医学影像学教学课件：Basics of Ultrasound and Echocardiography

BasicsofUltrasoundandEchocardiographyPartI

FundamentalphysicalprinciplesofdiagnosticultrasoundDefinitionofultrasoundUltrasoundreferstohigh-frequencysoundwaves,over20000cyclespersecond(20000Hzor20kHz)Mostdiagnosticapplicationsemployfrequenciesof1to13MHzTheunitoffrequencyishertz(Hz);kilohertz(kHz;1kHz=1000Hz);megahertz(MHz;1MHz=1,000,000Hz)

Physicalcharacteristicsofultrasound1.Soundwaves:Mechanicaloscillationsthataretransmittedbyparticles

2.Wavelength(λ),Waveperiod(T)and

frequency(f)Figure1Soundwavesλ:

ThedistanceoccupiedbyeachcycleT:

Thetimewhichisrequiredtoproduceeachcyclef:

Thenumberofcyclescompletedpersecond.Thefrequencyofthewaveis1/T

Physicalcharacteristicsofultrasound3.Velocityofsound(C)

Propagationvelocityofsoundisdeterminedbythephysicalpropertiesoftissue.Inthebody,propagationvelocityofsoundisassumedtobe1540

meterspersecond(m/sec).

Thepropagationvelocityofsound(c)isrelatedtofrequencyandwavelengthbythefollowingsimpleequation:

c=fλFigure2Propagationvelocity

Physicalcharacteristicsofultrasound4.AcousticImpedance

ResistanceofferedbytissuetomovementofparticlescausedbyultrasoundwavesAcousticimpedance(Z)isdeterminedbyproductofthedensity(ρ)ofthemediumpropagatingthesoundandthepropagationvelocity(c)ofsoundinthatmediumZ=ρc

Physicalcharacteristicsofultrasound5.Reflection/Refraction/ScatterDirectionofsoundwavewillchangewhenitstrikesaboundaryoftwodifferentmediumswithdifferentacousticimpedanceWhensoundpassesfromatissuewithoneacousticpropagationvelocitytoatissuewithahigherorlowersoundvelocity,thereisachangeinthedirectionofsoundwave

Scatteroccurswhenthedimensionofreflectorsismuchsmallerthanthewavelenthofsoundwaveθ2=86°θ1=70°Figure3

Reflection/Refraction/Scatter

Physicalcharacteristicsofultrasound6.Attenuation:

Assoundpassesthroughtissue,itlosesenergy,andthepressurewavesdecreaseinamplitudeastheytravelfartherfromtheirsourceAttenuationistheresultofthecombinedeffectsofabsorption,scatteringandreflectionFigure4

Tissueattenuationcausesgraduallossofdisplayofdeepertissues

Physicalcharacteristicsofultrasound7.Dopplereffect

Whenultrasoundistransmittedtowardsastationaryreflector,thereflectedwaveswillbeofthesamefrequencyasthoseoriginallytransmittedIfthereflectorismovingtowardsthetransmitter,thereflectedfrequencywillbehigherthanthetransmittedfrequency.Ifthereflectorismovingawayfromthetransmitter,thereflectedfrequencywillbelowerthanthetransmittedfrequency

Dopplerequation:Figure5

Dopplereffect

Differentmodesofdiagnosticultrasound1.Amode:

“A”

meanamplitude.Theechogenicitiesareshownaspeaks,andthedistancebetweenthevariousstructurescanbemeasured2.Bmode:

“B”

meanbrightness.Variationsinintensityorbrightnessareusedtoindicatereflectedsignalsofdifferenttissue.Theechogenicitymaybeclassifiedintofivelevelslistedbelow:Anechoic(noreflection)Hypoechoic(lessreflection)Isoechoic(lessreflection)Hyperechoic(morereflection)Strongecho(allreflection)

Differentmodesofdiagnosticultrasound3.Mmode:“M”meanmotionDisplaychangesofechoamplitudeandpositionwithtime.Displayofchangesinechopositionisusefulintheevaluationofrapidlymovingstructuressuchascardiacvalvesandchamberwalls

