只是基本平行于中心轴2延伸，即：将发射天线设计为略呈锥形(参见图1和图2)，和/或天线杆1像枪管膛线那样略呈螺旋状地环绕中心轴2延伸。也可将这两种措施结合起来。
举例而言，发射天线可设计为全身天线。发射天线优选设计为如图1所示的头部线圈。
下文所使用的“轴向”、“径向”和“切向”等概念总是以某一轴线(例如中心轴2)为基准。“轴向”这一概念表示的是平行于相应轴线的方向。“径向”和“切向”这两个概念表示的是与相应轴线正交的一个平面内的方向。“径向”表示这个平面内朝向或背离相应轴线的方向。“切向”表示的是与轴线正交的平面内环绕轴线的方向。如果本说明书在未明确指出以哪一轴线为基准的情况下使用“轴向”、“径向”和“切向”等概念，作为基准的轴线的就是中心轴2。如果是以其他轴线为基准，本说明书就会补充说明具体涉及的是那条轴线。
天线杆1在第一末端1′由第一端接元件3端接。第一端接元件3设计为端环，具有复数个端环段4。这些端环段4通过端环电容器5彼此耦合。
天线杆1在第二末端1″由第二端接元件6端接。如图1和图2所示，第二端接元件6设计为另一端环。但这一点并非是必须的(参见下文对图5和图6的实施方式描述)。无论第二端接元件6是否设计为另一端环，第二端接元件6都采取不同于第一端接元件3的设计。下文将联系图1至图6对此进行详细说明。
如图1所示，发射天线调整为谐振频率fR。谐振频率fR原则上可以是任意大小的频率。举例而言，谐振频率fR至少可与3特斯拉静态磁场中氢的拉莫尔频率fL(H，3T)一样大。
发射天线还具有一个失谐电路7。当失谐电路7未启动时(失谐情况)，发射天线不调整为谐振频率fR。也就是说，发射天线在谐振频率fR下不发生谐振，而是处于失谐状态。而当失谐电路7启动时(调谐情况)，发射天线在谐振频率fR下发生谐振，也就是说，发射天线调整为谐振频率fR。
图1和图2未对失谐电路7进行图示。但图3、图4和图5对其进行了图示。如图3、图4和图5所示，失谐电路7布置在第二端接元件6一侧。
以上是对本发明的基本原理的说明。下面将联系图1至图6对本发明的可行设计方案进行说明。
如图1和图2所示，发射天线具有一个射频屏蔽件8。射频屏蔽件8在径向外侧包围天线杆1。从径向看，第一端接元件3与射频屏蔽件8之间存在一个间距a，下文称之为第一端接元件间距a。从径向看，天线杆1与射频屏蔽件8之间存在一个间距b，下文称之为天线杆间距b。
在图1和图2所示的设计方案(即第二端接元件6设计为另一端环，因而构成一个不同于射频屏蔽件8的元件6)中，从径向看，第二端接元件6与射频屏蔽件8之间存在一个间距c，下文称之为第二端接元件间距c。
天线杆间距b在第一端接元件3到第二端接元件6之间可以保持恒定不变。无论天线杆1是平行于中心轴2延伸，还是定义一个截锥体(如图1和图2所示)，都可实现这一设计方案。但如果天线杆间距b在第一端接元件3到第二端接元件6之间发生变化(同样如图1所示)，就可使发射天线的发射特性得到优化。其中，天线杆间距b可做线性变化。个别情况下也可采用其他变化方式。举例而言，射频屏蔽件8可以呈直线延伸，天线杆1可以呈抛物线延伸或以其他方式发生弯曲。
在图1和图2所示的设计方案(即第二端接元件6构成一个不同于射频屏蔽件8的元件6)中，第二端接元件间距c可以等于第一端接元件间距a。但第二端接元件间距c与第一端接元件间距a优选不相等。
如图5和图6所示，作为图1和图2(以及图3和图4)所示的设计方案的替代方案，第二端接元件6和射频屏蔽件8可为同一元件。在此情况下就无需再定义第二端接元件间距。但其余的实施方案(尤其是与天线杆间距b的特性有关的实施方案)仍然是可用的。
如上文所述以及如图1至图4所示，第二端接元件6可设计为另一端环。在此情况下，这个另一端环(＝第二端接元件6)必须采用不同于端环(＝第一端接元件3)的设计。举例而言，另一端环6的截面可以大于端环3的截面。其中，实现这一较大截面的方法是，在(从径向看)端环3、6的厚度d1、d2相等的情况下，另一端环6(从轴向看)的宽度b2大于端环3的宽度b1。
另一端环6的截面优选应明显大于端环3的截面。“明显”这一概念在此指的是，另一端环6的截面至少是端环3的截面的两倍。另一端环6的截面优选至少是端环3的截面的三倍，例如四倍至六倍。
鉴于这种设计方案(特别是截面相对较大的设计方案)，另一端环6(＝第二端接元件6)的电感通常小于端环3(＝第一端接元件3)的电感。但这一点并非是必须的。
作为截面采用不同尺寸这一方案的替代或补充方案，另一端环6可设计为如图3和图4所示的连续式短路环。“连续式短路环”这一概念在此指的是，另一端环6(参见图3)采取完全连续式设计，即其总是且一定处于短接状态。在此情况下，失谐电路7如图3所示布置在天线杆1与另一端环6(＝第二端接元件6)之间。作为替代方案，“连续式短路环”这一概念也可表示，另一端环6虽然(和端环3一样)具有复数个端环段9。但另一端环6的这些端环段9之间并未布置端环电容器。采用这种方案的第二端接元件6中布置有失谐电路7。图4对这种设计方案进行了图示。
失谐电路7通常具有复数个PIN二极管10，参见图3、图4和图5。当PIN二极管10未接通时，发射天线优选不调整为谐振频率fR。但当PIN二极管10接通时，发射天线优选调整为谐振频率fR。
当PIN二极管10接通时，这些PIN二极管处于导电状态。因此，当PIN二极管10处于接通状态时(即在调谐情况下)，如果失谐电路7布置在另一端环6中，另一端环6就同样起到连续式短路环的作用。
需要向发射天线输送信号。这些信号可以是低频信号。这种低频信号的一个例子就是用来控制失谐电路7的失谐电压。输送给发射天线的信号也可以是射频信号。这种信号的一个例子就是输入发射天线的发射电流。此外，发射天线还可输出信号(特别是射频信号)。在发射天线也可用作接收天线的情况下，这种信号的一个例子就是发射天线所接收到的信号。可以输出的射频信号的另一例子就是由微波接收器接收的微波信号，这些微波接收器整合在天线杆1中。附图并未对这些微波接收器进行图示。
上述信号的输送和输出通过传输线11而实现。如图1至图6所示，传输线11优选布置在第二端接元件6一侧。但这一点并非是必须的。
本发明的发射天线优点众多。其设计简单，效率高，可灵活确定尺寸、加以使用。
以上只是本发明的说明。本发明的保护范围仅由所附的权利要求确定。
附图标记表
1          天线杆
1′、1″   末端
2          中心轴
3、6       端接元件
4、9       端环段
5          端环电容器
7          失谐电路
8          射频屏蔽件
10         PIN二极管
11         传输线
a、b、c    间距
b1、b2     宽度
d1、d2     厚度
fL、fR     频率

