SONOTRAX(2009) Series Ultrasonic Pocket Doppler User Manual
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A4.2 Ultrasound Safety and the ALARA
Principle
Ultrasound waves dissipate energy in the form of
heat and can therefore cause tissue warming.
Although this effect is extremely low with Doppler, it
is important to know how to control and limit patient
exposure. Major governing bodies in ultrasound have
issued statements to the effect that there are no
known adverse effects from the use of diagnostic
ultrasound, however, exposure levels should always
be limited to As Low As Reasonably Achievable (the
ALARA principle).
A4.3 Explanation of MI/TI
A4.3.1 MI (Mechanical Index)
Cavitations will be generated when ultrasound wave
passes through and contacts tissues, resulting in
instantaneous local overheating. This phenomenon is
determined by acoustic pressure, spectrum, focus,
transmission mode, and factors such as states and
properties of the tissue and boundary. This
mechanical bioeffect is a threshold phenomenon that
occurs when a certain level of ultrasound output is
exceeded. The threshold is related to the type of
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