A METHOD FOR CORRECTLY SETTING THE RF FLIP ANGLE
A METHOD FOR CORRECTLY SETTING THE RF FLIP ANGLE
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DOI：
10.1002/mrm.1910090104
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发表时间：
1989-01-01
影响因子：
3.3
通讯作者：
SANDSTROM, JC
中科院分区：
文献类型：
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作者：
PERMAN, WH;BERNSTEIN, MA;SANDSTROM, JC
目前公认的将正确的射频功率电平设置为90度的方法。180度。用于磁共振成像的RF脉冲是使RF自旋回波序列的回波幅度达到峰值。这个α-2α的回波幅度。脉冲序列与SIN3(α)成正比。并且有一个相对较宽的最大值。最近，另一种通过最大化受激回波与主回波幅度之比来设置RF翻转角度的方法(在3.a。序列)使用更短的重复时间证明了与自旋回波法类似的准确性。我们提出了一种新的、更灵敏、更准确的方法来设置90度的正确射频功率电平。180度。射频脉冲。在这种方法中，基于受激回波脉冲序列，我们能够准确地将射频功率设置在.+-以内。通过最小化第三自旋回波的信号幅度来降低0.1分贝。这种归零方法适用于翻转角为90度的选择性和非选择性射频脉冲。或180度，允许用户在单个脉冲序列内精确地调整四种RF脉冲类型的相对幅度。
Currently the accepted method for setting the correct rf power levels to achieve 90.degree. and 180.degree. rf pulses for MR imaging is to peak the echo amplitude of a rf spin-echo sequence. The echo amplitude of this .alpha.-2.alpha. pulse sequence is proportional to sin3(.alpha.) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3.alpha. sequence) demonstrated accuracy similar to that of the spin-echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90.degree. and 180.degree. rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within .+-. 0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90.degree. or 180.degree., allowing the user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence.