CT的質(zhì)量控制課件

QualityControlforComputed

Tomography(CT),

CT,的質(zhì)量控制

MelissaC.Martin,M.S.,DABRCertifiedMedicalPhysicistFellow-ACR,ACMP,AAPMNIM-ChinaMeetingJune13,2005QualityControlforComputed

QualificationsandProfessionalActivities

專業(yè)資質(zhì)和業(yè)務(wù)活動AmericanCollegeofRadiology美國放射學會 -CommissiononMedicalPhysics醫(yī)學物理學委員會 -ChairofGovernmentRelationsCommittee政府關(guān)系委員會主席 -MammographyAccreditationCommittee乳腺X線照相術(shù)認證委員會 -ImageQualityCommitteeforDigitalImaging數(shù)字影像質(zhì)量委員會AmericanAssociationofPhysicistsinMedicine(AAPM)美國醫(yī)學物理學家協(xié)會 -Liaison(Advisor)totheConferenceofRadiationControlProgramDirectors輻射控制計劃理事會大會顧問QualificationsandProfessionaCTDoseandImageQuality

CT輻射劑量和影像質(zhì)量QualityControlandQualityAssuranceProceduresandIssues質(zhì)量控制和質(zhì)量保證步驟CTDoseandImageQuality

CT輻射CTandMRIimagingmodalitieswerenamedasthemostimportantmedicaladvancesinthelasthalfofthe20thcenturyCT和MRI被認為是人類二十世紀下半葉最重要的進展CTandMRIimagingmodalitiesDevelopmentsinCTTechnology

CT技術(shù)的發(fā)展EarlyCTdetectorsandscanner早期的CT檢測和掃描裝置ModernMulti-SliceCTScanner現(xiàn)代多層CT掃描儀DevelopmentsinCTTechnologyEEarlyCTImage(Siemens)早期的CT影像EarlyCTImage(Siemens)Multi-SliceCTImages(2004)多層CT影像Multi-SliceCTImages(2004)QualityAssurance

質(zhì)量保證Thereareavarietyofartifactsthancanoccurbecauseofpooradjustmentofthescanner

由于掃描儀調(diào)節(jié)不到位，產(chǎn)生很多干擾偽影Lossofresolution

分辨率下降A(chǔ)ccuracyofCTnumbers

CT值的精度TableLocation

掃描床的定位CTisahighdoseprocedure

CT診斷是一個高劑量輻射的過程 -Itisimportanttoknowthedoseforvariousstudiesandtoselectappropriatedoseforoptimalclinicalperformance

重要的是了解各種研究所需的劑量，從而選擇適當?shù)牧恳垣@得最優(yōu)的臨床表現(xiàn)QualityAssurance

質(zhì)量保證TherearClinicalTechnique

臨床技術(shù)Oncethebasicdoseperformanceofthescannerisdetermined,thephysicistshouldworkwithphysiciancolleaguestooptimizeimage-qualityanddose

一旦確定了掃描儀的工作劑量，物理學家就要與臨床醫(yī)師合作優(yōu)化影像質(zhì)量Eachsiteshouldhavetechniquestailoredtothelocalneeds

每一個地區(qū)應(yīng)當使用滿足當?shù)匦枰募夹g(shù)Manufacturersuppliedtechniquesmaynotbeoptimum

制造商提供的技術(shù)并不一定是最適宜的ClinicalTechnique

臨床技術(shù)OncethClinicalTechnique

臨床技術(shù)Techniqueshouldbeadjustedsothatsmallpatientshavereduceddoseandlargepatientshaveincreaseddose

應(yīng)作適當?shù)恼{(diào)整，根據(jù)病人的實際情況增減劑量Thereconstructionfiltershouldbeselectedtotradenoisevsresolution

應(yīng)對重建濾波器進行選擇以提高分辨率、減少噪聲kV,pitchandslicethicknessshouldbeselectedtooptimizedose-imagequality

應(yīng)對kV值、螺距和層厚進行選擇以優(yōu)化劑量--影像關(guān)系ClinicalTechnique

臨床技術(shù)TechniqImageUniformity

影像均一性CTusesmanydetectors

CT使用很多檢測器Thedetectorsmaynotbecompletelyuniform

檢測器并不一定完全一致Theymaydrift

它們可能漂移Qualitycontrolisnecessarytoinsureuniformity

對于均一性而言，質(zhì)控是必需的ImageUniformity

影像均一性CTusesHounsfieldNumber

Hounsfield值A(chǔ)verageattenuationvalueforVoxel像素的平均衰減值TissueDensityX-rayEnergy組織密度X線能量utissue-uwuwCTnumber=1000HounsfieldNumber

Hounsfield值A(chǔ)UniformityChecked

均一性檢測ScanningAir掃描空氣“AirCals”空氣校準ScanningWater掃描水AccuracyofHounsfieldNumbersHounsfield值精度Uniformity均一性Noise噪聲AbsenceofArtifacts干擾偽影的消失UniformityChecked

