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HD11 XE Getting Started
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Safety
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. Biolog-
ical 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 ultra-
sound 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
]
Since the ultrasonic path during an examination is likely to pass through varying
lengths and types of tissue, it is difficult to estimate the true In Situ intensity. An
attenuation factor of 0.3 is used for general reporting purposes; therefore, the In
Situ value which is commonly reported uses the formula:
In Situ derated = Water [e
-0.069lf
]
Since this value is not the true In Situ intensity, the term “derated” is used.
Where: In Situ = In Situ Intensity Value
Water = Water Value Intensity
e=2.7183
a = Attenuation Factor
Tissue = a(dB/cm-MHz)
Amniotic
Fluid
= 0.006
Brain = 0.53
Heart = 0.66
Kidney = 0.79
Liver = 0.43
Muscle = 0.55
l = Skin line to measurement depth (cm)
f=Center frequency of the transducer/system/mode
combination (MHz)
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