Download - 2. X‐ray planar radiography and CT (2) - Biophotonics Labbiophotonics.gist.ac.kr/Course Materials/MI_spring_2017... · · 2017-03-14• This trade‐off can be shown by Bucky

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2.X‐rayplanarradiographyandCT(2)

Lectures3,4

MedicalImagingSystems

JaeGwan Kim

[email protected] ,X2220

DepartmentofBioMedical ScienceandEngineering

Gwangju InstituteofSciencesandTechnologyCopyright.Mostfigures/tables/textsinthislecturearefromthetextbook“IntroductiontoMedicalImaging:Physics,EngineeringandClinicalApplicationsbyNadineBarrieSmithAndrewWebb2011”andthismaterialisonlyforthosewhotakethisclassandcannotbedistributedtoanyonewithoutthepermissionfromthelecturer.

Contents

1. Instrumentationforplanarradiography1) X‐raytube(discussedinthepreviouslecture)

2) Collimators

3) Anti‐scattergrid

4) X‐raydetectors

2. QuantitativecharacteristicsofplanarX‐rayimages1) Signaltonoiseratio

2) Spatialresolution

3) Contrasttonoiseratio

3. X‐raycontrastagents4. SpecializedX‐rayimagingtechniques5. ClinicalapplicationsofplanarX‐rayimaging

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InstrumentationforplanarX‐ray

• X‐raytube– GeneratesX‐ray

• Collimator– ReduceX‐raydosetopatientsandComptonscatteredX‐ray

• Anti‐scattergrid– ReducefurtherthecontributionofscatteredX‐raytoimages

• Digitaldetector– ConvertsX‐rayintolight– Convertslightintovoltage– DigitizethevoltageusingADC


• Collimator(beam‐restrictor)– ThebevelangledeterminesthewidthofX‐raybeam

– X‐raybeamiswiderthanFOV,andthishas2undesirableeffects1) Patientdoseishigherthanitshouldbe2) UnnecessaryComptonscatteredX‐raysalso

increase

– Tominimizetheaboveeffects,acollimatorisplacedbetweenX‐raysourceandthepatient

– Thecollimatorconsistsofsheetsofleadandcanrestrictthebeamineitheroneortwodimensions

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• Imagesofacollimator

http://miac.unibas.ch/PMI/01‐BasicsOfXray.html


• Diagramsofcollimator(left)withoutlightbeamand(right)withlightbeam

http://www.e‐radiography.net/radtech/c/collimator.htm

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• Anti‐scattergrid– ComptonscatteredX‐raylowersCNR– Toreducethecontributionfromsecondaryradiation,ananti‐scattergridisplacedbetweenthepatientandtheX‐raydetector

– Leadortungsten

No anti‐scatter grid With an anti‐scatter grid


• Anti‐scattergridischaracterizedbytwoproperties,thegridratioandgridfrequency– Gridratio=h/d,4:1~16:1– Gridfrequency=1/(d+t),5~7lines/mmwherehistheheight,tisthethickness,distheseparationoftheleadstrips

h

d

http://www.mikrosystems.com/applications/computed‐tomography

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• However,usingananti‐scattergridrequirestohaveahigherradiationdose.(~10times)

• Thistrade‐offcanbeshownbyBuckyfactor(BF).• BFistheratioofmeasuredexposurewiththegridinplacetothatwithout.

• Buckyfactor=1/Gridpenetrationhttp://www.sprawls.org/ppmi2/SCATRAD/

X‐rayDetectors

• TraditionalX‐rayfilm

– Intensifyingscreen

– X‐rayfilm

• Digitaldetectortechnologies

– Computedradiography(CR):

cheaperandmorewidelyusedthandigitalradiography

– Digitalradiography(DR)

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X‐rayDetectors

• Intensifyingscreens– DirectexposureofX‐raytophotographicfilmhaslowsensitivityandthusconvertsX‐rayintolight(5‐20%ofX‐rays,otherstoheat)

– X‐rayfilmis100timesmoresensitivetolightthanX‐rays– Thisscreenhasthreebenefits

• Reductionofpatientdose• Reductionoftubeandgeneratorloading• Reductionofpatientmotionartifacts

