医学教学课件英文版：The Advancement of Multidetector-row Computed Tomography (MDCT)

TheAdvancementofmultidetector-

rowComputedTomography

(MDCT)一、DevelopmentofCT

CT

CT(Computedtomography)hasanexcellentradiodiagnosticcharacteristics.itisanorganiccombinationofcomputerandx-raymodality.

Traditionalradiodiagnosishasbeengreatlyimprovedintheneweraofcomputerprocessing,displayingandstoringimages.Hounsfieldscalesystem(HounsfieldUnit,HU)hasbeenusedtorepresentthedifferencesofx-rayattenuationindifferenttissues.Forthese,itobviouslyimprovesthesensitivityofinherentdensitycontrastandreplacestheconventionaltomographybasically

.

Conventionaltomographyisatechniqueofusingx-raystoproduceanimageorimagesofstructuresataparticulardepthwithinthebody,bringingthemintoasharperfocuswhiledeliberatelyblurringstructuresatotherdepths.

CTavoidsoverlappingoftheadjacentstructures,providinghighdensityresolutionandgoodimageswithshortexaminingduration.

In1971,thefirstCTapparatuscameout;onlytheheadcouldbescanned,butthiswasaverygreatimprovementovertraditionalradiodiagnosis.In1974,wholebodyCTwaspossible,whichextendeditsscopefromthenecktotherestofthebody,includingthelimbs,successfully.

DevelopementofCT

1、1971：FirstCTapparatus(Hounsfield,Britain)

2、1979：HounsfieldwonNobermedicalaward

3、1989:SpiralCT

4、1991:SpiralCTof2slices

5、1999:SpiralCTof4slices

6、2000;SpiralCTof8slices

7、2001;SpiralCTof16slices

8、2003:SpiralCTof64slices

9、2005;SpiralCTof2X-raytubes

10、2007:SpiralCTof320slices

Now,thistechniqueisstilldevelopingveryfast.CTscannerswith4ormoreandevenupto320detectorrowsarewidelyusedinclinicalpractice.MDCTrepresentsasignificantadvanceoversingle-slicedetectorCTsinceitallowsrapidassessmentoflargeareasofthebody.

Multidetector-rowComputedTomography(MDCT)haschangedCTfromacross-sectionaltoathree-dimensionaltool.IthasbecomethenewCTstandardanditstechnicalabilitiesarerapidlyexpandingthespectrumofapplicationwithclinicallyrelevantexaminationsthatwerepreviouslynotpossiblewithconventionalscanning.

ExceptforallthepossessedsuccessfulapplicationsineveryregionofwholebodyCT,MDCTstressesonshorterscanduration,longerscanrangeandthinnersections,especiallyincontrastenhancementandCTangiography(CTA)whichopensupnewhorizons.ValuableexplorationshavebeenmadeintheapplicationsofinterventionalCT,

functionalCTimagingincerebralinfarctionandoncology.

Thegreatchallengeofmultidetector-rowcomputedtomography(MDCT)isdealingwith“thedataexplosion”.Eachpatientrequiresseveralhundredimages.ForcarotidandintracranialCTangiograms,routinelythereare375images(300mmcoverage,reconstructedevery0.8mm);aorticstudieshave450-500images(600mmcoverage,reconstructedevery1.3mm);Therefore,tooptimizeourclinicalprotocolsandtakefulladvantageofthelatestCTtechnologies,weneedtochangethewaythatweanalyze,transfer,andstoreCTdata.

Filmisnolongeraviableoption.workstation-basedreviewoftransversereconstructionsisanecessity.However,CTimagesanddiagnoseshavetobetransportedtoclinicsandtotheoperatingroomassoonaspossible.

二、ApplicationsofMDCT1CardiovascularSystem

Duetotheincreasednumberofslicesin16-sliceand64-sliceCTsystems,doseutilizationisimprovedcomparedwith4-sliceCTscanners,andsub-millimetercollimationneednolongerberestrictedtospecialapplications.

Excellentvolumedata,whichareacquiredbyMDCT,generateserviceablethree-dimensionalimagesusingvariousreconstructionmethods,suchasmultiplanarreconstruction(MPR),maximumintensityprojection(MIP),minimumintensityprojection,shadedsurfacedisplay(SSD),volumerendering（VR)andvirtualendoscopy.MIPVR

TheincreasedscanspeedofMDCTsystemscanbeusedtocoveranentirecardiacvolumeinonesingle,shortbreath-holdperiod,producinganisotropicdatasetfreeofcardiacmotionifcombinedwithretrospectivecardiactriggering.

