CT+成像原理介绍.ppt

CT成像原理介紹,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,X-RayDiscovery,X-raywasdiscoveredbyaGermanscientistRoentgen100yearsago.Thismadepeopleforthefirsttimebeabletoviewtheanatomystructureofhumanbodywithoutoperation,ButitssuperimposedAndwecouldntviewsofttissue,MynameisGodfreyHounsfieldIworkfortheCentralResearchLabs.ofEMI,LtdinEnglandIdevelopedthethefirstclinicallyusefulCTscannerin1971,HistoryofComputedTomography,Early1970s,1963-AlanCormackdevelopedamathematicalmethodofreconstructingimagesfromx-rayprojections,Forthefirsttimewecouldview:,CTBroketheBarrier,-Tomographicor“Slice”anatomy-Densitydifference,ButitstimeconsumingAndresolutionneedstobeimproved,ConceptofX-rayAttenuation,AnX-raybeampassingthroughthebodyisattenuated(losesitsenergy)by:AbsorptionScattering,IncidentX-ray,Transmittedray,SCATTEREDX-RAYS,BODYTISSUE,Absorptionbythetissueisproportionaltothedensity,Lessdensetissue,Moredensetissue,MOREATTENUATION,LESSATTENUATION,HowdoesCTWork?,X-raygoesthroughcollimatorthereforepenetrateonlyanaxiallayeroftheobject,calledslice,HowdoesCTWork?,PatientisplacedinthecenterofthemeasurementfieldX-rayispassedthroughthepatientsslicefrommanydirectionalonga360pathThetransmittedbeamsarecapturedbythedetectorswhichdigitizesthesesignalsThesedigitizedsignalscalledrawdataaresenttoacomputerwhichcreatetheCTimage,HowdoesCTWork?,Theobjectsliceisdividedintosmallvolumeelementscalledvoxels.Eachvoxelisassignedavaluewhichisdependentontheaverageamountofattenuation,HowisCTImagegenerated?,Theattenuationvaluesaretransferredtothecomputerwheretheyarecoded&usedtocreateasliceimage,HowisCTImagegenerated?,CTGenerations&Design,“Generation”isusedtolabelCTtube-detectordesigns,3rdGenerationDesignRotatingtube&detector,4thGenerationDesignFixedringdetector,Slip-ringTechnology,PoweristransmittedthroughparallelsetsofconductiveringsinsteadofelectricalcablesContinuousGantryRotationPrerequisiteforSpiralCT,NonSlip-ringScanner,Slip-ringScanner,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,WhatisSpiralScan?-just4“C”,Continuouslyrotatingtube/detectorsystemContinuouslygeneratingX-rayContinuouslytablefeedContinuouslydataacquisition,Reconstructionofarbitraryslices(eithercontiguousoroverlapping)withinthescannedvolumeDistancebetweentheslicesiscalledIncrement,A,B,VolumeData,Continuousdataacquisition,Increment,SliceThickness,Increment=SliceThicknessNoOverlapNoGaps,ContiguousImageReconstruction,Increment,Overlap,Slice,Thickness,OverlappingImageReconstruction,IncrementSliceThicknessGapsbetweenslicesImagesarefurtherapartLessimagescreated,ImageReconstructionwithGaps,Increment,SliceThickness,StandardCT/SliceImaging,DeepInspiration,ShallowInspiration,Misregistrationduetodifferentrespiratorylevelsbetweenslices,PartialVolumeEffect,Unabletoresconstructimagesatarbitraryposition,Sliceimagingisslow,Scanthewholeregionofinterestinonebreathhold,Reconstructionofoverlappingimageswithoutadditionaldose,Retrospectivereconstructionofslicesinarbitrarypositionwithinthescannedvolume,Nogapssinceradiationalwaystransmitsthewholevolume,SpiralCT/VolumeImaging,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,ScanParameters,X-rayTubeVoltage(kVp)X-rayTubeCurrent(mA)ScanTime(s)SlicethicknessorCollimation(mm),TableSpeed(mm/rot)orFeedper360rotationPitchInterpolationProcessIncrement(mm),TableSpeed&Pitch,TableSpeedisdefinedasdistancetraveledinmmper360rotation