3D Dental Imaging by Spiral CT.docx

3D Dental Imaging by Spiral CT.docx

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3DDentalImagingbySpiralCT

3DDentalImagingbySpiralCT

MichaelW.Vannier,CharlesF.Hildebolt,

RobertH.Knapp,GaryConover,NaokoYokoyama-Crothers,GeWang

MallinckrodtInstituteofRadiology

WashingtonUniversitySchoolofMedicine,St.Louis,Missouri63110

ABSTRACT

Three-dimensionalimageacquisition,display,andanalysisofdentalstructureswasperformedandvalidatedusingspiralcomputedtomography（SCT）withmetalartifactsuppression.Isolatedextractedteeth,adrymandible,cadavermandible,andcadaverheadwerescannedandreconstructedusingaspiralCTscanner（SiemensSomatomPLUS-S）with1mmdetectorcollimation,1-mmtablefeed,and0.1-1mmreconstructionintervalusingspeciallydevelopedsoftware.Algorithmsformetalartifactreductionincludingextendedattenuationrangeandinterpolationofmissingprojectionswereapplied.Volumetricrenderingofvoxelsumimageswasperformedtosynthesizeimagescomparabletoconventionalintraoraldentalradiographs.Directcomparisonofvoxel-basedsyntheticanddigitizedfilmimageswasmade.Severalisolated,extractedteethweresectionedwithadiamondsawandsubmittedforhistomorphometricanalysistoaidindirectcomparisonwithCTsliceimagesobtainedbymultiplanarreconstruction.

Metalartifactreductionwassuccessfulinmarkedlyreducingthestreaksandstarpatternsthatusuallyaccompanymetallicrestorationsandintraoralappliances.IndividualteethwerecomparabletoCTsliceimages.Voxelsumimageswerecomparabletodentalradiographs;however,fortheSCTimages,thespatialresolutionwashigherwithintheplaneofsectionthanitwasorthogonaltotheplaneofsection.

SerialexaminationswereobtainedbySCT,registeredbysurfacematching,andintervalchangemeasuredby3Dsubtraction.Simulatedlesionsandrestorationswereintroducedandquantitativelyevaluatedpre-andpost-interventionallytoassessimagingmethodperformance.

Keywords:

spiralCT,helicalCT,dentalimaging,threedimensional

1.INTRODUCTION

Thedentomaxillofacialcomplexissusceptibletodiseasesthatmanifestearlyassubtlechangesinbonydensityandgeometry.Thesechangesmaybedetectedbyimaging.Ourlongtermgoalistodevelop,characterize,andapplyvolumetric3Dx-rayimagingbaseduponspiralx-raycomputedtomographytothedentomaxillofacialcomplex.Weanticipatemajorgainsindiagnosticperformanceforearlydiseasedetection,treatmentmonitoringandplanning,andpopulationstudiesusingthistechnology.

Conventionalfilm-baseddentalradiographyisthedefactostandardforclinicalandresearchexaminationoftheoralhardtissues.Withthistechnique,anextraoralx-raysourceisalignedwitharadiographicfilmplacedeitherinthepatient'smouthoralongthesideofthepatient'shead.Thex-raysareattenuatedbaseduponthephysicalcharacteristicsofthestructuresofinterest.Thetransmittedx-raybeaminteractswiththefilm'semulsionproducingalatentimage.Thefilmischemicallyprocessedtoprovideavisibleimage.[1]

Thevastmajorityofdentalradiographyisperformedforevaluation,location,magnitude,andextentofdentalcaries.Cariesdiagnosisismostcommonlyperformedwithintraoralperiapicalandbitewingradiographs.Theperiapicalfilmincludestheentiretoothand3?

mmofperiapicalbone.Thebitewingdisplaysthecrownsandseveral/mm誷oftherootsandsupportingboneofthemaxillaryandmandibularteeth.Becausethebitewingcontainsviewsofbothmaxillaryandmandibularteeth,itisthemostusedradiographforcariesdiagnosis.[2]Thereis,however,agreementthatbitewingshaveonlylimitedsuccessincariesdiagnosis,[3,4,5,6,7,8]withsomestudiesindicatingthatonly60%ofthelesionsaredetectedandthatoften20%ofnoncarioustoothsurfacesarediagnosedashavingcavities.[9,10]

Bitewingradiographsandperiapicalsarealsousedtodetectandmonitoralveolarboneloss,whichismostcommonlyattributedtobacteriaindentalplaque（periodontalorgumdisease）,smoking,anddiabetes.Treatmentstoreduceorpreventalveolarbonelossarealsoevaluatedwithbitewingsandperiapicals.Forthepastsevenyears,wehavebeeninvolvedwithdevelopingandevaluatingdigitalimagingmethodsforradiograph-basedquantificationofalveolarbone.[11,12,13,14,15,16,17,18,19]Althoughweandothershaveshownthatbitewingandperiapicalradiographscanbeeffectiveinquantifyingalveolarbone,thesemethodshaveoneseverelimitation:

theyarebasedupontwo-dimensionalrepresentationsofcomplexthree-dimensionalbonyanatomy.

