Andersons pediatric cardiology 171

Therearetwomaintechniques,eachwithitsstrengthsandweaknesses.Color
Dopplermyocardialimaging157recordsvelocitiesmeasuredattwopointsa
distanceapartandtheirchangewithinthecardiaccycle.Itrecordsastrainrate
fromwhichitderivesstraininthelongitudinalplane.154Thistechnologyalso
showstheextentoftorsionandtwistoftheheartduringthenormalcardiac
cycle.Thetechniqueisparticularlyusefulfollowingmyocardialinfarctioninthe
adultbecauseitenablesregionalabnormalitiestobedetected.Strainratehas
beenrecordedusingthistechniqueinsmallnumbersofchildrenwithaortic
valvaratresiaorhypoplasticleftheartsyndrome.158,159Theparticular
technologicdifficultiesofthisapproachinthefetusrelatetothesmall
myocardialmassinterrogatedbyeachpixelandalsotothefactthatmyocytes
arealignedlongitudinallyinthefetalrightventriclebutcircumferentiallyinthe
fetalleftventricle.114However,Dopplervelocitycolorcodingpermitsthe
detectionofmotionoftheaorticwallandmeasurementofthevelocityofthe
pulsewave,andthistechniquemayprovetobeausefulnoninvasivetechnique
toassessfetalarterialcompliance.
Speckletrackingorvectorvelocityimaging(VVI)isatechniquethattracks
theacousticmarkersseenfollowingconstructiveanddestructiveinteractionsof
theultrasoundbeamfromframetoframe.Itisanon-Dopplertechniqueanddoes
notrequiretheclosealignmentofDopplertechniques,butitisrecommendedto
captureimagesathighframeratesof140Hzormore.155Imageacquisition
shouldbemadeusinghighfrequency(withoutharmonics)andgoodcontrast
betweenthecavityandtheendocardium.
Thelimitationsofstrainassessmentusingboththesemethodsincludethe
difficultyintrackingacousticmarkersinthefetalheartbecauseofsmallsize,
fastheartrate,thevariablescanningdepthduringpregnancyandlackofECG
gatingintherecordingoftheoriginalframerates.Assessmentofstrainusing
colorDopplermyocardialimagingrequireshighframeratesofmorethan200
framespersecondandmaybelimitedinlatergestationifharmonicimagingis
requiredtoimagethefetalheart.154–156Itrequiresclosealignmentparalleltothe
wallmotionbecauseitisaDopplertechnique,andoneofthemoredifficult

aspectsofthismethodologyistoensurethattheDopplersampleremainswithin
theareaofinterest.150–153AswithallDoppler-basedmeasurementsinthefetus,
itispronetoartifactsfromfetalormaternalmovementormaternalaortic
pulsations.ThedifferencesinreportsusingVVImaybeexplainedbyseveral
technicalfactorsspecifictotheapplicationofthistothefetus.160Speckle


trackingisnotsuitableonstoredclips(unlesstheyarestoredinDICOM)
becausethevideocapturerateoftheseisbetween25and30Hz.
Ifcardiacfunctionisconsideredtobesimilartothatofapiston,itstime
intervalscanbemeasuredfromthechangeinstatictodynamicworkusing
dynamicadaptivepistonpumptechnology.Thecardiacstatediagramisanovel
visualizationtooltodisplaythephasesofcardiacfunctionandprovide
measurementofmyocardialtissuevelocitieswithoutasimultaneousECG
signal.142

ComparisonofDoppler,M-Mode,andNewer
Techniques
Applicationofnewertechniquestothefetusarelimitedbytechnicalissues,
particularlyinthetimedomain.148Frompairedstudiesofstrainmeasurement
usingspeckle-trackingVVIcomparinghighandlowframeraterecordings,itis
clearthatthepeakdiastolicvelocitiesandpeakpositivestrainratesarereduced
whenlowerframeraterecordingsareanalyzed.155Moreover,thedetectionof
biphasicdiastolicwaveformsrequiresatleast29framesperheartbeatandis
rarelydetectedusingspeckletracking,whereastheyareinvariablyseenwith
tissueDopplertechniques(Fig.6.16).154–156


FIG.6.16 Comparisonofvelocitiesattheatrioventricularannulus
recordedusingspeckletrackingvectorvelocityimaging(VVI;A)andtissue

Doppler(TDI;B)techniquesinthehumanfetus.TDIwasrecorded
between300HzandVVIat120Hz.Thesystolic(Sm),earlydiastolic(Em),
andlatediastolic(Am)myocardialvelocitiescanbemeasuredbyboth
techniques.However,inapairedcomparison,measurementoftheusual
biphasicdiastolicinflowpatternusingVVIrequiredatleast29framesper
heartbeat.

Asinmeasurementsoflongaxisfunction,velocitiesrecordedbyspeckle
trackingtechnologyarelowerthanthoserecordedusingspectraltissueDoppler
becausespeckletrackingcalculatesthemeanoftheXandYcoordinate
velocitiesanddoesnotprovidepeakvelocities.155Correlationofmyocardial
displacementmeasurementsmadeusingM-modeandVVIisgood.In
comparativestudies,VVIorspeckletrackingcorrelatesbetterwithtraditional
DopplerorM-modeinthespatialparameterssuchasdisplacementorstrainbut
morepoorlyinthoserequiringtemporalparameterssuchasstrainrateand
velocities.155Thesetechniquesremainsubjecttowidevariation,likelydueto
bothphysiologicvariabilityinthefetus,aswellasoperatorvariation.