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Pregnancy Gel

  1. Feb 15, 2008 #1
    (Not Spam :tongue:)

    I did a bit of reading today on partial reflection when using ultrasound. I was reading about a pregnancy gel that is applied to the womans stomach when detecting a baby. To put it briefly, if the ultrasound transmitter is held away from the body alot of energy is reflected, and this is also the case when the transmitter is directly on the surface of the skin. I read that a gel is applied to the stomach of a pregnant woman to try and eliminate any reflection. My question is, what does this Gel have in it, or what is it effect on the ultrasound? I do not understand how a Gel can eliminate most of the reflection.

  2. jcsd
  3. Feb 15, 2008 #2
    I don't know for certain but my guess would be that the gel simply has approximately the same density as the woman's body, so it has the same properties for transmitting the sound waves as her body. Whereas, on the other hand, the small air gap that would be there without the gel would have completely different acoustic properties.
  4. Feb 15, 2008 #3


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    Reflections occur at interfaces between layers of differing density. This is most commonly noticed optically, but it works just fine for any signal at an interface. In this case, I guess it would be the "sonic" density.

    The gel removes two interfaces between differing densities - the one between the device's lens and the air - and the one between the air and the flesh.

    In a nutshell, since the signal is passing directly from glass to human-density fluid and then directly to human flesh, there is no change in density, thus nothing to reflect off.

    The only property that the gel has is its "sonic" density.
    Last edited: Feb 15, 2008
  5. Feb 15, 2008 #4
    Thanks you two, that makes sense and also links into what I have been learning.
  6. Feb 15, 2008 #5
    I can see that the flesh/gel interface transmits most efficiently, but is the transducer/flesh density difference substantial from that of transducer/gel? Also, I believe the gel promotes a more coherent image due to its continuous contact.
  7. Feb 15, 2008 #6
    The stuff they use on me (bladder not womb) resembles KY jelly.
  8. Feb 15, 2008 #7


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    You wouldn't believe the stuff that ran through my mind when I read the title of this thread...
  9. Feb 15, 2008 #8


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    You mean why is the gel better than direct contact between transducer and skin?

    Because bodies come in all shapes, sizes and curvatures - and ultrasound wands do not.

    You can't seal out the air between flesh and hard plastic. At least, not while you're rovning all over the belly. The gel fills the gap.
  10. Feb 15, 2008 #9
    That seems to be my understanding.
  11. Feb 15, 2008 #10

    Math Is Hard

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    I thought it was just to let the ultrasound thingy slide easily over the belly. (had it done once when my doc suspected appendicitis.)
  12. Feb 15, 2008 #11


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    And it turned out to be twins. Man, you gotta hate it when that happens.
  13. Feb 16, 2008 #12
    Somewhere in Alberta, the RCMP found a note scrawled in lipstick on a gas station mirror, "Stop me before I post!":rolleyes:
  14. Feb 16, 2008 #13


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    The correct term would be acoustic gel, with roughly the same acoustic properties as human tissue. Basically as CQ and Dave explained, the gel facilitates the transmission of UT waves between transducer and tissue being surveyed, and is basically an acoustic coupling agent. The gel excludes air which would reduce the transmission of sound.

    Kytogenics has a patent on one type of gel - Acoustic Gel. U.S. patent #5,382,286 was issued Jan 17, 1995. A method of reducing cavitation around underwater acoustic projectors is described. The projector is cleaned with a surfactant and then encapsulated with an aqueous gel containing a polysaccharide polymer such as a chitosan derivative, a hydrophilic stabilizer and a biocide.

    I think gels are much like KY jelly and would be something like glycerol/glycerin.

    Here is a product description for ULTRAGEL II

    UT in other industries if often done in water. The piece being inspected or imaged is immersed in water, which serves at the coupling agent.
    Last edited: Feb 16, 2008
  15. Feb 16, 2008 #14
    I'll try not to be too gross, but I should have thought before comparing ultrasound gel to KY. KY and similar products is essentially benign; however, ultrasound gel is not. In particular, you do not want to ingest it.
  16. Feb 16, 2008 #15
    :rofl: That's why the first thing I wrote was (Not Spam!)

    Thanks for that Astronuc, suprisingly the answer to my question seems relatively straight forward which is nice :smile:

    So if oneday I get into a discussion on Preganancy Gel (Acoustic Gel) I could say:

    A The gel has roughly the same acoustic properties as human tissue

    B It excludes air, which would otherwise be reflected off and therefor not give as a good an image.
  17. Feb 16, 2008 #16


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    My my, you're a forward looking chap...
  18. Feb 16, 2008 #17
    The chances are minimal but it would be a pretty cool thing to say :tongue:
  19. Feb 16, 2008 #18
    Didn't Astronuc [post=1611693]contrast[/post] ultrasound gel to KY? The “biocide” part definitely puts me off from eating it, using it as an ice cream topping, etc.
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