P3V Veterinary Digital Ultrasonic Diagnostic Imaging System User Manual
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relatively conservative. Over-estimation of actual in situ intensity exposure, for the majority of
tissue paths, is made to the measurement and calculation process. For example, attenuation
coefficient of 0.3 dB/cm∙MHz, which is much lower than the actual value for most tissues of the
body, is adopted. And conservative values of tissue characteristics are selected for use in TI
models. Therefore, the display of MI and TI should be used as relative information to assist
operator in prudent use of ultrasound system and implementation of ALARA principle, and the
values should not be interpreted as the actual physical values in tissues or organs examined.
A2.4.3. Measurement Uncertainty
The uncertainties in the measurements were predominantly systematic in origin; the random
uncertainties were negligible in comparison. The overall systematic uncertainties were
determined as follows:
1.
Hydrophone Sensitivity:
± 23 percents for intensity, ± 11.5 percents for pressure. Based
on the hydrophone calibration report by ONDA. The uncertainty was determined within
±
1dB in frequency range 1-15MHz.
2.
Digitizer:
±4 percents for intensity. ± 1.5 percents for pressure.
Based on the stated accuracy of the 8-bit resolution of the Agilent DSO6012A Digital
Oscilloscope and the signal-to-noise ratio of the measurement.
3.
Temperature: ±
1 percent
Based on the temperature variation of the water bath of ± 1 ºC.
4.
Spatial Averaging:
± 10 percents for intensity, ± 5 percents for pressure.
5.
Non-linear Distortion:
N/A.
No effects of nonlinear propagation are observed
Since all the above error sources are independent, they may be added on an RMS basis, giving a
total uncertainty of ± 25.1 percents for all intensity values reported, ± 12.7 percents for all the
pressure values and ± 12.6 percents for the Mechanical Index.
A2.5: Operator Control Features
The possibility of producing mechanical/thermal biological effects can be influenced by three
kinds of controls: Direct Controls, Indiret Controls, and Receiver Controls. The qualified operator
may use the system controls to minimize the ultrasound output while acquiring necessary clinical
information.
Direct Controls
The acoustic output of the system can be controlled directly through the level of voltage
transmitted. In this case, the maximum acoustic output never exceeds the limits in any mode of
operation.
Indirect Controls
The acoustic output of the system can be controlled indirectly through many imaging parameters,
including imaging modes, probe frequency, focus number/position, depth and pulse repetition