Figure6

M-modedisplayofthefetalheart

Differentmodesofdiagnosticultrasound4.Dmode:

“D”meandopplerMeasurethevelocityofmovementofbloodflowwithinhumanbodyThespectrumisthecurvewithtwoaxiseslistedasfollowing:Figure7DopplerultrasoundTransverseaxis-time(s)Longitudinalaxis-velocity(cm/sorm/s)

DifferentmodesofdiagnosticultrasoundColorDopplerflowimaging(CDFI):Displayreal-timebloodflowin2DimagesDifferentcolorsshowdifferentdirectionsofbloodflow:Figure8CDFIRed-bloodflowtowardprobeBlue-bloodflowawayfromprobe

UltrasoundGeneratorsandEquipmentsTransducer

(1)

MaterialsPositivepiezoelectriceffect:

GenerateelectricpotentialswhencompressedReversepiezoelectriceffect:Respondtotheactionofanelectricfieldbychangingshape(2)Role

Capableofchangingelectricalsignalsintomechanicalwaves(ultrasoundwaves)

Receivethereflectedultrasoundandmakeitbackintoelectricalsignals

PartII

Echocardiography

Echocardiographyisanoninvasiveprocedurewhichillustratestheanatomyoftheheart,including:

Valvesandvalvemotion,chambersize,wallmotionandthicknessSeverityofvalvularregurgitation,gradientsacrossstenoticvalvesDetectionofintracardiacshunts

NormalCardiacAnatomy

Cardiacchambers

Leftatrium(LA)Leftventricle(LV)Rightatrium(RA)Rightventricle(RV)Cardiacvalves

MitralValve(MV)TricuspidValve(TV)AorticValve(AV)PulmonaryValve

(PV)Atrialandventricularseptum2.ApicalWindowFour-chamberviewFive-chamberview3.SubcostalwindowFour-chamberview4.SuprasternalWindowSuprasternalviewoftheaorticarchandtherightpulmonaryarteryBmode-StandardImagingPlanes

1.LeftParasternalWindowLong-axisviewoftheleftventricleShortaxisviewofthegreatarteriesShort-axisview

oftheheartfrombasetoapex

TransthoracicStandardImagingPlanes

Parasternallong-axisviewoftheleftventricleCardiacchambers

Leftatrium(LA)Leftventricle(LV)Rightventricle(RV)Cardiacvalves

MitralValve(MV)AorticValve(AV)

TransthoracicStandardImagingPlanes

ShortaxisviewofthegreatarteriesShortaxisatthemitralvalvelevelShortaxisoftheleftVentricleatthepapillarymusclelevelShortaxisoftheleftVentricleatApicallevel

ApicalStandardImagingPlanes

Four-chamberviewFive-chamberview

SubcostalPlanes

Four-chamberview

Suprasternalviewoftheaorticarchandtherightpulmonaryartery

M-modeEchocardiographyDifferentM-modecurvesunderguidanceof2Dplanes

M-modeofmitralvalveNormalM-modecurveofmitralvalveEpeak:initialopeningofvalveinventriculardiastoleApeak:

atrialcontractionattheenddiastole

D-modeEchocardiographyNormalspectrumofmitralorificeNormalspectrumoftricuspidorificeNormal

CDFIofmitralorificeNormal

CDFI

oftricuspidorificeEA

D-modeEchocardiographyNormalspectrumofaorticorificeNormalCDFIofpulmonaryorificeNormalCDFIofaorticorificeNormalspectrumofpulmonaryorifice

AbnormalEchocardiographyValvularheartdisease-Mitralstenosis(MS)Congenitalheartdisease-Atrialseptaldefect(ASD)Cardiomyopathy-Hypertrophic

cardiomyopathy(HCM)CoronaryarterydiseaseInfectiveendocarditisHearttumor

Valvularheartdiseases-Mitralstenosis(MS)Rheumaticfevercausesfusionofthecommissuresandthickeningofthevalvecusps,whichthenbecomeimmobileandstenosedinafish-mouthshape.

