User's Manual
Vave Personal Ultrasound • USER MANUAL
42
CONFIDENTIAL & PROPRIETARY. CAUTION — Investigational device. Limited by Federal law to investigational use. Not commercially available in the US.
• In situ, derated, & water value intensities
All intensity parameters are measured in water. Because 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:
Variable Value
In Situ In situ intensity value
Water Water value intensity
e 27183
a Attenuation factor
Tissue a9dB/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 sxanner/systme/mode combination (MHz)
Because the ultrasonic path during an examination is likely to pass through varying lengths and types of tissue,
it is dicult 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)]
Because this value is not the true in situ intensity, the term “derated” is used.
Mathematical derating of water based measurements using the 0.3 dB/cm MHz coecient may yield lower
acoustic exposure values than would be measured in a homogenous 0.3dB/cm MHz tissue. This is true because
nonlinearly propagating acoustic energy waveforms experience more distortion, saturation, and absorption in
water than in tissue, where attenuation present along the tissue path will dampen the buildup of nonlinear eects.
The maximum derated value and the maximum water value do not always occur at the same operating
conditions. Therefore, the reported maximum water and derated values may not be related by the in situ (derated)
formula. For example: A multi-zone array scanner that has maximum water value intensities in its deepest zone
may have its largest derated intensity in one of its most shallow focal zones.