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Wednesday, February 13, 2013

How to make your own ultrasound gel (which is also sterile and edible and environmentally friendly)

I have been doing lots of bedside ultrasound lately and realized how useful it would be in areas far off the beaten track like Haiti, for instance. With a bedside ultrasound (mine fits in my pocket) I could diagnose heart disease, kidney and gallbladder problems, various cancers as well as lung and intestinal diseases. Then I realized that I would have to take a whole bunch of ultrasound gel with me which would mean that I would have to check luggage, which is a real pain when traveling light to a place where luggage disappears. I heard that you can use water, or spit, in a pinch, or even lotion, though oil based coupling media apparently break down the surface of the transducer. Or, of course, you can just use ultrasound gel.

Ultrasound requires an aqueous interface between the transducer and the skin or else all you see is black. Ultrasound gel is a clear goo, looks like hair gel or aloe vera, and is made by several companies out of various combinations of propylene glycol, glycerine, perfume, dyes, phenoxyethanol or carbapol R 940 polymer along with lots of water. It is hard to find this information, but it is available in the material data safety sheets for the various companies that make it. The recipes are proprietary. Ultrasound gel is not super expensive, but it is not that easy to find in a store or in a developing country. It costs about $25 for 5 liters on Amazon, or $5 for a nice 8.7 oz squeeze bottle. It smells ever so slightly medicinal and leaves a sticky, then dry white residue as it dries.

There should really be some sort of powder that you mix up with water that makes ultrasound gel so we don't have to be shipping the water part of it, which is undoubtedly about 99% of the contents, long distances. But there isn't a powder. I have been looking. No instant ultrasound gel.

With a mixture of optimism and singularity of purpose I went to the kitchen and tried out 6 different recipes for an aqueous goo that would transmit sound waves. I thought that I could make ultrasound jam out of water and pectin, but that doesn't really work. Obviously there is something magic about fruit that makes pectin gel, maybe the acid or the sugar. Without fruit, even no-sugar pectin becomes about the consistency of spit. (I also tried spit, which does work, but has various obvious drawbacks.) I tried plain gelatin and water and got beautiful clear jello, which falls off the transducer, but kind of works, but is also messy. I tried corn starch and water, as if making extremely boring gravy. That was lovely and white, but the water wants to come out of it so it just slides off the transducer. I tried tapioca flour which I boiled with water, producing a nice clear, very mucoid gel which dries like glue on the skin and is very uncomfortable. I tried xanthan gum, a bacterial polysaccharide used to bind and thicken, boiled and cooled, and although it thickens the water it is slimy and falls off the transducer and makes a mess.

The recipe that worked (and worked great) is guar gum, salt and water. Guar gum has been used for a very long time in countries like India and Pakistan to thicken food and is now used often by people who can't eat gluten, to thicken gravies and make breads. Guar gum is the ground endosperm of the guar bean, which is very rich in a carbohydrate that avidly absorbs water. Guar beans are also eaten green and the pods are used as a vegetable ingredient after shelling out the beans. Guar gum is available in the flour section of many grocery stores and costs about $10 for a 220 gram bag. It is purported to be good for diarrhea, constipation, diabetes and lowering cholesterol. It has been added to infant tube feed formula in intensive care units to decrease stool frequency.

I messed with the recipe awhile and came up with a very nice slightly caramel tinged ultrasound gel this way:

1. Mix 2 teaspoons of guar gum with 1-2 teaspoons of salt. (The amount of salt isn't vitally important since it is just added to keep the guar gum from clumping. Using slightly less than a teaspoon of salt per 2 cups makes a gel with which is isotonic, which would be ideal for use near eyes or other mucus membranes or on open wounds).

2. Boil two cups of water.

3. Slowly sprinkle the guar gum/salt mixture into the boiling water while stirring vigorously with a fork or whisk.

4. Boil for about 1-2 minutes until thick and well mixed.

5. Cool before using. Save lives.

This is wonderful ultrasound gel (see photo above). I tried it and it works at least as well as the proprietary stuff, and probably doesn't dry out quite as fast. It wipes off easily and doesn't leave a sticky film. Even though it is not entirely transparent, there is no reduction in the quality of the ultrasound image compared with the standard clear ultrasound gel. It costs about 25 cents for a half pint, is sterile when you have finished making it and is completely non-toxic. The ingredients are available in many developing countries, not to mention the US. It is edible. It is not particularly bacteriostatic, though it could be made bacteriostatic with a little EDTA (but then it wouldn't be edible). It is probably best made and used for a couple or 3 days, then discarded if unused, though I kept some in a clean bottle at room temperature and it was stable and smelled fresh for over a week.

