LazarBibin,JérémieAnquez,TamyBoubekeur,ElsaAngelini,IsabelleBlochTélécomParisTech,CNRSLTCIAbdelhamidHadjem,JoeWiartOrangeLabsR&D

,WorkshoponAnatomicalModels,16‐17june20091

Electromagneticfields

  Topics:StudyingtheinteractionbetweenEMwavesfromcellularphonesorWiFisystemsandthetissueswithinthehumanbody.

  Withnewtechnologiesandhabits:  Exposureofchildrenandfoetuseshasbecomean

importantquestion(WHO).

  Toassessexposurewithinthebody,weneed:  Numericalsimulations(dosimetry)  Realistichumanmodelsofadults,children,

foetuses…

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Dosimetry:Numericalmethods  Overthepast15years,severalstudies

havebeenperformed:  NumericalmethodsforsimulationofEMwaves

propagationinhumantissues.  Creationofheadandwholebodymodels.

  Dosimetrysimulationsgetfasterandmorecomplex:  FDTDdiscretizationmethods.  GPU‐basedimplementations.  Multi‐coreprocessors.  Headmodelwith1mmresolution:9millionsofcells(10

minutesforrunning).  Wholebodywith2mmresolution:60millionsofcells(2h

ofrunningtimes).

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Dosimetry:Exposurecomputation

  Physicalvalues:E,Hbutalsothespecificabsorptionrate(SAR).

  TheSAR:  characterizesthepowerdepositedintissues  quantifiestheabsorbedpowerpermassunit(W.kg‐1)  isoftenaveragedoverthewholebodyoroverasmallmass(1or10g)

  islinkedtotheelectricfield.

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Dosimetry:SARmeasure

where  σisthesampleelectricalconductivity(S.m‐1)  ρisthemassdensity(kg.m‐3)  Eisthespatialmagnitudeoftheelectricfield(V.m‐1).

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Dosimetry:resolutionneeded

  SARapproximation:  1goftissuesisacubehavingedgesof1cm.  2mmresolutiontoestimateSARintissuesisacceptable.

HumanBodyModels:Background

  Onlyfewwhole‐bodymodelsofadultswereproposed.

  Evenfewerchildrenmodels…  Foetusmodelsarerare.  Difficulties:

  Berealistic.  Berepresentative.  Basedonrealdata…

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PregnantWomenModels:Previouswork…

PregnantWomenModels:RPI

PregnantWomenModels:KATJA

PregnantWomenModels:MedicalImages  3Dultrasound(US)images

  PortRoyalandBeaujonhospitals(Paris,France).  18datasets.  Embryosatdifferentgestationalagesduringthefirsttrimester.

  Spatialresolution:isotropic&sub‐millimetric.

  3DMRIimages  SaintVincentdePaulhospital(Paris,France).  22datasets.  Largefieldofview,fastacquisition  Foetushave30to34WA.

  Spatialresolution:1×1×4mm3.11

PregnantWomenModels:Utero‐foetalunitsegmentation

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  Automaticsegmentation:  Statisticaldistributionsofintensitiesintegratedinadeformablemodel(US).

  Morphologicalinformationandspatialpositioningofthestructures(MRI)

  Manualsegmentation:  Free‐softwaretools:

  MIPAV(http://mipav.cit.nih.gov/)  Slicer(www.slicer.org)

AnquezJ,AngeliniE,BlochI(2009)“AutomaticsegmentationofheadstructuresonfetalMRI”.ISBI’09,Boston,USA,.

AnquezJ,AngeliniE,BlochI(2008)“SegmentationofFetal3DUltrasoundImagesbasedonStatisticalPriorandDeformableModel”.ISBI’08pages17‐20,Paris,France

PregnantWomenModels:Segmentationon3DUSdata

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PregnantWomenModels:Tissuelabelling

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PregnantWomenModels:Surfacereconstruction

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PregnantWomenModels:SegmentationonMRI

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PregnantWomenModels:Tissuelabeling

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PregnantWomenModels:Smoothingfoetussurface  AnisotropicMRI(1x1x4mm3)staircaseeffects.

  Incompatibilitywithdosimetrystudiesthatrequiresmoothandisotropicobjects.

  Gaussianfilteringofthesegmentedobjectstoreducethiseffect.

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PregnantWomenModels:GaussianFilteringofSurfaces

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PregnantWomenModels:Point‐basedsurfacereconstruction

  Generationofatriangularmeshfroma3Dpointset

  P:Pointsetasasurfacesampling  Position  Normal

  Superiorsurfacequality  Intensivelyusedincomputergraphicsapplications

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1.  Samplingasurfacefromthesegmentedvolumedata,byextractingasetofpoints.

2.  Evaluatenormalvectors.

3.  Filterthepointset,toeliminate:1.  Smallscalehighfrequencynoise.2.  Outliers.

4.  Extractameshviacontouring

21J. Anquez, T. Boubekeur, L. Bibin, E. Angelini and I. Bloch. Utero-fetal unit and pregnant woman modeling using a computer graphics approach for dosimetry studies. MICCAI, London, UK, September 2009.

PregnantWomenModels:Point‐basedsurfacereconstruction

PregnantWomenModels:Pointsetextraction

  pi:supervisedsegmentation.  ai:vectorassociatedtopitodefinetheexteriororientation(off‐constraint).  Dilationoftheinitialsegmentedobject.

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ai

dilation pi

PregnantWomenModels:PointSetNormalEvaluation

  NormalOrientation:LocalPrincipleComponentAnalysisperpointsample[Hoppe92]  Covariancematrixonk‐nearestneighbourhoods.

  Eigenvectorassociatedtothesmallesteigenvalue.

