User's Manual

36
Sources of measurement errors
Ingeneral,twotypesoferrorscanbeintroducedintothemeasurement:
Acquisition Error Includeserrorsintroducedbytheultrasoundsystemelectronicsrelatingto
signalacquisition,signalconversion,andsignalprocessingfordisplay.Additionally,
computationalanddisplayerrorsareintroducedbythegenerationofthepixelscalefactor,
applicationofthatfactorto
thecaliperpositionsonthescreen,andthemeasurementdisplay.
Algorithmic Error Theerrorintroducedbymeasurements,whichareinputtohigherorder
calculations.Thiserrorisassociatedwithfloating‐pointversusinteger‐typemath,whichis
subjecttoerrorsintroducedbyroundingversustruncatingresults fordisplayofagivenlevel
ofsignificantdigitinthecalculation.
Table 1: 2D Measurement Accuracy and Range
2D Measure Accuracy
and Range
System
Tolerance
a
Accuracy
By
Tes t
Method
b
Range (cm)
Axial Distance < ±2% plus 1% of
full scale
Acquisition Phantom 0-26 cm
Lateral Distance < ±2% plus 1% of
full scale
Acquisition Phantom 0-35 cm
Diagonal Distance < ±2% plus 1% of
full scale
Acquisition Phantom 0-44 cm
Area
c
< ±4% plus (2% of
full scale/smallest
dimension) * 100
plus 0.5%
Acquisition Phantom
0.01-720 cm
2
Circumference
d
< ±3% plus (1.4%
of full scale/
smallest
dimension) * 100
plus 0.5%
Acquisition Phantom 0.01-96 cm
a.Full scale for distance implies the maximum depth of the image.
b.An RMI 413a model phantom with 0.7 dB/cm MHz attenuation was used.
c.The area accuracy is defined using the following equation:
% tolerance = ((1 + lateral error) * (1 + axial error) – 1) * 100 + 0.5%.
d.The circumference accuracy is defined as the greater of the lateral or axial accuracy and by the following
equation:
% tolerance = ( (maximum of 2 errors) * 100) + 0.5%.
2