磁共振基本原理1_原子核

1、gGE Medical SystemsTraining in PartnershipPart 1Part 1原子核結(jié)構(gòu)原子核結(jié)構(gòu)gGE Medical SystemsTraining in Partnership目的目的. 為什么在MR成像時(shí)使用氫原子核. 如何計(jì)算磁場(chǎng)強(qiáng)度總和gGE Medical SystemsTraining in Partnership+ +- -NUCLEUSNUCLEUSELECTRONELECTRONPROTONPROTONK SHELLK SHELL人體中人體中的物質(zhì)的物質(zhì)是氫原子核是氫原子核gGE Medical SystemsTraining in Part

2、nership亞原子粒子的三個(gè)特點(diǎn)：亞原子粒子的三個(gè)特點(diǎn)：chargecharge，massmass，spinspin當(dāng)有成對(duì)的中子和質(zhì)子存在時(shí)，他們的自旋效果就會(huì)相互抵消。 具有奇數(shù)質(zhì)子和中子的原子核會(huì)有剩余自旋的。這個(gè)剩余的自旋值就會(huì)產(chǎn)生一個(gè)或強(qiáng)或弱的磁矢量。具有較強(qiáng)的磁矢量的原子核容易受外加磁場(chǎng)的影響，這種原子核我們稱之為 MR Active.MR Active.gGE Medical SystemsTraining in Partnership磁場(chǎng)強(qiáng)度具有總合效應(yīng) = 000為什么利用 H1成像? H1具有MR活性 (在所有的可以進(jìn)行MR成像的原子核中，H1具有最大的磁化矢量) H1

3、在人體內(nèi)廣泛存在1.2.gGE Medical SystemsTraining in Partnership 同時(shí)具有大小和方向的量稱為矢量 磁場(chǎng)強(qiáng)度正是具有大小和方向的量 具有大小和方向的矢量可以分解為兩個(gè)相互正交的向量不同大小相同方向相同大小相反方向磁場(chǎng)強(qiáng)度的分解gGE Medical SystemsTraining in Partnership 當(dāng)指向一個(gè)方向的磁矢量（假設(shè)指向北極）vector較多時(shí)，總的磁場(chǎng)強(qiáng)度就會(huì)增加 當(dāng)磁矢量的方向同時(shí)有指向南極和北極時(shí)，總的磁場(chǎng)強(qiáng)度就會(huì)減弱gGE Medical SystemsTraining in Partnership對(duì)一個(gè)給定的采樣來說，所

4、有磁矢量的總合用MZ來表示M M z zgGE Medical SystemsTraining in PartnershipPart 2Part 2排列與運(yùn)動(dòng)排列與運(yùn)動(dòng)gGE Medical SystemsTraining in Partnership目的目的描述磁場(chǎng)對(duì)人體的作用確定為什么不同的磁場(chǎng)強(qiáng)度有不同的脈沖序列g(shù)GE Medical SystemsTraining in Partnership專業(yè)術(shù)語專業(yè)術(shù)語 V VocabularyocabularygGE Medical SystemsTraining in Partnership任意方向排列，總的磁矢量為零任意方向排列，總的磁矢量

5、為零gGE Medical SystemsTraining in PartnershipgGE Medical SystemsTraining in Partnership B B0 0低能級(jí)狀態(tài)低能級(jí)狀態(tài)NS高能級(jí)狀態(tài)高能級(jí)狀態(tài)NSgGE Medical SystemsTraining in Partnership B B0 06 in low E state3 in high E stategGE Medical SystemsTraining in Partnership B B0 07 excess contribute to our signalgGE Medical Systems