It is quite thick, like regular ultrasound gel, so it is a bit of a trick to get it into a squeeze bottle. A large bore funnel works, or the cooled gel can be squeezed into the bottle out of the cut end of a plastic bag. It can also be kept in a jar and used with a spoon.

This is kind of exciting. Now I will no longer be dependent on ultrasound gel manufacturers. If I was in Haiti, either I or someone at the house where I was staying could make up a batch of this the night before clinic and I would have fresh clean ultrasound gel with which I could be generous in my scans.  The water wouldn't even have to be sterile since the stuff is boiled when it is made. Let there now be ultrasound in places that Amazon.com does not reach!

Here's a YouTube video of how to do it.

10 comments:

  1. Dear Janice,
    I work in East Timor as an obstetrician with very limited resources. I have been using water instead of ultrasound gel for my obstetric scans , with very poor results. Today I managed to source some guar gum from Australia and make my own gel and it was fantastic! Thank you so much for the advice

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    1. Thanks for letting me know! Please post how and where you got it here in the comments

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  2. It is a trick to find guar gum in developing countries, even though it is produced in both Africa and India. It is an ingredient in various industrial products including hydrofracking fluid and so is available in huge lots, 2+ metric tons, at a cost of $1-2 per kg. Some producers will sell smaller lots or 1kg at a time. Alibaba.com, an amazon-like online warehouse out of China, has food and cosmetic grade guar gum and does deliver to Africa and all over Asia. It is possible to get it in the US online as well and in bags or bulk.

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  3. Janice
    THANK YOU! I am a researcher, but not an expert in US gel, trying to develop a new simple hybrid optical-ultrasound method to detect and monitor TBI. Your article was very very helpful.

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  4. Hi,
    I really appreciate the work you did and the post here to serve as a starting place for people like me. Can you tell me if you have any experience with how long a batch of guar gum gel might last at room temperature before things start growing in it or it becomes a microbial hazard?

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  5. When I was in Tanzania we used exclusively guar gum gel for teaching and a research project on malaria. We found that the gel can last as little as 2 days at room temperature before becoming a much thinner liquid. I think that was due to some bacterial growth. It did not smell bad, though. It lasted longer when I cleaned the bottles well and rinsed them with boiling water. It also lasted better if refrigerated, which is not often an option. We also found that it worked great for ocular ultrasound. We were looking at optic nerve diameter and it was completely non-irritating when used on the eyelid directly, even if a little got in the eye. We also found that the tiny sieves that they had in the market in Tanzania, I think they were for making tea, worked great as a way to sprinkle the powder into the boiling water. We sometimes used a little more than a teaspoon of guar gum for a cup of water, just depending on what consistency we were looking for. I would suggest re-making the gel every 2-3 days and cleaning the bottle or jar well with boiling water between batches. I also found that I could pour very hot water or gel into the standard gel containers and they held up fine, didn't melt, which was good for sterility. Also the just boiled gel pours much more easily than after it cools when it thickens considerably.

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  6. Janice,

    You.Are.Awesome.

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  7. Thanks for the feedback. I am a resident and will be traveling abroad in a couple months and saw that this might be helpful. I bought some guar gum and tried some experimenting and also noticed some growth after about two days. One thing that also seemed to be a potential challenge was having to boil water in order to make the gel. I tried stirring in some powder into room temperature water but as you mentioned this was likely thicker than the same ingredient ratios at a higher temperature, and I was stuck with all of these bubbles in the gel after mixing which would have ruined any images. It seems the water boiling part is not easily sidestepped. However perhaps there is still potential applicability. Thanks again for your informative post and response!

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  8. Hi,
    Mix the guar gum with vegetable glycerin (just enough to wet it) before adding to the water (which can be room temperature which takes care of the issue of boiled water). This will prevent the gum from forming into balls and you don't need to blend it as much. If you do get air bubbles in your gel, just smack the container on your open palm and the bubbles will work themselves up to the surface. Glycerin is also a preservative to a limited degree, but should make the gel last a bit longer. I've never made ultra sound gel, just lots of other natural product, fyi.

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  9. Might it be possible to use a Dakin's base if you needed a batch to last longer? - Phil

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