– However,italsoblursimagesduetoisotropicdiffusionofphotonsinthephosphor

Phosphor material was used to be calcium tungstate (CaWO4, K edge energy 69.4 keV), and now barium strontium sulfate (BaSrO4), gadolinium oxysulfide (Gd2O2S) are used since these have low K edge energy which can absorb more X‐ray energy

X‐rayDetectors

• Intensifyingscreens– X‐rayabsorptionspectraamongdifferenttypesofphosphormaterials

http://www.e‐radiography.net/radtech/f/film.htm

Barium strontium sulfate (BaSrO4), gadolinium oxysulfide (Gd2O2S) are advantageous to calcium tungstate (CaWO4, K edge energy 69.4 keV) at the 40‐50keV and at 50‐70keV, respectively.

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X‐rayDetectors

• Achartoftheprinciplecharacteristicsofthemostcommon“rareearth”basedscreenphosphors

X‐rayDetectors

• X‐rayfilm– LightconvertedfromX‐rayviaintensifyingscreensisexposedtoX‐rayfilm

– Base:structuralstrengthforthefilm– Emulsion:gelatin+silverhalide– Gelatinpreventsclumpingofgrains(1~2.3μm)– Silverhalideislightsensitivematerialandisamixtureofsilveriodide(1~10%)andsilverbromide(90~99%)

– Silverhalideitselfislesssensitivetolight,andthusitisheatedwithreducingagentcontainingsulphur.

– Silversulphide atthesurfaceofcrystalisasensitivityspeckwhichtrapselectronstobeginlatentimageformation

– Orthochromatic(green)andpanchromatic(redsensitive)film

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X‐rayDetectors

• X‐rayfilmprocessing– Development:theexposedgrainsarepreferentiallyreducedtoblackmetallicsilver

– Fixing:theremainedgrainsaredissolved– Washing:removethedissolvedgrainsfromemulsion– Replenishment:ensuresthechemicalbalanceismaintained

X‐rayDetectors

• Cassetteandintensifyingscreencombination

http://www.sure‐quality.com/x‐ray‐supplies.html

http://xraymachinesss.com/category/dental‐x‐ray‐film/

http://xrayrecycling.blogspot.com/2011/05/x‐ray‐film‐recycling‐and‐its.html

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X‐rayDetectors

• Computedradiography(CR)– HasanadvantageoffullycompatiblewithX‐rayfilmbasedsystem

– Adetectorplate• Athinlayerofphosphorcrystals• Sizerangesfrom18X24cm(mammography)to35X43cm(chestradiography)

• Highresolution(phosphorlayer~140μmthickness)andstandardplates(230μm)

• TransmittedX‐rayreleaseselectronsfromphosphorcrystals• Releasedelectronsaretrappedforafewhoursinsitesformedbydislocationinthephosphorcrystallattice forms‘latent’image

• ThenthedetectorplateisfedintoCRreader

X‐rayDetectors

• Computedradiography(CR)– CRreader

• Consistsoflaserdiodes,photodiodes,andlens• Laserilluminationto~50 μmcausestrappedelectronsbacktothegroundstateandthedifferenceofenergyisreleasedaslightintheendofbluecolor.(photostimulable luminescence)

• Theemittedbluelightisdetectedbyaphotodiode• Photodiodesconvertlightintoavoltage• Voltageisamplified,filteredanddigitized• Oncethescanningisdone,detectorplateis‘bleached’usingseveralhigh‐intensitylightandwillbereused

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X‐rayDetectors

• Photostimulable phosphor– BaFX:Eu2+, Ba2+,F‐,XcouldbeBr‐ orI‐ oramixtureofboth

Isosurface of the electron density for the (Eu )* excited state of BaFI:Eu showing strong localization on the Eu atom (pink), Ba (blue), F(green), I (orange).

