Imaging performance of scanning slot x-ray detectors for digital mammography

195 Pages·1997·6.9 MB·English

by  Jing, Zhenxue

IMAGINGPERFORMANCEOFSCANNINGSLOTX-RAYDETECTORSFOR
DIGITALMAMMOGRAPHY
By
ZHENXUEJING
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1997
DedicatedtoGuoying,mywife,andXiaoshan,my
forthehappinesstheybringtomylife
ACKNOWLEDGMENTS
Itismyprivilegetoacknowledgethehelpandguidancefrommanyindividuals
during my Ph.D. studies. I am indebted to my chairman, Dr. Walter Huda, forhis
invaluableadvice,encouragement,andpatience.Hisacademicsupervisionandcarefor
studentsaregreatlyappreciated. Iwishtothankmysupervisorycommitteemembers--
Drs.E.RaymondAndrew,JaniceC.Honeyman,ThomasH.Mareci,EdwardV.Staab,
andJamesS.Tulenkoforservingonthecommitteeandfortheirguidanceduringthe
course ofthis study. I would also like to thank Drs. Libby Brateman and Barbara
SteinbachforsupportingmyfellowshipapplicationtotheU.S.ArmyMedicalResearch
andDevelopmentCommand.
MyspecialthanksgotomycolleaguesatNanoptics,Inc.,Gainesville,Florida.I
amthankfultoDr.JamesK.Walkerforprovidingfinancialandacademicsupportwhich
guaranteesthesuccessfulcompletionofmydissertationwork.Iofferaspecialnoteof
thankstoDr.WonY.Choiforhisadviceandhelpduringmydoctoralstudies.Iwould
liketothankMs.JennyBrownforhercareforme,mywife,andmysonwhichmadeour
sociallifeveryenjoyable. Iamalsothankfultoseveralotherswhohaveassistedme
throughoutvariousstagesofthiswork.Thesepersonsinclude,amongmanyothers,Dr.
JacobTymiyanski,MikeSeuffert,MarkHertz,JamesMonroe,BruceY.Wang,andRaza
Hasan.
IwouldalsoliketoacknowledgehelpfromthedepartmentstaffintheNuclear
Engineering Sciences office (BarbaraandJoan) andtheRadiology office (Chris and
Darlene).
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This work has been supported by NASA and NIH under grants Nos.
lROlCA.65992-01, 1R41CA64988-01, and bythe U.S. Army Medical Researchand
Materiel Command(USAMRMC) intheformofapredoctoral fellowship grant(No.
DAMD17-94-J-4058). I am very grateful to these agencies for providing financial
assistancenecessarytocompletethiswork.
Iwouldliketothankmywife, Guoying, forherconstant encouragement and
patiencethroughoutmydoctoralstudies.Withoutherlovingsupport,thisworkwould
havebeenimpossible.Iamgreatlyblessedwiththebirthofourson,EdwardXiaoshan
Jing(bomonFebruary4,1996).
Andlastly,IamverythankfultoallofmyfamilyandfriendsbackhomeinChina
for giving me hope, encouragement, and happiness when I worked hard with my
education.
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TABLEOFCONTENTS
page
ACKNOWLEDGEMENTS
iii
LISTOFTABLES ix
LISTOFFIGURES xi
ABSTRACT xvii
CHAPTERS
INTRODUCTION
1 1
1.1.Background 1
1.1.1.BreastCancerScreening 1
1.1.2.Screen-FilmMammography 3
1.1.3.LimitationsofScreen-FilmMammography 4
1.2.DigitalMammography 8
1.2.1.DigitalMammographyandItsAdvantages 8
1.2.2.Cost-EffectivenessofDigitalMammography 10
1.3.LiteratureReview 12
1.3.1.CurrentApproachestoDigitalMammography 12
1.3.2.ScanningSlotDigitalMammographySystems 15
1.3.3.SpatialResolutioninDigitalMammography 19
1.3.4.DynamicRangeinDigitalMammography 22
1.3.5.X-raySpectraandX-rayTubeHeatingConsiderations 23
1.4.PurposeofStudy 24
1.4.1.PrimaryObjectives 24
1.4.2.ScattertoPrimaryRatios 26
1.4.3.Signal 27
1.4.4.Noise 27
2 SCANNINGSLOTX-RAYDETECTORSFORMAMMOGRAPHY 29
2.1.Introduction 29
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page
2.2.ScintillationScreens 30
2.2.1.MaterialsandStructures 30
2.2.2.X-rayConversion 32
2.2.3.ScintillationLightEmission 35
2.2.4.ScintillationLightCollection 37
2.3.SlotX-rayDetectors 41
2.3.1.DetectorStructures 41
2.3.2.FiberOpticImageGuide 41
2.3.3.CCDCameraandImageReadout 42
2.4.PrototypeImagingSystem 43
2.4.1.PrincipleStructure 43
2.4.2.Time-DelayedIntegrationModeofCCDOperation 43
2.4.3.SpatialResolutioninTDIModeOperation 46
2.4.4.CCDCameraNoise 47
2.4.5.DetectorNonuniformityCorrection 50
3 SCATTEREDRADIATIONINSCANNINGSLOTMAMMOGRAPHY 52
3.1.Introduction 52
3.1.1.SubjectContrastinMammography 52
3.1.2.TheEffectofScatteredRadiationonImageContrast 54
3.1.3.PurposeofThisStudy 56
