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【英文标准名称】:StandardTestMethodforCalibratingandMeausringCTDensity
【原文标准名称】:校准和测量计算机断层摄影密度的标准试验方法
【标准号】:ASTME1935-1997(2003)
【标准状态】:现行
【国别】:
【发布日期】:1997
【实施或试行日期】:
【发布单位】:美国材料与试验协会(ASTM)
【起草单位】:E07.01
【标准类型】:(TestMethod)
【标准水平】:()
【中文主题词】:计算机断层摄影;对比敏感度;计算机断层摄影密度分辨;密度校准;线性衰减系数;质量衰减系数
【英文主题词】:computedtomography;contrastsensitivity;CTdensityresolution;densitycalibration;linearattenuationcoefficient;massattenuationcoefficient
【摘要】:ThistestmethodallowsspecificationofthedensitycalibrationprocedurestobeusedtocalibrateandperformmaterialdensitymeasurementsusingCTimagedata.Suchmeasurementscanbeusedtoevaluateparts,characterizeaparticularsystem,orcomparedifferentsystems,providedthatobservedvariationsaredominatedbytruechangesinobjectdensityratherthanbyimageartifacts.ThespecifiedproceduremayalsobeusedtodeterminetheeffectiveX-rayenergyofaCTsystem.TherecommendedtestmethodismoreaccurateandlesssusceptibletoerrorsthanalternativeCT-basedapproaches,becauseittakesintoaccounttheeffectiveenergyoftheCTsystemandtheenergy-dependenteffectsoftheX-rayattenuationprocess.This(orany)testmethodformeasuringdensityisvalidonlytotheextentthatobservedCT-numbervariationsarereflectiveoftruechangesinobjectdensityratherthanimageartifacts.Artifactsarealwayspresentatsomelevelandcanmasqueradeasdensityvariations.Beamhardeningartifactsareparticularlydetrimental.Itistheresponsibilityoftheusertodetermineorestablish,orboth,thevalidityofthedensitymeasurements;thatis,theyareperformedinregionsoftheimagewhicharenotoverlyinfluencedbyartifacts.Linearattenuationandmassattenuationmaybemeasuredinvariousways.Foradiscussionofattenuationandattenuationmeasurement,seeGuideE1441andPracticeE1570.FIG.1DensityCalibrationPhantom1.1ThistestmethodcoversinstructionfordeterminingthedensitycalibrationofX-and947;-raycomputedtomography(CT)systemsandforusingthisinformationtomeasurematerialdensitiesfromCTimages.ThecalibrationisbasedonanexaminationoftheCTimageofadiskofmaterialwithembeddedspecimensofknowncompositionanddensity.ThemeasuredmeanCTvaluesoftheknownstandardsaredeterminedfromananalysisoftheimage,andtheirlinearattenuationcoefficientsaredeterminedbymultiplyingtheirmeasuredphysicaldensitybytheirpublishedmassattenuationcoefficient.Thedensitycalibrationisperformedbyapplyingalinearregressiontothedata.Oncecalibrated,thelinearattenuationcoefficientofanunknownfeatureinanimagecanbemeasuredfromadeterminationofitsmeanCTvalue.Itsdensitycanthenbeextractedfromaknowledgeofitsmassattenuationcoefficient,oronerepresentativeofthefeature.1.2CTprovidesanexcellentmethodofnondestructivelymeasuringdensityvariations,whichwouldbeverydifficulttoquantifyotherwise.Densityisinherentlyavolumetricpropertyofmatter.Asthemeasurementvolumeshrinks,localmaterialinhomogeneitiesbecomemoreimportant;andmeasuredvalueswillbegintovaryaboutthebulkdensityvalueofthematerial.1.3AllvaluesarestatedinSIunits.1.4Thisstandarddoesnotpurporttoaddressthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatorylimitationspriortouse.
【中国标准分类号】:H26
【国际标准分类号】:35_240_80
【页数】:5P.;A4
【正文语种】: