FujiFilm VisualSonics Vevo MD User Manual page 385

Attenuation factor (a) for various tissue types are given below:
brain = 0.53
heart = 0.66
kidney = 0.79
liver = 0.43
muscle = 0.55
l = skinline to measurement depth in cm
f = center frequency of the transducer/system/mode combination in MHz
Since the ultrasonic path during the exam is likely to pass through varying lengths and
types of tissue, it is difficult to estimate the true In Situ intensity. An attenuation factor
of 0.3 is used for general reporting purposes; therefore, the In Situ value commonly
reported uses the formula:
In Situ (derated) = Water e
Since this value is not the true In Situ intensity, the term "derated" is used to qualify it.
The maximum derated and the maximum water values do not always occur at the
same operating conditions; therefore, the reported maximum water and derated
values may not be related by the In Situ (derated) formula. For example: a multi-zone
array transducer that has maximum water value intensities in its deepest zone, but
also has the smallest derating factor in that zone. The same transducer may have its
largest derated intensity in one of its shallowest focal zone settings.
Tissue models and equipment survey
Tissue models are necessary to estimate attenuation and acoustic exposure levels In
Situ from measurements of acoustic output made in water. Currently, available
models may be limited in their accuracy because of varying tissue paths during
[-(0.069lf )]
Acoustic output measurement 385