Echography is image-forming checkup using ultrasound waves, not perceptible for people.
The transducer is moved over the skin, simultaneously transmitting the waves which rebound differently depending of the tissue density. This electric signal is by the computer translated into an image of that tissue. Ultrasound, however, cannot be transmitted through the air or bone, making usage of this method not applicable for bones examination or checkup of the body parts containing much air.
This test is used predominantly to examine soft tissues of e.g. organs or muscles. It is also widely used for pregnancy checks. The ultrasound test causes no damage to the tissue and is painless.