,Pitch=,TableFeedperrotationCollimation,10mmP1,10mmP2,30s,30s,MoreCoverageinthesametimewithextendedPitch!,Pitch2covers2xdistanceasPitch1,ScanRange=300mm,10mmP110mm/s,10mmP220mm/s,30s,15s,CoverthesamevolumeinshortertimewithextendedPitch,Toreduceartifactsduetotablemotionduringspiralscanning,weuseaspecialreconstructionprocesscalledINTERPOLATION,Interpolation,Convertsvolumedataintosliceimages,InterpolationAlgorithm,WideAlgorithm,SlimAlgorithm,2x360=720rawdata,2(180+52)=464rawdata,WidealgorithmproducesabroaderimagethicknessWidealgorithmusesmorerawdata=lessimagenoise,PITCH2,PITCH1,Pitch2scanningproducesabroaderimagethicknessPitch2scanningdoesnotincreaseimagenoise,30%increaseinimagethicknesswithPitch2,SliceSensitivityProfile(SSP),SSPdescribestheeffectiveslicethicknessofanimageandtowhatextentanatomywithinthatslicecontributetothesignal,SSP,RESOLUTION,Allpointswithintheslicecontributeequally&pointsoutsideoftheslicedonotcontributetotheimageatall.,Imagesignal,IdealSSP,Z-axis(mm),Collimation=widthofx-raybeam=sliceprofile,SliceProfile(SP),Effectiveslicethicknessofanimage,SliceProfileResolution,FactorsinfluencingSliceProfileCollimationPitchInterpolationalgorithm(360or180),FactorsinfluencingSSP,Collimatorwidthcollimation=SSPSpiralCTTablespeedorPitchInterpolationAlgorithm=mathematicalprocessrequiredtoreconstructaxialimagesfromthespiralvolumedataset,Pitch&SliceProfile,SlimvsWideSSPComparison,SliceProfileSlim%BroadenWide%BradenPitchOne5.0mm06.3mm26PitchTwo6.5mm3010.8mm116,WIDE720degreeMorephotons,SLIM464degreeLessphotons,SSPSpatialresolution,SSPSpatialresolution,Smootherimage,Noisierimage,Slim-Advantages,ImprovedZResolutionReducedpartialvolumeartifactsSlim+extendedPitchLongercoverageSamecoveragewithshorterscantimeorthinnerslicesLessradiationdose,Wide-Advantages,NoiseReductionSmootherimageUsefulforscanninghugepatientOnlyforscanningatPitchOne,SliceProfileComparison,Lesionsmallerthan1cm,SCANRANGE=150mm,10/10/10(15s),5/10/5(15s),SliceProfile=10mm,SliceProfile=6.5mm,OptimizingtheScanningParameters,SmallestPossibleEffectiveSliceThickness,ScanLength(mm),ScanDuration(s),TableSpeed(mm/s),SmallestCollimation(mm),ScanDuration,Dependsonthescanlength&patientsbreath-holdcompliance,TableSpeedPitchFactor,1Pitch2tocoverthewholevolumeinonebreath-hold,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,Peripheralveineg.antecubitalvein19-20gaugeneedleorIVcatheter,Volume,FlowRate,Concentration,InjectionProtocols,300mgI/mlnon-ioniccontrast,2-5ml/scardiacoutput,80-150mlpatientsweight®ionofinterest,Site,ScanDelay,Delaybetweeninjectioninitiation&thestartofthescansequence,TailoringScan&InjectionProtocols,InjectionDurationmustbeequaltoorgreaterthanScanTime,50,100,150,200,250,Times,HU,CONTRAST,50,100,150,200,250,Times,HU,CONTRAST,NaCl,BolusDurationscantimeInsufficient,inhomogeneousopacification,BolusDuration=scantimeUniform,maximumopacification,EnhancementCurveoftheTargetRegion,50,100,150,200,250,Times,HU,OptimalWindow,Early,Time-densitycurveofthetargetregion,Late,ContrastBolusTiming,DeterminesoptimalscandelayforspiralCTAsequence,CONTRAST,NaCl,TestBolusProcedure,ImagingVolumeforspiralCTA,10-20mlofcontrastisinjectedatthechosenrateforspiral,Afteradelayof8-10s,low-dose,single-levelaxialimagesareacquiredevery2satthestartingpointoftheimagingvolume,Dynamicscansatthisposition,DynamicEvaluationtogenerateaTime-densitycurve,DynamicEvaluation,Ti