AlthoughtheusefulnessofMDCTforvisualizationofcoronaryarterieshasbeenreportedwith4-or8-rowCTsystems,initialresultsfromstudieswith16-sliceMDCTsystemssuggestthatthistechnologynotonlyoffersthepossibilityofaccuratelyvisualizingcoronarystenosisnon-invasivelybutalsoofstudyingplaquemorphology.StenosisofcoronaryarteriesStenosisofcoronaryarteriesStenosisofcoronaryarteries

TheclinicalperformanceofcoronaryCTangiographyhascertainlybeensubstantiallyimproved,allowingvisualizationofsmallercoronarysegmentsandcoronarycalcifications.Inthefuture,MDCTwillbeusedtoscreenpatientspriortocardiaccatheterexaminationandtoeliminatemanyunwarrantedinvasiveprocedures.

ThetechnicaldevelopmentsofMDCThavealsodramaticallychangedtheapplicationofCTAoutsidetheheart.Thepossibilityofacquiringalargeisotropicscanningrangewiththinsliceswithoutanylossinspatialresolutionhasrevolutionizedtheassessmentofabdominalvascularpathologies.

With4-detectorrowCTscanners，thescanvolumehadtobefocusedononespecificabdominalvesselterritory;16-detectorrowtechnologynowallowsfullabdominalcoveragefromthediaphragmtothegroinwithfullspatialresolution.

Thistechniqueenablestheevaluationofthewholearterialvisceralvasculature，suchashepaticvessels,mesentericvessels,renalarteriesandtheaortic-iliacaxisinasingledataacquisition.

MDCThasbecomecriticalforthepre-procedureplanningandfollow-upofseveralendovascularprocedures,includingendovascularaneurysmrepair,lowerextremityrevascularization,andrenalarteryrevascularization.hepaticarteryrenalarteryhepaticarteryoflivercancermesentericarterystomachartery

Thehighspatialresolutionallowsevaluationofpulmonaryvesselsdowntosixth-orderbranchesandsignificantlyincreasesthedetectionrateofsegmentalandsubsegmentalpulmonaryemboli.Shorterbreath-holdtimesalsobenefitpatientswithunderlyinglungdisease.MDCThasthereforebecomeanattractivemeansforasafe,highlyaccurate,cost-effectivediagnosisofacutepulmonaryembolization(PE)andmayprovidealternativediagnoses.

pulmonaryembolization

Itisnowchallengingcatheterpulmonaryangiography.Withincreasinglyfasteracquisitionspeeds,contrastmediumdeliveryisbecomingincreasinglydifficult.Thevolume,concentration,andrateofinjection,allaffectthedegreeofenhancementthatisachievedwithaninjectionofcontrastmaterial.

Whilethearterialenhancementisgovernedbyinjectionspeedandiodineconcentration,themagnitudeofenhancementinparenchymalorgansisrelatedprimarilytotheamountofiodinethataccumulatesintheextravascularspace.

SincethehighspeedoftheMDCTscannerallowstherecordingofimagedataoverashorttimeperiod,modificationsoftotaliodinedosearebestachievedbyincreasingiodinecontrastconcentration,ratherthanincreasingthetotalvolumeofmediuminjected.ParticularattentiontomethodsofautomatedsalineflushinganddualinjectionspeedprotocolscanfurtherrefinethequalityofMDCTexaminations.

2.InterventionalCT

Duetoagrowingdemandforminimalinvasiveness,computedtomography(CT)isincreasinglyusedasanalternativetechniquetoconventionalfluoroscopy.Itssupportiveroleliesinitsuseasareliablediagnosticmodalityinthepre-interventionalwork-upandpost-interventionalfollow-upofminimallyinvasiveprocedures.Combininglowmorbidity,safety,minimalinvasiveness,andhighcost-effectiveness,inmanysituationsinterventionalCTispreferabletoalternativeinvasiveprocedures.

Post-interventionalCTexaminationsareagentlemeansoffollow-up,particularlyaftervascularinterventionssuchasatherectomy,percutaneoustransluminalangioplasty,stenting,orbypasssurgery.Inaddition,CTisincreasinglyusedfordirectlyleadingandmonitoringinterventionalprocedures.Amongtheseproceduresaresmall-needlebiopsies,insertionofdrainageorgastrictubes,post-traumaticfixationofunstablevertebralbodiesandetc.

