快速成像序列设计与伪影消除方法研究

发布时间：2018-06-23 07:25

  本文选题：磁共振成像 + EPI序列　； 参考：《电子科技大学》2014年硕士论文

【摘要】：核磁共振成像(Magnetic Resonance Imaging,MRI)技术是目前一种先进的医学成像方法,利用磁共振信号能够获得任何部位、任意方向的组织切片的医学图像。在核磁共振成像的过程中,需要成像序列控制谱仪产生相应的射频脉冲、选层梯度、相位编码梯度和频率编码梯度来产生图像。为了追求质量更高的图像,设计更好的成像序列是一个非常重要的条件,所以磁共振序列是磁共振成像技术最直接的载体。伴随着MRI在医学诊断领域的深入发展,序列从上世纪中期的自旋回波成像(spin echo,简写为SE)发展到20世纪80年代中期的梯度回波成像(gradient echo,简写为GRE),再发展到90年代的平面回波成像(echo planar imaging,简称EPI)。MRI序列为解剖结构的显示、组织的功能成像、分子成像等的最基本的支撑平台。所以,本文立足于现今MRI序列的需求状况,在EPI成像和真实稳态自由进动序列成像(true steady state free precession,True-SSFP)的基础上,设计出成像时间和成像质量相比于基础序列(EPI序列和True-SSFP序列)都有所改善的序列。本文主要研究内容如下:1、核磁共振成像的基本原理分析。本文分别从相位编码、频率编码、选层梯度和K空间等几个方面介绍了核磁共振序列的基本成像原理。2、EPI序列和True-SSFP序列分析。本文从序列成像原理、所用参数及其特点、临床适用范围等方面对EPI序列和True-SSFP序列分别进行分析。针对EPI,本文分别从单次激励的平面回波序列(single-shot EPI,SS-EPI)和多次激励的平面回波序列(multi-shot EPI,MS-EPI)两种情况进行详解。并且,本文在ODIN仿真软件上实现了EPI序列和True-SSFP序列的序列图仿真、K空间仿真以及图像仿真。3、single-shot EPI-SSFP序列的设计与实现。本文通过对EPI-SSFP序列的深入分析,针对multi-shot EPI-SSFP序列成像速度还不能满足心脏动态成像这一特点,设计了single-shot EPI-SSFP序列。本文解决了新序列中EPI序列的选择、射频脉冲激励方式的选择等问题,并运用梯度桥接技术解决了序列的重复时间太短无法实现双向补偿的问题,还解决了具体实现稳态过程这一技术难题。本文基于ODIN软件平台仿真出了single-shot EPI-SSFP序列的序列图、K空间数据填充过程及其成像效果图。4、快速成像序列的伪影消除方法研究与序列评估。本文对快速成像序列所产生伪影进行分析研究,结合EPI序列独有的消除Ghost伪影方法,对single-shot EPI-SSFP序列产生的伪影提出消除方法,并仿真实现所提出的伪影消除方法。最后,文章还就序列的成像时间和成像质量对所提出的伪影消除方法进行评估,结果显示所设计的新序列在成像时间和成像质量上与EPI序列、True-SSFP序列相比有较为明显的改善。
[Abstract]:Magnetic Resonance Imaging (MRI) is an advanced medical imaging method, which can obtain medical images of tissue sections in any position and any direction by using magnetic resonance signal. In the process of nuclear magnetic resonance imaging, it is necessary for the imaging sequence to produce the corresponding RF pulse, layer selection gradient, phase coding gradient and frequency coding gradient to generate the image. In order to achieve better image quality, it is very important to design better imaging sequence, so magnetic resonance sequence is the most direct carrier of magnetic resonance imaging technology. With the development of MRI in the field of medical diagnosis, The sequence developed from spin echo imaging (spin echo,) in the middle of the last century to gradient echo imaging (gradient echo,) in the mid-1980s, and then to planar echo imaging (echo planar imaging,) in the 1990s. Tissue functional imaging, molecular imaging and so on the most basic support platform. Therefore, this paper is based on the demand of (true steady state free sequence, based on EPI imaging and true steady-state free precession sequence imaging (true steady state free precession True-SSFP). The imaging time and quality are improved compared with the basic sequence (EPI sequence and True-SSFP sequence). The main contents of this paper are as follows: 1: 1, the basic principle of nuclear magnetic resonance imaging. In this paper, the basic imaging principles of nuclear magnetic resonance sequences, such as phase coding, frequency coding, layer selection gradient and K-space, are introduced, respectively. The analysis of EPI sequence and True-SSFP sequence of nuclear magnetic resonance sequences are presented. In this paper, EPI sequence and True-SSFP sequence are analyzed from the aspects of imaging principle, parameters and characteristics, clinical application range and so on. In this paper, the single excitation plane echo sequence (single-shot EPI SS-EPI) and the multiple excitation plane echo sequence (multi-shot EPI MS-EPI) are analyzed in detail. Furthermore, the design and implementation of EPI sequence and True-SSFP sequence are implemented in ODIN software. The design and implementation of EPI sequence and True-SSFP sequence are also presented in this paper, as well as the design and implementation of the image simulation of single-shot EPI-SSFP sequence. Based on the deep analysis of EPI-SSFP sequence, the single-shot EPI-SSFP sequence is designed in view of the fact that the imaging speed of EPI-SSFP sequence can not meet the requirement of dynamic cardiac imaging. In this paper, the selection of EPI sequence and the mode of RF pulse excitation in the new sequence are solved, and the gradient bridging technique is used to solve the problem that the repetition time of the sequence is too short to realize bidirectional compensation. The technical problem of realizing the steady-state process is also solved. Based on the ODIN software platform, this paper simulates the filling process of single-shot EPI-SSFP sequence map K spatial data and its imaging effect figure .4. the research on the method of fast imaging sequence artifact elimination and sequence evaluation is presented. In this paper, the artifact produced by fast imaging sequence is analyzed and studied. Combined with the unique method of eliminating ghost artifacts in single-shot EPI-SSFP sequence, the method of eliminating artifacts produced by EPI sequence is proposed, and the proposed method is realized by simulation. Finally, the image time and quality of the proposed method are evaluated. The results show that the new sequence has better imaging time and quality than the EPI sequence and True-SSFP sequence.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：R445.2
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本文编号：2056337