Panoramicradiographyisusedtosupplementbitewingandperiapicalradiographs.Thismodality,introducedinthe1950s,isemployedinover50%ofdentalpractices.Themethodproducesatomographicimageofthemandibleandmaxillaonasingle5x12-inchfilm.Thepanoramicimagesuffersfromthesamelimitationasbitewingsandperiapicalsduetoitstwo-dimensionalrepresentationofcomplexthree-dimensionalbonyanatomy.Onlystructureswithinanarrowcurvedslicethroughthemaxillaandmandibleareinfocus.Comparedtointraoralradiography,panoramicradiographyhaspooraccuracyforcariesdiagnosisandalveolarbonequantification.[20,21,22,23,24,25]

Withinendodontics,periapicalradiographsareusedtodiagnoseperiapicalboneloss,studyrootcanalmorphology,detectthepresenceoflateralcanals,determineworkinglengthsforthemechanicalenlargementofcanals,andperformpostoperativeevaluations.Restorativedentistryalsoutilizesbitewingsandperiapicalstocheckmarginsofrestorations（precementation）,evaluatecrown:

rootratios,andevaluatecavitypreparations.Panoramicandperiapicalradiographsareusedwithinoralsurgeryforpresurgicalevaluationsofbonyimpactions,implantsites,rootmorphology,mandibularcanalandmaxillarysinuslocation.Withinorthodontics,cephalometricradiographsareusedtoassessgrowthandtootheruptionpatternsandtopredicttreatmentoutcomes.Cephalometricradiographsarelateralandfrontalskullfilmstakenunderhighlycontrolledconditions.Cephalogramsarealsoincorporatedinorthognathicstudies,morphometricstudies,andstudiesofgrowthanddevelopment.

Allx-raytransmission-basedradiographssufferthelimitationinthattheyaretwo-dimensionalprojectionsofcomplexintrinsicallythree-dimensionalanatomy.Theresultisthatbuccal-lingual（facial-oral）structuresareusuallyindistinguishable.Thereiscurrentlynotraditionalmethodofdentalradiographythatpermitsviewinginternaldentalanatomywithoutthesuperimpositionofotherstructuresnoristhereatraditionalmethodofviewingdentalanatomyinabuccal-lingual,cross-sectionalperspective（tangentialview）.Insum,byvirtueofthesource-detectorgeometryrequirements,onlyalimitednumberandtypesofprojectionscanbeobtainedthroughtransmissionradiography.Softtissuesarenotdiagnosticallyimagedandforpracticalreasons,theexposuresettings,dose,andlevelofdetailarerelativelyfixedandrepresentasignificantcompromise.Withthesemethods,thereisanacknowledgedlackofsensitivityfordetectingandquantifyingsmallchangesinthehardtissues.

Theadventofcomputerizedtransverseaxialscanning（computedtomography,orCT）[26]greatlyfacilitatedaccesstotheinternalmorphologyofsofttissueandskeletalstructures.ConventionalCTscanningisaccomplishedbyacquiringaseriesofindividualimages.Typically,theimagesrepresentcross-sectionsthroughthebody.Theimageslicesarefrom1to10millimetersthickandthedistancesbetweenthemarefrom1to10or20millimeters.ProjectiondataareacquiredandreconstructedintoimagesasthepatientismovedincrementallythroughtheCTgantry（thatis,animageisobtained;thepatientismovedtothenextscanningposition,andthenextimageisobtained）.CTscanspossessnomagnificationerrorscausedbygeometricdistortions.Sucherrorsarecommoninconventionalradiographs.AlimitationofconventionalCTisthatalthoughithasahighdegreeofaccuracywithinindividualslices,ithasrelativelylowbetween-sliceaccuracy[27]evenwithrelativelynarrowcollimation（2mm）andnointerslicegaps.CTscansavoidthesuperimpositionofstructuresandare,therefore,moredesirablethanconventionalradiographyasamorphometrictool.Sinceitsinception,computedtomographyhasprovidedquantitativemeasurementsformanydifferentbiologicalsystemsandhasbeenusedinpre-andpost-surgicalmappingprocedures,[28]theevaluationofdevelopmentalandregressivedentalabnormalities,[29]facialtrauma,andtemporomandibularjointdisorders.[30,31,32,33]

Recently,anewCTtechnique,spiralCT（SCTorvolumeacquisitionCT）,hasbeendeveloped.ThismethodhasseveraladvantagesoverstandardCTimaging.Byemployingsimultaneouspatienttranslationthroughthex-raysourcewithcontinuousrotationofthesource-detectorassembly,SCTacquiresrawprojectiondatawithaspiralsamplinglocusinarelativelyshortperiod.[34]Withoutanyadditionalscanningtime,thesedatacanbeviewedasconventionaltransaxialimages,asmultiplanarreconstructions,orasthree-dimensional（3D）reconstructions.Suchimagesprovideanopportunitytoobtainaccurateimagesatanyarbitrarylocationwithinthevolumedataset.

Theuniquearrangementofthegantryandrotatingx-raysourceassemblyradicallyreducesscantimes.Partialbodyscanscanbecompletedduringasinglebreathhold.WithstandardincrementalCT,smallobjectscanbemissedortheirdetectioncompromisedifthepatient'sdegreeofinspirationandexpirationvariesfromscantoscan.Moreover,multiplanarand3DimagereconstructionsofstructuresfromstandardincrementalCTdataaredegradedbymotion-inducedmisregistrationar