本文選題：磁共振成像 + 譜儀��； 參考：《電子科技大學》2012年碩士論文

【摘要】：磁共振成像(MRI, Magnetic Resonance Imaging)相比于其他醫(yī)療設備,比如CT、XR等,具有無電磁輻射、任意切面成像、分辨率高等優(yōu)點,MRI在現(xiàn)代醫(yī)學影像診斷中具有非常重要的作用。近幾十年來,開放式永磁型MRI取得了巨大的提高和發(fā)展。開放式空間設計的MRI既能夠有效消除病人檢查時的幽閉感和不適,又能夠為醫(yī)生進行介入治療提供空間和方便。同時,永磁型的低場環(huán)境不存在生物體安全性問題,而且永磁型MRI維護費用較低,操作簡單。 譜儀(Spectrometer)是MRI設備的核心部件,控制著MRI系統(tǒng)的時序以及信號處理和生成,其性能直接影響著成像的質(zhì)量。目前國外只有少數(shù)幾家大公司能夠提供譜儀產(chǎn)品,國內(nèi)都是進口譜儀系統(tǒng)。因此,進行譜儀的自主研究和設計對我國磁共振事業(yè)發(fā)展具有重要的意義。 本文完成了開放式永磁型MRI譜儀系統(tǒng)的總體方案和關鍵模塊的硬件設計,并通過仿真實驗等驗證了其可行性,主要工作內(nèi)容如下： 1、完成總體方案的設計。根據(jù)譜儀的功能要求,對譜儀進行需求分析,并完成了譜儀硬件系統(tǒng)的總體設計方案,包括譜儀的詳細工作流程設計和功能模塊的劃分等,同時,研究了譜儀系統(tǒng)幾個關鍵模塊的技術問題,對各模塊提出了具體的設計方案。 2、梯度波形發(fā)生器的設計。在MRI譜儀系統(tǒng)中,梯度波形發(fā)生器用于產(chǎn)生線性梯度的磁場,分3路來完成對檢測物體進行空間坐標編碼的作用。梯度波形發(fā)生器的重要指標包括梯度切換率和精度,具有快速的梯度切換速率和精準的輸出精度,對于成像質(zhì)量有著重要的效果。本文使用PCM1704這款具有高精確度、高信噪比的音頻數(shù)模轉(zhuǎn)換芯片來實現(xiàn)對梯度信號的輸出,其可以在200ns的時間內(nèi)實現(xiàn)±1.2mA的滿量程快速切換,同時其還有24bit的DAC轉(zhuǎn)換精度并對噪聲很好的抑制效果。我們還對渦流補償進行了詳細的討論和分析,而且給出了算法的仿真實驗。 3、脈沖序列控制器的設計。脈沖序列控制器的設計是譜儀系統(tǒng)中必不可少的重要部分,其一般都要求觸發(fā)信號具有很高的精準度和很好的信號同步,脈沖序列控制器根據(jù)序列要求產(chǎn)生精準的脈沖序列觸發(fā)信號�；谝陨咸攸c,采用高性能FPGA來完成對觸發(fā)信號的實現(xiàn)就顯得尤為重要,我們采用Cyclone Ⅲ系列的EP3C40F484C6來實現(xiàn)該功能。脈沖序列控制器還有一個問題是內(nèi)存資源的優(yōu)化,因為事件延時表格占用較大的存儲空間,所以本文采用設置行程編碼循環(huán)機制的方式對事件延時表格進行了優(yōu)化,可以使內(nèi)存節(jié)省幾百倍的存儲空間,減小空間資源的浪費。 4、射頻發(fā)射器和接收器的設計。射頻發(fā)射器和射頻接收器也是譜儀系統(tǒng)設計的重要部分,射頻信號的頻率、相位和幅度等參數(shù)的改變直接會決定成像的質(zhì)量的好壞。磁共振信號的采樣接收檢波濾波等都是非常關鍵的技術。我們采用AD9957和AD6655實現(xiàn)射頻信號的發(fā)射以及共振信號的接收,其良好的性能使發(fā)射的可控性和接收采樣的同步性得到有效的提高。 5、實驗結(jié)果的討論。本文最后分別給出了設計過程中的幾個關鍵模塊的實驗結(jié)果,證明整套方案的設計是科學合理的,渦流補償?shù)姆抡嬉豺炞C了其設計的可行性,為日后譜儀樣機的生產(chǎn)打下了堅實的基礎。
[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.
【學位授予單位】：電子科技大學
【學位級別】：碩士
【學位授予年份】：2012
【分類號】：R310;TH776

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本文編號：2070520