How much water should you drink before an ultrasound?

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Ultrasound uses sound, or more accurately, sound waves or

vibrations, to travel through a medium of some sort to image what

is within that medium. Not unlike radar, some of the sound waves

bounce off of things within that medium allowing them to be seen.

In example, the dividing line between muscle and bone can be

thought of as an interface, something the sound waves can bounce

off of. The change in density from muscle to bone, allows the bone

to be image.

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ultrasound systems are designed to work best in water environments.

This is because most of the solid parts of a body, including

organs, bones, and other things, reside in, or are made up of

mostly water. Water can carry sound waves better than air.

Therefore, water-favoring ultrasound system can’t image well in

air. For a water-based ultrasound system, air can act like a

barrier to the sound waves. And, much like a brick wall stops you

from seeing what is on the other side of the wall, air can prevent

ultrasound from seeing what is there. By drinking water, one

reduces the amount of air in the stomach and, therefore, improves

the image quality of the ultrasound in that region of your

body.

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However, there are other systems that use sound to image such

things as geologic features underground, or things within the air

(like the natural imaging bats do using sound). So, what you want

to see or image, determines the type of sound-imaging system

used.