6、Training in Partnership1.5T1.0T.5T.2T磁體洞磁體洞Magnet BoreMagnet BoreB B0 0gGE Medical SystemsTraining in Partnership 當(dāng)凈矢量方向與當(dāng)凈矢量方向與B0B0方向方向一致時(shí)，我們將這時(shí)的一致時(shí)，我們將這時(shí)的磁 化 矢 量 稱 之 為磁 化 矢 量 稱 之 為 MM z . z . 當(dāng)凈矢量的方向移到與當(dāng)凈矢量的方向移到與B0B0方向垂直的平面時(shí)，我們方向垂直的平面時(shí)，我們將這時(shí)的磁化矢量稱之為將這時(shí)的磁化矢量稱之為MMxyxy. .gGE Medical SystemsTraining i

7、n Partnership主磁場(chǎng)引起的旋轉(zhuǎn)主磁場(chǎng)引起的旋轉(zhuǎn)Magnetic Field BMagnetic Field B0 0進(jìn)動(dòng)：磁化矢量進(jìn)動(dòng)：磁化矢量Precessing: Magnetic Precessing: Magnetic MomentumMomentumgGE Medical SystemsTraining in Partnership 低磁場(chǎng)低磁場(chǎng) B B0 0與主磁場(chǎng)的變化成正比高磁場(chǎng)高磁場(chǎng) B B0 0gGE Medical SystemsTraining in Partnership進(jìn)動(dòng)頻率Precessional Frequency氫質(zhì)子旋磁比氫質(zhì)子旋磁比HYDRO

8、GENHYDROGEN (42.6mHz)磁場(chǎng)強(qiáng)度Magnet Field StrengthgGE Medical SystemsTraining in Partnership 同位素同位素IsotopeIsotope 0.2 0.5 1.0 1.542.68.521.342.663.9g g10.7140.0417.2416.160.125.95.3520.038.6210.7340.117.262.148.015.05gGE Medical SystemsTraining in PartnershipB B0 0 低能級(jí)狀態(tài)的質(zhì)子 進(jìn)動(dòng)的頻率 Larmor 公式3.4.gGE Medica

9、l SystemsTraining in Partnership1. Larmors equation1. Larmors equation _ _2. Precessional frequency2. Precessional frequency _ _3. Net magnetization vector _3. Net magnetization vector _4. MR Active Nuclei4. MR Active Nuclei _ _5. Magnetogyric ratio5. Magnetogyric ratio _ _6. Magnetogyric ratio for

10、H1 _6. Magnetogyric ratio for H1 _7. Elements of an atom7. Elements of an atom _ _8. Vector8. Vector _ _9. M9. Mz z _10. M10. Mxyxy _11. Hertz11. Hertz _ _12. Phase12. Phase _ _13. Frequency13. Frequency _ _14. Magnetic moment14. Magnetic moment _ _ Progress CheckProgress CheckgGE Medical SystemsTra

11、ining in Partnership場(chǎng)景場(chǎng)景 1 1您所在科室的放射科醫(yī)師剛剛參加了一個(gè)研討會(huì)歸來，學(xué)習(xí)到了很多新知識(shí)?，F(xiàn)在想嘗試一個(gè)新的掃描垂體的脈沖序列。但是您的設(shè)備是1.5T，這位醫(yī)生拿回的參數(shù)是0.5T的。請(qǐng)問這些參數(shù)是否可以在您的設(shè)備上使用，請(qǐng)解釋請(qǐng)問這些參數(shù)是否可以在您的設(shè)備上使用，請(qǐng)解釋場(chǎng)景場(chǎng)景 2 2 您的MR系統(tǒng)是0.5T，您所在科室來了一位新醫(yī)生，他拿來一套1.5T系統(tǒng)的掃描參數(shù)，這是他以前常用的參數(shù)。請(qǐng)問他的參數(shù)可以使用嗎？請(qǐng)解釋請(qǐng)問他的參數(shù)可以使用嗎？請(qǐng)解釋Progress CheckProgress CheckgGE Medical SystemsTraining