Ref: Gundiah et al., IEEE Trans Nuclear Sci, 57(3) 1702‐5, 2010

http://home.fujifilm.com/info/products/science/ip/principle.html

X‐ray

Eu2+ Eu3+

e‐

+

Trapped in Br+

empty lattice

Eu3++e‐

X‐rayDetectors

• Photostimulable luminescence:aftertheinitialexposure,excitedelectronsinthephosphormaterialremain'trapped'in'colorcenters'inthecrystallatticeuntilstimulatedbythesecondillumination.Forexample,Fuji'sphotostimulable phosphorisdepositedonaflexiblepolyesterfilmsupportwithgrainsizeabout5micrometers,andisdescribedas“bariumfluorobromide containingatraceamountofbivalenteuropiumasaluminescencecenter”.Europiumisadivalentcation thatreplacesbariumtocreateasolidsolution.WhenEu2+ ionsarestruckbyionizingradiation,theyloseanadditionalelectrontobecomeEu3+ ions.Theseelectronsentertheconductionbandofthecrystalandbecometrappedinthebromineionemptylatticeofthecrystal.Thismetastablestateishigherinenergythantheoriginalcondition,soalower‐frequencylightsourcethatisinsufficientinenergytocreatemoreEu3+ ionscanreturnthetrappedelectronstotheconductionband.AsthesemobilizedelectronsencounterEu3+ ions,theyreleaseablue‐violet400nmluminescence.Thislightisproducedinproportiontothenumberoftrappedelectrons,andthusinproportiontotheoriginalX‐raysignal(CopiedfromWikipedia)

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X‐rayDetectors

http://en.wikibooks.org/wiki/Basic_Physics_of_Digital_Radiography/The_Image_Receptor

X‐rayDetectors

• VariationsinCRplate• Around1/2ofthelightproducedbylaserdiodesescapethroughthebottomofthedetector– Areflectivelayerbaseunderphosphorcrystalspreventsthelossoflightandimprovesthedetectionefficiency

– However,thespatialresolutiondecreasessincethereflectedlighttravelsmorelonger

– Forthedigitalmammography(highresolution),anabsorbentlayerisplacedatthebottomofthedetectortoreducethelightspreadfunction

– However,itreducesanefficiencytoo– DualsidedCRplatecancapturemorelight,butrequiresamoresophisticatedCRreader

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X‐rayDetectors

• NewmaterialsforCRplates– PreviouslyusedBaFX:Eu2+(bariumfluorohalide activatedwitheuropiumions,halideXisamixtureofbromineandiodine)israndomlyoriented

– CsBr:Eu2+:thincolumnarcrystalsactsasaverythinopticalfibers1) higherintrinsicspatialresolution,2) higherpackingefficiency increasesthesensitivity3) thicknessofthephosphorlayercanbeincreasedto600μm

increasethenumberofabsorbedX‐rays

– ThedynamicrangeofaCRsystemishigh,typicallytheoutputislineartoX‐rayinputfortherangeof4ordersofmagnitude.

X‐rayDetectors

• CRsystem– Thespatialresolutionislimitedby

• Laserbeamsize• Numberofsampleddatapoints• Thedegreeoflaserbeamscatteringbycrystalsinthephosphorscreen

• HRplateshavesmallerandthinnercrystals highspatialresolution

– HRisdigitizedas4096X4096andstandardis2048X2048– SNRofstandardisabouttwicehigherthanHRplateforthesameX‐rayinput

– DualsidedCRplatesandCsBr:Eu2+ increasestheSNRbyafactorof2comparedtosinglesidedandBaFX:Eu2+,respectively

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X‐rayDetectors

• WholeprocessofCRsystem

http://en.wikibooks.org/wiki/Basic_Physics_of_Digital_Radiography/The_Image_Receptor

X‐rayDetectors

• CRSystem

http://www.flatpaneldr.com/?p=631

$40,000~$45,000http://chesapeakemedical.wordpress.com/tag/computed‐radiography/

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X‐rayDetectors

• Idealdigitalradiographysystem

X‐rayDetectors

• Digitalradiography– Indirectconversion:mostcommonlyused

• First,convertsX‐rayenergyintolightbyaCsI:Tl (ThalliumdopedCesiumIodide)orGadoliniumoxysulfide scintillator

• Secondly,convertslightintoavoltageusinga2Dphotodiodearray

• CesiumandIodinehaveK‐edgesat36and33.2keV,therefore,theX‐rayattenuationcoefficientofCsI isveryhigh highlyefficientX‐raydetector

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X‐rayDetectors

• AschematicofindirectDRdetectorisshownbelow

• CsI:Tl isa‘needlecrystals’with5μmdiameter• Thisshapeprovidesanexcellentpackingefficiency(>80%)forbetterX‐rayabsorptionandenhancespatialresolution

• Thicknessofthislayerisaround0.6mm• ACCDcameraoralargeflatpaneldetector(FPD) consistedofthin‐filmtransistor(TFT)arraysisplacedrightunderthatCsI:Tl layer

X‐rayDetectors

• FPD:thisfilmamorphoussilicontransistorarrayislayeredontotheglass.

