医学影像物理学课件：13yj-MRI01

1、Magnetic Resonance Image,Magnetic Resonance Imaging(MRI) is a emerging, noninvasive medical imaging techniques, which is base on Nuclear Magnetic Resonance(NMR). It is similar with X-CT, but it uses magnetic field and radio frequency (rf) signals to obtain the anatomical information about a human bo

2、dy. Besides anatomical information, there is also information about biochemistry and physiology in its cross-sectional image. So we call it multi parameter imaging.,History of MRI,nuclear magnetic resonance，NMR ,1946, Block and Purcell NMR spectroscopy, 1960, be used to research enzyme, protein, and

3、 other biomolecular. MRI imaging principle , Lauterbur 1973 After 1976, The MRI image of human body,一种极重要的影像诊断手段。,Main Content,Spin, Magnetic moment, Procession Nuclear Magnetic Resonance Phenomena &Magnetic Imaging Parameter Magnetic Imaging Method &Magnetic Imaging Devices Pulse Sequence Design Ne

4、w Technology,Spin, (Nuclear )Magnetic moment, Procession,角动量与旋进/进动（刚体的转动） 角动量与磁矩（电流与磁矩，量子力学结论） 核的自旋磁矩（原子核组成） 水分子的磁矩 磁矩与外磁场的相互作用,Spin in classical mechanics,自旋的描述： 角动量:Angular omentum,Spin ： 沿自身对称轴的定轴转动,J: 转动惯量moment of inertia,力矩是改变角动量的原因,Procession 进动,陀螺在绕本身的对称轴旋转的同时，还绕竖直的轴线转动就是旋进。,陀螺的旋进，可以作为电子和原子核

5、在外磁场中作旋进的模型。熟悉陀螺旋进的原理是学习核磁共振和电子自旋共振的基础。,1.旋进原理（principle of precession）,Pure Procession : Outside torque is always perpendicular with the angular momentum of system.,根据角动量定理，冲量矩将使陀螺的角动量获得增量dL，dL的方向与M相同,dL=Mdt,自旋的角动量,L = J,陀螺自转的同时，质心受重力mg产生的重力矩M的作用,在时间dt内 ，重力矩M将产生一个与M方向相同的冲量矩Mdt。,dt过程中，dL始终垂直于 L,角动量L

6、末端的运动由OA变为OA。由于重力一直存在，L矢量的末端便绕OZ作圆周运动，这就是陀螺产生旋进的原因。,新的角动量与原来的角动量大小相等方向不同,自旋轴以角速度绕竖直轴OZ转动,2.旋进角速度( angular velocity of precession ),旋进角为d，,为旋进角速度,角动量的增量dL为,dL = Lsin d = Mdt,旋进角速度P为,上式说明：陀螺旋进的角速度与重力矩M成正比，与陀螺的角动量L成反比，与陀螺自旋对称轴OA与OZ轴的夹角 无关。,量子力学基础,FOUNDATION OF QUANTUM MECHANICS,Blackbody Radiation,普朗克,

7、十九世纪末，经典物理已相当成熟， 对物理现象本质的认识似乎已经完成。,但在喜悦的气氛中，还有两朵 小小的令人不安的乌云：,跳出传统的物理学框架！,引言,Matter Wave(德布罗意波）,The wave length of matter wave,mv is the momentum of motive particles,Matter wave actually is a odds wave which be used to describes the distribution of the particle in space.,In microcosmic world, we cant

8、 fix the spatial position and moving state of micro particles at same time.,Wave Function,We use wave function to describe the form of matter wave,It is a partial difference equation. In it the absolute value of represents the probability in certain point in space. The result of this equation concer

9、n the energy state of particles. For resolve it, we change the variables from orthogonal coordinate to polar coordinates,for electron: (Schrodinger equation),Quantum Number,Main quantum number Angular quantum number Magnetic quantum number Spin quantum number,For satisfy the condition of resolvable

10、equation, the value range of variables must obey some separate limitation.,For resolve it, separate variables in polar coordinates system,Magnetic moment,m, magnetic field strength Magnetic moment is appearance of magnetism of matter In outside magnetic filed, magnetic moment always deflect to direc

11、tion of outside magnetic field.,For current loop:,Magnetic Moment and outside Field,Energy of Magnetic Moment in outside Field,Moment in outside Field,0，Emin，负势能 180，Emax, 非稳定平衡 0180,Nuclear Spin,The spin can be pictured as due to a rotation somewhat like that of the earth about its axis.we can supp

12、ose the nuclei is a small spinning sphere. Nuclear spin is a kind of inherence of nuclei Describe spin with spin angular momentum,Spin Angular Momentum,Describe spin with angular momentum,I: nuclear spin quantum number, the value of it only can be integer(whole number) or half integer. (0、1/2、1、3/2、

13、 ). The concrete value is decided by component of nucleus.,Simplified form of Plank constant h,Nuclear Spin Angular Momentum,PN is Spin angular momentum. I is nuclear spin quantum number. I: 0, , 1, 3/2, 由质子数与中子数决定,Magnetic Moment, is corresponding magnetic moment，g is g factor, Its value change wit

14、h type of nucleus. E is the charge of proton, mP is mass of proton.,Spin leads to magnetic moment Because Nucleus carries an electric charge, the spinning motion leads to current loops and to a magnetic moment.,Nuclear magneton and gyromagnetic ratio,N is basic unit of magnetic moment ，called Nuclea

15、r magneton，The value is 5.0510-27JTl gyromagnetic ratio,In MRI, usually we adopt another way to express the relationship between Angular Momentum and Magnetic Moment：,Three Type Nuclear Spin,even-even nucleus proton = neutron, and both of them are even. I=0 Such as 16O, 12C odd-even nucleus one of p

16、roton or neutron is odd, the other is even. I=1/2, 3/2,Such as 1H, 31P, 15C, 15N odd-odd nucleus both of them are odd, I=1,2, Such as6Li, 14N,Nuclei Type in research of NMR,I = 0 these nuclei have not spins, so for them there is no magnetic moment and we cant observe them with NMR I = 1 these nuclei

17、 have not an uniform charge distribution and magnetic moment changing complexly in NMR, it is hard to observe with NMR. I=1/2 these nuclei have uniform magnetic moments, they are suitable for researching by NMR,hydrogen,1H数量最多，灵敏度最高,Nuclei in Magnetic Field,Motion Spin and Procession Energy State Ch

18、ange in outside static Magnetic Field,Interaction between Nuclear Magnetic Moment and Outside Magnetic Filed,Spin Magnetic Torque Procession,Larmor Relationship,Larmor Relationship: The angular frequency (Larmor frequency ) of the precession magnetization about the direction of the magnetic field is proportional to the strength of the magnetic field B is the gyromagnetic ratio,Spatial Quantizing,In static magnetic field, The Z component of L is,mI=I,I-1,I-2,-I,mI is magnetic quantum number,State of Nuclei Spin,Parallel Antipar