Safety Biological Safety
48 Lumify Ultrasound System
Philips Healthcare 4535 618 58571_A/795 * MAY 2016
Variable Value
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)
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.
Mathematical derating of water based measurements using the 0.3 dB/cm‑MHz coefficient may
yield lower acoustic exposure values than would be measured in a homogenous 0.3 dB/
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 all along the tissue path will dampen the buildup of nonlinear effects.
The maximum derated and the maximum water values 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 transducer that has
maximum water value intensities in its deepest zone may have its largest derated intensity in
one of its shallowest focal zones.
Conclusions Regarding Tissue Models and Equipment Survey
Tissue models are necessary to estimate attenuation and acoustic exposure levels in situ from
measurements of acoustic output made in water. Presently, available models may be limited in
their accuracy because of varying tissue paths during diagnostic ultrasound exposures and
uncertainties in acoustical properties of soft tissues. No single tissue model is adequate for
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