• AmorphoustransistorisusedinsteadofcrystallinesinceitcanbeexposedtohighdoseofX‐raywithoutdamage.

• Eachpixelofthedetectorconsistsof– Fabricatedphotodiode– Storagecapacitor– TFTswitch

• AbsorbedX‐raybyCsI rod,CsI produceslight(~green).LightgoestoTFTarrayandisconvertedtoavoltage(photodiode)andstoredincapacitors

• Multiplexerreadsthesignalline‐by‐lineandsignalsareamplifiedanddigitizedusinga14‐bitADC

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X‐rayDetectors

• AtypicalDRsystemhas– Flatpanel43X43cm– TFTarrayof3001X3001elements pixelsamplingintervalof143μm

– Anti‐scattergrid:gridratioof~13:1andgridlinedensityof~70lines/cm(~143 μm)

– Allofthesearepackagedto~50X50cmsquare,4.5cmthicknesswithaweightof~20kg

X‐rayDetectors

• Digitalradiography– Directconversion:

• EliminatesthestepofconvertingX‐rayenergyintolightX‐raytoelectricsignal

• DirectabsorptionoftheX‐rayphotonstoproduceelectricalsignalsusingaX‐rayphotoconductorsuchasamorphousselenium(alloyedwitharsenictopreventrecrystallization)

• Selenium(atomicnumberof34,K‐edgeat13keV)islessefficientthanCsI:Tl

• Amorphousseleniummaterialislayeredonthetopofamorphoussiliconetransistorarray

• Currently,indirectconversionismorecommon,butnewmaterialsareunderinvestigationforthebetterefficiencyofdirectDR

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X‐rayDetectors

• Photoconductors– Areasubsetofsemiconductors.– Inthedark,thesematerialsareinsulatorsbuteffectivelybecomeconductors

underillumination.– AslightorX‐rayphotonsareabsorbed,theenergyoftheincomingphoton

exciteselectronsinthephotoconductortoastateknownastheconductionbandandchargecarrierscalledelectron‐holepairsareproduced.

– Withoutanelectricfield,theexcitedelectronsreturntotheirgroundstate,thevalenceband.

– However,withanelectricfield,theelectronsintheconductionbandmovealongtheelectricfieldlines.

– ThenegativeelectronscancelthepositivesurfacechargeandthusproducevariationsinthesurfacechargethatcorrespondtotheincidentpatternoftheX‐raysoranX‐rayimage.

– Thechargecollectionwasguidedbytheelectricfield,sotheproducedchargepatternfaithfullyreproducestheX‐rayimage.TheresultinghighresolutionimageisnotstronglydependentontheSeleniumthickness.

X‐rayDetectors

• AmorphousSelenium– Anumberofphotoconductors(e.g.silicon,germanium,thalliumbromideand

mostsemiconductors)couldbeusedforX‐rayimagingdetectorsbutamorphousSelenium(a‐Se)hasmanyfeaturesthatmakeitwellsuitedforthistask.

– A‐SeiswelldevelopedtechnologicallyasithasbeenusedasaphotoconductorinphotocopiersandalsoinanX‐rayimagingtechniqueknownasxeroradiography fordecades.Itisusedinitsamorphousform,soamorphousseleniumplatescanbemadebyevaporation.Thus,incontrasttomanycrystallinephotoconductors,a‐Sebaseddetectorscanbemadelargeinarearelativelyeasilyandinexpensively.

– Theelectricproperties,namelythelowdarkorleakagecurrent,ofa‐SealsorenderitsuitableforX‐rayimaginguse.ItsotherX‐raypropertiesareasfollows:

– ~1000electron‐holepairs/50keV X‐rayatanelectricfieldof10V/um.InotherwordsW+/‐ =50eV atthisfieldstrength.

