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Basic Physics Principles of MRI MRI The physics basics Magnetic Resonance Imaging MRI Overview No ionizng radiation Superior soft tissue contrast High resolution and multiplanar capability History 1946 MR phenomenon - Bloch & Purcell 1952 Nobel Prize - Bloch & Purcell 1950 1960 NMR developed as analytical tool 1970 1972 Computerized Tomography 1973 Backprojection MRI - Lauterbur 1975 Fourier Imaging - Ernst 1977 Echo-planar imaging - Mansfield 1980 FT MRI demonstrated - Edelstein Gradient Echo Imaging 1986 NMR Microscope 1987 MR Angiography - Dumoulin 1991 Nobel Prize - Ernst 1992 Functional MRI 1994 Hyperpolarized 129Xe Imaging 2003 Nobel Prize - Lauterbur & Mansfield General description When B0 applied to it, the momentum rate will be: Substituting I we have: This is Larmor equation. From Larmor equation the Larmor frequency is: mp can be divided to mpz and mpxy (mpz is assumed to be in B0 direction) If mpxy=0 ===> dmp/dt=0 means that there is no change in the direction of dipole moment and no signal If the sample contain large amount of protons, net magnetic moment will be M If M is in Z direction there is no signal. When M direction changes as a results of an arbitrary B we have signal and B could be B0z+B1 Quantum mechanical discription From the quantum view any nucleus with angular momentum of I has a magnetic moment of For any atom magnitude of nuclear angular moment is l (l is nuclear spin quantum number): In a magnetic field B0 the z component of mp can have different possible orientation with values of For a single proton magnitude of I=1/2 and hence ml=±1/2 For 1H l=1/2 ==> ml=±1/2 For 31P l=1/2 ==> ml=±1/2 For 19F l=1/2 ==> ml=±1/2 For 23Na l=3/2 ==> ml=-3/2 , -1/2, ½, 3/2 Nucleus with I=1 have Quadrapole state Energy state of each proton is: If a proton move from one state to another a change of energy is happens which is equal to and hence Statistical distribution of spin states In a large amounts of proton and the absence of B0 there is no net magnetization If a magnetic field of B0 is applied to them; Changing from one state to another release a photon of: The life time of each spin is: Bloch equations Bloch equations describe the behavior of nuclear magnetic moment of a sample with large amount of dipole moment in a magnetic field B; If an stimulus changes the direction of M from B (assume B=Bz) then changes to the Mz is given by: Changes to x and y direction of M are: