MetalArtefactReductioninCTDANIEL MARRINER

MetalArtefactReductioninCT MetalArtefact

ClinicalIndicationsforMAR

SEMARandHowItWorks

TechnicalConsiderations

CaseStudiesutilisingSEMAR

MetalArtefactinCT PolychromaticBeam

Widespectrumofenergies,linearattenuationcoefficientverydependentonenergyofxraybeam

BeamHardeningArtefact

Attenuationonlowerenergyphotons,increasedeffectiveenergyofbeamandtissuereflectedbylowervalueof

Violationoflinearsuperimpositionofattenuationvaluesonce backprojected

PhotonStarvation Statisticalerroroflowphotoncounts

Darkandbrightstreakspreferablyindirectionofgreatestattenuation

Figure1:Beamhardeningartefactfrombilateralhipreplacements

Figure2:SEMARappliedtorevealanatomynormallyobscuredbybeamhardening

ClinicalIndicationsforMAR

DiagnosisofPostOperativeComplications

ProstheticLoosening

PolyethyleneWearing

Periprosthetic Fractures

PostOperativesofttissuemasses/lesions

AneurysmClips,Lumbarfusions,Billiary clips,anywheremetalwillimpedesurroundingstructuresandaccuratediagnosis.

SEMAR(SingleEnergyMetalArtefactReduction)

ToshibabasedMARtechnique

UsesDataSegmentation,ForwardProjection,andInterpolation

Canuncoverboneandsofttissuestructuresnormallyobscuredbybeamhardeningeffects

Iknowwhatitisbuthowdoesitwork!?

Figure3:SEMARalgorithm.BPJ;BackProjection.FPJ;ForwardProjection.

Asinogram ofalemonwithametalrodinserted.

Thehorizontaldirectionofthesinogramcorrespondstotheraydataineachprojection.

Theverticalaxisrepresentstheprojectionsacquiredatdifferentanglesthroughthelemon.

Thebrightregioncorrespondstothehighattenuationofthemetalrodandshowsasanobvioussinewave.

Figure4:Sinogram oflemonwithmetalrodandFBJimage

Figure5:Acomplete360degreesonogramofanabdominalcrosssectioniscomparedwiththereconstructedimageusingFBP.

SEMAR Rawdataisforwardprojectedtocreateasinogram

Samedataisreconstructedusingfilteredbackprojection(FPB)

Metalissegmentedinthisimageandthenforwardprojectedcreatingametalonlysinogram

Metalonlysinogram subtractedfromoriginalsonogram

Linearinterpolationusedtocalculatemissingdata

OriginalProjectionData MetalOnlySinogram ExtractionofMetalfromSinogram andInterpolation

OriginalImage SegmentationofMetal

SEMAR Interpolatedsinogram reconstructedusingFBP

Imagesegmentedagaintofurtherexcluderesidualmetalartefacts

Thisdataisagainforwardprojectedintoasinogram andlinearinterpolationusedtofillinthegaps

Imagevolumeisreconstructedandoriginalmetalsegmentationisreintroduced

BPJafterfirstpassinterpolation

Furthereliminationofmetalobjectsandcorrectedsinogram

BPJofcorrectedsinogram

FinalImage

OriginalMetalSegmentationReintroduced

AIDR

TechnicalConsiderations Toshiba160Slice

40mmdetectorwidthwith.5mmslices(abilitytodo.25mm)

Version6Software 10volumeblocksof40mmmakingtotalscancoverageof400mm(40cm)

Mostrecentsoftware(Version7)andscannershave16cmdetectorcoverageandcanbeappliedretrospectivelytoanyregion

Version7canbeappliedprospectivelyandretrospectivelytoregionofinterest canbeappliedtolongerscanranges

120kvandAIDRstandardprotocol howcanwechangetechnicalparameters?

Figure6:SEMAR6blockvolumeacquisitionscoutofbonewithmetalhardware

Figure7:Axial.5mmslicethroughbonedemonstratesbeamhardeningartefactandassociatedphotonstarvation.Theacquisitionprotocolused120kv,maxof250mA(modulating),andAIDRstandard.

Figure8:Demonstrationofhowincreasingkv decreasesmetalartefactinadditionwithSEMAR

80kv 100kv

120kv 135kv

Figure9:DemonstrationofhowincreasingAIDRfromstandardtostrongdecreasesnoiseassociatedwithmetalartefactwithSEMAR

Figure10:DemonstrationofhowloweringthestandarddeviationandincreasingmAvaluescanreducemetalartefact.

135kv250mA

135kv266mA

CaseStudy1ClinicalHistory

Periprosthetic fracturerightkneepostmechanicalfall?Assesspositionandextension.(1stpresentation)

RightTKRperiprosthetic fracture?PleaseperformfinesliceCTwithartefactreductionand3Drecons?stablevsunstableprosthesis.MayrequirelongstemTKRrevisionifunstable.(2ndpresentation)

CONVENTIONAL AXIAL SEMAR AXIAL

CONVENTIONAL AXIAL SEMAR AXIAL

CORONAL BONE SEMAR CORONAL SOFT SEMAR

Conclusion StudyofbetterdiagnosticqualitythanCTperformedadayprior

Periprosthetic fractureofthelateralfemoralcondyle

Verticalfracturelineextendingfromsupracondylarregiontolateralmarginofprosthesis

Approximately5mmoflateralandsuperiordisplacement

Moderatesizedlipohaemarthrosis noted

CaseStudy2ClinicalHistory

66FL3pathologicalfractureD3postposteriorinstrumentedfusion.ForCTlumberspineon21/4/15forpictureofbonymorphology?residualtumour.

Conclusion PediclescrewsbeenplacedatL1L2andL4L5withposteriorrods

L3laminectomyhasbeenperformedwithresectionofmostoftheposterioraspectoftheL3vertebralbody

L3bodydemonstratesextensivebonedestructionextendingintobothpedicles.

SofttissuedensitymaterialextendingposteriorlyinthespinalcanalisidentifiedattheL3level

Mostlikelyrepresentsresidualsofttissuetumourorhaematoma

Summary SEMARplaysacriticalroleinreducingmetalartefacttodiagnosepostoperativecomplications

Shouldbeusedforarangeofanatomywheremetalmayaffectanaccuratediagnosis

ImportanttounderstandhowrelevanttechnicalparameterscaninfluenceaSEMARimage

ApplyingSEMARcanbevitaltoapatientsdiagnosisandfuturemanagement

1. Boas,F.E&Fleischmann,D.(2012).CTartifacts:Causesandreductiontechniques.ImagingMed,4(2),229240.

2. Bushberg,J.T.,Seibert,J.A,Leidholdt jr,E.M&Boone,J.M(1994).TheEssentialPhysicsofMedicalImaging.Davis,CA:UniversityofCalifornia.

3. Teixeira,P.,Meyer,J.&Blum,A.(2014).SingleenergymetalartefactreductionalgorithmforCTevaluationofperiprosthetic softtissues:Clinicalapplications.ViSIONS,23,4345

4. ToshibaMedicalSystems(2014).CTClinicalCaseStudy BilateralHipReplacementEvaluationwithSEMAR.ToshibaLeadingInnovation.

5. Sofue,K.,Yoshikawa,T.,Negi,N.,Ohno,Y.,Sugihara,N.,Murakami,T.,Koyama,H.,Nishio,M.,Sugimura.,K,Kobe,JP.&Ohtawara,JP.(2014).AbdominalCTwithSingleEnergyMetalArtifact Reduction(SEMAR):InitialExperiences,EuropeanSocietyofRadiology,35.