MAGNETOMSystem

TheBuild-upofMaterialMoleculesBlockofMaterialAtomsWaterElectronNucleushydrogenoxygen

SpinNS

65%H2OHydrogen,H+ThemostcommonelementinthebodyHighestsensitivitytomagneticresonanceHydrogenionispositivelycharged

UMRisverysimple:

M=U

E-E+EMTwoEnergyLevel

PrecessionFrequency

f????(??/2p)?*?B0? = GyromagneticRatio (dependsonnuclei, e.g.protons:42MHz/T)B = MagneticFieldStrengthSomenucleiaremagnetic: HydrogenH-1 CarbonC-13 FluorineF-19 PhosphorusP-31ResonancePrinciple:

xyzRFResonanceForhydrogen?=42MHz/Teslax2pIrradiatedRFf=42MHz/TeslaxB0

zMxyElectromagneticInduction

Decay

Mxy37%T2tTransverseRelaxation= Decayofmagnetizationbyinteraction betweennuclei(Spin-Spin-Relaxation)TransverseRelaxationTimeT2

MoMzt63%T1LongitudinaleRelaxation= EnergytransferbetweenexcitedspinsandTissue(Spin-Lattice-Relaxation)??ReestablishingoflongitudinalmagnetizationwithtimeconstantT1LongitudinalRelaxationTimeT1

RelaxationTimesareTissueSpecificMzSTissue1Tissue2TRShortTEMediumTELongTELongitudinalRelaxationTransverseRelaxationTissue2Tissue1

90180FIDSpinEchoooTransverserelaxationT2*istoofasttoreceivespatiallyencodedsignals??Echoofsignalby180opulseT2T2*Inhomogeneitiesofthemagneticfieldshortenrelaxationprocess:T2?T2*SpinEcho

ShortTRShortTELongTRShortTELongTRLongTET1PDT2

RFPulseMRSignalPhaseEncodingGradientReadoutGradient TRTE2TE2FIDEchoSliceSelectionGradientSpinEchoPulseSequence

B=B0+Gz*zB?B0SliceExcitationat?????0lowerfield,?????0higherfield,?????0-z0+zzWeakerField?????0StrongerField?????0SliceSelection

RawDatap2f1p1f1p1f2p1f256p256f1p256f256(PhaseundFrequencyEncoding)SpatialResolutionwithintheSlice

FrequencyPhasexyFourierTransformation

LHerefilling