– ~50%attenuationofa50keV beamwith365umofSelenium;50%attenuationofa20keV beamwitha30umofSelenium.

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X‐rayDetectors

• Digitalradiography– Principleofoperation:Directconversion

Ref) Introduction to digital radiography _Kodak

X‐rayDetectors

• Indirectvs Directdigitalradiography

Indirect DR

Direct DR

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X‐rayDetectors

• Indirectvs Directdigitalradiography

Indirect DR Direct DRRef) Introduction to digital radiography _Kodak

X‐rayDetectors

• Digitalradiography

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X‐rayDetectors

• Digitalradiography

CCD DR Flat Panel Digital X‐Ray (indirect or direct)

http://www.flatpaneldr.com/?p=631

X‐rayDetectors

• MTFcomparisonamongvariousdetectingmethods

Ref) Introduction to digital radiography _Kodak

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Quant.Charact.ofplanarX‐rayimages

• Signaltonoise– Ideally,eachpartofthedetectorwillbehitwithsamenumberofX‐raysifthereisnothingbetweentheX‐raysourceandthedetector

– However,thereisavariationinthenumberofX‐raysperunitareacausesastatisticalfluctuationintothesignalintensityofeachpixelshownasanoiseintheimage

– ThedistributionofthenumberofX‐raysperunitareaisaPoissondistribution:

!whereμ is the mean value

P(N): the probability that N number of X‐rays hit the detector plate per unit area


• Thevalueofstandarddeviation,σ,inthePoissondistributionisgivenby:

• Aswecanseefromthefigurebelow,forverylargeN,thegraphbecomesadeltafunction,andthevalueofμ approachestoN

• SNRinimageistheratioofthesignalaveragetothestandarddeviationofthenoise:

• SNR=/σ

• ∝

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• TodoubletheSNR,therefore,numberofX‐raysdetectedneedstobe4timeshigher needtoincreaseradiationdose4times

• OperationalfactorsaffectSNRare– Thetubecurrentandexposuretime

∝

– ThetubekVp:higherkVp higherSNR,butinanon‐linearway

– Thepatientsizeandpartofthebodybeingimaged:thickerthebody lowertheSNR

– Thegeometryoftheanti‐scattergrid:thelargergridratio,thesmallerofSNR(butimprovestheCNR)


• OperationalfactorsaffectSNRare– Theefficiencyofthedetector:thiscanbequantifiedbyaparametercalledthedetectorquantumefficiency(DQE),

out andin representtheinputSNRandoutputSNRfromthedetector.– DQEisalwayslessthan1becauseadetectoralwaysintroducesomenoisetothesystem

• StandardCRplate:~0.25• HighresolutionCRplate:~0.12• DualsidedCRplate:~0.4• CsBr:Eu2+ basedplates:~0.8

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• TheeffectofradiationdoseontheSNRofaplanarimagewithnopatientinplace.

– Theimageonthelefthas100timesmoreX‐raynumbers,andthusithas10timeshigherSNRthanthatofright


• Majorcontributionsofspatialresolutionare1. ThesizeoftheeffectiveX‐rayfocalspotandtherelativedistances

betweentheX‐raytubeandthepatient,andtheX‐raytubeandthedetector

– Thesizeof‘penumbra’region,P,isgivenby

– Therefore,f needstobesmallwhileSo needstobelongandS1 isbettertobeclosetoSo toimprovethespatialresolution

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• Threedistinctpartsofashadow

• Inradiationoncology,penumbraisthespaceintheperipheryofthemaintargetofradiationtherapyandisdefinedasthevolumereceivingbetween80%and20%ofisodose


• Majorcontributionsofspatialresolutionare2. ThepropertiesoftheX‐raydetector– ACRreaderforCRandaflatpaneldetectorofDRdeterminethe

spatialresolutiontoo.– CRreader

• Laserbeamsize• Numberofsampleddatapoints• Thedegreeoflaserbeamscatteringbycrystalsinthephosphorscreen

• HRplateshavesmallerandthinnercrystals highspatialresolution

– DigitalRadiography• PixelsizeofFPD

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• Spatialresolution– TheoverallMTFcanbeobtainedbyconvolutingMTFofeachimagingcomponent.

