核磁共振前置放大器的設(shè)計

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摘要：本文先簡要敘述了磁共振的發(fā)展史以及磁共振成像技術(shù)的基本原理。核磁共振成像技術(shù)是80年代發(fā)展起來的一種全新的影像檢查技術(shù)。全稱是：核磁共振電子計算機(jī)斷層掃描。最開始用于磁共振成像的為永磁型低場磁共振，現(xiàn)代MRI已發(fā)展到3.0以上，立體三位MRI也已經(jīng)出現(xiàn)，極大地提高了診斷水平。
然后本文對磁共振成像系統(tǒng)進(jìn)行簡要分析，從射頻接收單元引出前置放大器。因為前置放大器所處的特殊位置，本文分析了前置放大器設(shè)計過程中應(yīng)該注意的各種問題，如射頻電路中器件的射頻特性以及放大器中的噪聲和電磁兼容性等。其次論文介紹了自制前置放大器的原理圖，并對電路圖進(jìn)行分析，在實際測量中與某公司產(chǎn)品進(jìn)行對比，得到相應(yīng)的放大器指標(biāo)，如增益，通頻帶，1dB壓縮點等。最后，在總結(jié)本文的基礎(chǔ)上，提出一些這次設(shè)計中存在的一些問題以及改進(jìn)的方向。

關(guān)鍵字：磁共振成像 前置放大器 噪聲模型 射頻特性

Design of MRI preamplifier
Abstract： This thesis briefly describes the history of MRI and the basic principles of MRI technology.MRI technology whose whole name is NMR computer tomography is a new imaging technology developed in 1980s. At the beginning people use permanent magnet-type low field magnetic resonance. Nowadays,MRI has developed into a modern 3.0 or more, three-dimensional MRI has also emerged, which greatly improved the diagnosis.
Then this paper give a brief analysis of magnetic resonance imaging system and leads out the preamplifier from the RF receiving unit. According to the special position of the preamplifier, then paper analyzes the preamplifier design process should pay attention to a variety of problems, such as radio frequency characteristics of the device and the RF amplifier circuit noise and electromagnetic compatibility. Second, the paper describes the homemade preamplifier schematics, circuit diagrams and analyzed in actual measurement and comparison of a company's products, the corresponding amplifier indicators, such as gain, passband, 1dB compression point and so on. Finally，we summarizing the whole passage and point out some problems，which should be resolved in later works.

Key words：MRI Pre-amplifier Noise model RF characteristics

目 錄
第一章 緒論................................................................1
1.1磁共振發(fā)展歷史........................................................1
1.2低場脈沖磁共振系統(tǒng)基本原理............................................2
1.3 前置放大器概述.......................................................2
1.4本文研究主要內(nèi)容......................................................3
第二章 磁共振成像設(shè)備...................................................4
2.1 磁共振成像系統(tǒng)的組成...............................................4
2.2 磁體子系統(tǒng).........................................................4
2.3 梯度子系統(tǒng).........................................................5
2.4 射頻子系統(tǒng).........................................................6
2.5信號采集和圖像重建子系統(tǒng)............................................7
2.6 主計算機(jī)和圖像顯示子系統(tǒng)...........................................8
第三章前置放大器主要問題分析..........................................9
3.1 射頻電路理論........................................................9
3.1.1 電阻的射頻特性.................................................9
3.1.2 電容的射頻特性.................................................9
3.1.3 電感的射頻特性................................................10
3.2 噪聲問題分析........................................................11
3.2.1電路中的噪聲源.................................................11
3.2.2放大器的噪聲模型...............................................13
3.2.3噪聲系數(shù)測量...................................................16
3.3 干擾及電磁兼容問題..................................................17
3.3.1 干擾的主要來源.................................................18
3.3.2 電磁干擾的抑制措施.............................................18
3.4 噪聲匹配網(wǎng)絡(luò)........................................................19
第四章低噪聲前置放大器設(shè)計.............................................21
4.1 前置放大器重要參數(shù)...................................................21
4.2 低噪聲放大器的設(shè)計...................................................23
第五章實測數(shù)據(jù)與分析....................................................23
5.1測試前網(wǎng)絡(luò)分析儀校準(zhǔn).................................................24
5.2 實驗問題分析........................................................26
致謝........................................................................31
參考文獻(xiàn)...................................................................32