Mi And Ti Output Display Accuracy; Factors That Contribute To Display Uncertainty; Related Guidance Documents - FujiFilm SonoSite Edge II User Manual

MI and TI output display accuracy

The accuracy result for the MI is stated statistically. With 95% confidence, 95% of the measured MI values
will be within +18% to -25% of the displayed MI value, or +0.2 of the displayed value, whichever value is
larger.
The accuracy result for the TI is stated statistically. With 95% confidence, 95% of the measured TI values will
be within +21% to -40% of the displayed TI value, or +0.2 of the displayed value, whichever value is larger.
The values equate to +1dB to -3dB.
A displayed value of 0.0 for MI or TI means that the calculated estimate for the index is less than 0.05.

Factors that contribute to display uncertainty

The net uncertainty of the displayed indices is derived by combining the quantified uncertainty from three
sources: measurement uncertainty, system and transducer variability, and engineering assumptions and
approximations made when calculating the display values.
Measurement errors of the acoustic parameters when taking the reference data are the major source of error
that contributes to the display uncertainty. The measurement error is described in "Acoustic measurement
precision and uncertainty" on page 10-70.
The displayed MI and TI values are based on calculations that use a set of acoustic output measurements
that were made using a single reference ultrasound system with a single reference transducer that is
representative of the population of transducers of that type. The reference system and transducer are chosen
from a sample population of systems and transducers taken from early production units, and they are
selected based on having an acoustic output that is representative of the nominal expected acoustic output
for all transducer/system combinations that might occur. Of course every transducer/system combination
has its own unique characteristic acoustic output, and will not match the nominal output on which the display
estimates are based. This variability between systems and transducers introduces an error into displayed
value. By doing acoustic output sampling testing during production, the amount of error introduced by the
variability is bounded. The sampling testing ensures that the acoustic output of transducers and systems
being manufactured stays within a specified range of the nominal acoustic output.
Another source of error arises from the assumptions and approximations that are made when deriving the
estimates for the display indices. Chief among these assumptions is that the acoustic output, and thus the
derived display indices, are linearly correlated with the transmit drive voltage of the transducer. Generally,
this assumption is very good, but it is not exact, and thus some error in the display can be attributed to the
assumption of voltage linearity.

Related guidance documents

Information for Manufacturers Seeking Marketing Clearance of Diagnostic Ultrasound Systems and
Transducers, FDA, 2008.
Acoustic Output 10-9