Chapter 12 - System Safety and Maintenance Acoustic Output Indices
Terason t3000 / Echo Ultrasound System User Guide 274
The remainder of this section lists the relative errors for the following items:
• Intensity measurements
• Spatial-peak derated pulse-intensity integral, defined as
SPPA.3
• Spatial-peak derated temporal average intensity for unscanned modes
• Spatial-peak derated temporal average intensity for scanned modes
• Peak derated rarefactional pressure
• Mechanical Index
• Soft-Tissue Thermal Index for scanned modes, total acoustic power at the scan/beam
entrance to the body
• Soft-Tissue Thermal Index for unscanned modes, when the beam-entrance dimension is
less than 1 cm
2
in area
• Soft-Tissue Thermal Index for unscanned modes, when the beam-entrance dimension is
greater than 1 cm
2
in area
• Bone Thermal Index for unscanned modes
• Cranial Thermal Index
The relative error in intensity measurements due to uncertainty in the hydrophone
calibration, defined as
k
, is approximately:
where the following are defined:
The relative error in the spatial-peak derated pulse-intensity integral, defined as
SPPA.3
, is approximately:
where the following is defined:
Cal
Calibration error, as supplied by the National Physical Laboratory;
8% at the frequency range of the transducers tested.
A
Relative error in the reproducibility of positioning the hydrophone
at the point of the spatial peak of the pulse intensity integral,
estimated as 5%
V
2
Relative error resulting from errors in reading peak squared
voltage in the recorded waveform, estimated as 4%
TI
Relative error due to hydrophone positioning and temporal
integration of the waveform, estimated as 4%
stab
Relative error due to temporal instability of the hydrophone,
estimated as 1%
.3
Relative error in estimating derating factor, due to
uncertainties in estimating frequency and reproducibility in
determining derating location, estimated as 4%
k
(
2
Cal
A
2
V
2
) 10.2%=
1
2
---
++=
SPPA.3
2
k
2
TI
2
stab
2
.3
2
lin
2
v
++ +++
2
PD
12/
12.8%
=+=
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