[Vol 2 Issue 9 March 3, 2000]:
Do most midwives regularly make use of the Doptone? Also, shouldn't each
woman be made fully aware that the Doptone is ultrasonic? Even though the
exposure periods are usually brief, I heard that 1 min. of Doptone is much
stronger--equal to 30 min of the other full-image type ultrasound. Is this
[Vol 2 Issue 10 March 10, 2000]:
I work for Nicolet Vascular (formerly Imex Medical). Following are excerpts
from a letter written to another person with the same concerns.
First, a Doppler auscultatory device in fact uses the same technology as an
ultrasound imager in that a high frequency sound wave (ultrasound) is
transmitted into the body and a return signal is analyzed and processed
either to display an image or transmit a sound. Doppler devices typically
emit a low power continuous wave ultrasound signal and detect the change in
frequency (Doppler effect) from the return signal. The frequency difference
between the transmitted and received signal is typically in the audio range
and can thus be heard if amplified to a speaker.
Ultrasound imaging devices emit a high powered pulsed wave ultrasound
signal and detect the length of time the signal takes to return. This
information is used to detect depths and can be displayed to see the image.
As you know, most imagers have a Doppler mode that will show colored blood
flow direction in addition to the image.
In either case, the revised AIUM statement issued in 1993, "No confirmed
biological effect...", applies to both technologies in that the concern is
power emitted into the body, not how you process the information you
Second, you stated that the frequency of Doppler devices is higher than an
imager device. This is also not true. The Hitachi unit ... has a
trans-abdominal probe that transmits at 3.5 MHz. The industry standard for
obstetrical Dopplers is either 2 or 3 MHz. Imex in fact sells both. Higher
probe frequencies that we sell such as 5 and 8 MHz are used for vascular
applications and are labeled "Not Designed For Fetal Use."
In addition, I would like to point out that the FDA limit for power
intensity emitted by a continuous wave ultrasound for fetal use is 0.094
watts per square centimeter. The FDA power intensity limit for pulsed wave
ultrasound for fetal use is 190 watts per square centimeter. The power
emitted by a Doppler can be 2,000 times less than an imager! Imex 3 MHz
probes emit 0.009 watts per square centimeter, a factor of ten times less
than the FDA limit.
Lastly, I also would like to point out that the duration of an auscultatory
Doppler exam typically lasts less than a minute. Though it is exciting to
hear your baby's heartbeat since there is nothing to see, the exam does not
take very long. At the demonstration, I understand you watched the twins
for at least 20 minutes. Taken with the above power limits, this can be
analogous to watching a night light for a minute as compared to watching a
photographer's strobe light for 20 minutes.
Reprinted from Midwifery Today E-News (Vol 2 Issue 10 March 10, 2000)
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