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Acoustic output measurement
Since the initial use of diagnostic ultrasound, the possible human biological effects
(bio effects) from ultrasound exposure have been studied by various scientific and
medical institutions. In October 1987, AIUM ratified a report from its Bio effects
Committee (Bio effects Considerations for the Safety of Diagnostic Ultrasound, J
Ultrasound Med., Sept. 1988: Vol. 7, No. 9 Supplement). The report, sometimes
referred to as the Stowe Report, reviewed available data on possible effects of
ultrasound exposure. Another report, “Bio effects and Safety of Diagnostic
Ultrasound,” dated January 28, 1993, provides more current information.
The acoustic output for this ultrasound system has been measured and calculated in
accordance with “Acoustic Output Measurement Standard for Diagnostic Ultrasound
Equipment” (NEMA UD2-2004), and “Standard for Real-Time Display of Thermal and
Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment” (NEMA
UD3-2004).
In Situ, derated, and water value intensities
All intensity parameters are measured in water. Since water does not absorb 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, type of tissue, and the frequency of the ultrasound passing through the
tissue. The intensity value in the tissue,
In Situ , has been estimated by using the
following formula:
In Situ = Water e
[-(0.023alf )]
where:
In Situ = In Situ intensity value
Water = Water intensity value
e = 2.7183
a = attenuation factor (dB/cm MHz)
384 Appendices