128 Sources of measurement errors
Sources of measurement
errors
Ingeneral,twotypesoferrorscanbeintroduced
intothemeasurement:
Acquisition Error Includeserrorsintroducedby
theultrasoundsystemelectronicsrelatingto
signalacquisition,signalconversion,andsignal
processingfordisplay.Additionally,
computationalanddisplayerrorsareintroduced
bythegenerationofthepixelscalefactor,
applicationofthatfactorto
thecaliperpositions
onthescreen,andthemeasurementdisplay.
Algorithmic Error Theerrorintroducedby
measurements,whichareinputtohigherorder
calculations.Thiserrorisassociatedwith
floating‐pointversusinteger‐typemath,whichis
subjecttoerrorsintroducedbyroundingversus
truncatingresultsfordisplayofagivenlevel
of
significantdigitinthecalculation.
Measurement publications
and terminology
Thefollowingsectionslistthepublicationsand
terminologyusedforeachcalculationresult.
Terminologyandmeasurementscomply with
AIUMpublishedstandards.
Cardiac references
Acceleration (ACC) in cm/s
2
Zwiebel,W.J.IntroductiontoVascular
Ultrasonography.4thed.,W.B.Saunders
Company,(2000),52.
ACC=abs(deltavelocity/deltatime)
Acceleration Time (AT) in msec
Oh,J.K.,J.B.Seward,A.J.Tajik.TheEchoManual.
2nded.,Lippincott,Williams,andWilkins,
(1999),219.
Aortic Valve Area (AVA) by Continuity
Equation in cm
2
Reynolds,Terry.TheEchocardiographer’sPocket
Reference.2nded.,SchoolofCardiacUltrasound,
ArizonaHeartInstitute,(2000),393,442.
A
2
=A
1
*V
1
/V
2
where: A
2
=Aovalvearea
A
1
=LVOTarea;V
1
=LVOTvelocity;
V
2
=Aovalvevelocity
LVOT=LeftVentricularOutflow
Tract
AVA(PV
LVOT
/PV
AO
)*CSA
LVOT
AVA(VTI
LVOT
/VTI
AO
)*CSA
LVOT
Body Surface Area (BSA) in m
2
Grossman,W.CardiacCatheterizationand
Angiography. Philadelphia:LeaandFebiger,
(1980),90.
BSA=0.007184*Weight
0.425
*Height
0.725
Weight=kilograms
Height=centimeters
Cardiac Index (CI) in l/min/m
2
Oh,J.K.,J.B.Seward,A.J.Tajik.TheEchoManual.
2ndEdition,Boston:Little,BrownandCompany,
(1999),59.
CI=CO/BSA
where: CO=CardiacOutput
BSA=BodySurfaceArea
Cardiac Output (CO) in l/min
Oh,J.K.,J.B.Seward,A.J.TajikTheEchoManual.
2nded.,Lippincott,Williams,andWilkins,
(1999),59.
CO=(SV*HR )/1000
where: CO=CardiacOutput
SV=StrokeVolume
HR=HeartRate
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