最新fmri physics mri nmr spectroscopy proton nuclear magnetic resonance imaging bydsavall-药学医学精品资料.ppt

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1、最新fMRIPhysicsMRINMRspectroscopyprotonnuclearmagneticresonanceimaging2006bydSavall-药学医学精品资料OutlineHistoryofNMRtoMRItofMRIPhysicsofprotons(1Hinparticular)CreatingMRIimagesFromMRItofMRIHistoryofNuclearMagneticResonanceNMR=nuclearmagneticresonanceFelixBl

2、ockandEdwardPurcell1946:atomicnucleiabsorbandre-emitradiofrequencyenergy1952:Nobelprizeinphysicsnuclear:propertiesofnucleiofatomsmagnetic:magneticfieldrequiredresonance:interactionbetweenmagneticfieldandradiofrequencyBlochPurcellNMRMRISource:JodyCul

3、ham’swebslidesPhysicsofprotons.motionofelectricallychargedparticlesresultsinamagneticforceorthogonaltothedirectionofmotionprotons(nuclearconstituentofatom)haveapropertyofangularmomentumknownasspinAngularmomentum(spin)ofaproton.Protonsaligningwithinam

4、agneticfieldIn“fieldfree”spacerandomlyorientedSource:MarkCohen’swebslidesSource:RobertCox’swebslidesSource:JodyCulham’swebslideswhenplacedinamagneticfield(B0;e.g.,ourMRImachines)protonswilleitheralignwiththemagneticfieldororthogonaltoit(processofreac

5、hingmagneticequilibrium)thereisasmalldifference(10:1million)inthenumberofprotonsinthelowandhighenergystates–withmoreinthelowstateleadingtoanetmagnetization(M)InsidemagneticfieldorientedwithoragainstB0M=netmagnetizationMAppliedMagneticField(B0)Precess

6、ion–thespinningtopanalogy.Source:CohenandBookheimerarticleWhatisactuallyalignedwiththeB0istheaxisaroundwhichtheprotonprecesses–thedecayofprecession(i.e.,itistherateofprecessionoutofalignmentwithB0togetherwiththeprotondensityofthetissueconcernedthatis

7、crucialinMRI)LarmorFrequencyLarmorequationf=B0=42.58MHz/TAt1.5T,f=63.76MHzAt4T,f=170.3MHzFieldStrength(Tesla)ResonanceFrequencyfor1H170.363.81.54.0theenergydifferencebetweenthehigh(orientedwithB0)andlow(orientedagainstB0)energyprotonsismeasurablean

8、disexpressedintheLarmorequationRFExcitationprotonscanflipbetweenlowandhighenergystates(i.e.,flipbetweenbeingalignedwithoragainstB0)todosotheenergytransfermustbeofapreciseamountandmustbefacilitatedbyanotherforce(e.g.,otherprotonsormolecules)inMRI,RF(r