• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Calculations of RF magnetic fields and SAR experienced by the human body during MRI.
【24h】

Calculations of RF magnetic fields and SAR experienced by the human body during MRI.

机译：MRI期间人体经历的RF磁场和SAR的计算。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The finite difference time domain (FDTD) method is used to evaluate the radiofrequency (RF) magnetic (B1) field in heterogeneous models of the human body as would be produced during MRI, and also to evaluate the energy absorbed by the body due to the generation of the B 1 field in human tissues. Evaluations of (1) model spatial resolution necessary to evaluate compliance with regulatory limits on Specific energy Absorption Rate (SAR) and (2) the agreement of the calculated B1 field distribution with experimentally measured fields for similar cases are performed. Methods for calculating experimentally valuable measures of B1 homogeneity, signal-to-noise ratio (SNR), and SAR are presented, and methods for determining what imaging parameters can be used without exceeding SAR level limits are demonstrated. Finally, calculations are performed at several frequencies as high as 345 MHz in both a surface coil over the chest and an idealized birdcage coil over the head. The method by which FDTD models of human anatomies were created using the Visual Human Project of the National Libraries of Medicine is also presented. Pertinent values from these calculations are presented so that in future experiments using such coils in these regions, estimates of expected image B 1 homogeneity, SNR, and SAR for specific imaging parameters can be derived. It is shown that B1 homogeneity and coil sensitivity decrease with increasing B1 frequency. Calculated SAR levels generally increase significantly with B1 frequency for a given set of imaging parameters. Most importantly, it is shown that trends in the B1 field pattern, SNR, and SAR for a specific human geometry and RF coil can be calculated with fairly good agreement with experiment using the methods presented here. While further experiments and calculations are suggested to better assess the accuracy of the calculations and to improve that accuracy, the methods presented here could potentially be very useful in designing coils for use in MRI at high B1 frequencies and in designing experiments at high B1 frequencies that will not exceed standard limits on SAR.
机译：时域有限差分（FDTD）方法用于评估MRI产生的人体异质模型中的射频（RF）磁场（B1），还用于评估人体因吸收能量而产生的能量。在人体组织中产生B 1场。对（1）模型空间分辨率进行评估，以评估对比能量吸收率（SAR）的监管限制的合规性；以及（2）对于类似情况，计算出的B1场分布与实验测量场的一致性。提出了计算B1同质性，信噪比（SNR）和SAR的实验上有价值的度量的方法，并展示了确定可以使用哪些成像参数而不会超出SAR水平限制的方法。最后，在胸部上方的表面线圈和头部上方的理想鸟笼线圈中，都以高达345 MHz的几个频率进行计算。还介绍了使用国家医学图书馆的Visual Human Project创建人体解剖结构FDTD模型的方法。提供了来自这些计算的相关值，以便在将来的实验中在这些区域中使用此类线圈，可以得出特定成像参数的预期图像B 1均匀性，SNR和SAR的估计值。结果表明，随着B1频率的增加，B1的均匀性和线圈灵敏度降低。对于给定的一组成像参数，计算得出的SAR值通常会随着B1频率而显着增加。最重要的是，它表明，对于特定人体几何形状和RF线圈，B1场模式，SNR和SAR的趋势可以使用此处介绍的方法与实验相当吻合地计算出来。虽然建议进行进一步的实验和计算以更好地评估计算的准确性并提高该准确性，但此处介绍的方法在设计用于高B1频率的MRI线圈以及在设计高B1频率的实验时可能非常有用。不会超过SAR的标准限制。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号