CT and MRITest.docx
- 文档编号:16332787
- 上传时间:2023-07-12
- 格式:DOCX
- 页数:54
- 大小:125.04KB
CT and MRITest.docx
《CT and MRITest.docx》由会员分享,可在线阅读,更多相关《CT and MRITest.docx(54页珍藏版)》请在冰点文库上搜索。
CTandMRITest
CTUnit
Vocabulary
1、geometry几何
2、axial断层
3、orthogonal正交
4、reconstruction重建
5、resolution分辨率
6、diagnose诊断
7、subsecond亚秒(小于1秒)
8、coronaryarteries冠状动脉
9、abdominaldiseases腹部疾病
10、high-contrast高对比度
11、helical/spiral螺旋
12、coronalplane冠状面
13、sagittalplane失状面
14、radiationdose射线剂量
15、pitch螺距(螺旋CT参数)
16、tube球管
17、contrastagent造影剂
18、phase相位
19、artifact伪影
20、detectors检测器
21、gantry机架
22、dataacquisition数据采集
23、iterative迭代
24、protocol协议
25、attenuation衰减
26、Hounsfieldunit(HU)霍斯菲尔德单位(CT数)
Pre-reading
HaveyouorsomeonethatyouknowhadaCTbefore?
Ifsowhy?
WhydopeopleonTVandintheMoviesgetCTscans?
DoyouknowwhatanX-Rayis?
Reading1
TextA:
X-rayComputedTomography
Focus
WhataretheadvantagesofCT?
Howdoesitfitinwithothertechnology?
X-raycomputedtomographyorComputertomography(CT),isamedicalimagingmethodemployingtomographycreatedbycomputerprocessing.[1]Digitalgeometryprocessingisusedtogenerateathree-dimensionalimageoftheinsideofanobjectfromalargeseriesoftwo-dimensionalX-rayimagestakenaroundasingleaxisofrotation.[2]
CTproducesavolumeofdatathatcanbemanipulated,throughaprocessknownas"windowing",inordertodemonstratevariousbodilystructuresbasedontheirabilitytoblocktheX-raybeam.Althoughhistoricallytheimagesgeneratedwereintheaxialortransverseplane,perpendiculartothelongaxisofthebody,modernscannersallowthisvolumeofdatatobereformattedinvariousplanesorevenasvolumetric(3D)representationsofstructures.Althoughmostcommoninmedicine,CTisalsousedinotherfields,suchasnondestructivematerialstesting.Anotherexampleisarchaeologicalusessuchasimagingthecontentsofsarcophagi.
UsageofCThasincreaseddramaticallyoverthelasttwodecadesinmanycountries.[3]Anestimated72millionscanswereperformedintheUnitedStatesin2007.[4]Itisestimatedthat0.4%ofcurrentcancersintheUnitedStatesareduetoCTsperformedinthepastandthatthismayincreasetoashighas1.5-2%with2007ratesofCTusage;[5]however,thisestimateisdisputed.[6]
ApatientisreceivingaCTscanforcancer.Outsideofthescanningroomisanimagingcomputerthatrevealsa3Dimageofthebody'sinterior.
Beforeyouproceed
WhataretheadvantagesofCT?
Howdoesitfitinwithothertechnology?
Terminology
Theword"tomography"isderivedfromtheGreektomos(slice)andgraphein(towrite).Computedtomographywasoriginallyknownasthe"EMIscan"asitwasdevelopedataresearchbranchofEMI,acompanybestknowntodayforitsmusicandrecordingbusiness.Itwaslaterknownascomputedaxialtomography(CATorCTscan)andbodysectionröntgenography.
Althoughtheterm"computedtomography"couldbeusedtodescribepositronemissiontomographyandsinglephotonemissioncomputedtomography,inpracticeitusuallyreferstothecomputationoftomographyfromX-rayimages,especiallyinoldermedicalliteratureandsmallermedicalfacilities.
InMeSH,"computedaxialtomography"wasusedfrom1977–79,butthecurrentindexingexplicitlyincludes"X-ray"inthetitle.[7]
Focus
Inthefollowingpayattentiontothemainusesforeachpartoforsystemofthebody,thewordsareinbold.Youshouldalsolearnthesewordsasyouwillseethemoften.
Diagnosticuse
Sinceitsintroductioninthe1970s,CThasbecomeanimportanttoolinmedicalimagingtosupplementX-raysandmedicalultrasonography.Ithasmorerecentlybeenusedforpreventivemedicineorscreeningfordisease,forexampleCTcolonographyforpatientswithahighriskofcoloncancer,orfull-motionheartscansforpatientswithhighriskofheartdisease.Anumberofinstitutionsofferfull-bodyscansforthegeneralpopulation.
Head
Computedtomography(CT)oftheheadorComputedAxialTomography(CAT)scanningusesaseriesofx-raysoftheheadtakenfrommanydifferentdirections.Typicallyusedforquicklyviewingbraininjuries,CTscanningusesacomputerprogramthatperformsanumericalintegralcalculation(theinverseRadontransform)onthemeasuredx-rayseriestoestimatehowmuchofanx-raybeamisabsorbedinasmallvolumeofthebrain.Typicallytheinformationispresentedascrosssectionsofthebrain.[8]
Inapproximation,thedenseramaterialis,thewhiteravolumeofitwillappearonthescan(justasinthemorefamiliar"flat"X-rays).CTscansareprimarilyusedforevaluatingswellingfromtissuedamageinthebrainandinassessmentofventriclesize.ModernCTscanningcanprovidereasonablygoodimagesinamatterofminutes.
