ULTRASOUND Messages for December, 1997: Re: ULTRASOUND digest 38

Re: ULTRASOUND digest 38

From: Joshua Copel

joshua.copel@yale.edu

Sat Dec 27 09:11:51 1997

Terry made several comments on Doppler, excerpted below. The CW Doppler we use in Ob has very low SPTA, around 4 mW/cm2, much lower than imaging in general, and especially lower than pulsed or color Doppler. I agree that M-mode is OK, and would even suggest that a videotape is best- after all what could be better than seeing the heart beating? That covers the bonding issue too. Just show the mother that heart moving. There is a strong movement in Europe against any use of pulsed or color Doppler in the first trimester outside of the investigational setting (i.e. with informed consent), to the point that some European journals have been giving investigators grief about research studies, even with consent.

I am not sure I agree with the comment about color Doppler versus pulsed in terms of energy. Pulsed Doppler concentrates the signal on a small area, and if there is a tissue-bone interface in the area there can be thermal effects. Color Doppler insonates a larger area, so there may be a greater opportunity for normal blood perfusion to help diffuse any heart that is generated. Most of this is theoretical as long as the calculated Thermal Index (TI) is below 1.

Bottom line: I would use tape as first choice, and m-mode as second. Always keep output as low as possible. With new machines that display MI and TI, watch the TI with all Doppler, including "power" Doppler (AKA color Doppler energy). Some Ob presets can take the TI well over 1, the safety threshold (examples that I know of include ATL, Acuson, and Diasonics machines).

Josh Copel Joshua.Copel @Yale.edu

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After 5.5 weeks, M-mode should tell the story, especially if you use an endovaginal transducer. I see no need for Doppler, however, I am not aware of any real risk as long as you keep it short and quick. Heating it the major danger, and Doppler does crank up the energy a bit.

I want make one other comment on this thread. The following message appears to be suggesting using Doppler to hear the embryonic heart beat. Now we know that color Doppler does increase the energy more than just pulsed Doppler. And all Doppler is a little more energetic than regular real-time and M-mode. HOwever, remember that OB labs have been using Doptones to hear the heart beat on fetuses for years. These small machines are not pulsed but are continious wave (CW) machines, and put out a good bit of energy even if they are small in size.

The question is are you following the principle of ALARA (As Low As Reasonably Achievable)? When asked about why we can't hear the heart beat I always reply, this is a imaging lab, we see the heart beat. Then I point it out to the mother. That seems as satisfying as hearing it. Should work just as well as hearing for anxiety or bonding or for what ever use Doppler is used. I still see no reason to use Doppler on the early embryo, except in very rare or difficult cases. M-mode will always document a beating heart in the hands of experienced sonographers. Peace, Terry J. DuBose

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