中南大口腔颌面医学影像诊断学双语教学课件第1章 前言及放射线产生的原理

OralandMaxillofacial

MedicalImaging(1)

XiangyaDentalSchoolX-rayHistoryX-raysdiscoveredonNov.8,1895,byWilhelmConradRoentgenDr.OttoWalkhofftookfirstdentalradiograph;25-minuteexposureDr.C.EdmundKellstookthefirstintraoralradiographinearly189600Earlyx-raymachine.Arrowpointsto“live”electricalwire.ClinicalExam+RadiographsDiagnosisTreatment

00BitewingRadiograph(X-rayFilm,“X-ray”)PeriapicalRadiograph0PanoramicRadiograph0CephalometricRadiograph0TMJRadiographX-rayProduction00Atom(electricallyneutral)AtomicNumber(Z)=#ofprotonsK-shellL-shellprotonsneutronselectronsM-shell0Atom(electricallyneutral)AtomicNumber(Z)=#ofprotonsK-shellL-shellprotonsneutronselectronsM-shell0Atom(electricallyneutral)AtomicNumber(Z)=#ofprotonsK-shellL-shellprotonsneutronselectronsM-shellAttractionbetweenprotonsandelectronsElectrostaticForce0CentrifugalForcePullselectronsawayfromnucleus0Balancebetweenelectrostaticforceandcentrifugalforcekeepselectronsinorbitaroundnucleus0EFCFTheamountofenergyrequiredtoremoveanelectronfromitsorbit

(=electrostaticforce).Dependsonatomicnumber(Z)(#ofprotons).BindingEnergy0Themovementofenergythroughspaceasacombinationofelectricandmagneticfields

ElectromagneticRadiationTravelatthespeedoflight(3x108meters/second)(186,000miles/second)0ElectromagneticRadiationX-rayGammarayMicrowavesVisiblelightTVwavesRadiowaves0WavelengthxFrequency=SpeedoflightFWW0ElectromagneticSpectrumradiotv

visiblelightx-raysgammarayscosmicrays0ENERGYAbilitytopenetrateShorterwavelength,higherenergyHigherfrequency,higherenergy0ABC0Highestenergy?HighestenergyShortestwavelengthHighestfrequencyX-rayCharacteristics0TravelinstraightlineCannotbefocusedtoapointDifferentiallyabsorbedCausefluorescenceHarmfultolivingtissueX-rayCharacteristics0HighenergywavesNomassNocharge(neutral)TravelatspeedoflightInvisibleX-rayMachine

TubeheadSupportarmsControlpanel0PID,BID(cone)PID=positionindicatingdeviceBID=beamindicatingdeviceX-rayTubehead0degreestubeheadcontrolpanelsupportarms0tubeheadsupportarmscontrolpanel0exposuretimeadjustmentControlPanel

ExposureTime

70kVp7mA0ControlPanel

0mAcontrolkVpcontrolexposuretimekVpreadoutControlPanel(50-100)(10-15)(3impulses-5minutes)0X-rayTube0(molybdenum)(tungsten)CathodeFocusingcupFilament00x-sectionoffilament

hotfilamentThehotterthefilamentgets,thegreaterthenumberofelectronsthatarereleased.

electrons

ThermionicEmissionReleaseofelectronsfromhotfilamentwhencurrentflowsafterdepressingexposureswitchAnodeDentalx-raymachineshavestationaryanode0Copperstem

Targetsideviewfrontview

TargetMedicalRadiographyElectronbeamstrikestargetinthisareaonlyAnode(blueedgeistungsten)Filament/FocusingCup0Tungsten

Highatomicnumber(Z=74)

Transfersheatreadily

Highmeltingpoint(3422ºC)Canbedrawnintofinewire(FilamentandTarget)0X-rayTubeComponentsberylliumwindow0TargetBerylliumWindowFocusingcupX-rayTube0Thesmallerthefocalspot(target),thesharpertheimage(teeth)willbe.Duringx-rayproduction,alotofheatisgenerated.Ifthetargetistoosmall,itwilloverheatandburnup.0LineFocusPrincipleLineFocusPrincipleApparent(effective)focalspotsizeActualfocalspotsizeTargetCathode(-)Anode(+)PID0LineFocusPrincipleApparent(effective)focalspotsize(lookingattargetsurfacethroughPID)Actualfocalspotsize(lookingperpendiculartothetargetsurface)0PIDX-rayMachineComponentsControlPanel

X-rayTubehead110,220lineTimerExposureswitchmAselectorkVpselectorAutotransformerStep-downtransformerStep-uptransformerX-rayTubeWiresOil0+110,220-110,2200positivenegative0DirectCurrent(ConstantPotential):800cycles/sec.