12、 in PartnershipPartPart 3: 3: 共振共振gGE Medical SystemsTraining in Partnership描述當(dāng)發(fā)射射頻脈沖時(shí)原子核和凈磁矢量的變化描述當(dāng)翻轉(zhuǎn)角變化時(shí)橫向磁化矢量的變化預(yù)算翻轉(zhuǎn)角變化時(shí)信噪比的變化目的目的gGE Medical SystemsTraining in Partnership術(shù)語術(shù)語VocabularyVocabularygGE Medical SystemsTraining in Partnership振幅Amplitude波長WavelengthgGE Medical SystemsTraining in Partn

13、ership()B0gGE Medical SystemsTraining in Partnership如果聲源音叉的頻率與靜止音叉的震動(dòng)頻率一致，就會(huì)發(fā)生共振G聲源聲源CDEFGABGCDEFGABgGE Medical SystemsTraining in Partnership如果射頻脈沖的頻率與原子核的進(jìn)動(dòng)頻率一致，就會(huì)發(fā)生共振gGE Medical SystemsTraining in Partnership氫核進(jìn)動(dòng)發(fā)生共振表現(xiàn)為氫原子核吸收射頻脈沖的能量，由低能級(jí)狀態(tài)躍遷到高能級(jí)狀態(tài)gGE Medical SystemsTraining in Partnership如果射頻脈沖的頻

14、率與原子核的進(jìn)動(dòng)頻率一致，就會(huì)發(fā)生共振90o射頻脈沖 gGE Medical SystemsTraining in Partnership如果射頻脈沖的頻率與原子核的進(jìn)動(dòng)頻率一致，就會(huì)發(fā)生共振180o射頻脈沖180o射頻脈沖gGE Medical SystemsTraining in Partnership能量交換能量交換(RF)(RF)當(dāng)發(fā)射射頻脈沖時(shí)，原子核吸收射頻脈沖的能量，從低能級(jí)狀態(tài)越遷到高能級(jí)狀態(tài)gGE Medical SystemsTraining in PartnershipEX. 90EX. 90(RF)(RF)射頻脈沖的能量決定縱向磁化矢量移向橫向平面的量gGE Medic

15、al SystemsTraining in PartnershipgGE Medical SystemsTraining in PartnershipProgress CheckProgress CheckgGE Medical SystemsTraining in PartnershipRF = precessional frequency 原子核的能量狀態(tài)就會(huì)從低能級(jí)躍遷到高能級(jí)散相位變成相位一致RF低SNR高SNR當(dāng)翻轉(zhuǎn)角變化時(shí)5.6.gGE Medical SystemsTraining in PartnershipPartPart 4: 4: MRMR信號(hào)的產(chǎn)生信號(hào)的產(chǎn)生gGE Me

16、dical SystemsTraining in Partnership目的目的gGE Medical SystemsTraining in Partnership術(shù)語術(shù)語VocabularyVocabularygGE Medical SystemsTraining in Partnership 當(dāng)射頻脈沖發(fā)射結(jié)束后，會(huì)發(fā)生：1. 原子核釋放能量，從高能級(jí)遷到低能級(jí)2. 磁矢量回到縱向平面發(fā)射結(jié)束gGE Medical SystemsTraining in PartnershipProgress CheckProgress CheckgGE Medical SystemsTraining in

17、 PartnershipSignal GenerationSignal Generation7.8.When the RF is stopped:T1: longitudinal regrowth(high - low energy)T2: transverse decay(nuclei dephase)SimultaneousSurface coilSurface coilSignalNoSignalgGE Medical SystemsTraining in PartnershipPart5Part5: : MRMR成像成像gGE Medical SystemsTraining in Partnership目的目的gGE Medical SystemsTraining in Partnership術(shù)語術(shù)語VocabularyVocabularygGE Medical SystemsTraining in Partnership0-11234-2-3-40-11 2 3 4 5 6-2-3-6 -5 -4B0gGE Medical SystemsTraining in Partnership 高頻低頻頻率編碼梯度 高頻低頻相位編碼梯度高頻低頻層面編碼梯度gGE Medical SystemsTraining in PartnershipgGE Med