Inbrief,MDCThasawiderangeofindicationspriorto,during,andafterminimallyinvasiveinterventions.Althoughmanualpuncturingofstructuressmallerthan8mmstillappearsunlikely,thegrowingavailabilityofhigh-precisionroboticsorsmartnavigationsystemsmaynotonlyhelptofurtherincreasetheaccuracyofthepuncturebutalsotoreducetheradiationdoseofbothpatientandinterventionalradiologist.

Onecanexpectthatinthefuture,newlayer-detectorarraysorflatpaneltechnologywillfurtherincreasediagnosticaccuracyandhencewidenthespectrumofindicationsforinterventionalMDCT.

3．FunctionalCT

Contrastenhancementiswidelyusedinmultidetector-rowcomputedtomography(CT)toimprovevisualizationofthevascularsystemandurinaryexcretorysystemandtoincreaselesion-to-tissuecontrast.Nevertheless,forpatientswithinthefirst6hoursofacutecerebralinfarction,thediagnosticandprognosticabilityofconventionalCTremainspoor.

Similarly,despiteconventionalcontrast-enhancedtechniques,masslesionsonCTmayremainhardtocharacterizeasbenignormalignant,bothatdiagnosisandfollowingcancertherapy.Furthermore,visualassessmentoftumorenhancementrarelyprovidesusefulprognosticinformationbeyondconventionalstaging.

ThispaperdescribeshowfunctionalCTtechniquescanmaximizethebenefitsofadministeringcontrastmediumandsoimprovetheassessmentofpatientssufferingacutecerebralinfarctionorcancer.(1)TechnicalConsiderations

Followingintravenousadministrationofcontrastmedium,theiodinecomponentofthecontrastmediumcausesalocalincreaseintheX-rayattenuationthatislinearlyproportionaltotheiodineconcentration.TheamountofattenuationchangeforagivenconcentrationofcontrastmediumdependsuponarangeoffactorsincludingtheCT

systemused,thetubevoltage(kilovoltspeak,KVP),andthebodyregionexamined.

AgreaterchangeinattenuationisobservedwithalowertubevoltageandfunctionalCTprotocolsmayadvocateatubevoltageaslowas80KVP.

Theconcentrationofcontrastmediumatcertaintime-pointsfollowinginjectioncanbeusedtocalculatearangeofphysiologicalparameters,includingcardiacoutputandglomerularfiltrationpergramofrenaltissue.

Atthetissuelevel,itispossibletomeasurebloodflow,bloodvolume,bloodvesselpermeabilityandthesizeoftheextracellularcompartmentwithineachvoxel.

Also,asimplemeasurementofpeaktissueconcentrationofcontrastmedium,whencombinedwiththedoseofcontrastmediumadministeredperkilogrambodyweight,canbeusedtocalculatetheratiooftissueperfusiontoaveragewhole-bodyperfusion.Commercialsoftwareisnowavailabletocalculatemanyoftheseparametersanddisplaythemascolour-codedfunctionalimages.

(2)AcuteCerebralinfarction

Bydemonstratingaregionalreductioninperfusionandprolongationoftransittime,functionalCTenablespositivediagnosisofacutecerebralischemiaandassessmentofprognosiswithinthefirstfewhoursofcerebralinfarctiononset,atimewhenconventionalCTimagesaretypicallynormal.

Bycomparingperfusionandbloodvolumeimages,itisalsopossibletodistinguishreversiblefromirreversiblechangeswithresultsthatarecomparabletodiffusion-weightedmagneticresonanceimaging.Areasofreversibleischemiademonstratereducedperfusionbutpreservedbloodvolume,reflectingpreservationofvascularautoregulationandhencetissueviability.

Irreversibleinfarctionischaracterizedbyreducedperfusionandbloodvolume.Theterm“penumbra”isgiventoaregionofreversibleischemiasurroundinganinfarctcore.Thedemonstrationofreversibleischemiahasbeenproposedasameanstoselectpatientsforthrombolysis.AcuteCerebralinfarction(3)Tumors

Contrastenhancementintumorscorrelateswithhistologicalassessmentsofmicrovesseldensityandthereforecanbeusedasaninvivomarkeroftumor