磁共振基本原理1_原子核

1、gGE Medical SystemsTraining in PartnershipPart 1Part 1原子核结构原子核结构gGE Medical SystemsTraining in Partnership目的目的. 为什么在MR成像时使用氢原子核. 如何计算磁场强度总和gGE Medical SystemsTraining in Partnership+ +- -NUCLEUSNUCLEUSELECTRONELECTRONPROTONPROTONK SHELLK SHELL人体中人体中的物质的物质是氢原子核是氢原子核gGE Medical SystemsTraining in Part

2、nership亚原子粒子的三个特点：亚原子粒子的三个特点：chargecharge，massmass，spinspin当有成对的中子和质子存在时，他们的自旋效果就会相互抵消。 具有奇数质子和中子的原子核会有剩余自旋的。这个剩余的自旋值就会产生一个或强或弱的磁矢量。具有较强的磁矢量的原子核容易受外加磁场的影响，这种原子核我们称之为 MR Active.MR Active.gGE Medical SystemsTraining in Partnership磁场强度具有总合效应 = 000为什么利用 H1成像? H1具有MR活性 (在所有的可以进行MR成像的原子核中，H1具有最大的磁化矢量) H1

3、在人体内广泛存在1.2.gGE Medical SystemsTraining in Partnership 同时具有大小和方向的量称为矢量 磁场强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为两个相互正交的向量不同大小相同方向相同大小相反方向磁场强度的分解gGE Medical SystemsTraining in Partnership 当指向一个方向的磁矢量（假设指向北极）vector较多时，总的磁场强度就会增加 当磁矢量的方向同时有指向南极和北极时，总的磁场强度就会减弱gGE Medical SystemsTraining in Partnership对一个给定的采样来说，所

4、有磁矢量的总合用MZ来表示M M z zgGE Medical SystemsTraining in PartnershipPart 2Part 2排列与运动排列与运动gGE Medical SystemsTraining in Partnership目的目的描述磁场对人体的作用确定为什么不同的磁场强度有不同的脉冲序列gGE Medical SystemsTraining in Partnership专业术语专业术语 V VocabularyocabularygGE Medical SystemsTraining in Partnership任意方向排列，总的磁矢量为零任意方向排列，总的磁矢量

5、为零gGE Medical SystemsTraining in PartnershipgGE Medical SystemsTraining in Partnership B B0 0低能级状态低能级状态NS高能级状态高能级状态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磁体洞磁体洞Magnet BoreMagnet BoreB B0 0gGE Medical SystemsTraining in Partnership 当净矢量方向与当净矢量方向与B0B0方向方向一致时，我们将这时的一致时，我们将这时的磁 化 矢 量 称 之 为磁 化 矢 量 称 之 为 MM z . z . 当净矢量的方向移到与当净矢量的方向移到与B0B0方向垂直的平面时，我们方向垂直的平面时，我们将这时的磁化矢量称之为将这时的磁化矢量称之为MMxyxy. .gGE Medical SystemsTraining i

7、n Partnership主磁场引起的旋转主磁场引起的旋转Magnetic Field BMagnetic Field B0 0进动：磁化矢量进动：磁化矢量Precessing: Magnetic Precessing: Magnetic MomentumMomentumgGE Medical SystemsTraining in Partnership 低磁场低磁场 B B0 0与主磁场的变化成正比高磁场高磁场 B B0 0gGE Medical SystemsTraining in Partnership进动频率Precessional Frequency氢质子旋磁比氢质子旋磁比HYDRO

8、GENHYDROGEN (42.6mHz)磁场强度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 低能级状态的质子 进动的频率 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场景场景 1 1您所在科室的放射科医师刚刚参加了一个研讨会归来，学习到了很多新知识。现在想尝试一个新的扫描垂体的脉冲序列。但是您的设备是1.5T，这位医生拿回的参数是0.5T的。请问这些参数是否可以在您的设备上使用，请解释请问这些参数是否可以在您的设备上使用，请解释场景场景 2 2 您的MR系统是0.5T，您所在科室来了一位新医生，他拿来一套1.5T系统的扫描参数，这是他以前常用的参数。请问他的参数可以使用吗？请解释请问他的参数可以使用吗？请解释Progress CheckProgress CheckgGE Medical SystemsTraining

12、 in PartnershipPartPart 3: 3: 共振共振gGE Medical SystemsTraining in Partnership描述当发射射频脉冲时原子核和净磁矢量的变化描述当翻转角变化时横向磁化矢量的变化预算翻转角变化时信噪比的变化目的目的gGE Medical SystemsTraining in Partnership术语术语VocabularyVocabularygGE Medical SystemsTraining in Partnership振幅Amplitude波长WavelengthgGE Medical SystemsTraining in Partn

13、ership()B0gGE Medical SystemsTraining in Partnership如果声源音叉的频率与静止音叉的震动频率一致，就会发生共振G声源声源CDEFGABGCDEFGABgGE Medical SystemsTraining in Partnership如果射频脉冲的频率与原子核的进动频率一致，就会发生共振gGE Medical SystemsTraining in Partnership氢核进动发生共振表现为氢原子核吸收射频脉冲的能量，由低能级状态跃迁到高能级状态gGE Medical SystemsTraining in Partnership如果射频脉冲的频

14、率与原子核的进动频率一致，就会发生共振90o射频脉冲 gGE Medical SystemsTraining in Partnership如果射频脉冲的频率与原子核的进动频率一致，就会发生共振180o射频脉冲180o射频脉冲gGE Medical SystemsTraining in Partnership能量交换能量交换(RF)(RF)当发射射频脉冲时，原子核吸收射频脉冲的能量，从低能级状态越迁到高能级状态gGE Medical SystemsTraining in PartnershipEX. 90EX. 90(RF)(RF)射频脉冲的能量决定纵向磁化矢量移向横向平面的量gGE Medic

15、al SystemsTraining in PartnershipgGE Medical SystemsTraining in PartnershipProgress CheckProgress CheckgGE Medical SystemsTraining in PartnershipRF = precessional frequency 原子核的能量状态就会从低能级跃迁到高能级散相位变成相位一致RF低SNR高SNR当翻转角变化时5.6.gGE Medical SystemsTraining in PartnershipPartPart 4: 4: MRMR信号的产生信号的产生gGE Me

16、dical SystemsTraining in Partnership目的目的gGE Medical SystemsTraining in Partnership术语术语VocabularyVocabularygGE Medical SystemsTraining in Partnership 当射频脉冲发射结束后，会发生：1. 原子核释放能量，从高能级迁到低能级2. 磁矢量回到纵向平面发射结束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术语术语VocabularyVocabularygGE Medical SystemsTraining in Partnership0-11234-2-3-40-11 2 3 4 5 6-2-3-6 -5 -4B0gGE Medical SystemsTraining in Partnership 高频低频频率编码梯度 高频低频相位编码梯度高频低频层面编码梯度gGE Medical SystemsTraining in PartnershipgGE Med