最新磁共振常用压脂技术[课件]]ppt课件.ppt

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1、磁共振常用压脂技术[课件]]Fatsuppression(FS)isusedinroutineMRimagingformanypurposes,buttwomainindicationscanbeidentified.1,FSisusedtosuppressthesignalfromnormaladiposetissuetoreducechemicalshiftartifact,motionartifactorimprovevisualizationofuptakeofcontrastmaterial.2,FSisusedtodetectadiposetiss

2、ue.Chemicalshiftselectivesaturation,CHESSwater-lipid≈3.5PPM(150Hz/T).Afrequency-selectivesaturationradio-frequencypulsewiththesameresonancefrequencyasthatoflipidsisappliedtoeachslice-selectionradio-frequencypulse.Ahomogeneityspoilinggradientpulseisappliedimmediatelyafterthesaturatio

3、npulsetodephasethelipidsignal.Advantages:1,FSislipidspecific2,FScanbeusedwithanyimagingsequence3,FShashighersignal-to-noiseratio4,RelativelyfastDisadvantages:1,SensitivetoB0andB1inhomogeneities2,SensitivetothemagneticfieldstrengthofB03,LowsequenceefficiencyInversion-recoveryimaging,

4、STIR1，ThedifferenceinT1betweenadiposetissueandwater.1.0T=150Hz;1.5T=225Hz;3.0T=420Hz2，after180。Inversionpulse,theT1ofadiposetissuewillrecoverfasterthanthatofwater.3,90。pulseisappliedatthenullpointofadiposetissue.Advantages:1,RobusttoB0andB1inhomogeneities2,ReliablefatsuppressionDisa

5、dvantages:1,OnlyworkswithPDandT2W2,Non-specific;suppressesshortT1speciesandenhancingtissueaftercontrast3,LowSNRefficiency4,LongscantimesCHESS-STIRimaging,FAT-SATAdvantages:1,Reliablefatsuppression2,Relativelyfast3,RobusttoB0/B1inhomogeneitiesandthestrengthofmagneticfieldOpposed-phas

6、eimaging,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

7、)]/2I(fat)=[I(in-phase)-I(out-phase)]/2Advantages:1,Robustfatsaturation2,Providesfat/waterimages3,Allowsrecombinedimages4,Universalcompatibility5,Quantitativeapplications6,HighSNRefficiency7,Relativelylipidspecific8,fastDisadvantages:1,Doesnotsuppressthesignalfromadiposetissue2,More

8、complexreconstructi