均一性檢測ScanniPhantoms

模體ScanningWaterRequires需要掃描水Waterfilledphantom充滿水的模體Carefullymade“solidwater”特制的“固體水”Solidwaterhasthesamedensityandatomicnumberaswater固體水具有與水相同的密度和原子數(shù)Phantoms

模體ScanningWaterRequPhantoms

模體Phantomssuppliedbyscannermanufacturer

模體由掃描儀制造商提供Oftendesignedtoworkwithscannerspecificsoftware

通常是被設(shè)計用來與掃描儀軟件配套的Softwaremaycheckandadjustthescanner

軟件可以用來檢查和調(diào)整掃描儀Somemanufacturersusetighterspecificationsthanothers

一些制造商使用比較苛刻的技術(shù)指標Phantoms

模體PhantomssuppliedbCT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件Standards

標準HounsfieldvaluesHounsfield值Dependonscanner取決于掃描儀Shouldbenomorethan+/-7應(yīng)在+/-7之內(nèi)Uniformitydependsonscanner均一性取決于掃描儀Noisedependsontechniqueusedforscan噪聲取決于所使用的掃描技術(shù)Datashouldbechartedsotrendscanbeseen應(yīng)將有關(guān)數(shù)據(jù)作圖以觀察趨勢變化Standards

標準HounsfieldvaluesCT的質(zhì)量控制課件CTNumberAccuracy

CT值精度Checkaccuracyandconstancyofknownmaterials

檢查已知物質(zhì)的精度和穩(wěn)定性CTNumberAccuracy

CT值精度CheckCTNumbers

CT值A(chǔ)ir空氣

-1000 -970Polyethylene聚乙烯

-107 -87Water水

-7 -7Acrylic 丙烯酸

110 130Youneedtoverifywhichmaterialisinthephantom.Ifindoubt,checkwiththemanufacturer.需確認模體中是何種物質(zhì)，如有疑問，與制造商溝通。CTNumbers

CT值A(chǔ)ir空氣 -1000 -CT的質(zhì)量控制課件Resolution

分辨率ResolutionTestObject受試目標分辨率Resolution

分辨率ResolutionTestCT的質(zhì)量控制課件CommercialPhantoms

商業(yè)模體Varietyofphantomsavailable可選的模體很多AccreditationprogramintheU.S.requiresuseofphantomdesignedbyAmericanCollegeofRadiology(ACR)whichmeasuresmorethanQCPhantomsfrommanufacturers

在美國，認證過程中需使用放射協(xié)會設(shè)計的模體，而不僅僅是制造商提供的質(zhì)控模體 -Costly昂貴 -Doesn’tworkwithmanufacturer‘ssoftware不能與制造商提供的軟件一起使用 -Requiresannualphysicistevaluation每年需要評估CommercialPhantoms

商業(yè)模體VarietCT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件MonitorDisplay&FilmPrinting

監(jiān)視器顯示和底片打印Monitorshouldbeadjustedtohaveapropergrayscale

監(jiān)視器應(yīng)進行調(diào)節(jié)，以便獲得適當?shù)幕叶萈rintedfilmsshouldmatchmonitordisplay

底片的打印應(yīng)與監(jiān)視器顯示狀態(tài)相匹配PrintersandmonitorsmustfunctioninDICOMformat

打印機和監(jiān)視器應(yīng)在DICOM格式狀態(tài)下工作SMPTETestPatternusedforimagequalityevaluationofbothmonitorsandprinters

對于打印機和監(jiān)視器，應(yīng)用SMPTE圖形進行影像質(zhì)量的監(jiān)測MonitorDisplay&FilmPrintinSMPTETestPatternSMPTETestPatternAccuracyofTableLocation

掃描床的定位精度AccuracyofPositioningLightsandTableMotionshouldbewithin+2mm

定位光與掃描床位移之間的精度應(yīng)在+2mm之內(nèi)Returnoftabletothesamelocationisespeciallyimportantforinterventionalstudies

掃描床的歸位對于干涉分析特別重要AccuracyofTableLocation

掃描床ProtocolforTableLocalization

掃描床定位步驟

Setslicewidthtothinnestavailable

將層厚設(shè)至最小值Positionradio-opaquewireontableandalignwithpositioninglights

將線定位于掃描床并與定位光對齊Scan–wireshouldappearinimage

掃描—線應(yīng)出現(xiàn)在影像中Movetableouttoextremeandrepositiontosamelocationusingnumericalindicators

