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One of the most exciting things about having a baby is seeing a picture of the little one on the screen of an ultrasound machine for the very first time. In order to get those priceless first glimpses, however, the soon-to-be mother must endure the slimy sensation of ultrasound gel squeezed all over her belly before the sonographer can get started. The gel is actually a vital part of the ultrasound process, and it would be impossible to get clear pictures of the little tyke to show off to loved ones without the stuff.
When applied directly to the skin, a thin layer of ultrasound gel serves as a coupling medium, or a bridge of sorts, that allows ultrasonic energy waves to travel freely between the skin and the sound head of the transducer. A transducer is a handheld wand that looks very much like a small microphone. When the transducer is rubbed along the skin, a picture of the inside of the body begins to emerge on the ultrasound monitor. The gel acts as both a lubricant and an energy conductor.
The ultrasound gel, or coupling agent, plays upon a basic principle of physics: sound waves tend to carry very well through some form of watery medium. The gel works best in conjunction with a full bladder. The full bladder also serves as a watery medium to bounce back a clear picture acoustically for a sonographer to examine on a video screen during an exam.
There are different types of ultrasound gel, and it is made by many medical supply companies around the world. There are salt-free varieties, water-soluble brands and hypoallergenic kinds. Some newer varieties even boast firming and revitalizing properties that claim to keep the skin looking fresh and vibrant. Sonographers also frequently use gel warmers during exams to reduce discomfort for patients and create a more pleasant ultrasound experience.
So, I assume that the more direct purpose of ultrasound gel would be as a mid-range phase-screen to account for aberration?