GE Logiq 500, Расширенное справочное руководство

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Bioeffects
LOGIQ 500 Advanced Reference Manual
2276614–100 Rev. 0
6–3

Thermal Bioeffect
As with most forms of energy, ultrasound is attenuated as it
passes through tissue and is converted to heat, which, if
produced at sufficient rates, will increase tissue temperature to
a point where tissue damage may result. Major factors
contributing to thermal bioeffect can be categorized as tissue
characteristics or control parameters:
Physical tissue characteristics like acoustic impedance,
attenuation, absorption, and perfusion determine the rates
of heat production and heat transfer. The susceptibility of
some tissues to injury from heat, such as developing fetal
tissue, further complicate the concern for long-term effects.
The time-average density of available ultrasound energy is
mainly determined by acoustic parameters like output
frequency, pulse amplitude, pulse duration, duty cycle,
beam shape, and beam motion. These parameters are
controlled by the operator through equipment selections
such as probe type, operating mode, focal depth, sample
volume location, and output control settings. The operator
also has significant influence by controlling probe motion
and dwell time. These “Control Parameters” form the
means through which the operator can minimize thermal
bioeffect.