Claims (16)

1.一种磁共振用发射天线，其中，
所述发射天线具有复数个自第一末端(1′)延伸至第二末端(1″)的天线杆(1)，
所述天线杆(1)围绕一中心轴(2)分布，
所述天线杆(1)在所述第一末端(1′)由第一端接元件(3)端接，在所述第二末端(1″)由第二端接元件(6)端接，
所述第一端接元件(3)设计为具有复数个端环段(4)的端环，所述端环段通过端环电容(5)彼此耦合，
所述发射天线具有一个能使所述发射天线失谐的失谐电路(7)，
其特征在于，
所述第二端接元件(6)采取不同于所述第一端接元件(3)的设计，所述失谐电路(7)布置在所述第二端接元件(6)一侧。
2.根据权利要求1所述的发射天线，其特征在于，
所述发射天线具有一个在径向外侧包围所述天线杆(1)的射频屏蔽件(8)。
3.根据权利要求2所述的发射天线，其特征在于，
从径向看，所述天线杆(1)与所述射频屏蔽件(8)之间存在一个天线杆间距(b)，所述天线杆间距(b)在所述第一端接元件(3)到所述第二端接元件(6)之间发生变化，特定而言是线性变化。
4.根据权利要求2或3所述的发射天线，其特征在于，
从径向看，所述第一端接元件(3)与所述射频屏蔽件(8)之间存在一个第一端接元件间距(a)，所述第二端接元件(6)与所述射频屏蔽件(8)之间存在一个第二端接元件间距(c)，所述端接元件间距(a，c)彼此不等。
5.根据权利要求2或3所述的发射天线，其特征在于，
所述第二端接元件(6)和所述射频屏蔽件(8)为同一元件。
6.根据权利要求1至4中任一项所述的发射天线，其特征在于，
所述第二端接元件(6)设计为另一端环。
7.根据权利要求6所述的发射天线，其特征在于，
所述第二端接元件(6)的电感小于所述第一端接元件(3)的电感。
8.根据权利要求6或7所述的发射天线，其特征在于，
所述第二端接元件(6)的截面大于所述第一端接元件(3)的截面，特定而言在径向厚度(d2)相同的情况下具有大于所述第一端接元件(3)的轴向宽度(b2)。
9.根据权利要求6、7或8所述的发射天线，其特征在于，
所述第二端接元件(6)设计为连续式短路环。
10.根据上述权利要求中任一项所述的发射天线，其特征在于，
所述发射天线设计为头部线圈。
11.根据上述权利要求中任一项所述的发射天线，其特征在于，
所述发射天线调整为至少与3特斯拉静态磁场中氢的拉莫尔频率(fL)一样大的谐振频率(fR)。
12.根据权利要求1至11中任一项所述的发射天线，其特征在于，
所述失谐电路(7)布置在所述天线杆(1)与所述第二端接元件(6)之间。
13.根据权利要求1至11中任一项所述的发射天线，其特征在于，
所述失谐电路(7)布置在所述第二端接元件(6)中。
14.根据上述权利要求中任一项所述的发射天线，其特征在于，
所述失谐电路(7)包括复数个PIN二极管(10)，其中，所述PIN二极管(10)在调谐情况下处于接通状态。
15.根据上述权利要求中任一项所述的发射天线，其特征在于，
所述第二端接元件(6)一侧布置有复数个用于向所述发射天线输送信号和/或用于从所述发射天线输出信号的传输线(11)。
16.根据上述权利要求中任一项所述的发射天线，其特征在于，所述天线杆(1)至少基本平行于所述中心轴(2)布置。
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US20090267606A1 (en) 2009-10-29
DE102007016312B4 (de) 2010-06-17
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WO2008122553A1 (de) 2008-10-16
DE102007016312A1 (de) 2008-10-09

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