Tissue Models And Equipment Survey - FujiFilm SonoSite M-Turbo User Manual

In Situ= Water [e
where:
In Situ = In Situ intensity value
Water = Water intensity value
e = 2.7183
a = attenuation factor (dB/cm MHz)
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.
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‐(0.23alf) ]
‐(0.069lf) ]