將掃描床移出頂端，使用數(shù)字指示重新將它定位Scan–wireshouldappearinimage

掃描—線應(yīng)出現(xiàn)在影像中ProtocolforTableLocalizatioFrequencyofTesting

測試頻度Testfrequencyisnotaswelldefinedasforsomeotherimagingmethods

測試頻度與其它的影像測試方法定義不同Physicistshoulddeterminetestfrequencybasedon

其定義基于Manufacturersrecommendations制造商的建議Experiencewithscanner對掃描儀的工作經(jīng)驗FrequencyofTesting

測試頻度TestFrequencyTestingRecommendations

測試頻度建議DoseEvaluation劑量評估

Annually每年Followingmajorservice大修后ClinicalTechniqueEvaluation臨床技術(shù)評估Annually

每年Whenanewtechniqueisdeveloped開發(fā)新技術(shù)時WaterEvaluation水測試Weekly每周FrequencyTestingRecommendatiFrequencyTestingRecommendations

測試頻度建議Monitor&FilmPrinterEvaluation監(jiān)視器和打印機評估Monthly每月TableMotionandAlignmentLights床位移和光定位Quarterly

每季W(wǎng)eeklyifusedfortherapyplanning對于治療方案，可每周進行FullPhysicsEvaluation全部評估Annually每年Followingmajorservice大修后FrequencyTestingRecommendatiEssentialQCActivities

基本質(zhì)控Determinedosesfromscanner確定掃描劑量Workingwithphysiciancolleaguesdetermineappropriateimagingprotocols與臨床人員協(xié)調(diào)確定適當?shù)墓ぷ鞣桨窱nsurethatwaterhasaappropriateCTnumber

確定水測試時獲得適當?shù)腃T值

Accurate精度Noartifacts無偽影Uniform均一Appropriatenoise噪聲適當EssentialQCActivities

基本質(zhì)控DeEssentialQCActivities

基本質(zhì)控Insurethatthemonitorsandfilmprintersworkcorrectly確認監(jiān)視器和底片打印機工作正常Insurethatpositioninglightsandtablemotionarecorrect確認定位光和掃描床定位正確Determinedosesfromscanner確定掃描劑量EssentialQCActivities

基本質(zhì)控InCTDoseFundamentals

基本原則CTDoseTerminology

術(shù)語CTDoseVariations–Equipment

劑量變化—設(shè)備CTDoseVariations–Exams

劑量變化—測試CTDoseOptimization

劑量優(yōu)化CTDoseEvaluationCT計量評估CTDoseFundamentals基本原則CTDXZYCTCoordinatesCT坐標XZYCTCoordinatesCT坐標IdealWorld….

理想狀態(tài)…Radiationdeliveredonlytotheimagedvolume

輻射僅涵蓋成像部分-5mm0+5mmPeakdose=“dose”IdealWorld….

理想狀態(tài)…RadiationRealWorld….

現(xiàn)實情況…Radiationdistribution

crossestheimagedvolume

輻射跨越成像區(qū)域-5mm0+5mmPeakdose“Tails”ofdosedistribution

劑量分布尾跡RealWorld….

現(xiàn)實情況…RadiationdComputedTomographyDoseIndex

(CTDI)

CT劑量指數(shù)（CTDI）IntegralunderONEradiationdoseprofile

在單一劑量曲線下積分Doseprofilehasverylong“tails”

劑量曲線有很長的尾跡FDAusesfiniteintegrationlimits(±7T)

FDA使用定積分極限（±7T）TypicallymeasuredwithTLD(laborious)

典型測量使用TLDUnderestimatestaildoseforslices<7mm

低估了尾跡劑量，層厚在7mm之內(nèi)Ionchambermethodintegratesover100mm

電離室法積分100mmCTDI100

CTDI100singleconvenientmeasurement

單一實用的測試ComputedTomographyDoseIndexCTDI=Integralundertheradiationdoseprofilealongthez-axisfromasingleaxialscanofwidthnT.CTDI=沿Z軸的輻射劑量曲線積分，寬度為nT的單一軸向掃描nT“nominalbeamwidth”=“totalnominalscanwidth”Zradiationdoseprofile

輻射劑量曲線CTDI=IntegralunderthenTZraCTDI100MSADCTDIwCTDIvolDLPEffectiveDoseCTDosimetryCT劑量CTDI100CTDIwCTDIvolDLPEffectiv100mmIonizationChamber

100mm電離室CTDImeasurementsareusuallymadeusinga100mmionizationchamber

CTDI測量通常使用100mm電離室進行ThereforetheCTDIisdefinedforusewiththischamber

因此，這一電離室被確定為CTDI測試的使用工具

100mmIonizationChamber

100CTDImeasurements

CTDI測量Inphantoms

在模體中Polymethylmethacrylate(acrylic)

丙烯酸32cmdiameter,?16cmlength(body)

頭部模體16cmdiameter,?14cmlength(head)

體部模體Atleastfive1cmholesforexposuremeasurementsthroughoutFOV

至少五個1cm測試空，暴露于全部視場中Inair

在空氣中atisocenter(centerofrotation)

等量點CTDImeasurements

CTDI測量InphaCTDIPhantomsCTDI模體CTDIPhantomsCTDI模體TypicalFOVdosedistributions(%)

典型視場劑量分布(%)10010010010050Body

32cm100100100100100Head

16cmCTDIW=83CTDIW=100TypicalFOVdosedistributionsCTDIW

CTDIWWeightedaverageofcenterandperipherydoses中心和外圍劑量的加權(quán)平均

=2/3CTDI100(edge) +1/3CTDI100

(center)CTDIWCTDIWWeightedaverageRealWorld….

