基于FPGA与DDS的磁共振成像射频脉冲发生器的研制

发布时间：2018-08-14 12:17

【摘要】：随着磁共振成像（Magnetic Resonance Imaging: MRI)技术的迅速发展，作为主流的临床医学成像技术之一，MRI得到了越来越广泛的应用。在NMR与MRI领域，整个系统的电子控制器称为谱仪(Spectrometer),谱仪是MRI系统的核心设备之一，，它的性能对于MRI系统有着重要意义。射频（Radio-Frequency: RF)脉冲发生是谱仪的一个重要的功能，在MRI中，射频脉冲激励磁场中的样本，产生核磁共振，通过接收载有空间编码信息的回波信号，得到样本的内部信息。随着MRI技术和数字技术的快速发展，特别是集成芯片FPGA与DDS器件的出现，为研制高集成、高性能射频脉冲发生器提供了良好的基础。为了适应谱仪的控制模式，实现灵活而精确地发生软、硬脉冲的功能，并且降低设备的成本，本课题研制基于FPGA与DDS的磁共振成像射频脉冲发生器，实现预定的功能指标。作为高性能的，具有自主知识产权谱仪的一部分。本文的主要内容如下： (1)介绍了核磁共振成像的基本原理以及谱仪的组成结构，包括序列控制器、射频发生模块、梯度发生模块、数据懫集模块以及网络通信单元。 (2)提出了一种基于FPGA与DDS的磁共振成像射频脉冲发生器的硬件设计方案。利用直接数字频率合成器(DDS)完成频率合成、数模转换等功能，使得输出波形具有精确的相位、频率分辨力。其快速的相位、频率、幅度切换速度等特性能够满足磁共振成像谱仪的性能需求。 (3)完成射频脉冲发生器的功能测试与试验，并对试验结果进行分析。实现射频发生模块产生硬脉冲以及软脉冲（Sine脉冲、高斯脉冲）；测试分析射频信号频谱纯度即相位噪声、杂散以及噪声基底。
[Abstract]:With the rapid development of (Magnetic Resonance imaging: MRI (Magnetic Resonance Imaging), one of the main clinical imaging techniques has been more and more widely used. In the field of NMR and MRI, the electronic controller of the whole system called spectrometer (Spectrometer), spectrometer is one of the core devices of MRI system, and its performance is of great significance to MRI system. Radio-frequency (RF) pulse generation is an important function of spectrometer. In MRI, RF pulse excites samples in magnetic field to generate nuclear magnetic resonance (NMR). The internal information of the sample is obtained by receiving echo signal with space-coded information. With the rapid development of MRI technology and digital technology, especially the appearance of integrated chip FPGA and DDS devices, it provides a good foundation for the development of high integrated and high performance RF pulse generator. In order to adapt to the control mode of spectrometer, realize the function of flexible and accurate soft and hard pulse generation, and reduce the cost of the equipment, a RF pulse generator for magnetic resonance imaging based on FPGA and DDS is developed in this paper. As a part of high performance and independent intellectual property spectrometer. The main contents of this paper are as follows: (1) the basic principle of NMR and the structure of spectrometer, including sequence controller, RF module, gradient generation module, are introduced. Data collection module and network communication unit. (2) A design scheme of RF pulse generator for magnetic resonance imaging based on FPGA and DDS is proposed. The direct digital frequency synthesizer (DDS) is used to complete the frequency synthesis, digital-to-analog conversion and so on, which makes the output waveform have accurate phase and frequency resolution. Its fast phase, frequency, amplitude switching speed and other characteristics can meet the performance requirements of magnetic resonance imaging spectrometer. (3) the functional test and test of RF pulse generator are completed, and the test results are analyzed. The hard pulse and soft pulse (Sine pulse, Gao Si pulse) are generated by RF generating module, and the spectral purity of RF signal is measured and analyzed, that is, phase noise, spurious and noise substrate.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TN782;TN74

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