– ThemostusefulmeasureofspatialresolutionforX‐rayimagingistomeasurealinespreadfunction(LSF)byusingagrid(parallelleadsepta)


• Threetypesoffactoraffectingcontrasttonoise1. ComptonscatteredX‐rays:theseareaffectedby

1) TheX‐rayenergyspectrumHigherX‐rayenergymoreComptonscattering

2) ThefieldofviewoftheX‐rayimageLargerFOVmoreComptonscattering

3) ThethicknessofbodypartbeingimagedThickermoreComptonscattering lowCNR

4) Thegeometryoftheanti‐scattergridHighergridratio betterCNR lowSNR

2. SNR3. Spatialresolution

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X‐rayContrastAgents

• Needtodesigntomaximizethecontrastwiththeminimaldoseandtohaveaassmalldegreeofsideeffectsaspossible

• X‐raycontrastagentisdesignedtoabsorbX‐raysveryefficiently(tohaveastrongphotoelectricinteractions)

• TwobasicapplicationsofX‐raycontrastagents– Forgastrointestinal(GI)tractdisorders– Forvisualizationofvasculatureinthebrain,heart,andperipheryarteriesandveins


• ContrastagentsfortheGItract:– Bariumsulphate:tofindulcers,polyps,tumorsorhernias(탈장)inGItract

– BariumhasaK‐edgeat37.4keV,efficientforX‐rayabsorption

– Bariumsulphate isapowder,soitispreparedasathicksuspensioninwater

– ForstudiesofupperGItract,itisorallyadministered– ForstudiesoflowerGItract,itisrectallyadministered– Itentirelyfillsthelumen,andtheplacewhereitisabsentcanbeseenasalowX‐rayabsorbedarea

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• GIdiseases

ulcers polyps

hernias


• Bariumenematest• Bariumsulphate first,thenadministerair

• Bariumsulphate fillsthesurfaceoftheGItract

• Airdistendsthelumen• Thisisusedtocharacterizesmallpathologiesinthelargeintestine,colonandrectum

• Colonoscopyismorepopularnow

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• Iodinebasedcontrastagents– Administeredintravenouslyintopatient– IodinehasK‐edgeat33.2keV anditabsorbsX‐raygreatlyinbloodallows~50μmdiametersmallvesselsimaging

– CurrentlyusedIodinecontrastsarebasedontri‐iodinatedbenzeneringwithdifferentsidegroups

– Toreducesideeffects,thecontrastagentneedstobenon‐ionicwithlowosmolality

– Iodixanol hasaosmolalityclosetothatofbloodandCSF(290mOsm/kg)

– Osmolarity (Osm/L)andosmolality(Osm/kg)– Hypertonicsolution:hashigherosmolality causewatercomesoutfromthecell cellshrink(isusedtotreatcerebralhemorrhage)

– Hypotonicsolution:haslowerosmolality causethecellswellbyabsorbingwatercytolysis


• Iodinebasedcontrastagents– Theseareeithermonomeric(MW650~800)ordimeric (MW1300~1600)andhaveverylowbindingtoplasmaproteinsinbloodexcretedunmetabolized intheurinewithin24hrs

– Osmolalityofdimeric agentsaremuchlowerthanmonomericagent– Majorapplicationsofiodinatedcontrastagentsaredigitalsubtractionangiography,intravenousurography(IVU),pyelography(IVP),cholangiography(imagingbileduct)

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• Iodinebasedcontrastagents

IV urographyIV cholangiography:Bile duct imaging

SpecializedX‐rayImagingTech.

