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首页> 外文学位 >Compensation of static and dynamic magnetic field perturbations in functional magnetic resonance imaging.
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Compensation of static and dynamic magnetic field perturbations in functional magnetic resonance imaging.

机译：功能磁共振成像中静态和动态磁场扰动的补偿。

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摘要

The recent trend in magnetic resonance (MR) imaging has been to deploy higher field systems to exploit the larger magnetic resonance signal and signal-to-noise ratio (SNR) predicted by the underlying physics. Three Tesla systems have been approved for clinical use by the United States Food and Drug Administration, and fields above 7 T are now routinely used for animal imaging. With stronger magnetic fields also come new technical challenges. The shorter T*2 and the accompanying signal dropout, as well as increased geometric distortions, are the primary obstacles that must be overcome when dealing with magnetic field perturbations at high main field strengths.;One solution to this problem is to acquire the MR signal at a higher bandwidth, which requires stronger and faster magnetic field gradients and higher bandwidth receivers for acquisition. These improvements entail upgrading gradient coils, gradient amplifiers, and analog to digital (A/D) hardware, which generally require extensive hardware modifications to current MR systems.;Another method is to reduce susceptibility effects by improving magnetic field uniformity. Achieving magnetic field uniformities better than one part per million is possible using a variety of active and passive shimming techniques already published in the literature. There are also several pulse sequences and protocols that can be used to compensate for through-slice susceptibility effects. This work focuses on relatively minor hardware enhancements that can be easily implemented on almost any MR system, and the accompanying pulse sequences and processing software that can help compensate for magnetic field inhomogeneities.;The initial chapters of this thesis detail enhancements to a technique developed by Jesmanowicz to compensate for high order magnetic field perturbations in the human brain. First, the limits of the technique are explored via simulations. From these simulations, parameters for mapping the magnetic field perturbations in a human brain are determined. The simulations also define the optimal distribution of magnetic material on the surface of a cylinder surrounding the head that is needed to correct the measured perturbations. The magnetic dipole model will be used to approximate the effect of the material on the main magnetic field.;Several dipole distributions have been created and used to correct the magnetic field perturbations within the brain of a subject.;Later chapters in this work describe a new echo-planar type of pulse sequence in which magnetic field maps can be collected and computed in real time. (Abstract shortened by UMI.).
机译：磁共振（MR）成像的最新趋势是部署更高的磁场系统，以利用基础物理学预测的更大的磁共振信号和信噪比（SNR）。美国食品药品监督管理局已批准将三种特斯拉系统用于临床，目前常规将7 T以上的磁场用于动物成像。随着更强的磁场也带来了新的技术挑战。较短的T * 2和随之而来的信号丢失以及增大的几何失真是在高主场强下处理磁场扰动时必须克服的主要障碍。;解决此问题的一种方法是获取MR信号在更高的带宽下，需要更强，更快的磁场梯度和更高带宽的接收器来进行采集。这些改进需要升级梯度线圈，梯度放大器和模数（A / D）硬件，这些硬件通常需要对当前MR系统进行大量的硬件修改。另一种方法是通过改善磁场均匀性来降低磁化率效应。使用文献中已经公开的各种有源和无源匀场技术，可以使磁场均匀性好于百万分之一。还有一些脉冲序列和协议可用于补偿贯穿切片的磁敏效应。这项工作的重点是可以在几乎所有MR系统上轻松实现的相对较小的硬件增强功能，以及可以帮助补偿磁场不均匀性的随附脉冲序列和处理软件。本论文的初始章节详细介绍了对由MR技术开发的技术的增强功能。 Jesmanowicz可以补偿人脑中的高阶磁场扰动。首先，通过模拟探索了该技术的局限性。从这些模拟中，确定用于映射人脑中的磁场扰动的参数。模拟还定义了磁材料在磁头周围圆柱体表面上的最佳分布，这是校正测得的扰动所必需的。磁偶极子模型将用于近似估算材料对主磁场的影响。;已经创建了多个偶极子分布，并用于校正对象大脑内的磁场扰动。本工作的后续章节将描述一种新型的回波平面型脉冲序列，其中可以实时收集和计算磁场图。 （摘要由UMI缩短。）。

著录项

  • 作者

    Roopchansingh, Vinai.;

  • 作者单位

    The Medical College of Wisconsin.;

  • 授予单位 The Medical College of Wisconsin.;
  • 学科 Biophysics.;Biophysics.;Biomedical engineering.;Medical imaging.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 83 p.
  • 总页数 83
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 高分子化学（高聚物）;
  • 关键词

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