現(xiàn)實情況…Radiationdistribution

crossestheimagedvolume

輻射跨越成像區(qū)域-5mm0+5mmPeakdose“Tails”ofdosedistribution

劑量分布尾跡RealWorld….

現(xiàn)實情況…RadiationdRealWorld….

現(xiàn)實情況…Radiationdistribution

crossestheimagedvolume

輻射跨越成像區(qū)域-5mm0+5mmRealWorld….

現(xiàn)實情況…RadiationdMSADMSADMultipleScanAverageDose

多掃描平均計量MSADistheaveragedoseoverthe

centralscanofamultiplescanexam

MSAD是多掃描檢測時中心掃描的平均劑量Typically2-4timeshigherthanpeakdoseslice

典型情況為層峰劑量的2-4倍

DependentonpositionintheFieldofView(FOV)

取決于在視場中的位置Overestimatespatientdoseatbeginning&endofscanvolume

高估了病人在掃描開始和結(jié)束時的劑量MeasureddirectlywithTLD&multiplescans

直接進行TLD和多掃描MultipleScanAverageDose

多掃描Whenthescansareseparatedbythetotalnominalscanthickness(I=nT)andALLdoseunderthetailsismeasured當掃描被總標稱掃描厚度分割以及所有尾跡下的劑量均被測量時MSAD=CTDIWhenI1nTMSAD=nT?CTDIIWhenthescansareseparatedbVolumeCTDIw(CTDIvol)

體積（空間）CTDIw(CTDIvol)NewtermrecentlyagreeduponbytheIEC

IEC最新使用的術(shù)語CTDI100integratesover100mm

CTDI100積分100mmCTDIwaveragesoverx(L/R)andy(A/P)

CTDIw計算x和y軸的平均CTDIvolaveragesoverx,yandz(C/C)

CTDIvol計算x，y和z軸的平均CTDIvolestimatestheMSADwandisoperationallyeasiertomeasureandcompute

CTDIvol估算MSADw而且使得測試和運算更簡便

VolumeCTDIw(CTDIvol)

體積（空間）WhenI=N·TCTDIvol=CTDIwWhenI1

N·TCTDIvol=N·T?CTDIwIWhenI=N·TPITCH=tableindexperrotation total

nominalscanwidthCTDIvol=1?CTDIwpitchestimateofaveragepatientdose平均病人劑量的估算值measurementfromoneaxialscan來自軸向掃描的測量值PITCH=tableindexperrotatiWhenapatientasks…

“Whatismydose”

theytypicallymean

“Whatismyrisk”

當病人說“我的劑量是多少？”時，

其實他們在問“我承受了多大風險？”Whenapatientasks…

“WhatisBiologicalinjuryincludes

生物傷害包括

deterministiceffects(skinburns,cataractformation)

確定效應(yīng)（皮膚灼傷，白內(nèi)障形成）stochasticeffects(cancerinduction,geneticeffects)

隨機效應(yīng)（癌癥的誘發(fā)，遺傳效應(yīng)）Riskestimatesarederivedfrom

風險評估來源于atomicbombsurvivordata,otherexposedgroups

原子彈生存者的數(shù)據(jù)，其它暴露人群Riskestimatesaredependenton

風險評估有賴于organdose

and

type,age,gender,reproductivestatus

器官劑量和類型，年齡，性別，生殖狀態(tài)organdosesdependonpatientsize

器官劑量有賴于病人的身高與體重RiskTBiologicalInjury風險=>生物傷害

Biologicalinjuryincludes生物What’sthedosefromanabdominalCTscan?

腹部CT掃描的劑量？RadiationAbsorbedDose(rad)Energy(100ergs)Mass(1gram)=What’sthedosefromanabdomiWhat’sthedosefromanabdominalCTscan?

腹部CT掃描的劑量？Intuitively,weunderstandthatthebiologicriskfrom20CTslicesisgreaterthanfrom10CTslices.

直覺上，我們認為20層CT掃描的危害大于10層掃描Iftheaveragedoseis2radfor10slices,

whatisthedosefor20slices?

