Why do they have to use the jelly to get a reading ? What’s the purpose ? Also bonus if you tell me what it is.
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An ultrasound uses pulses of sound waves to image the tissue and other structures within the body. Those pulses are tuned to travel through flesh and don’t travel well through air, so there needs to be something between the transducer and the skin to carry the waves. That is what the jelly is for, it is a medium which is designed to carry those waves well.
The particular ingredients of ultrasound jelly vary but they are usually composed mainly of propylene glycol.
You know how when you look down at a body of water, the image is distorted? That’s because light rays get bent when they pass between two different types of material. Sound does something similar. Ultrasound devices emit sound waves and listen for the “echo” it makes when it comes back. However, the instrument they use is flat and rigid, while bellies are usually round and squishy. So it’s hard to get the device perfectly placed against an abdomen without any air gaps between them. As a result, the sound waves get jumbled twice, once on the way in and once on the way out, which makes them harder to read. The jelly has a similar consistency to human tissue (at least from the point of view of how sound travels through it), so it lets the instrument make a better “seal” with the skin for a clearer picture.
Allows better contact with what you’re trying to measure.
We used corn starch/water mix on industrial ultra-sounding of boiler tubes.
Sonographer here.
The gel is a transmission medium used to help transmit the sound waves through the skin and into the body and back to the transducer again. If no gel is used, a thin layer of air is trapped between the ultrasound transducer and the skin and no sound can be transmitted or received.
It’s usually a water-based gel, which is viscous enough that it stays on the skin. Technically saline can be used, but it has low viscosity and therefore won’t stay where you want it to.
Ultrasound makes images by sending sound waves into tissue from the wand, and listening for the echoes that bounce back. Kind of like sonar. Each time sound goes from one medium to another (water to air to water, for instance) it loses power. The gel minimizes the loss of sound energy. This is like shouting at someone in another room through the wall (air-solid-air) vs hearing sounds entirely underwater.
https://radiologyblog.cincinnatichildrens.org/ultrasound-gel-a-necessary-mess/
Found by a Google search for “ultrasound gel”, btw. There were a lot of products so you might also try “ultrasound gel why”.
This page https://nationaltherapy.com/how-much-do-you-really-know-about-ultrasound-gel/#:~:text=What%20Is%20Ultrasound%20Gel%20Made,is%20quite%20sticky%20and%20thick. says propylene glycol and water. They do also make warmers for it.
Something you could actually do with a 5 year old: Put a waterproof speaker by a pool then put your head underwater. The sound will be muffled and unclear. Now put your speaker underwater with you and it will sound crystal clear. The ultrasound gel is like putting the speaker underwater with you.
Ultrasound is transmitted as waves, and this wave nature is important.
Waves travel at a certain speed, which is related to the medium that the wave is travelling through and the type of wave. Whenever a wave changes in speed, some of the energy in the wave is reflected. The bigger the difference in speed the more reflects back.
The speed of sound is different in different types of material – it’s slow in air, and faster in water, and even faster in harder materials. This means that every time sound moves from air into water, or water into tough body tissue, some gets reflected. In fact, this is exactly how ultasound forms an image anyway. The machine sends out a burst of sound, and listens for the echo. The echos are produced whenever the sound goes from one type of tissue into another. Because the speed of sound in different body organs is quite close (but not identical), a weak echo comes back and most of the sound carries on going forward into the next organ.
Because the speed of sound in air is WAY slower than in body organs, the reflections that come when the beam hits air are extreme – almost all the sound echoes back, and almost nothing is left to keep going forward. Because not much sound gets into the body, you don’t get any echoes back from inside, so can’t see the organs.
The solution is to put a material between the probe and the skin, that has roughly the same speed of sound as the body. Water works fine, but it’s very liquid and just runs off (you could dam it up, but it’s messy and fiddly – although this is used sometimes for surgical ultrasound – for example, this is how ultrasound brain surgery for thigns like Parkinson’s disease is done).
So, water with some sort of thickener is usually used – typically a high molecular weight polyether such as polyethylene glycol (not propylene glycol as several other posts have stated – propylene glycol is something completely different)
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