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▌ Acoustic Output and Measurement
Since the first use of diagnostic ultrasound, the possible human biological effects
(bioeffects) of ultrasound exposure have been studied by various scientific and medical
institutions. In October 1987, the American Institute of Ultrasound in Medicine(AIUM) ratified
a report prepared by its Bioeffects Committee (Bioeffects Considerations for the Safety of
Diagnostic Ultrasound, J Ultrasound Med., Sept. 1988: Vol.7, No.9 Supplement), sometimes
referred to as the Stowe Report, which reviewed available data on possible effects of
ultrasound exposure. Another report, “Bioeffects and Safety of Diagnostic Ultrasound”,
dated January 28, 1993, provides more up-to-date information.
The acoustic output for this system has been measured and calculated in accordance with
the December 1985 “510(K) Guide for Measuring and Reporting Acoustic Output of
Diagnostic Ultrasound Medical Devices”, except for the hydrophone, which meets the
requirements of “Acoustic Output Measurement Standard for Diagnostic Ultrasound
Equipment” (NEMA UD 2-1992).
▌ In Situ, De-rated, and Water Value Intensities
All intensity parameters are measured in water. Since water does not absorb acoustic energy,
these water measurements represent the largest possible value. Biological tissue absorbs
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 using the following formula:
In Situ = Water
)23.0( alf
e
where: In Situ = In Situ Intensity Value
Water = Water Value Intensity
e = 2.7183
a = Attenuation Factor
Tissue a(dB/cm-MHz)
Brain .53
Heart .66
Kidney .79
Liver .43
Muscle .55
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