Tissue Models And Equipment Survey - FujiFilm SonoSite Edge II User Manual

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 zones.

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 diagnostic ultrasound exposures and uncertainties in the acoustic
properties of soft tissues. No single tissue model is adequate for predicting exposures in all situations from
measurements made in water, and continued improvement and verification of these models is necessary for
making exposure assessments for specific exam types.
A homogeneous tissue model with attenuation coefficient of 0.3 dB/cm MHz throughout the beam path is
commonly used when estimating exposure levels. The model is conservative in that it overestimates the
In Situ acoustic exposure when the path between the transducer and site of interest is composed entirely
of soft tissue. When the path contains significant amounts of fluid, as in many first and second-trimester
pregnancies scanned transabdominally, this model may underestimate the In Situ acoustic exposure. The
amount of underestimation depends upon each specific situation.
10-12
-(0.069lf)
]
Acoustic Output