Etiology:Pathophysiology:MS

leftatrial

pressure

leftatrialdilation

pulmonaryvenouspressure

pulmonarycongestion

pulmonaryhypertension

rightheartdilation

rightheartfailure2DEchocardiographyfindingsThickening,calcificationandfusionofthemitralvalveThemitralvalveopeningisrestricted,(Area≤2.5cm2)EnlargedleftatriumSecondarypulmonaryhypertension:dilationsofthepulmonaryarteryandtherightheart

M-mode

EchocardiographyfindingsE-FslopebecomesflatandthedoublepeaksofanteriormitralleafletdisappearindiastoleTheanteriorleafletpresentswith“hockeystick”Theposteriorleafletmovesinthesamedirectionwiththeanteriorleaflet

D-mode

EchocardiographyfindingsThediastolicredfestooninstenosedorificeMarkeddelayinthedegradationoftheE–FslopeandsignificantspectralbroadeningThepeakvelocityintheearlydiastoleisusuallygreaterthan1.5m/smitralstenosisNormalmitralorifice

Echo/Dopplercriteria

Table1GradingmitralstenosisseverityMeangradient(mmHg)Mitralvalvearea(cm2)Mild<101.5-2.5Moderate10-201.1-1.5Severe>20≤1.0Meangradientisdeterminedusingthebernoulliequation

(ΔP=4v2)

Congenitalheartdisease-Atrialseptaldefect(ASD)Classification:

Primumdefect(15–20%):itislocatedneartheatrioventricularjunction

Secundumdefect(70–75%):aholeinthetissuethatcoversthefossaovalis

Superiorsinusvenosusdefect(5%):locatedinthesuperiorportionoftheatrialseptumneartheSVC

Inferiorsinusvenosusdefect(2%):locatedoutsidethelimbusofthefossaovalisbutneartheinferiorvenacavaentryCoronarysinusdefect(<1%):

Congenitalheartdisease-Atrialseptaldefect(ASD)PathophysiologyASD

ashuntflowfromtheleftatriumtotherightatrium

dilationofthepulmonaryartery

pulmonaryarterialpressure

enlargementoftherightatriumandventricle

rightheartfailure2DEchocardiographyfindingsDiscretediscontinuityorechogenicity“dropout”oftheatrialseptumEnlargementoftherightatriumandrightventricledilationofthepulmonaryarteryD-modeEchocardiographyfindingsRedfestoonflowacrosstheinteratrialseptumLefttorightturbulentspectruminlateventricularsystoleandearlydiastole(1-1.3m/s)Eisenmengersyndrome:righttoleftshunt

LARALVRVCardiomyopathy-Hypertrophiccardiomyopathy(HCM)HCMiscurrentlydefinedasaninherited,primarydiseaseoftheheartmusclecharacterizedbyventricularhypertrophy,impaireddiastolicfunction,andvigorousventricularcontractionintheabsenceofacardiacorsystemiccauseDefinition:

AsymmetricalhypertrophyofcardiacseptumSymmetricalhypertrophyofleftventricle

ApicalHCMClassification:SymmetricalHCMCardiomyopathy-Hypertrophiccardiomyopathy(HCM)PathophysiologyType

HCMwithobstructionofleftventricularoutflowtractHCMwithoutobstructionofleftventricularoutflowtract

forceful,overactiveventricularcontractionoftenwithcompleteemptyingachievinganejectionfractionof80–100%inDiastolewithimpairedrelaxationandfillingoftheventricles

Clinicalsymptoms

Exertionalshortnessofbreath,chestpain,syncopeandevensuddendeath2DfindingsThepresenceofasymmetricalhypertrophyoftheventricularseptum,definedastheratioofseptalandposteriorleftventricularwallthicknessatend-diastolebeenequalorgreaterthan1.3Theechotextureoftheimpairedinterventricularseptumishyperech