Chapter 12 - System Safety and Maintenance
Accuracy Measures
Terason t3000 / Echo Ultrasound System User Guide
281
Accuracy Measures
The following general assumptions can be made about the accuracy of any ultrasound
system:
• Velocity of sound uncertainty = 5%
• Tissue shape is modeled as an ellipse or an ellipsoid
• Caliper placement accuracy is one pixel (operator dependent)
• Measurement accuracy is based on the root-mean-square combination of all
independent sources of error
• RMS errors are due to velocity of sound uncertainty, pixel error, and typical transducer
geometry
Distance Accuracy
Distance accuracy measures are as follows:
Formula
:
where (x
1
,y
1
) and (x
2
,y
2
) are the coordinates of the end points.
Range
: 0-20 cm
Accuracy
: For a 20 cm measurement, a 1 pixel error is 0.2 mm.
RMS errors
:
• For D = 10mm, accuracy = 9%
• For D = 20mm, accuracy = 6%
• For D > 50mm, accuracy = 5%
Area
Area accuracy measures are as follows:
Assumptions
: Circular cross section, length of axes: 2a, 2b
Formula
: K=
ab
Range
: 0-300 cm
2
Accuracy
: Determined by two independent distance measurements. The derivation of a
particular tissue shape from the circular model cannot be quantified.
RMS errors:
For A=3.1 cm2, accuracy=4%
Circumference
Circumference accuracy measures are as follows:
Assumptions
: Elliptical cross section, length of axes: 2a, 2b
D
x1 x2
+
2
y1 y2
+
+
2
=
