Designation:E1935−97(Reapproved2013)StandardTestMethodforCalibratingandMeasuringCTDensity1ThisstandardisissuedunderthefixeddesignationE1935;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1ThistestmethodcoversinstructionfordeterminingthedensitycalibrationofX-andγ-raycomputedtomography(CT)systemsandforusingthisinformationtomeasurematerialdensitiesfromCTimages.ThecalibrationisbasedonanexaminationoftheCTimageofadiskofmaterialwithembeddedspecimensofknowncompositionanddensity.ThemeasuredmeanCTvaluesoftheknownstandardsaredeter-minedfromananalysisoftheimage,andtheirlinearattenu-ationcoefficientsaredeterminedbymultiplyingtheirmeasuredphysicaldensitybytheirpublishedmassattenuationcoeffi-cient.Thedensitycalibrationisperformedbyapplyingalinearregressiontothedata.Oncecalibrated,thelinearattenuationcoefficientofanunknownfeatureinanimagecanbemeasuredfromadeterminationofitsmeanCTvalue.Itsdensitycanthenbeextractedfromaknowledgeofitsmassattenuationcoefficient,oronerepresentativeofthefeature.1.2CTprovidesanexcellentmethodofnondestructivelymeasuringdensityvariations,whichwouldbeverydifficulttoquantifyotherwise.Densityisinherentlyavolumetricpropertyofmatter.Asthemeasurementvolumeshrinks,localmaterialinhomogeneitiesbecomemoreimportant;andmeasuredvalueswillbegintovaryaboutthebulkdensityvalueofthematerial.1.3AllvaluesarestatedinSIunits.1.4Thisstandarddoesnotpurporttoaddressthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatorylimitationspriortouse.2.ReferencedDocuments2.1ASTMStandards:2E1316TerminologyforNondestructiveExaminationsE1441GuideforComputedTomography(CT)ImagingE1570PracticeforComputedTomographic(CT)Examina-tion3.Terminology3.1Definitions:3....