  Direction:decidedwiththeoff‐constraint

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pointspi normals ni

PregnantWomenModels:PointSetSurface(PSS)

  Definition:Smoothsurfacerepresentationfromapointcloud.

  Operator:MovingLeastSquare(MLS).  Properties:Approximatingorinterpolatingasetofpointstodefineacontinuoussurface.

  Evaluation:  Projectionprocedurethatleadstosurfacepoints(stationarypoints)

  Implicitform(f(p)=0).24

PregnantWomenModels:MLSoperator

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q

Hq

Π (q)

Wendland’s Quartic kernel

Projection operator

PregnantWomenModels:PointSetFiltering

  Noiseremoval:MLSprojectiondirectlyappliedoninputsamples.

  Outlierremoval:iterativemethodbasedonthePlaneFitCriterion[Weyrich2003]

  Criterionbasedonvarianceofprojectiondistancesonlocalaverageplane

  Iterativeoutliersearchoveraquadraticdecreasingbound

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PregnantWomenModels:Surfacemeshing

  Generalcase:  ImplicitPSS  Contouredbymarchingcubes

  Incaseoflargemissingareas:  PoissonSurfaceReconstruction[Kazhdan2006]

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PregnantWomenModels:Results

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Our reconstruction Direct Meshing

PregnantWomenModels:Foetalorgans

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Brain

Eyes

Heart

Lungs

Stomach

Kidneys

Urinary bladder

PregnantWomenModels:Foetuspositioning  Onlypartialinformationonthemotherbody

syntheticwomanmodel(Dazstudio©)

  Deformationstofittheabdominalpartpartiallyvisibleonimagingdata(FFDlattice).

  Insertionandpositioningofthefoetus(validatedbymedicalexperts).

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PregnantWomenModels:Womanbodydeformations

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PregnantWomenModels:Womanbodydeformations

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PregnantWomenModels:Foetuspositioning

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PregnantWomenModels:Setofmodels

  4pregnantwomenwithembryossegmentedfromUSimagesat8,9,10and13WA.

  5pregnantwomenwithfoetusessegmentedfromMRIimagesat30,32,32,33and34WA(variousrepresentativepositions).

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PregnantWomenModels:Results

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13 WA 35 WA

PregnantWomenModels:Voxelizedmodel  Resolution:2x2x2mm3.

  Onelabelforeachtissue.

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PregnantWomenModels:Armature  Allowarbitraryfoetalpositions.  Unrealisticdeformations.  Automaticfoetalsegmentationfromageneric

model.

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Dosimetry:Preliminaryresults

foetalage(weekofamenorrhea) 30 32 32 33 34.5

WholebodySAR(mW/kg/1W/m²)(foetus)

1 1.6 2 1 1.1

RatiowholebodySAR(foetus/pregnantwomen) 0.16 0.25 0.31 0.18 0.18

Ratio10gSAR(foetus/pregnantwomen) 0.026 0.028 0.042 0.033 0.025

MaximumSARover10g(foetus)mW/kg 5.8 7.8 10.7 8.1 6.2

Exposition: Planar frontal wave, Vertical polarization, Frequency: 900 MHz

E

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L. Bibin, J. Anquez, A. Hadjem, E. D. Angelini, J. Wiart and I. Bloch. Dosimetry studies on a fetus model combining medical image information and synthetic woman body. 11th World Congress on Medical Physics and Biomedical Engineering, Munich, Germany, September 2009.

Dosimetry:otherstudies

SARvstissues:Multilayersmodel

PregnantWomenModels:Preliminarydosimetrystudies

ValidityofanHomogeneousmothermodel

  WhatistheinfluenceofthemotherhomogenizationonthefoetusSAR?

  Testmodels  Heterogeneousadultmodel  Homogenizationoftissuesexcepta

ROI(shapeoffetus34.5s)

  Testwave  Planewave  E=1V/m,F=900MHz

PregnantWomenModels:Preliminarydosimetrystudies

Model WBSARμW/kgVH+Foetus

WBSARμW/kgFoetus

RatioWBSAR(VH+foetus)/foetus

VH(heterogeneous)&foetalROI(heterogeneous)

7.6 2.7 36%

VH(homogeneous)&foetalROI(heterogeneous)

6.1 0.8 13%

VH(homogenous)&foetus(heterogeneous)

6.2 0.8 13%

VH(skin+homogenous)&foetalROI(heterogeneous)

6.1 0.8 13%

VH(skin+homogenous)&foetus(heterogeneous)

6.1 0.9 15%

Victoria(homogenous)&foetus(real)

16 3.0 19%

NAOMI(heterogeneous)&foetus(real)

11 4.3 39%

  With a plane wave exposure, the homogenization (of the mother tissues) induces an underestimation of the foetus exposure

  Is it possible to have an equivalent tissues valid for the whole body?

  Is it possible to locally characterize the mother tissues?

PregnantWomenModels:Preliminarydosimetrystudies

HumanBodyModels:Preliminarydosimetrystudies

  Animalstudies:variationofthedielectricpropertieswiththeage

Conclusions

  Wehavedevelopedmodelsofpregnantwomenwithdetailedutero‐foetalunits:  atdifferentperiodsofthegestation,  indifferentpositions,  validatedbymedicalexperts!

  DosimetrysimulationsofSARmeasurementsshowthat:  Globalandlocalexposuresofthefoetusaremuchlowerthanforthemother.

  Foetalexposuredependsofthefoetalposition!44

Thankyouforyourattention.

FEMONUMproject:http://www.tsi.enst.fr/~anquez/Pages/femonum.html

Contacts:Lazar.bibin@telecom‐paristech.frelsa.angelini@telecom‐paristech.frjoe.wiart@orange‐ftgroup.com

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