如果10層CT掃描的劑量是2rad，20層的劑量是多少哪？What’sthedosefromanabdomiMSADw=2radten1-cmslicesMSADw

STILL=2radtwenty1-cmslicesSohowdowerepresentthegreaterbiologicrisk?因此，我們?nèi)绾蚊枋鲚^嚴重的生物風險哪？MSADw=2radMSADwSTILL=2rIntegraldose

累計計量Averagedose

?#slices=integraldose

平均計量乘以層數(shù)等于累計計量But,doseandintegraldosehavesameunits

(leadstoconfusion)andisnotspecificenough(doesn’treflectthedifferencebetween1or10mmslices)

但是，劑量和累計劑量具有相同的單位，而且并不明確Betterconcept….

更好的概念…

Integraldose

累計計量AveragedoseDoseLengthProduct(DLP)

劑量長度積Representsintegrateddoseintermsof

totalscanlength(#slices?slicewidth)

代表了總掃描路徑中的累計劑量（層數(shù)乘以層厚）Relatedtoenergyimpartedbutmore

intuitivethanusingenergyunits(Joules)

涉及應(yīng)用的能量，但與使用能量單位相比更直觀RequiredinEurope,migratingtoUS

歐洲要求使用，后被美國采用DLP=CTDIvol(mGy)?scanlength

(cm)DoseLengthProduct(DLP)

劑量長度So,DLPrepresentthegreaterbiologicrisk!所以，DLP代表了更高的生物風險！DLP=20rad?cmDLP=40rad?cmCTDIvol=2radten1-cmslicesCTDIvol

STILL=2radtwenty1-cmslicesSo,DLPrepresentthegreaterSIunits(1rad=10mGy)

國際單位(1rad=10mGy)DLP:20mGy?20cm=400mGy?cmDLPgivesanindicationoftheoverall“risk”DLP表明了總的風險DLPcanfrom

scanlengthor

CTDI(primarilymAs,kVp,detectormode)

CTDIvol(scanoverlaporgap,e.g.pitch)

Needtopayattentiontoallthree!

需特別注意這三個值（scanlength，CTDI和CTDIvol

）！SIunits(1rad=10mGy)

國際單位What’sthedose(risk)?

劑量（風險）是多少？Radiationdetrimentbetterexpressedby

EffectiveDose(E

輻射損害的較好表達為有效劑量asingledoseparameterwhichreflectstheriskofanon-uniformexposureintermsofawhole-bodyexposure

就整個軀體的而言，單個劑量參數(shù)反映了非均勻暴露的風險PublishedvaluesofeffectivedoseperDLPprovidesaquickestimateofeffectivedose

已出版的每DLP的有效劑量值提供了一個快速估算途徑What’sthedose(risk)?

劑量（風險）ICRP60WeightingValues

國際輻射防護委員會的60加權(quán)值Gonads 0.20RBM,colon,lung,stomach 0.12Bladder,breast,liver 0.05Esophagus,thyroid 0.05Skin,bonesurface 0.01Remainder 0.05

1.00ICRP60WeightingValues

國際輻射防Typicaleffectivedosevalues

典型的有效劑量

HeadCT

頭CT 1-2mSv(100-200mrem)ChestCT胸CT 5-7mSv(500-700mrem)AbdomenCT腹部CT 5-7mSv(500-700mrem)PelvisCT骨盆CT

3-4mSv(300-400mrem)Abdomen&pelvisCT 8-11mSv(800-1100mrem)

腹部和骨盆CTAverageU.S.backgroundradiation平均本底輻射

?3.6mSv(360mrem)Typicaleffectivedosevalues

Effectivedosevalues(cont.)

典型的有效劑量Stereochestx-ray 0.1mSv(10mrem)立體胸部X線LowdosechestCT 0.7mSv(70mrem)低劑量胸部CTMammogram 1.8mSv(180mrem)乳腺CTC(5mm) 5.5mSv(550mrem)CTC(5mm)DoublecontrastBE 7.5mSv(750mrem)增強對比BE

CTC(2.5mm) 9.8mSv(980mrem)CTC(2.5mm)CTliverperfusion 15mSv(1500mrem)CT肝灌注Effectivedosevalues(cont.)WhyisMulti-SliceCT

RadiationDoseofInterest?

多層CT輻射劑量的意義何在？ToevaluatedifferentMSCTsystems

評估不同的CT系統(tǒng)TotriageapplicationsbetweenMSandSSCT

在多層CT與單層CT之間進行應(yīng)用比較TodesignandoptimizeMSCTProtocols

設(shè)計和優(yōu)化多層CT應(yīng)用方案Tradeoff:Thinnerslicesvs.radiationdose

權(quán)衡：薄層vs.劑量IncreaseduseofCTwarrantsincreasedattentiontoradiationdose

良好的CT應(yīng)用需要提升對輻射劑量的關(guān)注WhyisMulti-SliceCT

RadiatiWhyisMultiSlicedosedependenton

totalslicewidth(detectorconfiguration)?

