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Safety and performance considerations for interactions between electromagnetic fields and biological tissue: Applications to high field human magnetic resonance imaging and tissue-implanted devices.

机译：电磁场与生物组织之间相互作用的安全性和性能考虑：在高场人体磁共振成像和组织植入设备中的应用。

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摘要

The principal advantage of magnetic resonance imaging (MRI) at high field is the increase in signal to noise ratio (SNR), however, high field imaging also leads to an increased Larmor (operating) frequency, thus the wavelength in tissue can become comparable to the size of the load and/or the coil. The performance of the radiofrequency (RF) coil, as a result, becomes increasingly dependent on its electromagnetic interactions with the load, human body or head.;Invasive brain machine interface (BMI) technology uses implanted microelectrodes to capture the action potentials of many individual neurons, especially those that code for movement or its intent. Traditionally, stimulating nerves or brain tissue involves cumbersome wiring to power/communicate with the chip. To avoid the limit of the BMI's mobility and freedom, RF powered wireless implementation of a BMI chip has been proposed to widely extend BMI applications. It is essential to perform an analysis of electromagnetic power deposition throughout the human head to determine the amount of power available to BMI devices.;In this dissertation, a complete electromagnetic computational (full wave) analysis, the finite difference time domain (FDTD) method, is applied to calculate the interaction between the radio frequency (RF) magnetic field and the subjects during ultra high field MRI exams and wireless BMI operations. The interactions between the high frequency RF fields with the human head and the body models severely affect the performances of MRI and BMI operations, and they also cause heating safety concerns to the tissues exposed to the RF radiation. Through precisely numerical calculations, we accomplished in this dissertation (1) an improved optimization scheme using variable phase and variable amplitude excitation to improve the performance of RF transverse electromagnetic (TEM) coils in MRI with safety concerns; and (2) evaluations of the performance and safety for a prototype of the wireless invasive BMI. Temperature changes caused by RF power deposition are calculated in both MRI and BMI applications.
机译：高场磁共振成像（MRI）的主要优点是信噪比（SNR）的增加，但是，高场成像也会导致拉莫尔（手术）频率增加，因此组织中的波长可以与负载和/或线圈的大小。结果，射频（RF）线圈的性能变得越来越依赖于其与负载，人体或头部的电磁相互作用。;侵入式脑机接口（BMI）技术使用植入的微电极来捕获许多个体的动作电位神经元，尤其是那些编码运动或其意图的神经元。传统上，刺激神经或脑组织需要繁琐的接线来为芯片供电/通信。为了避免BMI的移动性和自由度的限制，已经提出了BMI芯片的RF供电无线实现，以广泛扩展BMI应用。必须对整个人的头部的电磁功率沉积进行分析，以确定BMI设备可用的功率量。;本文是一种完整的电磁计算（全波）分析，时差有限时域（FDTD）方法，用于计算超高场MRI检查和无线BMI操作期间射频（RF）磁场与受试者之间的相互作用。高频RF场与人体头部和人体模型之间的相互作用会严重影响MRI和BMI操作的性能，并且还会对暴露于RF辐射的组织造成加热安全隐患。通过精确的数值计算，我们在本文中完成了以下工作：（1）一种改进的优化方案，该方案使用可变相位​​和可变幅度激励来提高具有射频安全性的MRI中的射频横向电磁线圈的性能； （2）对无线侵入式BMI原型的性能和安全性进行评估。在MRI和BMI应用中都计算了由RF功率沉积引起的温度变化。

著录项

  • 作者

    Tang, Lin.;

  • 作者单位

    The University of Oklahoma.;

  • 授予单位 The University of Oklahoma.;
  • 学科 Engineering Electronics and Electrical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 239 p.
  • 总页数 239
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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