Avdievich Nikolai I, Krymov Vladimir N, Hetherington Hoby P
Department of Radiology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Magn Reson Med. 2003 Jul;50(1):13-8. doi: 10.1002/mrm.10539.
A modified perturbation method for tuning and testing volume head coils was developed. The common perturbation method, utilizing the change in resonance frequency of a resonator in response to the presence of a small dielectric or magnetic probe, was modified to modulate the frequency shift due to rotation of a probe. This modification enabled the RF magnetic and electric fields as well as the angular distribution of current in the longitudinal elements of the coil to be mapped. The latter serves as a quick test of magnetic field homogeneity by comparing the measured distribution with the sinusoidal function required for the field to be homogenous. The method was experimentally applied to tune and test a transverse electromagnetic (TEM) head coil.
开发了一种用于调谐和测试体积头部线圈的改进型微扰方法。利用谐振器共振频率响应小介电或磁探针的存在而发生的变化的常见微扰方法，被改进为调制由于探针旋转引起的频移。这种改进使得能够绘制射频磁场和电场以及线圈纵向元件中电流的角分布。通过将测量分布与场均匀所需的正弦函数进行比较，后者可作为磁场均匀性的快速测试。该方法已通过实验应用于调谐和测试横向电磁（TEM）头部线圈。
