磁共振常用压脂技术

FatSuppressioninMRImagingCengLi2014-10-20Fatsuppression(FS)isusedinroutineMRimagingformanypurposes,buttwomainindicationscanbeidentified.1,FSisusedtosuppressthesignalfromnormaladiposetissuetoreducechemicalshiftartifact,motionartifactorimprovevisualizationofuptakeofcontrastmaterial.2,FSisusedtodetectadiposetissue.Fatcharacteristics1,Thereisasmalldifferenceinresonancefrequencybetweenlipidandwaterprotons.water-lipid≈3.5PPM(150Hz/T).2,ThedifferenceinT1betweenadiposetissueandwater.1.0T=150Hu;1.5T=225Hz;3.0T=420HzFatsuppressionisagenerictermthatincludesvarioustechniques:Chemicalshiftselectivesaturation,CHESSInversion-recoveryimaging,STIRCHESS-STIRimaging,FAT-SATopposed-phaseimaging,DixonSelectivewaterexcitationtechniqueChemicalshiftselectivesaturation,CHESSwater-lipid≈3.5PPM(150Hz/T).Afrequency-selectivesaturationradio-frequencypulsewiththesameresonancefrequencyasthatoflipidsisappliedtoeachslice-selectionradio-frequencypulse.Ahomogeneityspoilinggradientpulseisappliedimmediatelyafterthesaturationpulsetodephasethelipidsignal.Advantages:1,FSislipidspecific2,FScanbeusedwithanyimagingsequence3,FShashighersignal-to-noiseratio4,RelativelyfastDisadvantages:1,SensitivetoB0andB1inhomogeneities2,SensitivetothemagneticfieldstrengthofB03,LowsequenceefficiencyInversion-recoveryimaging,STIR1，ThedifferenceinT1betweenadiposetissueandwater.1.0T=150Hz;1.5T=225Hz;3.0T=420Hz2，after180。Inversionpulse,theT1ofadiposetissuewillrecoverfasterthanthatofwater.3,90。pulseisappliedatthenullpointofadiposetissue.Advantages:1,RobusttoB0andB1inhomogeneities2,ReliablefatsuppressionDisadvantages:1,OnlyworkswithPDandT2W2,Non-specific;suppressesshortT1speciesandenhancingtissueaftercontrast3,LowSNRefficiency4,LongscantimesCHESS-STIRimaging,FAT-SATAdvantages:1,Reliablefatsuppression2,Relativelyfast3,RobusttoB0/B1inhomogeneitiesandthestrengthofmagneticfieldOpposed-phaseimaging,Dixon1,lipidprotonsandwaterprotonshavedifferentfrequencies.waterprotonsprecessfractionallyfasterthanlipidprotons.≈3.5PPM(150Hz/T)2,therewillbecyclicalin-phaseandout-of-phasealternationsofthetwowavesI(in-phase)=water+fatI(out-phase)=water-fatI(water)=[I(in-phase)+I(out-phase)]/2I(fat)=[I(in-phase)-I(out-phase)]/2Advantages:1,Robustfatsaturation2,Providesfat/waterimages3,Allowsrecombinedimages4,Universalcompatibility5,Quantitativeapplications6,HighSNRefficiency7,Relativelylipidspecific8,fastDisadvantages:1,Doesnotsuppressthesignalfromadiposetissue2,MorecomplexreconstructionSelectivewaterexcitationtechnique1,ThedifferenceinT1betweenadiposetissueandwater2,TheprocessisverycomplexTakea90。pulseasanexample1-1mode:45+451-2-1mode:22.5+45+22.51-3-3-1mode:11.25+33.75+33.75+11.25Advantages:1,InsensitivetoB1inhomogeneities2,Versatile;PracticaltomostpulsesequencesexceptFSE3,RelativelyfastDisadvantages:1,SensitivetoB0inhomogeneities2,Lowsequenceefficiency3,LongerexcitationpulsesThankyou