為何多層CT的劑量取決于檢測器配置結(jié)構(gòu)？Theradiationdoseprofilesarelargerthanactivedetectorwidth

輻射劑量分布大于檢測器寬度RequiredinMultiSlicegeometrytokeepthepenumbraoffoftheactivedetectors

就幾何形狀而言，半影區(qū)要避開檢測器Sizeofpenumbralregionrelativelyconstant

半影區(qū)的尺寸要相對恒定Differentpercentage“inefficiency”fordifferenttotalscanwidth

對不同的掃描厚度具有不同的無效百分比WhyisMultiSlicedosedependeGoodimaging,goodphysics...

好的成像，好的物理特性…

UseCTDI,CTDIvolandDLPtohelpoptimizeprocedures(ALARA)

運用CTDI，CTDIvol和DLP幫助優(yōu)化操作程序lowdose(increasedimagenoise)doesnotmeanpoorimagequality

低劑量并不意味著損失影像質(zhì)量noiselevelshouldbeappropriateforthespecificdiagnostictask-notjusttoget“pretty”pictures

對于特殊的診斷任務(wù)，噪聲應(yīng)控制在適當?shù)乃健恢皇菫榈玫胶玫漠嬅鎛arrowslicewidths(narrowbeamwidth)shouldbeappropriateforthespecificdiagnostictask

對于某些診斷，縮窄層厚是必要的Goodimaging,goodphysics...DoseConclusions

結(jié)論MultiSlice(MS)systemshavesimilardosecharacteristics

多層CT具有相同的劑量MSdoseisprimarilydeterminedbytheprospectivechoiceofdetectorconfiguration

其劑量主要取決于檢測器配置結(jié)構(gòu)的選擇dosevariationsamongdetectorconfigurationsweregreaterthanthevariationsamongmanufacturers

劑量變化更多的來源于檢測器而不是制造商MSCTprotocolsshouldbecarefullyoptimized

多層CT應(yīng)用方案應(yīng)進行仔細的優(yōu)化Thinnerslicesrequirenarrowerbeamcollimation,whichcurrentlyleadstohigherdoses

較薄的層厚需要窄光束進行瞄準，這就加大了劑量ThinnerslicesalsorequiremAstomatchnoise

就噪聲而言，較薄的層厚也要求mAs值增高

DoseConclusions

結(jié)論MultiSliceSummary

總述“What’sthedose?”isnotasimplequestion

劑量不是一個簡單問題Know,understand,&optimize

知曉，理解和優(yōu)化

CTDImax

,CTDIvol,DLP,andEReferencedoseshadpositiveeffectinUK,usedaspartoftheACRaccreditationprocessintheUS

在英國，參考劑量具有積極的效果；在美國，它被應(yīng)用于認證過程Useeffectivedosetoassessrelativerisk

應(yīng)用有效劑量評估風險Summary

總述“What’sthedose?”iSummary

總述CT:largepercentageofthemedicalcollectivedosetopopulation

CT:對人群使用醫(yī)療檢查劑量的高百分比Prudentresponse:ApplyALARAprinciples

審慎響應(yīng)：使用ALARA原則CTAutomaticExposureControl-alongoverdueproductisnowavailableonnewscanners-makesdosecalculationsmoredifficult.CTdoseworthyofcloserattention

CT自動曝光控制—一個姍姍來遲的、應(yīng)用于新掃描儀的產(chǎn)品—使得劑量計算更困難。CT計量需要嚴密關(guān)注。Summary

總述CT:largepercentageQualityControlforComputed

Tomography(CT),

CT,的質(zhì)量控制

MelissaC.Martin,M.S.,DABRCertifiedMedicalPhysicistFellow-ACR,ACMP,AAPMNIM-ChinaMeetingJune13,2005QualityControlforComputed

QualificationsandProfessionalActivities

專業(yè)資質(zhì)和業(yè)務(wù)活動AmericanCollegeofRadiology美國放射學會 -CommissiononMedicalPhysics醫(yī)學物理學委員會 -ChairofGovernmentRelationsCommittee政府關(guān)系委員會主席 -MammographyAccreditationCommittee乳腺X線照相術(shù)認證委員會 -ImageQualityCommitteeforDigitalImaging數(shù)字影像質(zhì)量委員會AmericanAssociationofPhysicistsinMedicine(AAPM)美國醫(yī)學物理學家協(xié)會 -Liaison(Advisor)totheConferenceofRadiationControlProgramDirectors輻射控制計劃理事會大會顧問QualificationsandProfessionaCTDoseandImageQuality

CT輻射劑量和影像質(zhì)量QualityControlandQualityAssuranceProceduresandIssues質(zhì)量控制和質(zhì)量保證步驟CTDoseandImageQuality

CT輻射CTandMRIimagingmodalitieswerenamedasthemostimportantmedicaladvancesinthelasthalfofthe20thcenturyCT和MRI被認為是人類二十世紀下半葉最重要的進展CTandMRIimagingmodalitiesDevelopmentsinCTTechnology

