Huntleigh Sonicaid Team 3 Series - Ultrasound Safety Considerations; General

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Ultrasound Safety Considerations
20. Ultrasound Safety Considerations
General
Diagnostic ultrasound has been in use for over 35 years with no confi rmed
adverse effects on patients or instrument operators at the intensities typical
of present diagnostic instruments. However, available data are not wholly
conclusive, and the possibility remains that biological effects may be identifi ed in
the future.
Because fetal tissue could be more sensitive to biological effects by reason of
rapid cell division, it is particularly desirable that ultrasound exposure of pregnant
subjects be kept to a minimum.
Medical and scientifi c authorities therefore recommend that ultrasound
procedures be performed in accordance with the “ALARA” principle, which
states that the energy delivered to the patient should always be kept As Low As
Reasonably Achievable.
The transmitted acoustic power of the Sonicaid Team 3 fetal monitor is fi xed
and cannot be adjusted by the operator. Therefore, the user can best observe
the ALARA principle by ensuring that each examination is medically indicated
and by limiting the duration of the study to the extent appropriate for the clinical
objectives.
Acoustic output data for the transducers for use with the Sonicaid Team 3 fetal
monitors is summarized in the following tables. The values given are based
on measurements in water using a calibrated hydrophone and are stated as
the estimated de-rated intensities. The de-rated intensity constitutes the most
biologically relevant parameter available, since true determinations of the actual
absorbed dose in tissue would require invasive measurement techniques. The
de-rated intensity is, therefore, calculated mathematically using a de-rating factor
consisting of a constant (the assumed attenuation coeffi cient) and allowing for
the frequency of the transducer and the distance from the transducer face to the
measurement hydrophone.
The calculated de-rated intensity values for the Sonicaid Team 3 fetal monitors
compare very favourably with previously reported acoustic safety data for
Doppler ultrasound instruments and are appropriate for all clinical applications
recommended in this manual.
At present, there is a clear consensus that the benefi ts to patients of prudent use
of diagnostic ultrasound outweigh the risks that may be present. See:
a) Report No. 24, National Council on Radiation and Protection:
biological effects of ultrasound, clinical effects and observations.
b) Ziskin M.C., in World Policies on the Use of Diagnostic Ultrasound
in Obstetrics: The American Institute of Ultrasound Policy and
Statement on Safety. Ultrasound in Medicine and Biology 12: 711-
714, 1986.