M y L a b
–
S A F E T Y A N D S T A N D A R D
2-13
The Mechanical Index is defined as the peak rarefactional pressure in MPa (derated
by a tissue attenuation coefficient of 0.3 dB/cm/MHz) divided by the square root
of the probe central frequency in MHz.
The Thermal Index is the ratio between the acoustic power and the power required
to raise tissue temperature by 1°C, estimated on thermal models.
The peak rarefactional pressure (p
r
in MPa) is the temporal peak rarefactional
pressure amplitude at a specified point.
The Pulse Intensity Integral (PII) is the time integral of instantaneous velocity for
any specific point and for any specific pulse, integrated over the time in which the
envelope of acoustic pressure or the envelope of hydrophone signal for the specific
pulse is non-zero. It is equal to the energy fluence per pulse.
Mechanical Index
Thermal Index
Peak Rarefactional
Pressure
Pulse Intensity
Integral