核医学影像中的数据处理.ppt
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1、核医学影像中的数据处理核医学影像中的数据处理Modern Nuclear Medical ImagingAcquireAcquireProcessProcessApplyApplyScanners Computers UsersOutline lData organizationlCorrection methodslRebinning lImage reconstructionlImage registration and fusionlDICOM and PACSOutline lData organizationlCorrection methodslRebinning lImage r
2、econstructionlImage registration and fusionlDICOM and PACSData organizationlList modelHistgramlSinogramlLinogramSinogramPETSinogram rlProjections and SinogramSinogramPETSinogramrlProjections and SinogramSinogramSPECT2D VS.3DlSepta between crystal ringslLower sensitivitylLower randomlLower scatterl2D
3、 reconstructionlNo septalHigher sensitivitylHigher randomlHigher scatterl3D reconstruction or hybrid reconstructionOutline lData organizationlCorrection methodslRebinning lImage reconstructionlImage registration and fusionlDICOM and PACSScatter CoincidenceTrues CoincidenceRandom CoincidenceTrue Coun
4、ts&NoiseNormalizationABCDAttenuationABCDScatterABCDNeed to correct the dataCorrection methodslrandoml“dead time”lnormalizationlscatterlattenuationldecaylArc correctionlDepth of interactionlMotion correctionlPartial volumelAxial of rotationlCamera head tiltRandomFinite time window withEnergy window C
5、oincidence timing windowActivity Random lTail fittinglsimplestlSmall changes in tail,great changes in estimatelEstimation from singles rateslMeasure the single count rate on each detector for a given time windowlSubtracting from the prompts between detector pairlSingles rate is much larger than that
6、 of coincidence eventslSingle rates change in the same way over timeDelayed coincidence channel estimationlOne channel is delayed before being sent to coincidence processinglSubtracted form prompt coincidenceslAdvantage lAccuratelSame dead time environment as prompt channellDisadvantage lIncreased s
7、ystem dead timelDoubling of the statistical noise due to randomDead time correctionlDecaying source experiment is performedDead time correction(con)lLook up tablelUniform sourcelKnown quantitylShort livedlLinear extrapolation from count rate for a given level of activityNormalization lCauses of sens
8、itivity variationslSumming of adjacent data elementslDetector efficiency variationslGeometric and solid angle effectslRotational samplinglTime window alignmentlStructural alignmentlseptaSumming of adjacent data elementsGeometric and solid angle effectsRotational samplinglLOR at the edge are sampled
9、less than LOR close to the centerCrystal interface factorsTime window alignment factorsNormalization methods(con)lDirect normalizationlSimplest approachlAdequate statistical qualitylVery uniform activity sourceslScatter in normalization should be substantially different from normal imagingNormalizat
10、ion methods(con)lComponent-based normalizationScatter correctionlLORs recorded outside object boundary can only be explained by scatterlThe scatter distribution is very broadlScattered coincidences fall within the photo-peak window mainly due to scattered once Scatter correctionlEnergy spectra distr
11、ibution of scattered 511KeV photons according to the number of times each photon scattersScatter correctionlEmpirical scatter correctionslFitting the scatter tailslDirect measurement techniquelEnergy window techniqueslDual energy window methodslMultiple energy window methodslConvolution and de-convo
12、lutionlSimulation-based scatter correctionlAnalytical simulationlMonte Carlo simulationFitting the scatter tailslSimplest approachlFit an analytical function to scatter tailslSecond order polynomial or 1D GaussianlCoincidences outside the object are entirely scatter eventslNot always well approximat
13、ed,particularly in thoraxDirect measurement techniquelOnly applicable to PET with retractable septalStepslMake a measurement of the same object with and without septalScaling septa extended projections for different efficiencylSubtract from projections of polar angle 0lEstimate the oblique scatter b
14、y interpolation of the direct plane scatterDual energy window methodsDual energy window methodsMultiple energy window methodsScatter CorrectionAnalytical simulationScatter CorrectionA AB BSingle Scatter-Model based correctionCalculate the contribution for an arbitrary scatter point using the Klein-N
15、ishina equationBeforeScattercorrectionAfterScattercorrectionAttenuation correctionlAttenuation in the body is equal to that of source lying along the same LORZaidi H,Hasegawa B.J Nucl Med 2003;44:291-315.SPECTPETAttenuation correction(con)lMeasured attenuation correctionlCoincidence transmission dat
16、alLong-lived positron emitterlNormally more than one rod source are usedlSinogram windowing is applied provide location of rodlImpractical in 3DlSingles transmission datalShielded point transmission sourcelSeparate blank scan is neededlSignificant scatter and broad beamMeasured attenuation correctio
17、nlCoincidence measurement using rod sourcelTransmission measurement using point sourceCT scanlAdvantage lHigh statistical qualitylHigh spatial resolutionlSignificant reduction in scan timelDisadvantagelFaster CT,slower PETlSmaller FOV of CTlDifficulty in registrationl values do not scale linearlyAtt
18、enuation correction for PETTypes of transmission imagesCoincident photon Ge-68/Ga-68(511 keV)high noise15-30 min scan timelow biaslow contrastSingle photon Cs-137(662 keV)lower noise5-10 min scan timesome biaslower contrastX-ray(30-140kVp)no noise1 min scan timepotential for biashigh contrastOther a
19、ttenuation correction methodslCalculated attenuationlRegular geometric outlinelConstant tissuelSegmented attenuationlSegment transmission image according to tissue typelAssigning known attenuation coefficientslForward projectionattenuation correctionAttenuation/Scatter correctionUniversity of Pennsy
20、lvania PET CenterNo AC or Scatter CorrAC and Scatter CorrPhilips AllegroArc correctionlDifferent sampling distance at different radial positionlEqual sampling distance is required in analytical methodlInterpolation methodlNearest interpolationlLinear interpolationlB-spline interpolation(negative val
21、ues!)DOIdepth of interactionDOIdepth of interaction(con)Dual LayerA Point Spread Function(PSF)describes the response of an imaging system to a point source or point object.A system that knows the response of a point source from everywhere in its field of view can use this information to recover the
22、original shape and form of imaged objects.PSFs are used in precision imaging instruments,such as microscopy,ophthalmology,and astronomy(e.g.the Hubble telescope)to make geometric corrections to the final image.Point Spread Function(PSF)Motion correctionlCardiac motion and respirationMotion correctio
23、n(con)lGated frameslList modelRespiratory motion is distributed throughout the whole bodylImpact is rarely on detection,but often affects quantitationStatic wholebodySingle respiratory phase(1 of 7,so noisier)1 cc lesion on CTWhole-body respiratory gated PET/CT:PatientsPartial volume effectlCharacte
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- 核医学 影像 中的 数据处理
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