Acoustic Output Tables - FujiFilm SonoSite M-Turbo User Manual

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.
Fixed‐path tissue models, in which soft tissue thickness is held constant, sometimes are used to
estimate In Situ acoustic exposures when the beam path is longer than 3 cm and consists largely
of fluid. When this model is used to estimate maximum exposure to the fetus during
transabdominal scans, a value of 1 dB/cm MHz may be used during all trimesters.
Existing tissue models that are based on linear propagation may underestimate acoustic
exposures when significant saturation due to non‐linear distortion of beams in water is present
during the output measurement.
The maximum acoustic output levels of diagnostic ultrasound devices extend over a broad
range of values:
• A survey of 1990‐equipment models yielded MI values between 0.1 and 1.0 at their highest
output settings. Maximum MI values of approximately 2.0 are known to occur for currently
available equipment. Maximum MI values are similar for real‐time 2D and M Mode
imaging.
• Computed estimates of upper limits to temperature elevations during transabdominal
scans were obtained in a survey of 1988 and 1990 pulsed Doppler equipment. The vast
majority of models yielded upper limits less than 1° and 4°C (1.8° and 7.2°F) for exposures
of first‐trimester fetal tissue and second‐trimester fetal bone, respectively. The largest values
obtained were approximately 1.5°C (2.7°F) for first‐trimester fetal tissue and 7°C (12.6°F) for
second‐trimester fetal bone. Estimated maximum temperature elevations given here are for
a "fixed path" tissue model and are for devices having I
cm 2 . The temperature elevations for fetal bone and tissue were computed based on
calculation procedures given in Sections 4.3.2.1‐4.3.2.6 in "Bioeffects and Safety of
Diagnostic Ultrasound" (AIUM, 1993).

Acoustic output tables

Table 10 through Table
combinations with a TI or MI equal to or greater than one. These tables are organized by
transducer model and imaging mode. For a definition of terms used in the tables, see "Terms
used in the acoustic output tables" on page 164.
43 indicate the acoustic output for the system and transducer
values greater than 500 mW/
SPTA
Chapter 6: Safety 123