• Digitalsubtractionangiography(DSA)– Providesveryhighresolutionofbloodvessels(<100μmindiameter)

– Procedure1) Acquirearegularimage2) Injectabolusofiodinated

contrastagentsi.v.3) Acquireasecondimage4) Performanimagesubtractionof

thosetwoimages– DSAisusedtoinvestigatediseasessuchasstenosis(bloodvesselnarrowing)andclottingofarteriesandveins,irregularitiesofsystemicbloodflow

Cerebral angiogram

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• Digitalmammography:todetectsmalltumorsormicrocalcifications inthebreast

• Requiresaveryhighspatialresolution(<1mm)andCNR

26keV, solid line is from applying a 30μm thickness of Mo filter


• Alowradiationdoseisnecessarytoavoidtissuedamageusemolybdenum(K‐edgesat17.9and19.6keV)asananodeforX‐raytube

• Cathodefilamentisflat(nothelical)toproduceamorefocusedelectronbeam

• Thebevelangleissmallerthanusualtoproduceaneffectivefocalsizeof0.3mmorless

• TheglasswindowofX‐raytubeisreplacedbyberylliumtopreventalossoflowX‐rayenergybeam

• Amolybdenumfilter(30mthickness)isusedtoreducetheamountofhighenergyX‐rays(>20keV)

• Sometimes,analuminumfilterisusedwhenthebreastisradio‐opaque(attenuationofX‐rayishigh)

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• ThedetectorcanbeeitherCRorDR‐based• Alargefocal‐spot‐to‐detectordistance(45~80cm)isusedtoreducetheeffectsofgeometricunsharpness

• Theanti‐scattergridhasa4:1or5:1gridratio,25~50linespercmseptadensity,aseptal thicknessislessthan20m,andseptal heightislessthan1mm

• Needtocompressbreastto~4cmthicknesstoimprovelowenergyX‐rayspenetrationandtoreducetheComptonscatteringeffect


• Digitalfluoroscopy:usesacontinuousX‐rayimagingmonitorinterventionalsurgery(catheters,guide‐wires,stents,pacemakers)aswellasfordynamicstudiesofGItractandcardiovascularsystemusingacontrastagent

• UsesamodifiedDRdetectorsystem– ThicknessofCsI:Tl isincreasedto550‐650mtoincreasedetectionefficiency reducetheX‐raydose

• UsesaveryshortpulsesofX‐rays(~5‐20ms)• Typicallyacquireimagesupto30frames/sec• TheX‐raydoseperframeis~1/1000th ofthatusedduringserialimageacquisition

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• (left)acardiaccatheterizationlaboratory,• (right)aneurointerventional unitwithaC‐armdigitalfluoroscopy

ClinicalAppl.PlanarX‐rayImaging

• Thepresenceandseverityoffracturesorcracksinthebonestructureinthehead,chest,pelvis,arms,legs,handsandfeet

• Vascularimagingusingaiodinebasedcontrasttostudybloodflow,mainlyinthebrainandheart,andalsointheperipheryarterialandvenoussystems

• GItractdiseasesusingabariumsulphate usuallywithcontinuousmonitoringwithX‐rayfluoroscopictechniques

• Urinarytract:kidney,utreter andbladder(KUB)scansbyintravenouspyelograms(IVPs)

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• DentalX‐ray– Thispreoperativephotooftooth#3,(A),

revealsnoclinicallyapparentdecayotherthanasmallspotwithinthecentralfossa.Infact,decaycouldnotbedetectedwithanexplorer.Radiographicevaluation,(B),however,revealedanextensiveregionofdemineralizationwithinthedentin(arrows)ofthemesial halfofthetooth.Whenaburrwasusedtoremovetheocclusal enameloverlyingthedecay,(C),alargehollowwasfoundwithinthecrownanditwasdiscoveredthataholeinthesideofthetoothlargeenoughtoallowthetipoftheexplorertopasswascontiguouswiththishollow.Afterallofthedecayhadbeenremoved,(D),thepulpchamber hadbeenexposedandmostofthemesialhalfofthecrownwaseithermissingorpoorlysupported.

http://en.wikipedia.org/wiki/Dental_radiography

A selection of carbide burrs

A No. 23 explorer, also known as a 'sickle probe'


• IVPisperformedwithiodinatedcontrastagentinjectiontovisualizethefillingandemptyingoftheurinarysystem.Anexampleisshowntotheright.

• Normalexcretionoftheagenttakesabout30minutesfromthebloodstreamviakidneys

• IVPimagesareobtainedinseriesafteragentinjectiontofindanyobstructions

Renal pelvis

Several kidney cancers occurs at here