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Doppler was, Re: ULTRASOUND digest 38 From: Terry J. DuBose (tjdubose@juno.com) Mon Dec 29 11:55:25 1997 Messages sorted by: [ date ][ thread ][ subject ][ author ] Next message: Terry J. DuBose: "Re:Message-ID: <19971229.132848.10182.8.tjdubose@juno.com>" Previous message: Terry J. DuBose: "Re: ob protocols" The intensity levels I was referring to were very generalized since there are a great many variables involved. Most of my information on medical sonic intensity comes from Ziskin MC: Ultrasonic Exposimetry. CRC Press, 1993. In that text Marvin Ziskin has a table (p. 320) that shows intensity readings in 1990 as being 37-850 mWcm2 for CW SPTA. For the same year (1990) the table shows 0.11-4.52 mWcm2 for pulsed Doppler SPTA. I disagree that pulsed Doppler concentrates the energy on a small area, the energy passes through all the tissue, it only samples from a small, selective area. As I understand it the primary reason for these readings is that CW is generating energy continuously and pulsed is listening for echoes for over 95% of the time. While it is true that the Power (mW) for pulsed Doppler is higher (8.7-210 mW) than CW Doppler (2.3-90 mW), the SPTA (spatial peak, temporal average) appears to be much lower because while the pulsed Doppler is listening it isn't generating energy. According to Ziskin, if you only consider SATA (spatial average, temporal average) intensities then CW is about 3/4 of pulsed Doppler (320 max vs 440 max). In reality the differences in CW and pulsed Doppler may not be much different, and the differences will be due to a great extent on the conditions (patient habitus), distances, focusing, frequencies, and other variables (time being the most important) than to the actual modality used. I do agree that I see no reason to use Doppler (CW, pulsed color, spectral or power) in the 1st trimester. However, I do prefer M-mode to video tape alone. Video only implies that the heart rate has no significance and we found in our 1993 data that when we followed up on 6 pregnancies that had embryonic heart rates below the 5th percentile, 5 ended in spontaneous AB (for more detail on this study, search the OBGYN.net http://wwweb site for my article "Embryonic Heart Rate"). That study convinced me that the heart rate in early pregnancy is as important as it is at term... but for very different reasons. Peace, Terry J. DuBose On Sat, 27 Dec 1997 10:12:05 -0600 "Joshua Copel" <joshua.copel@yale.edu> writes: > Reply to: RE>ULTRASOUND digest 38 > >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 > >----------- > >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 > Next message: Terry J. DuBose: "Re:Message-ID: <19971229.132848.10182.8.tjdubose@juno.com>" Previous message: Terry J. DuBose: "Re: ob protocols"

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