CT技術(shù)的發(fā)展EarlyCTdetectorsandscanner早期的CT檢測和掃描裝置ModernMulti-SliceCTScanner現(xiàn)代多層CT掃描儀DevelopmentsinCTTechnologyEEarlyCTImage(Siemens)早期的CT影像EarlyCTImage(Siemens)Multi-SliceCTImages(2004)多層CT影像Multi-SliceCTImages(2004)QualityAssurance

質(zhì)量保證Thereareavarietyofartifactsthancanoccurbecauseofpooradjustmentofthescanner

由于掃描儀調(diào)節(jié)不到位，產(chǎn)生很多干擾偽影Lossofresolution

分辨率下降A(chǔ)ccuracyofCTnumbers

CT值的精度TableLocation

掃描床的定位CTisahighdoseprocedure

CT診斷是一個高劑量輻射的過程 -Itisimportanttoknowthedoseforvariousstudiesandtoselectappropriatedoseforoptimalclinicalperformance

重要的是了解各種研究所需的劑量，從而選擇適當?shù)牧恳垣@得最優(yōu)的臨床表現(xiàn)QualityAssurance

質(zhì)量保證TherearClinicalTechnique

臨床技術(shù)Oncethebasicdoseperformanceofthescannerisdetermined,thephysicistshouldworkwithphysiciancolleaguestooptimizeimage-qualityanddose

一旦確定了掃描儀的工作劑量，物理學家就要與臨床醫(yī)師合作優(yōu)化影像質(zhì)量Eachsiteshouldhavetechniquestailoredtothelocalneeds

每一個地區(qū)應(yīng)當使用滿足當?shù)匦枰募夹g(shù)Manufacturersuppliedtechniquesmaynotbeoptimum

制造商提供的技術(shù)并不一定是最適宜的ClinicalTechnique

臨床技術(shù)OncethClinicalTechnique

臨床技術(shù)Techniqueshouldbeadjustedsothatsmallpatientshavereduceddoseandlargepatientshaveincreaseddose

應(yīng)作適當?shù)恼{(diào)整，根據(jù)病人的實際情況增減劑量Thereconstructionfiltershouldbeselectedtotradenoisevsresolution

應(yīng)對重建濾波器進行選擇以提高分辨率、減少噪聲kV,pitchandslicethicknessshouldbeselectedtooptimizedose-imagequality

應(yīng)對kV值、螺距和層厚進行選擇以優(yōu)化劑量--影像關(guān)系ClinicalTechnique

臨床技術(shù)TechniqImageUniformity

影像均一性CTusesmanydetectors

CT使用很多檢測器Thedetectorsmaynotbecompletelyuniform

檢測器并不一定完全一致Theymaydrift

它們可能漂移Qualitycontrolisnecessarytoinsureuniformity

對于均一性而言，質(zhì)控是必需的ImageUniformity

影像均一性CTusesHounsfieldNumber

Hounsfield值A(chǔ)verageattenuationvalueforVoxel像素的平均衰減值TissueDensityX-rayEnergy組織密度X線能量utissue-uwuwCTnumber=1000HounsfieldNumber

Hounsfield值A(chǔ)UniformityChecked

均一性檢測ScanningAir掃描空氣“AirCals”空氣校準ScanningWater掃描水AccuracyofHounsfieldNumbersHounsfield值精度Uniformity均一性Noise噪聲AbsenceofArtifacts干擾偽影的消失UniformityChecked

均一性檢測ScanniPhantoms

模體ScanningWaterRequires需要掃描水Waterfilledphantom充滿水的模體Carefullymade“solidwater”特制的“固體水”Solidwaterhasthesamedensityandatomicnumberaswater固體水具有與水相同的密度和原子數(shù)Phantoms

模體ScanningWaterRequPhantoms

模體Phantomssuppliedbyscannermanufacturer

模體由掃描儀制造商提供Oftendesignedtoworkwithscannerspecificsoftware

通常是被設(shè)計用來與掃描儀軟件配套的Softwaremaycheckandadjustthescanner

軟件可以用來檢查和調(diào)整掃描儀Somemanufacturersusetighterspecificationsthanothers

一些制造商使用比較苛刻的技術(shù)指標Phantoms

模體PhantomssuppliedbCT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件Standards

標準HounsfieldvaluesHounsfield值Dependonscanner取決于掃描儀Shouldbenomorethan+/-7應(yīng)在+/-7之內(nèi)Uniformitydependsonscanner均一性取決于掃描儀Noisedependsontechniqueusedforscan噪聲取決于所使用的掃描技術(shù)Datashouldbechartedsotrendscanbeseen應(yīng)將有關(guān)數(shù)據(jù)作圖以觀察趨勢變化Standards

