开放式永磁型MRI谱仪硬件系统的研究与设计

发布时间：2018-06-26 13:27

本文选题：磁共振成像 + 谱仪　；参考：《电子科技大学》2012年硕士论文

【摘要】：磁共振成像(MRI, Magnetic Resonance Imaging)相比于其他医疗设备,比如CT、XR等,具有无电磁辐射、任意切面成像、分辨率高等优点,MRI在现代医学影像诊断中具有非常重要的作用。近几十年来,开放式永磁型MRI取得了巨大的提高和发展。开放式空间设计的MRI既能够有效消除病人检查时的幽闭感和不适,又能够为医生进行介入治疗提供空间和方便。同时,永磁型的低场环境不存在生物体安全性问题,而且永磁型MRI维护费用较低,操作简单。谱仪(Spectrometer)是MRI设备的核心部件,控制着MRI系统的时序以及信号处理和生成,其性能直接影响着成像的质量。目前国外只有少数几家大公司能够提供谱仪产品,国内都是进口谱仪系统。因此,进行谱仪的自主研究和设计对我国磁共振事业发展具有重要的意义。本文完成了开放式永磁型MRI谱仪系统的总体方案和关键模块的硬件设计,并通过仿真实验等验证了其可行性,主要工作内容如下： 1、完成总体方案的设计。根据谱仪的功能要求,对谱仪进行需求分析,并完成了谱仪硬件系统的总体设计方案,包括谱仪的详细工作流程设计和功能模块的划分等,同时,研究了谱仪系统几个关键模块的技术问题,对各模块提出了具体的设计方案。 2、梯度波形发生器的设计。在MRI谱仪系统中,梯度波形发生器用于产生线性梯度的磁场,分3路来完成对检测物体进行空间坐标编码的作用。梯度波形发生器的重要指标包括梯度切换率和精度,具有快速的梯度切换速率和精准的输出精度,对于成像质量有着重要的效果。本文使用PCM1704这款具有高精确度、高信噪比的音频数模转换芯片来实现对梯度信号的输出,其可以在200ns的时间内实现±1.2mA的满量程快速切换,同时其还有24bit的DAC转换精度并对噪声很好的抑制效果。我们还对涡流补偿进行了详细的讨论和分析,而且给出了算法的仿真实验。 3、脉冲序列控制器的设计。脉冲序列控制器的设计是谱仪系统中必不可少的重要部分,其一般都要求触发信号具有很高的精准度和很好的信号同步,脉冲序列控制器根据序列要求产生精准的脉冲序列触发信号。基于以上特点,采用高性能FPGA来完成对触发信号的实现就显得尤为重要,我们采用Cyclone Ⅲ系列的EP3C40F484C6来实现该功能。脉冲序列控制器还有一个问题是内存资源的优化,因为事件延时表格占用较大的存储空间,所以本文采用设置行程编码循环机制的方式对事件延时表格进行了优化,可以使内存节省几百倍的存储空间,减小空间资源的浪费。 4、射频发射器和接收器的设计。射频发射器和射频接收器也是谱仪系统设计的重要部分,射频信号的频率、相位和幅度等参数的改变直接会决定成像的质量的好坏。磁共振信号的采样接收检波滤波等都是非常关键的技术。我们采用AD9957和AD6655实现射频信号的发射以及共振信号的接收,其良好的性能使发射的可控性和接收采样的同步性得到有效的提高。 5、实验结果的讨论。本文最后分别给出了设计过程中的几个关键模块的实验结果,证明整套方案的设计是科学合理的,涡流补偿的仿真也验证了其设计的可行性,为日后谱仪样机的生产打下了坚实的基础。
[Abstract]:MRI (Magnetic Resonance Imaging) compared to other medical equipment, such as CT, XR and so on, has the advantages of no electromagnetic radiation, arbitrary section imaging, and high resolution, MRI plays a very important role in modern medical imaging diagnosis. In recent decades, open and open type permanent magnet MRI has been greatly improved and developed. Open air space has been achieved. The MRI can not only effectively eliminate the claustrophobic feeling and discomfort in the patient's examination, but also provide space and convenience for the doctor to intervene treatment. At the same time, the permanent magnetic low field environment does not have the problem of biological safety, and the maintenance cost of permanent magnetic type MRI is low and the operation is simple.
Spectrometer is the core component of the MRI device, which controls the timing of the MRI system and the processing and generation of the signal. Its performance directly affects the quality of the imaging. At present, only a few large companies in the country can provide the spectrometer products, and the domestic are imported spectrometer systems. Therefore, the autonomous research and design of the spectrometer have been designed for the magnetic resonance of our country. The development of the cause is of great significance.
In this paper, the overall scheme of the open permanent magnet MRI spectrometer system and the hardware design of the key modules are completed, and the feasibility is verified by the simulation experiment. The main work contents are as follows:
1, complete the design of the overall plan. According to the functional requirements of the spectrometer, the needs of the spectrometer are analyzed, and the overall design scheme of the spectrometer hardware system is completed, including the detailed work flow design and the division of the functional modules of the spectrometer. At the same time, the technical problems of several key modules of the spectrometer system are studied, and the specific modules are put forward. Design scheme.
2, the design of the gradient waveform generator. In the MRI spectrometer system, the gradient waveform generator is used to produce a linear gradient magnetic field, which is divided into 3 ways to perform the space coordinate encoding of the object. The important index of the gradient waveform generator includes the gradient switching rate and precision, with a fast gradient switching rate and accurate output precision. It has an important effect on the quality of imaging. This paper uses PCM1704, an audio digital analog conversion chip with high accuracy and high signal to noise ratio, to realize the output of the gradient signal. It can achieve a full range of full range of + 1.2mA in the time of 200ns, and it also has the DAC conversion precision of 24bit and a good noise suppression effect on the noise. We also discussed and analyzed the eddy compensation in detail, and gave the simulation experiment of the algorithm.
3, the design of the pulse sequence controller. The design of the pulse sequence controller is an essential part of the spectrometer system. It generally requires that the trigger signal has high precision and good signal synchronization. The pulse sequence controller produces a precise pulse sequence trigger signal according to the sequence requirements. Based on the above features, high sex is used. It is particularly important to achieve the realization of the trigger signal by FPGA. We use the Cyclone III series of EP3C40F484C6 to achieve this function. The pulse sequence controller also has a problem that is the optimization of memory resources, because the event delay table takes up large storage space, so this article adopts the way of setting the travel coding cycle mechanism. The event delay table is optimized to save hundreds of times of memory and reduce the waste of space resources.
4, the design of radiofrequency emitter and receiver. Radio frequency transmitter and radio frequency receiver are also important parts of the design of spectrometer system. The change of frequency, phase and amplitude of radio frequency signals will directly determine the quality of imaging. The sampling and receiving of magnetic resonance signal is a very key technology. We use AD9957 The transmission of radio frequency signal and the reception of resonance signal are realized by AD6655, and its good performance improves the controllability and synchronization of the received sampling.
5, the experiment results are discussed. At the end of this paper, the experimental results of several key modules in the design process are given respectively. It is proved that the design of the whole scheme is scientific and reasonable. The simulation of eddy current compensation also validates the feasibility of the design. It lays a solid foundation for the production of the prototype of the future spectrometer.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R310;TH776

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