fundamentals of image quality evaluation

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1、23/12/2010FundamentalsofimagequalityevaluationDavidPlattenNorthamptonGeneralHospitalImagequalitymeasures•Spatialresolution–Limitsasstem’sabilittodepictsmallobjectsLimitsasystem’sabilitytodepictsmallobjects•Contrastresolution–Thesmallestattenuationdifferencebetweentwoo

2、bjectswheretheyremaindistinguishable•Imagenoise–Limitsasystem’scontrastresolution123/12/2010Spatialresolution•Canbeassessedbyimaging……aseriesofbarpatterns•thenvisuallyassessingthelimitingvalue•ornumericallyassessingtheimagetogeneratepointsonthemodulationtransferfuncti

3、on(MTF)…ahigh-contrastedge,beadorwire•thenanalysetogenerateacompleteMTFSpatialresolution•Visualassessmentofabarpatternimage–Positionbarpatternasclosetodetectorsurfaceaspossible–Nofiltersinthebeam–LowkVifpossible–Visuallyygassesswhichisthelastvisiblegroupp–ForCT,ensure

4、thatthesamereconstructionalgorithmisusedeachtime–Onlyassessingresolutionatthelocationofthetestobject223/12/2010SpatialresolutionSpatialresolution•Analysisofabarpatternimage–Usetheimageacquiredforthepreviousslide–Numericallyassesstogeneratepointsonthemodulationtransfer

5、function–Droegg,eandMorin,MedPhyys9((5)):758-780–Onlyassessingresolutionatthelocationofthetestobject323/12/2010Spatialresolutionpv=meanROIpixelvaluesd=standarddeviationofROIpixelvaluesM0=[pv(bgd)+pv(signal)]/2N=[sd([sd(bgd)2+sd(+sd(signal)2]1/22sd(barpattern)−NMTF(f)=

6、π4M0DroegeandMorin,MedPhys9(5):758-780Spatialresolution0.0181.00.0160.0140.80.0120.60.010MTF0.008NMTF0.40.0060.0040.20.0020.0000.000.0.011.0.022.0.033.0.044.0.055.0.066.0.0-1Frequency(mm)423/12/2010Spatialresolution•Ahigh-contrastedge–SitableforflatSuitableforflat-pan

7、eldetectorspaneldetectors–Edgetestobjectplacedascloseaspossibletothedetector–Placetestobjectatasmallangle(1to5degrees)tothedetectorarray–AcquireimageAcquireimage–ApplySTPpixeltransformation–CalculateMTF–OnlyassessingresolutionatthelocationofthetestobjectSpatialresolut

8、ionStartoffwithanobjectthathasaverystraightedgeTakeanimageofitandtheresultisnotaperfectrepresentationoftheoriginal523/12/201