CT成像原理介绍(英文版)ppt课件

CT成像原理介紹,1,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,2,X-RayDiscovery,X-raywasdiscoveredbyaGermanscientistRoentgen100yearsago.Thismadepeopleforthefirsttimebeabletoviewtheanatomystructureofhumanbodywithoutoperation,ButitssuperimposedAndwecouldntviewsofttissue,3,MynameisGodfreyHounsfieldIworkfortheCentralResearchLabs.ofEMI,LtdinEnglandIdevelopedthethefirstclinicallyusefulCTscannerin1971,HistoryofComputedTomography,Early1970s,1963-AlanCormackdevelopedamathematicalmethodofreconstructingimagesfromx-rayprojections,4,Forthefirsttimewecouldview:,CTBroketheBarrier,-Tomographicor“Slice”anatomy-Densitydifference,ButitstimeconsumingAndresolutionneedstobeimproved,5,ConceptofX-rayAttenuation,AnX-raybeampassingthroughthebodyisattenuated(losesitsenergy)by:AbsorptionScattering,IncidentX-ray,Transmittedray,SCATTEREDX-RAYS,BODYTISSUE,Absorptionbythetissueisproportionaltothedensity,Lessdensetissue,Moredensetissue,MOREATTENUATION,LESSATTENUATION,6,HowdoesCTWork?,7,X-raygoesthroughcollimatorthereforepenetrateonlyanaxiallayeroftheobject,calledslice,HowdoesCTWork?,8,PatientisplacedinthecenterofthemeasurementfieldX-rayispassedthroughthepatientsslicefrommanydirectionalonga360pathThetransmittedbeamsarecapturedbythedetectorswhichdigitizesthesesignalsThesedigitizedsignalscalledrawdataaresenttoacomputerwhichcreatetheCTimage,HowdoesCTWork?,9,Theobjectsliceisdividedintosmallvolumeelementscalledvoxels.Eachvoxelisassignedavaluewhichisdependentontheaverageamountofattenuation,HowisCTImagegenerated?,10,Theattenuationvaluesaretransferredtothecomputerwheretheyarecoded&usedtocreateasliceimage,HowisCTImagegenerated?,11,CTGenerations&Design,“Generation”isusedtolabelCTtube-detectordesigns,3rdGenerationDesignRotatingtube&detector,4thGenerationDesignFixedringdetector,12,Slip-ringTechnology,PoweristransmittedthroughparallelsetsofconductiveringsinsteadofelectricalcablesContinuousGantryRotationPrerequisiteforSpiralCT,NonSlip-ringScanner,Slip-ringScanner,13,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,14,WhatisSpiralScan?-just4“C”,Continuouslyrotatingtube/detectorsystemContinuouslygeneratingX-rayContinuouslytablefeedContinuouslydataacquisition,15,Reconstructionofarbitraryslices(eithercontiguousoroverlapping)withinthescannedvolumeDistancebetweentheslicesiscalledIncrement,A,B,VolumeData,Continuousdataacquisition,16,Increment,SliceThickness,Increment=SliceThicknessNoOverlapNoGaps,ContiguousImageReconstruction,17,Increment,Overlap,Slice,Thickness,OverlappingImageReconstruction,IncrementSliceThicknessGapsbetweenslicesImagesarefurtherapartLessimagescreated,ImageReconstructionwithGaps,Increment,SliceThickness,19,StandardCT/SliceImaging,DeepInspiration,ShallowInspiration,Misregistrationduetodifferentrespiratorylevelsbetweenslices,PartialVolumeEffect,Unabletoresconstructimagesatarbitraryposition,Sliceimagingisslow,20,Scanthewholeregionofinterestinonebreathhold,Reconstructionofoverlappingimageswithoutadditionaldose,Retrospectivereconstructionofslicesinarbitrarypositionwithinthescannedvolume,Nogapssinceradiationalwaystransmitsthewholevolume,SpiralCT/VolumeImaging,21,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,22,ScanParameters,X-rayTubeVoltage(kVp)X-rayTubeCurrent(mA)ScanTime(s)SlicethicknessorCollimation(mm),TableSpeed(mm/rot)orFeedper360rotationPitchInterpolationProcessIncrement(mm),23,TableSpeed&Pitch,TableSpeedisdefinedasdistancetraveledinmmper360rotation,Pitch=,TableFeedperrotationCollimation,24,10mmP1,10mmP2,30s,30s,MoreCoverageinthesametimewithextendedPitch!,Pitch2covers2xdistanceasPitch1,25,ScanRange=300mm,10mmP110mm/s,10mmP220mm/s,30s,15s,CoverthesamevolumeinshortertimewithextendedPitch,26,Toreduceartifactsduetotablemotionduringspiralscanning,weuseaspecialreconstructionprocesscalledINTERPOLATION,Interpolation,Convertsvolumedataintosliceimages,InterpolationAlgorithm,27,WideAlgorithm,SlimAlgorithm,2x360=720rawdata,2(180+52)=464rawdata,WidealgorithmproducesabroaderimagethicknessWidealgorithmusesmorerawdata=lessimagenoise,28,PITCH2,PITCH1,Pitch2scanningproducesabroaderimagethicknessPitch2scanningdoesnotincreaseimagenoise,30%increaseinimagethicknesswithPitch2,29,SliceSensitivityProfile(SSP),SSPdescribestheeffectiveslicethicknessofanimageandtowhatextentanatomywithinthatslicecontributetothesignal,SSP,RESOLUTION,Allpointswithintheslicecontributeequally&pointsoutsideoftheslicedonotcontributetotheimageatall.,Imagesignal,IdealSSP,Z-axis(mm),Collimation=widthofx-raybeam=sliceprofile,30,SliceProfile(SP),Effectiveslicethicknessofanimage,SliceProfileResolution,FactorsinfluencingSliceProfileCollimationPitchInterpolationalgorithm(360or180),31,FactorsinfluencingSSP,Collimatorwidthcollimation=SSPSpiralCTTablespeedorPitchInterpolationAlgorithm=mathematicalprocessrequiredtoreconstructaxialimagesfromthespiralvolumedataset,32,Pitch&SliceProfile,33,SlimvsWideSSPComparison,SliceProfileSlim%BroadenWide%BradenPitchOne5.0mm06.3mm26PitchTwo6.5mm3010.8mm116,34,WIDE720degreeMorephotons,SLIM464degreeLessphotons,SSPSpatialresolution,SSPSpatialresolution,Smootherimage,Noisierimage,35,Slim-Advantages,ImprovedZResolutionReducedpartialvolumeartifactsSlim+extendedPitchLongercoverageSamecoveragewithshorterscantimeorthinnerslicesLessradiationdose,36,Wide-Advantages,NoiseReductionSmootherimageUsefulforscanninghugepatientOnlyforscanningatPitchOne,37,SliceProfileComparison,38,Lesionsmallerthan1cm,SCANRANGE=150mm,10/10/10(15s),5/10/5(15s),SliceProfile=10mm,SliceProfile=6.5mm,OptimizingtheScanningParameters,39,SmallestPossibleEffectiveSliceThickness,ScanLength(mm),ScanDuration(s),TableSpeed(mm/s),SmallestCollimation(mm),ScanDuration,Dependsonthescanlength&patientsbreath-holdcompliance,TableSpeedPitchFactor,1Pitch2tocoverthewholevolumeinonebreath-hold,40,ComputedTomography,CTBasicsPrincipleofSpiralCTScanParameter&ImageQualityOptimizingInjectionProtocolsClinicalApplications,41,Peripheralveineg.antecubitalvein19-20gaugeneedleorIVcatheter,Volume,FlowRate,Concentration,InjectionProtocols,300mgI/mlnon-ioniccontrast,2-5ml/scardiacoutput,80-150mlpatientsweight®ionofinterest,Site,ScanDelay,Delaybetweeninjectioninitiation&thestartofthescansequence,42,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,43,50,100,150,200,250,Times,HU,OptimalWindow,Early,Time-densitycurveofthetargetregion,Late,ContrastBolusTiming,DeterminesoptimalscandelayforspiralCTAsequence,CONTRAST,NaCl,44,TestBolusProcedure,ImagingVolumeforspiralCTA,10-20mlofcontrastisinjectedatthechosenrateforspiral,Afteradelayof8-10s,low-dose,single-levelaxialimagesareacquiredevery2satthestartingpointoftheimagingvolume,Dynamicscansatthisposition,DynamicEvaluationtogenerateaTime-densitycurve,45,DynamicEvaluation,Time-densitycu