Effect of Changing X-ray Tube Voltage (kV) | Radiology

The increase in x-ray tube voltage increases the amount of radiation coming out of the x-ray tube, as well as the average photon energy (i.e., increased ... [SkiptoContent] HomePatientCareImagingServicesBreastImaging/MammographyCT(ComputedTomography)GeneralDiagnosticImagingScienceandInformaticsInterventional/NeuroRadiologyMagneticResonanceImaging(MRI)NuclearMedicineUltrasoundPhysiciansMedicalImagingTechnologistsRadiologyNursingContactUsDriving&ParkingDirectionsUniversityRadiologyAssociates(Physicians'PrivatePractice)SamplingofProceduresAcademicsFacultyResidencyProgramPhysicsTeachingFile(RSNA)MedicalStudentTeachingProgramNeuroradiologyFellowshipProgramResearchinvivoMicro-CTFacultyTogglemainmenuvisibilityRadiologyPatientCareImagingServicesBreastImaging/MammographyAppointmentsandLocationsOurTeamCT(ComputedTomography)GeneralDiagnosticImagingScienceandInformaticsInterventional/NeuroRadiologyOurTeamAboutIRConditionsTreatedTreatments/ProceduresTechnologyMagneticResonanceImaging(MRI)NuclearMedicineUltrasoundPhysiciansMedicalImagingTechnologistsRadiologyNursingContactUsDriving&ParkingDirectionsUniversityRadiologyAssociates(Physicians'PrivatePractice)SamplingofProceduresContactUsAcademicsFacultyResidencyProgramProgramOverviewAnInvitationFrequentlyAskedQuestionsDepartmentataGlanceFacultyResidentsMeetOurResidentsWhereResidentsGoAfterGraduationAboutSyracuse&CentralNewYorkPhysicsTeachingFile(RSNA)Introduction:ImagesDigitalImagesDisplayingimagesImageQualityOverviewRadiographyTechnique:X-raytubevoltage(kV)Technique:CurrentExposureTimeProduct(mAs)Resolution:FocalSpot(Contact)Resolution:FocalSpot(Mag)Resolution:PixelSizeScatterImportanceScatterandCollimationScatterandkVScatterRemovalGridsDualEnergyRadiographyExposureIssuesImageArtifactsFluoroFluoroscopy&DigitalPhotospotImageIntensifierSizeCollimationEffectsArtifactsInterventionalRadiographyDigitalSubtractionAngiographyDigitalAngiographyCT(ComputedTomography)RadiographicTechniquesAcquisitionGeometryImageReconstructionArtifactsMammographyAutomaticExposureBeamQualityRadiationDoseArtifactsImageProcessingDisplayingimagesImageQualityOverviewMedicalStudentTeachingProgramNeuroradiologyFellowshipProgramResearchinvivoMicro-CTResourcesPricingFrequentlyAskedQuestionsImageAnalysisResourcesCurrentProjectsOralCancerMouseModelImagingCerebralBloodPerfusionStudiesonRatsPredictingBoneFractureinMetastaticBreastCancerLesionsFacultyHome>Academics>PhysicsTeachingFile(RSNA)>RadiographyRadiographyTechnique:X-raytubevoltage(kV)Technique:CurrentExposureTimeProduct(mAs)Resolution:FocalSpot(Contact)Resolution:FocalSpot(Mag)Resolution:PixelSizeScatterImportanceScatterandCollimationScatterandkVScatterRemovalGridsDualEnergyRadiographyExposureIssuesImageArtifactsEffectofChangingX-rayTubeVoltage(kV) Inscreenfilmradiography,thechoiceofx-raytubevoltage(kV)affectedtheimagecontrast;thisisnolongerthecaseforanydigitalradiographicsystem.Inthisexample,imageswereobtainedofapelvicphantomatthreekVvaluesusingacommercialcomputedradiography(CR)imagingplates.Allexposureswereperformedusingphototiming.Thisimagewasgeneratedat60kV,andrequiredarelativelyhighradiationintensityof141mAs.TheSnumbergeneratedbythesystemwas~140,whichcorrespondstoanaverageairkermaincidentontheimagingplateoftheorderof7mGy.TheLnumbergeneratedbythisimagingsystemwas2.3,whichmeansthattherangeofintensitiesincidentontheplatedifferedbyafactorof200orso(10^2.3~200).Theskindoseforthisexaminationwasestimatedtobe7.6mGy;foragivenirradiationgeometryandx-raysystem,thefactorsthataffecttheskindosearethekVandmAsthatareusedtogeneratetheimage. Theimageshownabovewasgeneratedat75kVandrequiredanexposureof36mAs.Theincreaseinx-raytubevoltageincreasestheamountofradiationcomingoutofthex-raytube,aswellastheaveragephotonenergy(i.e.,increasedpenetration).Accordingly,thetubecurrentexposuretimeproductvalue(mAs)isreducedto36mAs;whereasat60kV,thevaluewasmuchhigher(141mAs).TheresultantSnumbergeneratedbytheCTsystemwas~150,indicatingthattheaverageradiationincidentontheimagingplatewasverysimilartothevaluefortheimagegeneratedat60kV;thisistobeexpectedbecausetheimageswereobtainedusingphototiming,wheretheexposuretimeisdeterminedautomatically(i.e.,whentheimagingplatehasreceivedthecorrectexposure).TheLvalueforthisimagewas2.1,showingthatincreasingthex-raytubevoltagefrom60reducedthedynamicrangefrom200:1at60kVto125:1. Notethattheimageappearanceat75kVisverysimilartothatobtainedat60kV;differencesindynamicrangearecompensatedforusingdifferentdisplaywindows.ImagesatlowerkVs,whichhaveawidedynamicrange,mustuseawiderwindow;increasingthekVreducesthedynamicrange,butpermitstheuseofnarrowerdisplaywindows.Asaresult,imagesobtainedatdifferentkVvalues,andthesameintensityattheimagingplate,willhaveverysimilarappearance.Theskindoseisnow3.2mGy,whichislowerthanthe7.6mGyassociatedwiththeradiographtakenat60kV.Foramorepenetratingbeam,lessradiationisrequiredatthepatiententrancetoachievetherequiredintensityattheimagingplate(i.e.,7mGy). Theimageshownabovewasgeneratedat120kVandrequiredanexposureofonly6mAs.ThisismuchlowerthanthemAswhereasat60kV(141mAs)and75kV(36mAs).TheresultantSnumbergeneratedbytheCRsystemwas~160,againindicatingthattheaverageradiationincidentontheimagingplatewasverysimilartothevaluefortheimagegeneratedat60kVand75kV,becauseoftheuseofphototiming.TheLvalueforthisimagewas1.8,correspondingtoadynamicrangeof60:1;itisgenerallytruethatincreasedkVvalues,correspondingtomorepenetratingx-raybeams,willreducethedynamicrangeofthedetectedx-raybeamintensitiesattheimagereceptor.Notethattheimageappearanceat120kVissimilartothoseat60kVand75kV.Differencesindynamicrangearegenerallycompensatedforusingdifferentdisplaywindows.Theskindoseisnowmuchlowerat1.4mGy,whichislowerthanthe7.6mGyassociatedwiththeradiographtakenat60kV.AlthoughincreasingkVwillalwaysreducethepatientdose,thisalsoincreasestheamountofscatterintheimage(seebelow).Top