【作者】 董薛；

【导师】 刘延申；

【作者基本信息】 华中师范大学 ， 通信与信息系统， 2011， 硕士

【摘要】 在我国,因造价低廉,维护方便,目前应用最为广泛的是永磁型磁共振成像系统,其中磁场均匀性是决定设备好坏的极为关键的技术参数,但是,由于受采用的铁磁质原料和加工工艺的影响,永磁型核磁共振成像系统常常会存在磁场不均匀性等设备缺陷,这会极大地降低成像质量,最终妨碍了病情的诊断。为了解决这一问题,研究人员做了大量的研究,其中,利用外部的设备对主磁场进行校正,即均匀主磁场被认为是最为简单有效的方式。本文主要针对磁共振成像系统中直径为20cm的球域设计匀场线圈,通过在磁场上另外使用一套辅助设备,在磁极中间设计一定形状的匀场线圈,并调整线圈中的通电电流,通过控制线圈中的电流产生不同方向的磁场分量叠加到主磁场上,针对磁体磁场变化进行实时再校正,从而使成像区域内的主磁场变得更加均匀。本文首先介绍了核磁共振成像理论,了解了磁共振成像的三个必要条件,简要介绍了磁共振成像设备的一般结构组成。然后根据电磁场理论得出Z轴上磁场强度的级数表达式,通过分析通电载流圆弧产生的磁场强度泰勒级数展开式的分布规律,系统阐述了径向和轴向匀场线圈设计的思路和方法,通过设计通电圆弧的不同半径、对称方式、通电方向等达到设计不同阶线圈的目的。考虑到分布匀场线圈的设计不仅需要分析永磁体产生的不均匀磁场的特点,而且还需要结合匀场线圈的工程实践应用。本文运用Matlab仿真软件,通过设计具体的参数,对比分析了设计匀场线圈的半径和极板间隔、线性度之间的关系,进而优化匀场线圈设计。最后在低阶线圈的基础上分析了高阶线圈的设计方向。更多还原

【Abstract】 In our country, due to low cost and convenient maintenance, the magnetic resonance imaging system of permanent magnet type have been most widely used. Magnetic field uniformity is the crucial technical parameters that affect the equipment’s quality.However, with the influence of raw ferromagnetic material and processing technology, magnetic fields is often inhomogeneous.The equipment defects greatly reduce image quality and finally hinder illness diagnoses. In order to solve this problem, the researchers have done lots of research. Among of all works, using external equipment to correct the main field is considered the most simple and effective way.In this paper, we will pay attention to designing shim coils in the 20cm diameter spherical volume field for magnetic resonance imaging system.We can use a set of auxiliary equipment and design a certain shape shimming coils in the magnetic field.Then adjust the current of the coil to generate the magnetic field components in different directions. Finally the main magnetic field in the region becomes more uniform. This paper introduces the theory about magnetic resonance imaging.Three conditions must be needed for magnetic resonance imaging.Then the paper gives a brief introduction to the general structure of magnetic resonance imaging system.Learning from the electromagnetic theory, we can get the series expression of magnetic field intensity of Z axis.With discussing Taylor series expansion of magnetic field generated through the arc, the methods of the design of radial and axial shimming coils can be found. Designing shimming coils not only need pay attention to analyzing the characteristics of the non-uniform magnetic field produced by permanent magnet, but also require a combination of shim coils for engineering application. In order to optimize the design, we use the Matlab simulation software, through the design of specific parameters, find the relationship among the radius of shim coils,the plate spacing and the magnet field linear. Finally, on the basis of the coils in the low-level,the paper analyzes the design direction of the high-level coils.更多还原