Ultrasound is very high frequency sound, so high that human ears cannot hear it. It is used to make images of bodily organs, and especially of fetuses, because ultrasound images, sonograms, can be made without exposing a patient to radiation or surgery.
The process is to bounce sound waves off the structure being studied, much as bats bounce sound waves off objects in their path and let the echoes tell them where things are and how they are shaped. Bats have very sophisticated ears, as well as brains that can sort out the echoes and translate them into images.
Humans, however, must use computers to translate the shapes that the ultrasound echoes of a sonogram describe, because our brains evolved to use light waves to tell us the shapes of objects, and generally cannot translate sound waves into anything but sound.
Images made with ultrasound are called sonograms, but people use the term ultrasound to describe them too, just as we say tan to describe the process of lying in the sun as well as the color we turn when we do it. Tanning, of course, is not a good idea, but ultrasound is. It can be used to make a sonogram that will tell a patient and her health care providers quite a bit about the shape and function of her organs without invasive surgery, worrying radiation, or noisy MRI.
Getting a sonogram can be one of the most pleasant adventures of pregnancy. A parent gets to see an image of the fetus, and often hears the fetal heartbeat as well.
An echocardiogram is a sonogram of the heart. This too is a surprisingly pleasant and interesting procedure, assuming it is not done under emergency conditions. It is used to show shape and function without invading this essential organ. A variation of the Doppler effect is often used during an echocardiogram to investigate blood flow in the heart by measuring the time it takes for an echo to arrive. The patient hears rhythmic sounds that bear comparison to an old style washing machine or a horse trotting through mud.
Echogram is still another term for a sonogram or ultrasound. This term refers to the fact that the images are made with echoes, bounced sound waves. An instrument called a transducer, which looks like a small wand or handpiece is placed on the skin, over a layer of water-soluble gel.
The transducer sends sound waves into the body, and picks up the echoes as they bounce back. The transducer turns these sound vibrations into electrical impulses, which are fed into the computer. The computer reads the impulses, and constructs images that medical personal can study, and parents-to-be can enjoy.
Ultrasound is sound of a frequency so high that human ears cannot hear it, and human bodies cannot detect it when it is applied to the skin. Sonographers, highly skilled medical technicians, use ultrasound to produce sonograms, images of bodily organs. These images may also be called echograms, because they are made with bounced sound waves, and some people, including some doctors, even call them ultrasounds.