SonoSite iLook - Volume Measurement; Acquisition Error

78 Chapter 8: References
References
Volume Measurement
The volume measurement performed by iLook is an ellipsoid approximation of the actual volume
of the anatomical feature. That is, the formula used for the volume measurement is
where d
1
, d
2
, and d
3
are the three measurements taken in cm., as described in “Volume Calculation”
on page 28. Additionally, there are system tolerances related to the iLook volume measurement.
These system tolerances are given as a percentage based on the following formula:
where εg = 0.01, ε0 = 0.02, and dmax = screen depth in cm. When each measurement taken is at least
20% of the screen depth, the variation in the system tolerance for the volume measurement ranges
from +/- 10% to +/- 35% in almost all cases.
Acquisition Error
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.
Table 1: 2D Measurement Accuracy and Range Table
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 0.1-30 cm
Lateral Distance < ±2% plus 1% of full scale Acquisition Phantom 0.1-35 cm
Diagonal Distance < ±2% plus 1% of full scale Acquisition Phantom 0.1-30 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.
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=
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d
dd
Volume
π
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+±=
1111100
3
max
0
2
max
0
1
max
0
d
d
d
d
d
d
ToleranceSystem
ggg
Volume
εεεεεε