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Methods for the design, optimization, and image correction of local insert gradient sysem in magnetic resonance imaging.

机译：磁共振成像中局部插入梯度系统的设计，优化和图像校正方法。

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摘要

Developing faster Magnetic Resonance Imaging (MRI) gradient systems is desirable for fast imaging pulse sequences. Because of their large size, reduced efficiency, and higher inductance, system body gradient coils are limited in performance. This limitation can be reduced by designing proper local gradient coils. In this dissertation, various types of local insert gradient coil designs, as well as their optimization and image correction techniques are investigated.;Conventional method of designing planar gradient systems that uses two-dimensional stream functions can be more computationally intensive than optimizing the one dimensional stream functions required for cylindrical gradients. In this dissertation, a novel planar gradient design method, which simplifies the two-dimensional planar gradient coil design problem to a faster and easier one-dimensional problem by using a conformal mapping technique. The simulated gradient filed maps prove that the proposed gradient design technique creates same homogeneous gradient and works well throughout the imaging volume.;Many MRI applications such as DCE-MRI of the breast require high spatial and temporal resolution. The planar gradient systems as currently designed cannot create an imaging volume large enough to accommodate both breasts. A new concept for designing planar gradient systems, which has a superellipse shape and the addition of a field-modifying layer, has been presented. Homogeneous gradient volumes (HGVs) of the proposed superelliptical coil are increased as much as 182% (x-gradient) over those of the original planar system. In addition, adding an extra field-modifying layer allows the further enlargement of the HGVs by 214% (z-gradient).;Gradient homogeneity of the flat gradient systems is worse compared to cylindrical gradient systems, because the magnetic field and gradient strength drop nearly exponentially with distance from the coil surface. As a result, imaging with a planar insert gradient coil is challenging and prone to image distortions. A new concept of image de-warping has been demonstrated that calculates the nonlinear gradient field as an analytical function, and applies to de-warp collected image data. The simulated results indicate that the usable imaging region (in plane) has improved by 450% over the conventional linear gradient imaging.
机译：对于快速成像脉冲序列，需要开发更快的磁共振成像（MRI）梯度系统。由于它们的大尺寸，降低的效率和更高的电感，系统主体梯度线圈的性能受到限制。通过设计适当的局部梯度线圈可以减少这种限制。本文研究了各种类型的局部插入梯度线圈设计及其优化和图像校正技术。;使用二维流函数设计平面梯度系统的常规方法比优化一维方法更耗费计算资源圆柱渐变所需的流函数。本文采用共形映射技术，将二维平面梯度线圈设计问题简化为一个更快，更简单的一维问题。仿真的梯度场图证明，所提出的梯度设计技术可创建相同的均匀梯度，并且在整个成像体积中均能很好地工作。；许多MRI应用（如乳腺的DCE-MRI）需要较高的空间和时间分辨率。当前设计的平面梯度系统无法产生足够容纳两个乳房的成像体积。提出了一种设计平面梯度系统的新概念，该概念具有超椭圆形状并添加了场修改层。所提出的超椭圆线圈的均匀梯度体积（HGV）比原始平面系统的均匀梯度体积增加了182％（x梯度）。此外，增加一个额外的场修改层可使HGV进一步扩大214％（z梯度）。;与圆柱梯度系统相比，平面梯度系统的梯度均匀性更差，因为磁场和梯度强度下降与线圈表面的距离几乎成指数增长。结果，利用平面插入梯度线圈成像是具有挑战性的，并且易于产生图像失真。已经证明了图像变形的新概念，该概念将非线性梯度场计算为解析函数，并应用于变形的采集图像数据。仿真结果表明，可用的成像区域（平面内）比常规的线性梯度成像提高了450％。

著录项

  • 作者

    Moon, Sung Man.;

  • 作者单位

    The University of Utah.;

  • 授予单位 The University of Utah.;
  • 学科 Engineering Electronics and Electrical.;Health Sciences Radiology.;Physics Electricity and Magnetism.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 158 p.
  • 总页数 158
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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