3.2.MonteCarloMethod 57
3.2.1MonteCarloSimulation 57
3.2.2.SimulationModel 59
3.2.3.X-rayEnergyandBreastPhantoms 60
3.2.4.CalculationofScattertoPrimaryRatios 62
3.2.5.ValidationofMonteCarloCalculations 63
3.3.ScattertoPrimaryRatios 64
3.3.1.DependenceofS/PRatioonSlotDetectorWidth 64
3.3.2.DependenceofS/PRatioonLucitePhantomThickness 64
3.3.3.DependenceofS/PRatioonIncidentX-rayPhotonEnergy 66
3.3.4.S/PRatioProfileintheSlotDetectorPlane 67
3.4.PracticalConsiderationsofScatterinScanningSlotMammography 68
3.4.1.ScatterRejectionbyAirGapMethod 68
3.4.2.RelativeContributionsfromComptonandCoherentScatter 71
3.4.3.DependenceofS/PRatioonX-rayDetectionMaterials 73
3.4.4.TheEffectonPatientDosebytheUseofanAirGap 75
4 SIGNALTRANSFERINTHESLOTX-RAYDETECTORS 77
4.1.ScanningSlotX-rayDetectors 77
4.1.1.Introduction 77
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page
4.1.2.ScintillatingFiberScreenBasedSlotX-rayDetector 78
4.1.3.ACsI:TlScreenBasedSlotX-rayDetector 80
4.2.Methods 83
4.2.1.QuantumAccountingDiagram 83
4.2.2.ModulationTransferFunction 85
4.2.3.MonteCarloCalculation 86
4.2.4.ScintillationScreenOpticalMTF 88
4.3.SignalPropagationintheSlotX-rayDetectors 91
4.3.1.X-rayInteractionEfficiency 91
4.3.2.X-raytoLightConversionintheScintillatingFiberScreens 94
4.3.3.QuantumAccountingDiagramoftheSlotX-rayDetectors 98
4.3.4.MeasurementofSignalIntensityintheSlotX-rayDetectors 102
4.4.ModulationTransferFunctionoftheSlotX-rayDetectors 103
4.4.1.EnergyDepositionLineSpreadFunction 103
4.4.2.ScintillationScreenMTF 107
4.4.3.MTFoftheSlotX-rayDetectors 112
4.4.4.MeasurementofSpatialResolutionintheSlotX-rayDetectors 115
4.4.5.MeasurementofaPrototypeScintillatingFiberScreen
SpatialResolution 119
5 NOISEPROPAGATIONINTHESLOTX-RAYDETECTORS 122
5.1.DetectiveQuantumEfficiencyandNoisePropagationTheory 122
5.1.1.DetectiveQuantumEfficiency(DQE) 122
5.1.2.NoisePropagationintheMulti-stageImagingSystem 125
5.2.NoiseinCascadedSlotX-rayDetectors 128
5.2.1.IncidentX-rayFluence 128
5.2.2.ScreenModel 129
5.2.3.ImageGuidetoCCDCoupling 131
5.2.4.DetectorDQE(/) 132
5.3.ZeroSpatialFrequencyDetectiveQuantumEfficiency 135
5.3.1.ScintillationLightIntensityDistribution 135
5.3.2.ScreenandDetectorDQE(O) 140
5.3.3.DQE(O)andX-rayExposureandCCDElectronicNoise 144
5.3.4.ComparisonwithPublishedWorks 146
5.4.SpatialFrequencyDependentDetectiveQuantumEfficiency 147
5.4.1.X-rayExposure 147
5.4.2.CCDElectronicNoise 148
5.4.3.ImageGuideCouplingEfficiency 150
5.4.4.CCDQuantumEfficiency 152
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6 CONCLUSIONSANDFUTUREWORK 154
6.1.ConclusionsBasedonResultsfromScatterStudy 154
6.2.ConclusionsBasedonResultsfromSignalPropagationStudy 157
6.3.ConclusionsBasedonResultsfromNoisePropagationStudy 161
6.4.FutureWork 163
REFERENCES 165
BIOGRAPHICALSKETCH 175
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0
LISTOFTABLES
Table page
2-1 Refractiveindexofselectedpolymersandscintillationlightcollection
efficiencyofthecorrespondingfibers 39
2-2 SpecificationsoftheCCDfromEastmanKodakCompany.
ModelKAF-0360 42
3-1 S/Pvaluesvs.circularx-rayfielddiameter(d)fortwoLucite
phantomthicknesses(T) 63
3-2 S/Pvaluesasafunctionofslotdetectorwidth(W)for
a4cmthickLucitephantom 64
3-3 Scatterreductionfactor,/,vs.Lucitephantomthickness(T)
fortwoairgapsat20keVx-rayenergy 70
4-1 Energyconversionefficiency(s),lightloss(I)duetoreabsorption
ofthescintillatingdye,andfraction(q)ofthescintillationlightlost
duetoquenchingforthefiveplasticscintillatingfiberscreens
investigatedinthisstudy 79
4-2 Numberofquantaineachstageoftheslotx-raydetectorsusing
thethreetypesofSFSsof20mmthicknessat20keVx-rayenergy 98
4-3 NumberofQuantaineachstageoftheCsLTlscreenbasedslotx-raydetector....101
4-4 MTFsFsC/)valuesforthreetypesofSFSsat20keVincidentx-rayenergy 11
4-5 Limitingspatialresolution,/nax,asafunctionofscanningspeedfor
theCsLTlscreenbasedslotx-raydetector 117
4-6 Limitingspatialresolution,/max,asafunctionofscanningspeedfor
theGd202S:Tbphosphorscreenbasedslotx-raydetector 118
ix
Table page
5-1 ComparisonofSwankfactors,As,calculatedfromthisstudywith
theworkdonebySwank(1973) 146
X