Why is saline gel used in ultrasound scanning?
It’s called a coupling gel and it exploits the principle that sound travels nicely through an watery medium. Whenever you are scanned, the transducer needs this gel and a special “acoustic window” like the urinary bladder is used, ideally , to get really good diagnostic pics (that’s why we have to fill pregnant ladies up with urine or insert a foley cath. for the transvesical portion of the exam. If you were to try to scan air, the air would simply cause a lot of attenuation artifact and your picture would come out all white and be on no diagnostic value. So the reason we use a coupling gel is purely because of the physics of sound and to minimize artifact. Interestingly, if something is really close to the skin, a special “step off” device is used which is essentially a big glob of jel so that we can see things on the surface, which would ordinarily be out of the focal point of the ultrasound.
