FujiFilm VisualSonics Vevo MD User Manual page 402

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.
402 Appendices