Ultrasound Equipment” (Revision 3, AIUM, NEMA, 2004), the “Standard for
Real-Time Display of Thermal and Mechanical Acoustic Output Indices on
Diagnostic Ultrasound Equipment” (Revision 2, AIUM, NEMA, 2004), and the
September 2008 FDA document "Information for Manufacturers Seeking
Marketing Clearance of Diagnostic Ultrasound Systems and Transducers."
In Situ, Derated, and Water Value Intensities
All intensity parameters are measured in water. Since water absorbs very little
acoustic energy, these water measurements represent a worst case value.
Biological tissue does absorb acoustic energy. The true value of the intensity at
any point depends on the amount and type of tissue and the frequency of the
ultrasound that passes through the tissue. The intensity value in the tissue, In
Situ, has been estimated by using the following formula:
In Situ = Water [e
-0.23alf
]
Where:
In Situ intensity value=In Situ
Water value intensity=Water
2.7183=e
Attenuation factor=a
a(dB/cm-MHz)=Tissue
0.006=Amniotic
Fluid
0.53=Brain
0.66=Heart
0.79=Kidney
0.43=Liver
0.55=Muscle
Skin line to measurement depth (cm)=l
iU22 User Manual
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Safety
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