U60 Diagnostic Ultrasound System User Manual Ultrasound Intensity and Safety
- 199 -
Measurement variability and accuracy
The number of operating conditions of which the system is capable and the number tested in
obtaining display accuracy results
Whether display accuracy will be determined by specific combinations of system, mode,
transducer assembly and transmit patterns, or all allowed combinations of them
Accuracy of system software MI and TI calculation algorithms.
Engineering approximations for real-time calculations
A2.4.2. Differences between Actual and Displayed MI/TI
Actually, many assumptions adopted in the process of measurement and calculations are
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. So the intensity and pressure measurement
uncertainties were showed in table 1 and table 2. The power, the center frequency and MI
measurement uncertainties were showed in table 3.
Table 1 The intensity and pressure measurement uncertainties table
To Next Page
Loading...
