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3.SabineIserhardt-Bauer,DiplInf,
4.NielsC.Kö
stner,
5.MiriamSchempershofe,
6.WalterJ.Huk,MD,
7.ThomasErtl,PhD,
8.ChristianStrauss,MDand
9.JohannRomstock,MD
+AuthorAffiliations
1.1FromtheDepartmentsofNeuroradiology(B.F.T.,N.C.K.,M.S.,W.J.H.)andNeurosurgery(P.H.,C.S.,J.R.),UniversityofErlangen-Nuremberg,Germany;
andtheVisualizationandInteractiveSystemsGroup,UniversityofStuttgart,Germany(S.I-B.,T.E.).Presentedasascientificexhibitatthe2001RSNAscientificassembly.ReceivedSeptember18,2002,revisionrequestedOctober22,revisionreceivedandacceptedOctober23.AddresscorrespondencetoB.F.T.(e-mail:
tomandl@neuroradiologie-erlangen.de).
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Abstract
Computedtomography(CT)angiographyisawell-knownimagingtechniquecommonlyappliedtoboththedetectionandtherapyplanningofintracranialaneurysms.Forthispurpose,currentstudiespredominantlyfocusonthree-dimensional(3D)representationsofCTangiographicvolumesobtainedwithvaryingvisualizationapproachesondifferentcomputers.Interactivemanipulationperformedbyusersindividuallyisanimportantprerequisitefordataanalysis.However,thisleadstoinconsistentandbarelyreproducible3Dvisualizationresults.Furthermore,thequalityofany3Drepresentationdependsontheappliedvisualizationstrategy(eg,maximum-intensityprojection,shaded-surfacedisplay,directvolumerendering).Toovercometheselimitations,theauthorspresentanovelmethodforstandardizedvisualizationofCTangiographicvolumes,consistingofthreesteps:
(a)transferoftheimagedatatoaremotehigh-endgraphicsworkstation,(b)automatic3Dvisualizationwithhigh-resolutiondirectvolumerendering,and(c)consecutivevideogenerationperformedaccordingtoastandardizedprotocol.Therecordedvideosequencesaretransferredforevaluationtoalocaldesktopcomputer.Intheexperimentalsetup,high-qualityvideosbasedon3Dvisualizationswereproducedinlessthan60minutesperpatient.Althoughaneurysmsabovetheskullbaseareusuallyvisualizedwithexcellentquality,theanalysisofaneurysmsattheskullbaseisstilldifficult.
©
RSNA,2002
∙Aneurysm,CT,17.12112,17.12115,17.12116,17.12117
∙Aneurysm,intracranial,17.73
∙Cerebralbloodvessels,CT,17.12112,17.12115,17.12116,17.12117
∙Computedtomography(CT),three-dimensional,17.12117
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Introduction
Suddenonsetofsevereheadacheisthetypicalleadingsymptominpatientswithsubarachnoidhemorrhage.Thecauseofsubarachnoidhemorrhageisarupturedaneurysmin75%ndash;
85%ofcases,nonaneurysmalperimesencephalichemorrhageinabout10%ofcases,andavarietyofrareconditionssuchasarteriovenousmalformationsinabout5%ofcases
(1).Computedtomography(CT)isthefirststepintheexaminationofthesepatients.Ifsubarachnoidhemorrhageisconfirmed,itisnecessarytodetectthesourceofbleedingforappropriatetherapy.Whiledigitalsubtractionangiography(DSA)isstillthemostsensitivetoolforthedetectionofintracranialaneurysmsandothervascularmalformations,manystudieshaveshowntheusefulnessofCTangiographyforthispurpose.ThereportedsensitivityofCTangiographyhasbeenreportedtobeintherangeof70%ndash;
96%(2–7),dependingonthesizeandlocationoftheaneurysm(8).Inmostofthesestudiesthree-dimensional(3D)visualizationsoftheintracranialvesselswereusedtoassesthevalueofCTangiography.Inthistechnique,thesectionimagesaretransferredtoaworkstationand3Dvisualizationofvascularstructuresisperformed.Theaimof3Dvisualizationistoextractthevascularstructuredatafromthevolume.Thesemethodsalwaysleadtolossofinformation,regardlesoftheappliedalgorithm.Althoughthesuppressionofbraintissuesurroundingtheintracranialvesselsisaprerequisiteforprovidinganopenviewoftheintracranialarteriesina3Drepresentation,itispossiblethatimportantinformationsuchascalcificationorthrombosedpartsofananeurysmisnotseen.Therefore,itismandatorytoaccuratelystudythesectionimagesbefore3Dvisualizationisperformed(Fig1).
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Figure1a.
ComparisonofsectionimagesfromCTangiographyto3Drepresentationinapatientwithseveresubarachnoidhemorrhageandaneurysmsofbothinternalcarotidartery(ICA)bifurcations.Theleftaneurysmiscalcified.(a)AxialsectionimageatthelevelofthecircleofWillisshowsananeurysmatthebifurcationoftherightICA(arrow).Thebasalcisternsarefilledwithsubarachnoidblood(arrowheads).Forabettercomparisonwiththe3Dimage,theviewisfromabove.(b)AxialsectionimageatthelevelofacalcifiedaneurysmoftheleftICAbifurcation(arrow).Theextentoftheintramuralcalcificationisclearlydemonstrated(arrowheads).Again,theviewisfromabove.(c)Superoinferior3Dvisualizationwithdirectvolumerenderingshowsthetwoaneurysms(arrows)inrelationtotheintracranialarteriesandtheskullbase.Theintramuralcalcificationwithintheleftaneurysmisdemonstrated,butitsextentisnotclearlyseen(arrowhead).Notethatbraintissueandsubarachnoidbloodarenotdemonstratedwithinthe3Drepresentationbecausetheselectedthresholdsdonotincludethevoxelscontainingthisinformation.
Figure1b.
Figure1c.
Littleisknownabouttheinfluenceofpostprocessingmethodssuchasmaximum-intensityprojection(MIP),shaded-surfacedisplay,anddirectvolumerendering(9–11).However,itcanbeassumedthatthesameCTangiographydatamayresultindifferentdetectionrateswhenvariousvisualizationstrategies,computerplatforms,andgraphicshardwareareused(8,12–15).Inaddition,theuseroftheworkstationmustbefamiliarwithseveralmanipulationtools.Thesecomprisethetoolsthatpositionobjectssuchasclippingplanes,definethresholds,andadjustso-calledtransferfunctionsforcolorandopacityvalues.RatherthaninvestigatingthevalueofCTangiographyfortheevaluationofintracranialaneurysms,availablestudieshavebeenanalyzingspecificsystems.Ingeneral,thesehaveconsistedoftheinvestigationmodality,suchasCTormagneticresonance(MR)angiography,asthesourceofthedata;
theavailableworkstation,includingrenderingsoftware;
andfinally,aninvestigatorsteeringthe3Dvisualizationprocess.Figure2illustratesthetypicalworkflowinsuchasystem.
Figure2.
TraditionalworkflowofCTangiography(CTA).Thedataareanalyzedbyanindividualuseronacommerciallyavailableworkstation.
Reproducibleprotocolscontaininginformationaboutthesectionthickness,theinjectionrateofcontrastmedium,andthereconstructionofthesectionimagesareusuallystandardintheseinvestigations.Astandardizedvisualizationmethodthatprovidesreproducible3DrepresentationsofCTangiographicdatarequirestheuseofaunique