User's Manual

Chapter 7: References 139
References
Chapter 7: References
Measurement accuracy
Themeasurementsprovidedbythesystemdo
notdefineaspecificphysiologicaloranatomical
parameter.Rather,themeasurementsareofa
physicalproperty suchasdistanceforevaluation
bytheclinician.Theaccuracyvaluesrequirethat
youcanplacethecalipersoveronepixel.The
valuesdonotincludeacousticanomalies
ofthe
body.
The2Dlineardistancemeasurementresultsare
displayedincentimeterswithoneplacepastthe
decimalpoint,ifthemeasurementistenor
greater;twoplacespastthedecimalpoint,ifthe
measurementislessthanten.
Thelineardistancemeasurementcomponents
havetheaccuracyandrangeshown
inthe
followingtables.
Table 1: 2D Measurement Accuracy and Range
2D Measure
Accuracy
and Range
System
Tolerance
a
Accuracy
By
Test 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
Circumfer-
ence
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