Computedtomography(CT)hasbecomethediagnosticmodalityofchoiceforheadtraumaduetoitsaccuracy,reliability,safety,andwideavailability.Thechangesinmicrocirculation,impairedauto-regulation,cerebraledema,andaxonalinjurystartassoonasheadinjuryoccursandmanifestasclinical,biochemical,andradiologicalchanges.Propertherapeuticmanagementofbraininjuryisbasedoncorrectdiagnosisandappreciationofthetemporalcourseofthediseaseprocess.CTscandetectsandpreciselylocalizestheintracranialhematomas,braincontusions,edemaandforeignbodies.BecauseofthewidespreadavailabilityofCT,thereisreductioninarteriography,surgicalinterventionandskullradiography.OneadvantageoverabrainMRIisintheevaluationofintracerebralcalcifications.[9]
Lungs
CTcanbeusedfordetectingbothacuteandchronicchangesinthelungparenchyma,thatis,theinternalsofthelungs.Itisparticularlyrelevantherebecausenormaltwo-dimensionalX-raysdonotshowsuchdefects.Avarietyoftechniquesareused,dependingonthesuspectedabnormality.Forevaluationofchronicinterstitialprocesses(emphysema,fibrosis,andsoforth),thinsectionswithhighspatialfrequencyreconstructionsareused;oftenscansareperformedbothininspirationandexpiration.ThisspecialtechniqueiscalledhighresolutionCT.Therefore,itproducesasamplingofthelungandnotcontinuousimages.
Pulmonaryangiogram
CTpulmonaryangiogram(CTPA)isamedicaldiagnostictestthatemployscomputedtomographytoobtainanimageofthepulmonaryarteries.Itsmainuseistodiagnosepulmonaryembolism(PE).[1]ItisapreferredchoiceofimaginginthediagnosisofPEduetoitsminimallyinvasivenatureforthepatient,whoseonlyrequirementforthescanisanintravenousline.
MDCT(multi-detectorCT)scannersgivetheoptimumresolutionandimagequalityforthistest.Imagesareusuallytakenona0.625 mmslicethickness,although2 mmissufficient.Acontrastof50–100mlsisgiventothepatientatarateof4ml/s.Thetracker/locatorisplacedatthelevelofthepulmonaryarteries,whichsitroughlyatthelevelofthecarina.Imagesareacquiredwiththemaximumintensityofradio-opaquecontrastinthepulmonaryarteries.Thisisdoneusingbolustracking.
CTmachinesarenowsosophisticatedthatthetestcanbedonewithapatientvisitof5minuteswithanapproximatescantimeofonly5secondsorless.
AnormalCTPAscanwillshowthecontrastfillingthepulmonaryvessels,appearingasbrightwhite.Inidealconditions,theaortashouldbeemptyofcontrast,toreduceanypartialvolumeartifactthatmayresultinafalsepositive.Anymassfillingdefects,suchasanembolus,willappeardarkinplaceofthecontrast,filling/blockingthespacewherebloodshouldbeflowingintothelungs.
Cardiac
Withtheadventofsubsecondrotationcombinedwithmulti-sliceCT(upto320-slices),highresolutionandhighspeedcanbeobtainedatthesametime,allowingexcellentimagingofthecoronaryarteries(cardiacCTangiography).ImageswithanevenhighertemporalresolutioncanbeformedusingretrospectiveECGgating.Inthistechnique,eachportionoftheheartisimagedmorethanoncewhileanECGtraceisrecorded.TheECGisthenusedtocorrelatetheCTdatawiththeircorrespondingphasesofcardiaccontraction.Oncethiscorrelationiscomplete,alldatathatwererecordedwhiletheheartwasinmotion(systole)canbeignoredandimagescanbemadefromtheremainingdatathathappenedtobeacquiredwhiletheheartwasatrest(diastole).Inthisway,individualframesinacardiacCTinvestigationhaveabettertemporalresolutionthantheshortesttuberotationtime.
Becausetheheartiseffectivelyimagedmorethanonce(asdescribedabove),cardiacCTangiographyresultsinarelativelyhighradiationexposurearound12millisievert.Atthecurrenttime,neweracquisitionprotocolshavebeendevelopeddrasticallyreducingthexRaysradiationexposure,downto1mSv(cfr.Pavone,Fioranelli,Dowe:
ComputedTomographyorCoronaryArteries,Springer2009).Forthesakeofcomparison,achestX-raycarriesadoseofapproximately0.02[10]to0.2mSvandnaturalbackgroundradiationexposureisaround0.01mSv/day.Thus,cardiacCTAisequivalenttoapproximately100-600chestX-raysorover3years'worthofnaturalbackgroundradiation.Methodsareavailabletodecreasethisexposure,however,suchasprospectivelydecreasingradiationoutputbasedontheconcurrentlyacquiredECG(akatubecurrentmodulation.)Thiscanresultinasignificantdecreaseinradiationexposure,attheriskofcompromisingimagequalityifthereisanyarrhythmiaduringtheacquisition.Thesignificanceofradiationdosesinthediagnosticimagingrangehasnotbeenproven,althoughthepossibilityofinducinganincreasedcancerriskacrossapopulationisasourceofsignificantconcern.Thispotentialriskmustbeweighedagainstthecompetingriskofnotperformingatestandpotentiallynotdiagnosingasignificanthealthproblemsuchascoronaryarterydisease.
Itisuncertainw
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- CT and MRI Test