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3.
Tomographicmethods
3.1.Genesisandtypesoftomography
Tomographyisatechniqueusedtoimagetheinteriorofatestedobject,based
onmeasurementsmadeonitsboundary.Inordertoobtaininformationaboutthe
objectinvestigated,variousphysicalphenomenaareused,wheretheinformation
carriersare:X-rays,gammarays,ultrasounds,electronbeams,electriccurrents,
magneticfields,photons.Dependingonthespecificsofagiventomographictech-
nique,therearebothadvantagesanddisadvantagesintheareasofaccuracy,fre-
quencyandresolutionofreconstructedimages.Familiarizationwiththecharac-
teristicsofindividualtomographictechniquesallowsforaproperselectionofthe
methodofimagereconstruction.Thetheoreticalbasisoftomographyoccurredat
thebeginningofthe19thcentury.Theideaforobjectswithaxialsymmetrywas
presentedbytheNorwegianphysicistAbelin1826,andtheideawaselaboratedto
includeextensionstoobjectsofanyshapebytheAustrianmathematicianRadon
in1917.Intheearlyfifties,theideaofmeasuringandobservingtheparameters
offuelmixturesbasedontheirelectricalpropertieswasusedinthefuelandgas
industry.Smallcapacitiveprobeswereusedtomeasurelocalconcentrationsof
gas-solidflows.IntheseventiesmanyapplicationsbasedontheuseofX-raysand
isotopesourcesweredeveloped.Unfortunately,thesewerenotoptimalsolutions
duetothehighcostoftheequipmentandthelimitedsafetyoftheiruse.Mostofthe
methodsbasedonirradiatingtheobjectwithXraysalsohadanotherdisadvantage,
thetechniquerequiredalongexposuretime,whichisunacceptableinthecaseof
real-timephenomenameasurements.In1979,GodfreyHounsfieldandAllenCor-
mackwerejointlyawardedtheNobelPrizefortheirpioneeringachievementsinthe
fieldofX-raytomography.Inthemid-eighties,theirworkbegantoformthebasis
oftoday’stomography.AttheInstituteofScienceandTechnologyattheUniversity
ofManchester(UMIST)intheUnitedKingdom,aprojectconcerningcapacitive
tomographytoillustratemulticomponentflowsinoilwellswasinitiated.Simulta-
neously,intheCenterofEnergyTechnologyinMorgantownintheUSA,thedesign
ofacapacitancetomographysystemformeasuringthevacuumdistributioninliquid
gasbedswasinitiated.However,thecapacitivetransducersusedinbothsystems
wereonlysuitableforuseincasesofelectricallynon-conductiveenvironments.
Manyinterestingtomographictechniqueshavebeendevelopedovertheyears,suchas:
•
X-rayTomography
•
ElectricalImpedanceTomography
•
ElectricalCapacitanceTomography
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