60-cycleAlternatingCurrentTimer0NumberofImpulses60=Seconds30impulses/60=0.5second15impulses/60=0.25second1/60060impulses/60=1.0secondYoucannotoverexposebyholdingtheexposureswitchdowntoolong!Allowscurrenttoflowtocompletehighandlowvoltagecircuits.ExposureSwitch0IndicatorlightandsoundmilliAmpere(mA)selector0mAsettingFilamentcurrentStep-DownTransformer110volt3–5voltsFilamentCircuit0Step-DownTransformerPrimarySecondary0110voltscurrentflow3-5voltscurrentflowkiloVoltpeak(kVp)selector0kVpcontrolkVpreadoutAutotransformerControlsvoltagebetweenanodeandcathodeRegulatedbykVpselector(Similartoarheostat)0110V65VcurrentflowAutotransformer080V65-90V65,000-90,000V(65kVp-90kVp)kVp=kiloVoltagepeakStep-UpTransformer0Step-UpTransformerPrimarySecondary0110voltscurrentflow65,000to90,000voltscurrentflow10-MINUTEBREAK0exposurebuttonoilfilterfilament0X-rayMachineComponentsfilament0110volts3-5volts65,000to90,000volts65-90volts<110voltskVp03X-rayProductionX-rayProductionBremmstrahlungCharacteristic0X-raysproducedwhenhigh-speedelectronsfromthefilamentaresloweddownastheypasscloseto,orstrike,thenucleiofthetargetatomsBremsstrahlungRadiation

(Brakingradiation,generalradiation)0BremsstrahlungX-rayProduction+0High-speedelectronfromfilamententerstungstenatomElectronsloweddownbypositivechargeofnucelus;energyreleasedinformofx-rayElectroncontinuesontootheratomsuntilallofitsenergyislostBremsstrahlungX-rayProductionMaximumenergy0High-speedelectronfromfilamententerstungstenatomandstrikesnucleus,losingallitsenergyanddisappearingThex-rayproducedhasenergyequaltotheenergyofthehigh-speedelectron;thisisthemaximumenergypossible+Theenergyofthehigh-speedelectronfromthefilamentmustbehigherthanthebindingenergyofthetargetelectronwithwhichitinteractsinordertoejectthetargetelectronX-rayshaveenergiescharacteristicofthetargetmaterial(energy=differencebetweenbindingenergiesoftargetelectronsinvolved,e.g.,K&L,K&M,etc.)CharacteristicRadiation0K-shellbindingenergy=70keVL-shellbindingenergy=11keVM-shellbindingenergy=3keVTungsten0Atomicnumber=74CharacteristicX-rayProductionLKMHigh-speedelectronwithatleast70keVofenergy(mustbemorethanthebindingenergyofk-shellTungstenatom)strikeselectronintheKshellEjectedelectronleavesatomRecoilelectron(withverylittleenergy)exitsatom0vacancyCharacteristicX-rayProductionKLMOuter-shellelectrondropsintovacantspot0X-raywith59keVofenergyproduced.70(bindingenergyofK-shellelectron)minus11(bindingenergyofL-shellelectron)=59.X-rayenergy(keV)characteristicx-rays(59&67keV)#ofx-raysX-raySpectrum(variablex-rayenergies)0Bremsstrahlungx-raysaverageenergyofx-raybeamX-raySpectrumresultsfrom:Varyingelectron/nucleusdistancesMultipleelectroninteractionsVaryingvoltage(AC)0Electroninteractionswithtargetatoms

1%producex-rays99%produceheatTheexcessheatiscontrolledbyhighmeltingpointoftungsten,conductivepropertiesofcoppersleeve,andcoolingfromoilsurroundingx-raytube0X-rayBeamModifiers0ExposureFactorskVpmAExposuretime0Incorrectexposurefactors(toomanyx-raysortoomuchenergy;filmtoodark)CorrectexposurefactorsIncorrectexposurefactors(notenoughx-raysorenergytoolow;filmtoolight)0kVp(kiloVoltpeak)0X-rayEnergy(keV)NumberofX-rays709090kVp70kVpmaximumenergyaverageenergy

Higheraverageenergy

ofx-rays

Greatermaximumenergy

x-rays

More

x-raysIncreasingkVpresultsin:0mA(milliamperes)0X-rayEnergy(keV)NumberofX-rays7010mA5mAmaximumenergyaverageenergy(nochange)(nochange)Exposuretime0X-rayEnergy(keV)NumberofX-rays7010impulses5impulsesmaximumenergyaverageenergy(nochange)(nochange)Increasing

mA

orExposureTime

resultsin:Anincreaseinthenumberofx-raysproducedNochangeintheenergyofthex-raybeam0

mAsormAimilliamperes(mA)xseconds(s)milliamperes(mA)ximpulses(i)

60impulses=1second10mAx.5seconds=5mAs20mAx.25seconds=5mAsmAi=60xmAs0

ConstantpatientsizeProperkVp,mA,exposuretime(e.t.)IncreasemA;nochangeinkVp,e.t.Decreasee.t.;nochangeinkVp,mAIncreasekVp;nochangeinmA,e.t.DoublemA,halvee.t.;nochangeinkVpACBBACAB0FiltrationTheprocessofremovinglow-energyx-raysfromthex-raybeam0InherentGlasswindowofx-raytubeAddedAluminumfilter(s)Total70kVp1.5mm2.5mmTotalFiltrationOil/Metalbarrier0filterPIDThefilterisusuallylocatedintheendofthePIDwhichattachestothetubehead.0CollimationRegulatesthesizeand/orshapeofthex-raybeamareacovered(lesspatientexposure)scatterradiation0primaryx-rayscatteredx-rayScatterRadiation0Collimator0YouarelookingupthroughthePIDatthecollimator,whichisacircularleadwasherwithacircularcutoutinthemiddle.Thiswillproducearoundx-raybeam.Thelightgrayareainthecenterisanal