CT成像原理介绍(英文版)ppt课件

CT成像原理介紹 ComputedTomography CTBasicsPrincipleofSpiralCTScanParameter ImageQualityOptimizingInjectionProtocolsClinicalApplications X RayDiscovery X raywasdiscoveredbyaGermanscientistRoentgen100yearsago Thismadepeopleforthefirsttimebeabletoviewtheanatomystructureofhumanbodywithoutoperation Butit ssuperimposedAndwecouldn tviewsofttissue MynameisGodfreyHounsfieldIworkfortheCentralResearchLabs ofEMI LtdinEnglandIdevelopedthethefirstclinicallyusefulCTscannerin1971 HistoryofComputedTomography Early1970s 1963 AlanCormackdevelopedamathematicalmethodofreconstructingimagesfromx rayprojections Forthefirsttimewecouldview CTBroketheBarrier Tomographicor Slice anatomy Densitydifference Butit stimeconsumingAndresolutionneedstobeimproved ConceptofX rayAttenuation AnX raybeampassingthroughthebodyisattenuated losesitsenergy by AbsorptionScattering IncidentX ray Transmittedray SCATTEREDX RAYS BODYTISSUE Absorptionbythetissueisproportionaltothedensity Lessdensetissue Moredensetissue MOREATTENUATION LESSATTENUATION HowdoesCTWork X raygoesthroughcollimatorthereforepenetrateonlyanaxiallayeroftheobject called slice HowdoesCTWork PatientisplacedinthecenterofthemeasurementfieldX rayispassedthroughthepatient sslicefrommanydirectionalonga360 pathThetransmittedbeamsarecapturedbythedetectorswhichdigitizesthesesignalsThesedigitizedsignalscalledrawdataaresenttoacomputerwhichcreatetheCTimage HowdoesCTWork Theobjectsliceisdividedintosmallvolumeelementscalledvoxels Eachvoxelisassignedavaluewhichisdependentontheaverageamountofattenuation HowisCTImagegenerated Theattenuationvaluesaretransferredtothecomputerwheretheyarecoded usedtocreateasliceimage HowisCTImagegenerated CTGenerations Design Generation isusedtolabelCTtube detectordesigns 3rdGenerationDesignRotatingtube detector 4thGenerationDesignFixedringdetector Slip ringTechnology Poweristransmittedthroughparallelsetsofconductiveringsinsteadofelectricalcables ContinuousGantryRotation PrerequisiteforSpiralCT 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 Increment SliceThicknessOverlapofslicesCloserimageintervalMoreimagescreated Increment SliceThicknessGapsbetweenslicesImagesarefurtherapartLessimagescreated 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 TableSpeedisdefinedasdistancetraveledinmmper360 rotation 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 720 rawdata 2 180 52 464 rawdata 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 360 or180 FactorsinfluencingSSP Collimatorwidthcollimation SSPSpiralCTTablespeedorPitchInterpolationAlgorithm mathematicalprocessrequiredtoreconstructaxialimagesfromthespiralvolumedataset Pitch SliceProfile SlimvsWide SSPComparison SliceProfileSlim BroadenWide BradenPitchOne5 0mm06 3mm26PitchTwo6 5mm3010 8mm116 WIDE720degreeMorephotons SLIM464degreeLessphotons SSPSpatialresolution SSPSpatialresolution Smootherimage Noisierimage Slim Advantages ImprovedZ ResolutionReducedpartialvolumeartifactsSlim 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 patient sbreath holdcompliance TableSpeedPitchFactor 1 Pitch 2 tocoverthewholevolumeinonebreath hold ComputedTomography CTBasicsPrincipleofSpiralCTScanParameter ImageQualityOptimizingInjectionProtocolsClinicalApplications Peripheralveineg antecubitalvein19 20gaugeneedleorIVcatheter Volume FlowRate Concentration InjectionProtocols 300mgI mlnon ioniccontrast 2 5ml s cardiacoutput 80 150ml patients weight regionofinterest Site ScanDelay Delaybetweeninjectioninitiation thestartofthescansequence TailoringScan InjectionProtocols InjectionDurationmustbeequaltoorgreaterthanScanTime 50 100 150 200 250 Time s HU CONTRAST 50 100 150 200 250 Time s HU CONTRAST NaCl BolusDuration scantimeInsufficient inhomogeneousopacification BolusDuration scantimeUniform maximumopacification EnhancementCurveoftheTargetRegion 50 100 150 200 250 Time s HU OptimalWindow Early Time densitycurveofthetargetregion Late ContrastBolusTiming DeterminesoptimalscandelayforspiralCTAsequence CONTRAST NaCl TestBolusProcedure ImagingVolumeforspiralCTA 10 20mlofcontrastisinjectedatthechosenrateforspiral Afteradelayof8 10s low dose single levelaxialimagesareacquiredevery2satthestartingpointoftheimagingvolume Dynamicscansatthisposition DynamicEvaluationtogenerateaTime densitycurve DynamicEvaluation Time densitycurveScanDelay PeakE