本文選題：磁共振成像 + 譜儀�。� 參考：《電子科技大學(xué)》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(shè)備,比如CT、XR等,具有無(wú)電磁輻射、任意切面成像、分辨率高等優(yōu)點(diǎn),MRI在現(xiàn)代醫(yī)學(xué)影像診斷中具有非常重要的作用。近幾十年來(lái),開(kāi)放式永磁型MRI取得了巨大的提高和發(fā)展。開(kāi)放式空間設(shè)計(jì)的MRI既能夠有效消除病人檢查時(shí)的幽閉感和不適,又能夠?yàn)獒t(yī)生進(jìn)行介入治療提供空間和方便。同時(shí),永磁型的低場(chǎng)環(huán)境不存在生物體安全性問(wèn)題,而且永磁型MRI維護(hù)費(fèi)用較低,操作簡(jiǎn)單。 譜儀(Spectrometer)是MRI設(shè)備的核心部件,控制著MRI系統(tǒng)的時(shí)序以及信號(hào)處理和生成,其性能直接影響著成像的質(zhì)量。目前國(guó)外只有少數(shù)幾家大公司能夠提供譜儀產(chǎn)品,國(guó)內(nèi)都是進(jìn)口譜儀系統(tǒng)。因此,進(jìn)行譜儀的自主研究和設(shè)計(jì)對(duì)我國(guó)磁共振事業(yè)發(fā)展具有重要的意義。 本文完成了開(kāi)放式永磁型MRI譜儀系統(tǒng)的總體方案和關(guān)鍵模塊的硬件設(shè)計(jì),并通過(guò)仿真實(shí)驗(yàn)等驗(yàn)證了其可行性,主要工作內(nèi)容如下： 1、完成總體方案的設(shè)計(jì)。根據(jù)譜儀的功能要求,對(duì)譜儀進(jìn)行需求分析,并完成了譜儀硬件系統(tǒng)的總體設(shè)計(jì)方案,包括譜儀的詳細(xì)工作流程設(shè)計(jì)和功能模塊的劃分等,同時(shí),研究了譜儀系統(tǒng)幾個(gè)關(guān)鍵模塊的技術(shù)問(wèn)題,對(duì)各模塊提出了具體的設(shè)計(jì)方案。 2、梯度波形發(fā)生器的設(shè)計(jì)。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(chǎng),分3路來(lái)完成對(duì)檢測(cè)物體進(jìn)行空間坐標(biāo)編碼的作用。梯度波形發(fā)生器的重要指標(biāo)包括梯度切換率和精度,具有快速的梯度切換速率和精準(zhǔn)的輸出精度,對(duì)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(lái)實(shí)現(xiàn)對(duì)梯度信號(hào)的輸出,其可以在200ns的時(shí)間內(nèi)實(shí)現(xiàn)±1.2mA的滿量程快速切換,同時(shí)其還有24bit的DAC轉(zhuǎn)換精度并對(duì)噪聲很好的抑制效果。我們還對(duì)渦流補(bǔ)償進(jìn)行了詳細(xì)的討論和分析,而且給出了算法的仿真實(shí)驗(yàn)。 3、脈沖序列控制器的設(shè)計(jì)。脈沖序列控制器的設(shè)計(jì)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(hào)具有很高的精準(zhǔn)度和很好的信號(hào)同步,脈沖序列控制器根據(jù)序列要求產(chǎn)生精準(zhǔn)的脈沖序列觸發(fā)信號(hào)。基于以上特點(diǎn),采用高性能FPGA來(lái)完成對(duì)觸發(fā)信號(hào)的實(shí)現(xiàn)就顯得尤為重要,我們采用Cyclone Ⅲ系列的EP3C40F484C6來(lái)實(shí)現(xiàn)該功能。脈沖序列控制器還有一個(gè)問(wèn)題是內(nèi)存資源的優(yōu)化,因?yàn)槭录訒r(shí)表格占用較大的存儲(chǔ)空間,所以本文采用設(shè)置行程編碼循環(huán)機(jī)制的方式對(duì)事件延時(shí)表格進(jìn)行了優(yōu)化,可以使內(nèi)存節(jié)省幾百倍的存儲(chǔ)空間,減小空間資源的浪費(fèi)。 4、射頻發(fā)射器和接收器的設(shè)計(jì)。射頻發(fā)射器和射頻接收器也是譜儀系統(tǒng)設(shè)計(jì)的重要部分,射頻信號(hào)的頻率、相位和幅度等參數(shù)的改變直接會(huì)決定成像的質(zhì)量的好壞。磁共振信號(hào)的采樣接收檢波濾波等都是非常關(guān)鍵的技術(shù)。我們采用AD9957和AD6655實(shí)現(xiàn)射頻信號(hào)的發(fā)射以及共振信號(hào)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(shí)驗(yàn)結(jié)果的討論。本文最后分別給出了設(shè)計(jì)過(guò)程中的幾個(gè)關(guān)鍵模塊的實(shí)驗(yàn)結(jié)果,證明整套方案的設(shè)計(jì)是科學(xué)合理的,渦流補(bǔ)償?shù)姆抡嬉豺?yàn)證了其設(shè)計(jì)的可行性,為日后譜儀樣機(jī)的生產(chǎn)打下了堅(jiān)實(shí)的基礎(chǔ)。
[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(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2012
【分類(lèi)號(hào)】：R310;TH776

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本文編號(hào)：2070520