標準HounsfieldvaluesCT的質(zhì)量控制課件CTNumberAccuracy

CT值精度Checkaccuracyandconstancyofknownmaterials

檢查已知物質(zhì)的精度和穩(wěn)定性CTNumberAccuracy

CT值精度CheckCTNumbers

CT值A(chǔ)ir空氣

-1000 -970Polyethylene聚乙烯

-107 -87Water水

-7 -7Acrylic 丙烯酸

110 130Youneedtoverifywhichmaterialisinthephantom.Ifindoubt,checkwiththemanufacturer.需確認模體中是何種物質(zhì)，如有疑問，與制造商溝通。CTNumbers

CT值A(chǔ)ir空氣 -1000 -CT的質(zhì)量控制課件Resolution

分辨率ResolutionTestObject受試目標分辨率Resolution

分辨率ResolutionTestCT的質(zhì)量控制課件CommercialPhantoms

商業(yè)模體Varietyofphantomsavailable可選的模體很多AccreditationprogramintheU.S.requiresuseofphantomdesignedbyAmericanCollegeofRadiology(ACR)whichmeasuresmorethanQCPhantomsfrommanufacturers

在美國，認證過程中需使用放射協(xié)會設(shè)計的模體，而不僅僅是制造商提供的質(zhì)控模體 -Costly昂貴 -Doesn’tworkwithmanufacturer‘ssoftware不能與制造商提供的軟件一起使用 -Requiresannualphysicistevaluation每年需要評估CommercialPhantoms

商業(yè)模體VarietCT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件CT的質(zhì)量控制課件MonitorDisplay&FilmPrinting

監(jiān)視器顯示和底片打印Monitorshouldbeadjustedtohaveapropergrayscale

監(jiān)視器應(yīng)進行調(diào)節(jié)，以便獲得適當?shù)幕叶萈rintedfilmsshouldmatchmonitordisplay

底片的打印應(yīng)與監(jiān)視器顯示狀態(tài)相匹配PrintersandmonitorsmustfunctioninDICOMformat

打印機和監(jiān)視器應(yīng)在DICOM格式狀態(tài)下工作SMPTETestPatternusedforimagequalityevaluationofbothmonitorsandprinters

對于打印機和監(jiān)視器，應(yīng)用SMPTE圖形進行影像質(zhì)量的監(jiān)測MonitorDisplay&FilmPrintinSMPTETestPatternSMPTETestPatternAccuracyofTableLocation

掃描床的定位精度AccuracyofPositioningLightsandTableMotionshouldbewithin+2mm

定位光與掃描床位移之間的精度應(yīng)在+2mm之內(nèi)Returnoftabletothesamelocationisespeciallyimportantforinterventionalstudies

掃描床的歸位對于干涉分析特別重要AccuracyofTableLocation

掃描床ProtocolforTableLocalization

掃描床定位步驟

Setslicewidthtothinnestavailable

將層厚設(shè)至最小值Positionradio-opaquewireontableandalignwithpositioninglights

將線定位于掃描床并與定位光對齊Scan–wireshouldappearinimage

掃描—線應(yīng)出現(xiàn)在影像中Movetableouttoextremeandrepositiontosamelocationusingnumericalindicators

將掃描床移出頂端，使用數(shù)字指示重新將它定位Scan–wireshouldappearinimage

掃描—線應(yīng)出現(xiàn)在影像中ProtocolforTableLocalizatioFrequencyofTesting

測試頻度Testfrequencyisnotaswelldefinedasforsomeotherimagingmethods

測試頻度與其它的影像測試方法定義不同Physicistshoulddeterminetestfrequencybasedon

其定義基于Manufacturersrecommendations制造商的建議Experiencewithscanner對掃描儀的工作經(jīng)驗FrequencyofTesting

測試頻度TestFrequencyTestingRecommendations

測試頻度建議DoseEvaluation劑量評估

Annually每年Followingmajorservice大修后ClinicalTechniqueEvaluation臨床技術(shù)評估Annually

每年Whenanewtechniqueisdeveloped開發(fā)新技術(shù)時WaterEvaluation水測試Weekly每周FrequencyTestingRecommendatiFrequencyTestingRecommendations

測試頻度建議Monitor&FilmPrinterEvaluation監(jiān)視器和打印機評估Monthly每月TableMotionandAlignmentLights床位移和光定位Quarterly

每季W(wǎng)eeklyifusedfortherapyplanning對于治療方案，可每周進行FullPhysicsEvaluation全部評估Annually每年Followingmajorservice大修后FrequencyTestingRecommendatiEssentialQCActivities

基本質(zhì)控Determinedosesfromscanner確定掃描劑量Workingwithphysiciancolleaguesdetermineappropriateimagingprotocols與臨床人員協(xié)調(diào)確定適當?shù)墓ぷ鞣桨窱nsurethatwaterhasaappropriateCTnumber

確定水測試時獲得適當?shù)腃T值

Accurate精度Noart